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Use of GIS and high resolution LiDAR in salt marsh restoration site suitability assessments in the upper Bay of Fundy, Canada
Abstract
Salt marshes exhibit striking vegetation zonation corresponding to spatially variable elevation gradients which dictate their frequency of inundation by the tides. The salt marshes in the upper Bay of Fundy, a dynamic hypertidal system, are of considerable interest due to increasing recognition of salt marsh ecosystem values and the extent of prior conversion of salt marshes to agricultural lands, much of which are no longer in use. To determine the suitability of two potential restoration sites at Beausejour Marsh in New Brunswick, Canada, geomatics technologies and techniques were used to assess vegetation and elevation patterns in an adjacent reference salt marsh and the proposed restoration sites. Light detection and ranging digital elevation models (DEMs) were created for the reference marsh and the restoration sites in both the spring (leaf-off) and late summer (leaf-on, maximum biomass) periods. Aerial photographs and Quickbird multispectral imagery were used to visually interpret vegetation zones on the reference marsh and were field validated using vegetation characteristics from quadrats referenced with differential GPS. Elevation limits of the salt marsh vegetation zones were extracted from the DEM of the reference marsh and applied to the DEM of the restoration sites to determine the percentage area of each site that would be immediately suitable for new salt marsh growth. Of the two restoration sites assessed, one had experienced significant subsidence since dyking; only about 40 % of the site area was determined to be of sufficient elevation for immediate vegetation colonization. The second site, while more than 88 % suitable, would require the installation of a large dyke on the landward side of the restoration site to prevent flooding of adjacent lands. This study provides essential high resolution elevation and vegetation zonation data for use in restoration site assessments, and highlights the usefulness of applied geomatics in the salt marsh restoration planning process.
... Webster et al. 2006;Feagin et al. 2010), saltmarsh restoration (e.g. Millard et al. 2013;Athearn et al. 2010) and the detection of estuarine and tidal river hydromorphology (e.g. Gilvear et al. 2004). ...
... On the basis that there are limitations for the use of LiDAR in saltmarshes, and the need for high accuracy data in research and management applications in these environments, some authors (e.g. Hladik and Alber 2012;Hopkinson et al. 2004;Populus et al. 2001;Schmid et al. 2011;Millard et al. 2013) have investigated the vertical accuracy of the elevation data from LiDAR, and the possibilities of calibration for these environments (Table 1). For example, several studies (Montané and Torres 2006;Rosso et al. 2006;Schmid et al. 2011) that focus on Spartina alterniflora marshes note that elevations within LiDAR-derived DTMs are overestimated with a mean error between 7 and 17 cm depending on study site, where the error seems to increase with vegetation density and height (Montané and Torres 2006;Morris et al. 2007;Rosso et al. 2006;Schmid et al. 2011). ...
... These particular features have been identified as the main limitations in saltmarsh mapping by different authors in the literature (e.g. Silva et al. 2008;Adam et al. 2009;Kelly et al. 2011;Millard et al. 2013) complicating the classification process more than in other coastal environments. Due to the difficulties in separating saltmarsh plant species or communities, some authors have included elevation data in the classification process to distinguish species of low spectral contrast located at different elevations within the marsh (Chust et al. 2008;Gilmore et al. 2008;Arroyo et al. 2010). ...
Accurate digital elevation models of saltmarshes are crucial for both conservation and management goals. Light detection and ranging (LiDAR) is increasingly used for topographic surveys due to the ability to acquire high resolution data over spatially-extensive areas. This capability is ideally suited to saltmarsh environments, which are often vast, inaccessible systems where topographic variations can be very subtle. Derivation of surface (DSMs) (ground elevation plus vegetation) versus terrain (bare ground elevation) models (DTMs) relies on the ability of the LiDAR sensor to accurately record multiple returns. In saltmarshes however, the dense stands of low (< 1 m) vegetation commonly found precludes the acquisition of more than one return, and the resulting DTM is not different to the DSM. Establishing the offset between ground and vegetation surface in order to correct the LiDAR-derived DTM can be challenging due to the spatial variability in saltmarsh habitats. Here we show the development and application of a habitat-specific correction factor (HSCF) for the Odiel Saltmarshes using a combination of habitat object-based classification (82% overall accuracy) and ground control surveys that reduces the DTM error to within that associated with the LiDAR sensor (average error 0.1 m). We also show that the true accuracy of supplied (unmodified) DTMs can be >0.5 m in saltmarshes dominated by dense vegetation such as Spartina densiflora. In particular, global projections of sea-level rise across the next 80 years (0.18–0.59 m) significantly overlaps this accuracy margin, implying that assessments and modelling of sea-level impacts in saltmarsh systems will likely be erroneous if based on Lidar-derived DTMs. Erroneous assumptions and conclusions can result if the real accuracy of DTMs (bare ground) on vegetated saltmarshes is not considered, and the consequences of the propagation of this misinformation through to management decisions should not be over-looked.
... In October 2010, the old agricultural dike was mechanically breached to reintroduce tidal seawater and initiate the restoration process in former pastureland sites (sites B and C). At that time, these sites to be restored were at a much lower elevation compared to the reference saltmarsh sites (sites A and D) [11,51]. Since the dike breaching, the recovery rate of the pioneer marsh species, i.e., saltwater cordgrass (Spartina alterniflora L.; syn. ...
... patens dominant) consistently across the years (Table 10, Figures 3 and 4). This is consistent with the fact that these established sites are mostly high marsh zones [11,51,54]. The main changes in the reference sites involved Classes 5 (S. ...
Saltmarshes provide important ecosystem services, including coastline protection, but face decline due to human activities and climate change. There are increasing efforts to conserve and restore saltmarshes worldwide. Our study evaluated the effectiveness of Sentinel-2 satellite imagery to monitor landcover changes using a saltmarsh restoration project undergoing its 9th to 12th year of recovery in the megatidal Bay of Fundy in Maritime Canada. Specifically, in 2019–2022, five satellite images per growing season were acquired. Random Forests classification for 13 landcover classes (ranging from bare mud to various plant communities) achieved a high overall classification accuracy, peaking at 96.43% in 2021. Field validation points confirmed this, with high validation accuracies reaching 93.02%. The classification results successfully distinguished ecologically significant classes, such as Spartina alterniflora–S. patens mix. Our results reveal the appearance of high marsh species in restoration sites and elevational-based zonation patterns, indicating progression. They demonstrate the potential of Sentinel-2 imagery for monitoring saltmarsh restoration projects in north temperate latitudes, aiding management efforts.
... Semi-diurnal tidal amplitudes in the Cumberland Basin reach more than 12 m [57]. A managed realignment salt marsh restoration project began here in 2009 under the leadership of Ducks Unlimited Canada (DUC) and partners [23,[58][59][60]. The project consists of two restoration (B, C) and two reference (A, D) sites; the study areas of focus for the present paper were the Western reference and restoration sites (A and B, Figure 1). ...
... Our study solely used input variables derived from the reflectance data acquired with the MicaSense dual-camera system, and future studies could benefit from incorporating DSMs, DTMs, and canopy height models derived from RTK GPS and Lidar data. These additional data sources have been valuable in various studies [35,58], especially considering the strong influence of elevation on salt marshes and its role in driving vegetation zonation in these habitats. Overall, there are many future research directions that, if followed, will further assist with the selection of appropriate remote sensing methods for mapping salt marshes. ...
Monitoring salt marshes with remote sensing is necessary to evaluate their state and restoration. Determining appropriate techniques for this can be overwhelming. Our study provides insight into whether a pixel-or object-based Random Forest classification approach is best for mapping vegetation in north temperate salt marshes. We used input variables from drone images (raw reflectances, vegetation indices, and textural features) acquired in June, July, and August 2021 of a salt marsh restoration and reference site in Aulac, New Brunswick, Canada. We also investigated the importance of input variables and whether using landcover classes representing areas of change was a practical way to evaluate variation in the monthly images. Our results indicated that (1) the classifiers achieved overall validation accuracies of 91.1-95.2%; (2) pixel-based classifiers outperformed object-based classifiers by 1.3-2.0%; (3) input variables extracted from the August images were more important than those extracted from the June and July images; (4) certain raw reflectances, vegetation indices, and textural features were among the most important variables; and (5) classes that changed temporally were mapped with user's and producer's validation accuracies of 86.7-100.0%. Knowledge gained during this study will inform assessments of salt marsh restoration trajectories spanning multiple years.
... The combination of active and passive sensors within a range of spectral, spatial, and temporal resolutions, and the ability to develop complimentary data information, has also increased the variety of wetland data products derived (e.g., References [35][36][37]) using data conflation frameworks. The combination of information streams from different sensors has allowed users to characterise wetland attributes that may be difficult to identify using single sensors. ...
... Furthermore, some sensors record spectral or backscattered/reflected responses within a range or spectral resolution appropriate for differentiating classes and features or attributes of interest. For example, SAR easily differentiates inundated marshes from other wetland types [234][235][236], but fen and bog are not easily differentiated with single-date imagery due to inseparable backscatter from similar physical characteristics (e.g., tree species composition) [37,[237][238][239]. This often results in lower classification accuracies. ...
Wetlands have and continue to undergo rapid environmental and anthropogenic modification and change to their extent, condition, and therefore, ecosystem services. In this first part of a two-part review, we provide decision-makers with an overview on the use of remote sensing technologies for the 'wise use of wetlands', following Ramsar Convention protocols. The objectives of this review are to provide: (1) a synthesis of the history of remote sensing of wetlands, (2) a feasibility study to quantify the accuracy of remotely sensed data products when compared with field data based on 286 comparisons found in the literature from 209 articles, (3) recommendations for best approaches based on case studies, and (4) a decision tree to assist users and policymakers at numerous governmental levels and industrial agencies to identify optimal remote sensing approaches based on needs, feasibility, and cost. We argue that in order for remote sensing approaches to be adopted by wetland scientists, land-use managers, and policymakers, there is a need for greater understanding of the use of remote sensing for wetland inventory, condition, and underlying processes at scales relevant for management and policy decisions. The literature review focuses on boreal wetlands primarily from a Canadian perspective, but the results are broadly applicable to policymakers and wetland scientists globally, providing knowledge on how to best incorporate remotely sensed data into their monitoring and measurement procedures. This is the first review quantifying the accuracy and feasibility of remotely sensed data and data combinations needed for monitoring and assessment. These include, baseline classification for wetland inventory, monitoring through time, and prediction of ecosystem processes from individual wetlands to a national scale.
... To prolong the useful life of the new dike and create wetland habitat, Ducks Unlimited Canada and several partners, including private, government, and academic, proposed that the old dike be deliberately breached to encourage salt marsh development between the old and new dikes. Following hydrodynamic and geomorphic modelling (Millard et al., 2013;Boone et al., 2017), the old dike was mechanically breached at 3 locations in October 2010 (Fig. 2). Briefly, each breach was designed to be wide enough (45-75 m wide) to accommodate movement of winter ice and allow maximum flooding at high tide, but slow draining at ebbing tide, thus maximising sediment deposition. ...
... We selected two large (>15 ha) adjacent established salt marshes as reference sites (Fig. 1). For a more detailed explanation of planning this salt marsh restoration project, see Millard et al. (2013) and Boone et al. (2017). ...
... At Cogmagun, historical agricultural use is evident by the presence of ditches that have been assimilated into a hybrid tidal creek network system. Previous studies in nearby regions have found that these historic agricultural disturbances are reflected in the vegetation communities (e.g., Jacobson and Jacobson 1989;Millard et al. 2013). While it could be argued that these study sites do not represent a pristine condition, the absence of current disturbance and the time elapsed because agriculture use is typical of this region, and therefore suitable as reference sites for restoration efforts. ...
... Two additional sample plots were collected from pools that contained no vegetation but were fringed by the Spartina alterniflora and Carex paleacea associations. Other studies in the region also identify shallow water pools colonized by the submergent aquatic Ruppia maritima or that are fringed by dominant graminoids found in this study, especially Spartina alterniflora (Bleakney and Meyer 1979;Patriquin 1981;Chmura et al. 1997;Millard et al. 2013). Shallow pools of standing water contribute to overall marsh biodiversity, and are worthy of mention because they are more common on northern marshes (Noël and Chmura 2011) and because their habitat value is well recognized (Bleakney and Meyer 1979;Roberts and Robertson 1986). ...
We numerically classified tidal wetland vegetation and determined the relationships between variation in plant species composition and environmental factors. Sampling was conducted at eight sites along a range of tidal magnitudes (<2 to >14 m). Cluster analysis revealed seven distinct salt or brackish marsh plant associations, usually dominated by a single graminoid species. Redundancy analysis showed continuous variation among community units and identified inundation time, elevation, soil salinity, and organic matter content as key correlates of plant community patterns. Associations detected were similar to those found in New Brunswick’s Bay of Fundy and Northumberland Strait wetlands, and to those farther south in northern New England, but two new brackish associations were also identified within this study (Juncus balticus Willd. – Festuca rubra L. and Spartina pectinata Link). Although elevation is understood to drive vegetation types in salt marshes in the region, here we show that salinity can differentiate vegetation types at the same elevation. These data provide a quantitative baseline and allow for better predictions of tidal wetland ecological restoration trajectories in Nova Scotia.
... At Cogmagun, historical agricultural use is evident by the presence of ditches that have been assimilated into a hybrid tidal creek network system. Previous studies in nearby regions have found that these historic agricultural disturbances are reflected in the vegetation communities (e.g., Jacobson and Jacobson 1989; Millard et al. 2013). While it could be argued that these study sites do not represent a pristine condition, the absence of current disturbance and the time elapsed because agriculture use is typical of this region, and therefore suitable as reference sites for restoration efforts. ...
... Two additional sample plots were collected from pools that contained no vegetation but were fringed by the Spartina alterniflora and Carex paleacea associations . Other studies in the region also identify shallow water pools colonized by the submergent aquatic Ruppia maritima or that are fringed by dominant graminoids found in this study, especially Spartina alterniflora (Bleakney and Meyer 1979; Patriquin 1981; Chmura et al. 1997; Millard et al. 2013). Shallow pools of standing water contribute to overall marsh biodiversity, and are worthy of mention because they are more common on northern marshes (Noël and Chmura 2011 ) and because their habitat value is well recognized (Bleakney and Meyer 1979; Roberts and Robertson 1986). ...
... Similarly, collecting historical high-resolution DEM data for coastal intertidal zones is challenging. Salt marshes are periodically inundated by tides, and DEM data in intertidal zones, especially those affected by intense human activities, could influence salt marsh distribution, particularly during restoration projects (Millard et al., 2013). Utilizing remote sensing to interpret DEM data from various waterlines at different tides, combined with actual elevation data, could be an effective method for constructing historical high-resolution DEM data (Kang et al., 2017;Yang et al., 2021). ...
... The potential for a salt marsh restoration was rst assessed in 2006 following the re-alignment of the agricultural dike by the New Brunswick (NB) Department of Agriculture (Millard et al. 2013). A new dike was constructed inland as the seaward dike was eroding more quickly than was feasible to maintain. ...
... However, berms trap rainwater draining from uplands and saline water from overtopping events, leading to high variability in salinity levels and the formation of marshes landward of the levee (Santoro et al. 2023) (Figure 1b). Exposure of previously anaerobic soils in diked and drained wetlands can enhance decomposition and subsidence (Millard et al. 2013), leading to the formation of ponds (Smith et al. 2017) if the berms are breached or overtopped. The costs of maintaining privately owned berms have increased over time, making them less economically viable as a method to limit SWI (Smith et al. 2017). ...
The impact of saltwater intrusion on coastal forests and farmland is typically understood as sea-level-driven inundation of a static terrestrial landscape, where ecosystems neither adapt to nor influence saltwater intrusion. Yet recent observations of tree mortality and reduced crop yields have inspired new process-based research into the hydrologic, geomorphic, biotic, and anthropogenic mechanisms involved. We review several negative feedbacks that help stabilize ecosystems in the early stages of salinity stress (e.g., reduced water use and resource competition in surviving trees, soil accretion, and farmland management). However, processes that reduce salinity are often accompanied by increases in hypoxia and other changes that may amplify saltwater intrusion and vegetation shifts after a threshold is exceeded (e.g., subsidence following tree root mortality). This conceptual framework helps explain observed rates of vegetation change that are less than predicted for a static landscape while recognizing the inevitability of large-scale change.
... Compared to traditional field survey methods used to identify land use types, vegetation coverage, and community structural complexity [49,50], indexbased approaches using remote sensing can provide timely and efficient assessment methods. Nevertheless, most studies rarely comprehensively evaluate the ecological assets of the study area based on changes in area, quality, and index [51,52]. Moreover, they only use single indicators for assessment, which may not be systematic and comprehensive enough. ...
The benefits provided by ecological assets play a crucial role in enhancing human well-being. However, there is a scarcity of viable methods for assessing their status. This study is grounded in Land Use and Land Cover Change (LUCC) and integrates both the quantity and quality aspects of these assets. Utilizing the ecological asset index (EQ and EQi), this study conducts a quantitative assessment of the assets in the Shibing karst and the Libo-Huanjiang karst heritage sites, while also qualitatively analyzing their influencing factors. The findings reveal that: (1) In the Shibing heritage site, forest and impervious surface assets exhibited an upward trend, whereas cropland and grassland experienced a decline; meanwhile, shrub and water body assets remained relatively stable. The total area of assets rated as excellent or good increased by 95.371 km², resulting in an EQ enhancement of 45.427. (2) Likewise, in the Libo-Huanjiang heritage site, forest and impervious surface assets demonstrated an upward trajectory, while shrub assets declined. Cropland, grassland, and water body assets experienced minimal variation. The total area of assets rated as excellent or good expanded by 168.227 km², resulting in an EQ enhancement of 80.806. (3) The execution of a series of ecological protection projects and management plans for heritage site conservation primarily accounts for the enhancement of regional assets. Notably, ecological resources, socio-economic conditions, human resources, and conservation management policies serve as pivotal drivers influencing the alterations in heritage site assets.
... With global marshes predicted to struggle to keep pace with SLR in the vertical dimension (Saintilan et al., 2022), lateral migration is becoming a dominant large-scale conservation option. Conservation efforts may be implemented at regional or local levels (Coastal Protection and Restoration Authority of Louisiana, 2017; Millard et al., 2013). Therefore, local-regional predictions based on higher resolution input data sets (Enwright et al., 2016;Van Coppenolle & Temmerman, 2020) are needed to inform management of coastal ecosystems and ensure maintenance of global marsh area into the coming decades. ...
Sea level rise is leading to the rapid migration of marshes into coastal forests and other terrestrial ecosystems. Although complex biophysical interactions likely govern these ecosystem transitions, projections of sea level driven land conversion commonly rely on a simplified “threshold elevation” that represents the elevation of the marsh‐upland boundary based on tidal datums alone. To determine the influence of biophysical drivers on threshold elevations, and their implication for land conversion, we examined almost 100,000 high‐resolution marsh‐forest boundary elevation points, determined independently from tidal datums, alongside hydrologic, ecologic, and geomorphic data in the Chesapeake Bay, the largest estuary in the U.S. located along the mid‐Atlantic coast. We find five‐fold variations in threshold elevation across the entire estuary, driven not only by tidal range, but also salinity and slope. However, more than half of the variability is unexplained by these variables, which we attribute largely to uncaptured local factors including groundwater discharge, microtopography, and anthropogenic impacts. In the Chesapeake Bay, observed threshold elevations deviate from predicted elevations used to determine sea level driven land conversion by as much as the amount of projected regional sea level rise by 2050. These results suggest that local drivers strongly mediate coastal ecosystem transitions, and that predictions based on elevation and tidal datums alone may misrepresent future land conversion.
... Compared with traditional eld survey methods used to identify land use types, vegetation coverage, and community structure complexity [40,41], remote sensing based indices can provide timely and effective methods for evaluating ecological assets. However, most studies rarely comprehensively evaluate the ecological assets of the study area through changes in area, quality, and index [42,43], only using a single indicator for evaluation, and the evaluation of ecological assets is not systematic and comprehensive enough. And most previous studies were based on RS at a large spatial scale, without eliminating the impact of spatial heterogeneity of environmental factors on ecological asset quality assessment [44,38]. ...
The ecological benefits provided by ecological assets play an important role in im-proving human well-being, but there are few feasible methods to describe their status and trends by combining the quantity and quality data of ecological assets. This study is based on LUCC and integrates data on the quantity and quality of ecological assets. Based on the ecological asset index (EQ and EQi), the ecological assets of the Shibing karst and the Libo-Huanjiang Karst heritage sites are quantitatively evaluated, and their influencing factors are qualitatively analyzed. The results show that, (1) The ecological assets of the Shibing Karst and the Libo-Huanjiang Karst are mainly forest ecological assets, accounting for 89.31% and 89.98% of the ecological assets of the heritage sites, respectively. The proportion of ecological assets in cropland, shrubs, grasslands, water bodies, and impermeable surfaces is small. (2) The ecological asset quality of the two heritage sites is similar, with a two-level differentiation state. The ecological asset quality of forests and shrubs is mainly excellent, good, and moderate, while the ecological asset quality of cropland and grassland is mainly inferior and poor. From the overall quality perspective, the ecological asset quality of both heritage sites has significantly improved. (3) From 2000 to 2021, the EQ of the Shibing Karst increased from 180.179 to 225.606. The EQ of the Libo-Huanjiang Karst has increased from 560.463 to 641.269. Among the EQi of the two sites, forest > cropland > shrubs > grassland in the Shibing Karst, and forest > shrubs > cropland > grassland in the Libo-Huanjiang Karst. The implementation of a series of eco-logical protection projects and heritage site protection and management plans is the main reason for the improvement of regional ecological assets. Overall, this method can quickly and accurately assess the status and trends of ecological assets, guide ecosystem management within heritage sites, and provide effective solutions for ecological asset assessment in other karst world heritage sites.
... The Aulac site took longer to dewater due to drainage issues possibly created by borrow pits in close proximity to the restoration site. In addition, the initial site elevations relative to the tidal frame were initially too low to support halophytic vegetation establishment (Millard et al., 2013). High sediment deposition rates paired with rapid dewatering and sheltered conditions inland on tidal estuaries seem to have led to rapid revegetation at BEL and SC. ...
Introduction
Tidal wetland restoration in the Bay of Fundy involves restoring tidal hydrology to sites with tidal restrictions. Most have focused on salt marsh sites close to the mouth of estuaries, but there are also many tidally restricted wetlands closer to the freshwater end of tidal rivers. Recovery of salt marsh vegetation has been rapid in past projects, but little is known about sediment and vegetation dynamics post restoration in tidal brackish or freshwater environments.
Methods
We implemented tidal wetland restoration projects on two tidal rivers near the inland limit of saltwater. Hydrological restoration involved breaching (St. Croix) or realigning agricultural dykes (Belcher Street). We monitored hydrology, sediment accretion and vegetation at replicated plots on restoration sites and nearby reference tidal marshes; and conducted habitat mapping and elevation surveys using drones.
Results
After re-establishing tidal flow, sediment accretion was very rapid, leading to a deep layer of new sediments. Plant colonization at both sites resulted in a high diversity of halophytes in the first 2 years post restoration, but the St. Croix site transitioned to freshwater wetland species dominating by the fifth year post- restoration. The Belcher St. site has a mix of freshwater and brackish wetland species after the fourth-year post-restoration.
Discussion
High suspended sediment concentrations at both sites suggest that each site was positioned closed to the estuarine turbidity maximum within its river. Tidal wetland restoration at the head of estuaries may benefit from the large ecological disturbance associated with rapid sediment accretion, providing a productive substrate with little competition from prior vegetation. However ultimate vegetation patterns may take longer to develop as elevation gains alter tidal flooding frequency. Low salinities suggest that the physical disturbance of sediment burying prior vegetation is the main mechanism creating a clean slate for plant recolonization, rather than mortality of terrestrial vegetation due to salt water. The majority of elevation change was due to allochthonous sediment deposition, with belowground processes playing a minor role. The wetlands restored showed substantial net elevation gains in the first years following tidal hydrological restoration, but long-term monitoring is required to track their overall resilience in the face of sea level rise.
... Starting from the morphology computed in STEP 1, we simulate two scenarios in which the dyke is retreated by 2.5 km and 7.5 km ( Figure 1d, e). We run the simulations for 100 years, which is a duration comparable with the age of coastal dyke retreat strategies adopted worldwide (Emmerson, 1997;Millard et al., 2013;Van Proosdij et al., 2010). As for the initial morphology, we consider only the two different bathymetries computed for two sediment inputs (5 mg l À1 and 50 mg l À1 ) and starting from a DL slope of 0.07%. ...
A hybrid coastal defense consisting of a salt‐marsh system at the seaward side and dykes on the landward side has been globally implemented to improve coastal resilience. In this approach, marshes are valuable ecosystems that dampen storm surges and have an intrinsic ability to keep up with sea‐level rise (SLR). Dykes instead, prevent the surge from penetrating inland. Therefore, dyke retreat is now considered a valuable option that allows the creation of new marshland in front of the relocated dyke, thus maximizing surge damping. The studies investigating the effect of dyke retreat on surge modification do not incorporate the morphodynamic expansion of tidal networks in the de‐reclaimed land, which is modeled as an unchannelized marsh. Here, we use the morphodynamic model Delft3D and a marsh evolution module to study the formation of tidal networks in a de‐reclaimed land after dyke retreat and evaluate their effect on surge modification (damping or amplification), and thus, the maximum water level reached at the dyke during a storm surge event. For this purpose, we consider different combinations of hydrodynamic (storm surge peak and duration, SLR), and morphodynamic (sediment input, dyke retreat distance, and de‐reclaimed land slope) parameters. Our results suggest that an increase in tidal prism, which depends on retreat distance, de‐reclaimed land slope, and SLR, drives the century‐scale morphodynamic evolution of the marsh. Results also show that surge damping is overestimated if the morphodynamic evolution of the tidal network after dyke retreat is neglected since the new creeks favor the landward propagation of the surge. Finally, a genetic algorithm is used to determine a relationship between surge modification, marsh morphology, and the morphodynamic and hydrodynamic parameters of the simulations. The relationship indicates that relative surge damping increases for shallower tidal networks, smaller surge peaks, higher marsh platforms, and smaller percentages of channelized area.
... The sites of the salt marsh restoration project are located in Aulac, New Brunswick ( Figure 1). The restoration project began in 2009 and is led by Ducks Unlimited Canada (DUC) and partners (Millard et al., 2013;Boone et al., 2017). Before the old dike was breached in fall 2010, the geomorphology of the site was assessed, and hydrodynamic modeling was done to encourage the reestablishment of salt marsh. ...
Vegetation patterns during salt marsh restoration reflect underlying processes related to colonization, reproduction, and interactions of halotolerant plants. Examining both pattern and process during recovery is valuable for understanding and managing salt marsh restoration projects. We present a decade of vegetation dynamics during salt marsh restoration (2011–2020) at a study site in the Bay of Fundy with megatidal amplitudes, strong currents, cold winter temperatures, and ice. We mainly investigated reproduction (asexual and sexual) and associated spread rates of Spartina grasses, and their health-related states (stem density, canopy height, and percent flowering) which help inform the probability of processes occurring. We also estimated modes of colonization and began quantifying the effects of interspecific interactions and environmental conditions on plant state. Spartina pectinata was the only pastureland plant to survive dike-breaching and saltwater intrusion in 2010; however, it was stunted compared to reference plants. Spartina pectinata patches remained consistent initially, before decreasing in size, and disappearing by the fifth year (2015). This early dynamic may provide initial protection to a developing salt marsh before Spartina alterniflora becomes established. Spartina alterniflora first colonized the sites in year 2 (2012), likely via deposition of rhizomal material, and then spread asexually before seedlings (sexual reproduction) appeared in year 4 (2014). Vegetation cover subsequently increased greatly until near-complete in year 9 (2019). The early successional dynamics of S. pectinata and S. alterniflora occurred spatially independently of each other, and likely contributed to sediment retention, creating an improved environment for S. patens, the dominant high marsh species in our region. Spartina patens have been slowly spreading into restoration sites from high elevation areas since year 6 (2016). We expect that competition between S. alterniflora and S. patens will result in the typical distinct zonation between high and low marsh zones. A next study will use the quantified processes for spatial-explicit modeling to simulate patterns of vegetation recovery, and to evaluate different salt marsh restoration strategies for the Bay of Fundy and elsewhere. Thus, proper identification and quantification of pattern-building processes in salt marsh vegetation recovery, the focus of our present study, was an essential step.
... For new wetland creations and enhancements, increase habitat heterogeneity by 1) increasing amount of edge through creation of irregularly-shaped shorelines (i.e., higher perimeter-to-area ratio), and 2) increasing topographic/elevational heterogeneity within the basin through creation of mounds ranging in size from small hummocks to nesting islands to promote a wider range of microsites for species establishment during both high and low water levels (NRCS 2003). Engineered heterogeneity can be facilitated by technological advances in design and construction such as the widespread availability of LIDAR topographic mapping and highly detailed survey data for design input, analysis and design with Geographic Information System (GIS) and Computer Assisted Drafting and Design (CADD) software, and precision construction methods such as GPS and laser guided earthmoving equipment (Moser et al. 2007, Millard et al. 2013). 2. Incorporate long-term dynamic simulations into hydrologic and hydraulic analysis to simulate wetland response to a changing climate, e.g., changing 100-year floods and five-year storms (Steward et al. 2011, Carlson Mazur et al. 2014). ...
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... Satellite images, with a spatial resolution from 0.5 m to 10-100 m [37,38], are appropriate to monitor large portions (several square kilometres) of coastal areas, but they do not sufficiently capture small-scale evolution, which requires higher vertical accuracy. Lidar-based DEMs in vegetated areas are usually characterised by vertical errors from 0.1 to 0.45 m [39][40][41][42] while Lidar products in bare mud can reach errors of 0.09 m [43]. Their reliability also depends on the rates of accretion and erosion affecting the intertidal area. ...
The use of Unmanned Aerial Vehicles (UAV) on wetlands is becoming a common survey technique that is extremely useful for understanding tidal flats and salt marshes. However, its implementation is not straightforward because of the complexity of the environment and fieldwork conditions. This paper presents the morphological evolution of the Po della Pila tidal flat in the municipality of Porto Tolle (Italy) and discusses the reliability of UAV-derived Digital Surface Models (DSMs) for such environments. Four UAV surveys were performed between October 2018 and February 2020 on an 8 ha young tidal flat that was generated, amongst others, as a consequence of the massive sediment injection into the Po Delta system due to the floods of the 1950s and 1960s. The DSM accuracy was tested by processing (i.e., photogrammetry) diverse sets of pictures taken at different altitudes during the same survey day. The DSMs and the orthophotos show that the tidal flat is characterised by several crevasse splays and that the sediment provision depends strictly on the river. During the study period, the sediment budget was positive (gaining 800 m3/year and an average rate of vertical changes of 1.3 cm/year). Comparisons of DSMs demonstrated that neither lower flight altitudes (i.e., 20–100 m) nor the combination of more photos from different flights during the same surveys necessarily reduce the error in such environments. However, centimetric errors (i.e., RMSEs) are achievable flying at 80–100 m, as the increase of GCP (Ground Control Point) density is the most effective solution for enhancing the resolution. Guidelines are suggested for implementing high-quality UAV surveys in wetlands.
... Ecosystem impacts associated with embankments are primarily related to habitat fragmentation, specifically restricting movement of water, nutrients, sediment, animals, and plant propagules, often resulting in declining biodiversity (Casagrande, 1997a;Hood, 2004;Ibarra-Obando et al., 2010;Roni et al., 2002;van Proosdij et al., 2009). Changes to water circulation modifies sediment deposition and erosion dynamics, altering substrate elevation within the estuary and marsh, usually by decreasing sediment accretion and lowering estuary elevation over time (Frenkel and Morlan, 1990;Millard et al., 2013;Orson et al., 1997aOrson et al., , 1997bPethick, 2002;Philipp, 2005). Changing circulation will modify water and sediment biogeochemistry, often resulting in a decrease in the ecosystems services (flood protection, erosion control, water filtration, etc.) provided by the estuary (Boumans et al., 2002;Casagrande, 1997a;Chmura et al., 2012;Jacobs et al., 2009;Portnoy, 1999). ...
Breaching of coastal causeways and dikes (embankments) is a common method used to restore estuaries and marshes to a more natural state. Here, we reviewed literature pertaining to embankment breaches to assess the effectiveness of this restoration method and to provide practical advice for future breaches. While all methods of embankment breaching can be successful, active measures appear to be more successful than allowing breaches to occur naturally. Restoring tidal flow sooner, and to a greater degree, will speed recovery of impacted systems. Overall, recovery is often quick, with hydrology changing immediately. Sedimentation and erosion patterns also change soon after breaching, but it can take up to 15 years for sediment elevation to stabilize, and 60-100 years for equilibrium conditions to develop. Marsh plant communities recover rapidly, with most systems almost fully recovering within 5-20 years. Fish, bird, and invertebrate communities also mostly recover within five years. Unfortunately, recovery is often not complete. Even with large investments of time and money, systems can still exhibit variation from reference habitats in their biotic and abiotic conditions up to 130 years post breach. In some cases, this may be due to embankment remnants still impacting the system. Conversely, the systems may have changed too much, and/or global climate change may have altered successional pathways to such a degree that recovery to pre-disturbance conditions is unlikely. Regardless, breaching of coastal embankments often restores conditions that are more natural and increases estuary similarity to reference systems. As such, breaching is a useful prescription for coastal restoration, one that can deliver a considerable return on investment.
... Though the benefits of vegetated foreshores are increasingly recognized, many foreshores, including salt marshes, suffer erosion [9,10]. While the erosion rate of a salt marsh cliff (typically tens of centimeters in height) exhibits a linear relation with wave power [11], the start of erosion is linked to having a stable marsh next to a dynamic tidal flat. ...
Salt marshes are increasingly recognized as resilient and sustainable supplements to traditional engineering structures for protecting coasts against flooding. Nevertheless, many salt marshes face severe erosion. There is a consensus that providing structures that create sheltered conditions from high energetic conditions can improve the potential for salt marsh growth. However, little proof is provided on the explicit influence of structures to promote salt marsh growth. This paper investigates how artificial structures can be used to steer the morphological development of salt marshes. A morphological model (Delft3D Flexible Mesh) was applied, which enabled the analysis of various artificial structures with realistic representation. A salt marsh in the Wadden Sea which has seen heavy erosion (lateral retreat rate of 0.9 m/year) served as case study. We simulate both daily and storm conditions. Hereby, vegetation is represented by an increased bed roughness. The model is able to simulate the governing processes of salt marsh development. Results show that, without artificial structures, erosion of the salt marsh and tidal flat continues. With structures implemented, results indicate that there is potential for salt marsh growth in the study area. Moreover, traditional structures, which were widely implemented in the past, proved to be most effective to stimulate marsh growth. More broadly, the paper indicates how morphological development of a salt marsh can be steered by various configurations of artificial structures.
... Canada (e.g., Millard et al., 2013), Brazil (e.g., Lima et al., 2018;Rorato et al., 2018) and Europe 45 (e.g., Andersen et al., 2017;Ockendon et al., 2018). The implementation of these programs has 46 significantly contributed to improving the quantity or quality of ecosystem assets in terms of 47 unilateral indicators (e.g., vegetation coverage, forest ecosystem area) ( Song et al., 2018;Vackaru 48 and Grammatikopoulou, 2019). ...
Ecological benefits provided by ecosystem assets play an important role in improving human wellbeing. However, there are few feasible methods to combine data on the quantity and quality of ecosystem assets to describe their state and trend. Here, we developed a new remote-sensing-based indicator by synthesizing ecosystem asset quantity and quality data for effective assessment at a regional or national scale. The new indicator includes a typological ecosystem asset index (TEAI) (e.g., forest ecosystem asset index) and an integrated ecosystem asset index (IEAI). The TEAI and IEAI can be used to assess the state and trend of a specific ecosystem or set of regional ecosystems, respectively. We applied the new indicator in the context of ecological protection policy in the Three-Rivers Source Region (TRSR), a region known as the ‘Chinese water tower’. From 2000 to 2015, the IEAI increased by 4.02% due to an increase in the ecosystem asset area (0.2%) and the ecosystem asset quality (0.66% and 0.02% increases in excellent and good level ecosystem assets, respectively). The implementation of ecological protection and ecological restoration programs was the main direct driver of regional ecological asset improvement. Our results suggest the new indicator is feasible for quickly and accurately evaluating the state and trend of ecosystem assets and can be used to guide ecosystem management at a large regional scale.
... When integrating land cover classification maps and digital elevation models (DEMs) for flood inundation mapping, a common issue over permanent tidal salt marsh regions (and migrating marsh communities) is the surface elevation error, specifically in DEMs derived from light detection and ranging (LiDAR) methods. Despite the usefulness and widespread application of LiDAR-derived DEMs over coastal areas [29][30][31][32][33], several studies have argued that elevation errors arise in vegetated areas, especially in salt marsh species [6,8,23,34,35]. The surface elevation error is calculated as the difference in elevation between LiDAR-derived DEMs and true ground-surface elevation; usually collected during real-time kinematic (RTK) topographic surveys [6,23,34,36]. ...
Emergent herbaceous wetlands are characterized by complex salt marsh ecosystems that play a key role in diverse coastal processes including carbon storage, nutrient cycling, flood attenuation and shoreline protection. Surface elevation characterization and spatiotemporal distribution of these ecosystems are commonly obtained from LiDAR measurements as this low-cost airborne technique has a wide range of applicability and usefulness in coastal environments. LiDAR techniques, despite significant advantages, show poor performance in generation of digital elevation models (DEMs) in tidal salt marshes due to large vertical errors. In this study, we present a methodology to (i) update emergent herbaceous wetlands (i.e., the ones delineated in the 2016 National Land Cover Database) to present-day conditions; and (ii) automate salt marsh elevation correction in estuarine systems. We integrate object-based image analysis and random forest technique with surface reflectance Landsat imagery to map three emergent U.S. wetlands in Weeks Bay, Alabama, Savannah Estuary, Georgia and Fire Island, New York. Conducting a hyperparameter tuning of random forest and following a hierarchical approach with three nomenclature levels for land cover classification, we are able to better map wetlands and improve overall accuracies in Weeks Bay (0.91), Savannah Estuary (0.97) and Fire Island (0.95). We then develop a tool in ArcGIS to automate salt marsh elevation correction. We use this ‘DEM-correction’ tool to modify an existing DEM (model input) with the calculated elevation correction over salt marsh regions. Our method and tool are validated with real-time kinematic elevation data and helps correct overestimated salt marsh elevation up to 0.50 m in the studied estuaries. The proposed tool can be easily adapted to different vegetation species in wetlands, and thus help provide accurate DEMs for flood inundation mapping in estuarine systems.
... Notice that accuracy depends on the Lidar sensor resolution (Wehr and Lohr, 1999), the landscape features of the intertidal environment (Evans et al., 2019) and the presence of vegetation (Hladik and Alber, 2012). In low and high marshes, the vegetation clearly influences the accuracy, causing errors from 0.1 to 0.45 m (Morris et al., 2005;Rosso et al., 2006;Wang et al., 2009;Schmid et al., 2011;Millard et al., 2013), requiring corrections to DTMs. As in Perkpolder, the tidal flat is completely un-vegetated and with no large bed features, it was considered unnecessary to re-process further the DTMs. ...
In the present context of sea-level rise, the reconstruction of previously reclaimed intertidal areas represents an opportunity to build dynamic coastal defences to decrease flooding under storm conditions by the dissipation of wave and surge energy across the vegetated domain. In Europe, this approach started in the late 1990s along the coast of eastern and southern England, but it is becoming common to many European countries around the North Sea margin. The process of salt-marsh restoration normally develops around the opening or removal of flood protection structures and gradual flooding of the hinterland. If the intertidal zone starts to experience vertical accretion, vegetation will colonize the area and a saltmarsh will develop. This paper presents the morphological evolution and sediment distribution in the Perkpolder basin, SW Netherlands (NL), following the conversion of a reclaimed area into a tidal flat, after the opening of an inlet in the flood defence structures in June 2015. The main focus of this study is the description of the evolution of the tidal flat since the opening of the inlet and the identification of spatio-temporal conditions for the evolution of a salt marsh. To reach this objective, several topographic surveys were undertaken, together with sediment surface sampling. Sedimentation rates at fixed sampling stations were assessed during the transition between neap and spring tides over a period of 1 month and 2 weeks. The morphological analysis of the inlet evolution proved that 6–8 months after the opening the inlet reached an equilibrium state. The average accretion rate across the whole study area was about 6–7 cm per year–1. The average deposited sediment was about 100 g per m–2 per day. Considering the sedimentation rates in the most elevated regions, 80–110 cm above NAP (Normaal Amsterdams Peil), and assuming that the sedimentation rate will remain constant in time, the conditions for the on-set of salt-marsh formation will not be reached before 8–10 years. Projections indicate that the area located at +50 cm above NAP will not become a mature marsh before 50 years.
... LiDAR data acquisition involves the use of lasers to measure accurate distances from the lasers' source to the earth's surface, and these data are thus often used for the development of high-resolution digital elevation models (DEMs) that characterize the earth's bare surface. The increasing availability of these high-resolution digital elevation models have assisted a variety of disciples to identify and characterize many specific landscape features such as karst depressions, vernal pools, prairie potholes, coastal notches, and tidal creeks [22][23][24][25][26]. The characterization of these features often involves training models to describe and identify unique combinations of morphometric and/or topographic signatures that characterize them. ...
Anthropogenic development of floodplains and alteration to natural hydrological regimes have resulted in extensive loss of off-channel habitat. Interest has grown in restoring these habitats as an effective conservation strategy for numerous aquatic species. This study developed a process to reproducibly identify areas of former stream meanders to assist future off-channel restoration site selections. Three watersheds in Iowa and Minnesota where off-channel restorations are currently being conducted to aid the conservation of the Topeka Shiner (Notropis topeka) were selected as the study area. Floodplain depressions were identified with LiDAR-derived digital elevation models, and their morphologic and topographic characteristics were described. Classification tree models were developed to distinguish relic streams and oxbows from other landscape features. All models demonstrated a strong ability to distinguish between target and non-target features with area under the receiver operator curve (AUC) values ≥ 0.82 and correct classification rates ≥ 0.88. Solidity, concavity, and mean height above channel metrics were among the first splits in all trees. To compensate for the noise associated with the final model designation, features were ranked by their conditional probability. The results of this study will provide conservation managers with an improved process to identify candidate restoration sites.
... Furthermore, through the use of separate control points in model construction and as an independent check, the quality of the model can be assessed; an option not available using just dGPS measurements. The DSM produced is also at a higher, more suitable, resolution than standard remote sensing techniques, such as LiDAR, which have previously been used in the design and prediction of ecological response to MR schemes (e.g., Blott and Pye 2004;Millard et al. 2013;Krolik-Root et al. 2015), increasing the likelihood that small (but important) changes in elevation will be captured. This technique could, therefore, be utilised to provide a more detailed understanding of how creek features develop within intertidal wetland environments. ...
Managed realignment (MR) schemes are being implemented to compensate for the degradation of coastal habitats. However, evidence suggests that MR sites have lower biodiversity than anticipated, which has been linked to poor drainage. Despite creek networks playing an important role in enhancing site drainage in natural intertidal environments , there remains a shortage of data on the formation and evolution of creeks within MR sites. This study evaluates creek development at the Medmerry Managed Realignment Site, UK. Creek development is investigated using differential global positioning system (dGPS) data, supported by sedimentological analyses and a high-resolution digital surface model (DSM) derived from images taken using a small unmanned aerial vehicle. Measurements indicated that creeks will develop relatively quickly, but are influenced by differences in the sub-surface sedimentological conditions. A suitable level of agreement was found between the DSM and dGPS measurements, demonstrating the appropriateness of this method to study creek development within intertidal environments at a higher resolution than traditional surveying techniques. These results are used to propose the collapse of sub-surface piping as the primary creek formation mechanism. Findings are discussed in terms of increasing the success of MR schemes and enhancing site design to maximise the ecosystem services provided.
... That is, is the site in a location where key processes can be expected to adaptively sustain the wetland and the particular functions which other wetlands of its type usually support, e.g., its "site potential?" (Millard et al. 2013). Although WESP-AC uses many landscape-scale indicators to estimate wetland functions, WESP-AC is less practical for identifying the relative influence of multiple processes that support a single wetland. ...
WESP-AC is a standardised method for rapidly assessing some of the important natural functions of tidal wetlands in Atlantic Canada. An accompanying document contains a standardised method for rapidly assessing some of the important natural functions of non-tidal wetlands in the same region.
Tidal wetlands are defined as areas predominantly vegetated by vascular plants which experience surface water flooding by tides at least once annually, regardless of salinity. Normally, their vegetation is predominantly herbaceous, i.e., salt marsh, but in estuaries such as the St. John where tidal influence extends dozens of kilometers inland, water becomes fresh rather than saline as one proceeds upriver, and tidal floodplains in many segments are wooded. This Tidal WESP-AC is recommended for assessing functions of those areas. This version is not applicable to assessing the functions of mud flats, eelgrass, or macroalgal beds.
The tidal WESP-AC consists of this manual and its appendices, some supporting electronic files, and an Excel® spreadsheet calculator containing data forms and models (formulas). WESP-AC generates scores (0 to 10 scale) and ratings (Lower, Moderate, Higher) for each of the following wetland attributes: Storm Surge Interception; Water Purification; Organic Nutrient Export; Fish Habitat; Waterbird Habitat; Songbird and Raptor Habitat; Biodiversity Maintenance; Wetland Stability; Public Use or Recognition. For each attribute, the scores and ratings represent a particular wetland’s standing relative to those in a statistical sample of tidal wetlands previously assessed by this study in the relevant province: 43 in New Brunswick, 34 in Nova Scotia, 39 in Newfoundland-Labrador, and 19 on Prince Edward Island.
The scores and ratings are intended to inform decisions about wetland avoidance, minimisation, and replacement. WESP-AC can also be used with other tools and measurements to monitor wetland restoration projects and to help assure that wetland restoration efforts offset the unavoidable loss of specific functions and benefits in other wetlands, not just loss of their area.
... Our research has identified variables that can be used in relatively simple models to simulate short-term C accumulation in flooded dykelands which could be applied to dykeland sites assessed as suitable for restoration by digital terrain and GIS modeling e.g. [48,49]. The organic C content of local suspended sediment could be used in deposition models to predict C accumulation following MR. ...
Salt marshes are highly effective carbon (C) sinks and have higher rates of soil C burial (per square meter) than terrestrial ecosystems. Marsh reclamation and anthropogenic impacts, however, have resulted in extensive losses of salt marshes. Restoration of marshes drained and “reclaimed” for agriculture (referred to in Canada as dykelands) and degraded marshes can generate C credits, but only if C burial is reliably quantified. To date, studies reporting on C burial rates have been limited primarily to restored marshes which are more than 10 years old. Here we report on a study which assessed C burial six years after the return of tidal flooding to a section of dykeland in Aulac, New Brunswick on Canada’s Bay of Fundy. The C burial rate in the restored marsh averaged 1 329 g C m⁻² yr⁻¹, more than five times the rate reported for a nearby mature marsh. Carbon density in the recovering marsh was relatively consistent with depth and although salt marsh cordgrass (Spartina alterniflora) became established in 2012, the bulk of the C in the new marsh deposit is assumed to be allochthonous. Financial constraints are a barrier to marsh restoration projects and C markets could provide a considerable source of funding for restoration work in the future. For marsh restoration projects to be recognized in C crediting systems, however, it must also be demonstrated that the allochthonous C would not otherwise have been sequestered; the potential for this is discussed.
... Some manual check and manual reclassification were also conducted because classification routine would most likely misclassify some points. The misclassification of point clouds could result in significant errors in the LiDAR derived DEM and vegetation structural parameters (Millard et al., 2013). ...
... We examined elevation patterns of tidal marsh across the study area using a LiDAR-derived digital elevation model for southern New Jersey (NOAA, 2008). There are known issues with LiDAR measurement error in tidal marsh, specifically it overestimates elevation in areas of taller, denser vegetation because point returns from above-ground vegetation are more likely to be misclassified as ground points (Chassereau et al., 2011;Millard et al., 2013;Schmid et al., 2011). To understand the magnitude and patterns of LiDAR elevation measurement error with this particular LiDAR dataset and study region, we collected a set of RTK GPS elevation measurements and characterized vegetation at each point (n ¼ 329) in April and July 2015 at a 55 ha Delaware Bay tidal marsh study site We used Classification and Regression Trees (CART, De'ath and Fabricius, 2000) to classify elevation thresholds that correspond to unvegetated intertidal areas, low marsh and high marsh. ...
... The potential for a salt marsh restoration was rst assessed in 2006 following the re-alignment of the agricultural dike by the New Brunswick (NB) Department of Agriculture (Millard et al. 2013). A new dike was constructed inland as the seaward dike was eroding more quickly than was feasible to maintain. ...
The objectives of this chapter are to (1) document lessons learned from the design, implementation and monitoring of a salt marsh restoration in the upper Bay of Fundy, Canada, and (2) consider how the lessons can be applied to future restoration projects. The Fort Beauséjour salt marsh restoration sites are exposed to very large tides (up to 14 m), waves, and snow and ice in winter. This project involved a managed re-alignment, with two restoration cells and two reference sites. Before breaching, design criteria were established (e.g., the restoration cells must fully flood at high tide and drain slowly) and a hydrodynamic model was used to test breaching options. Pre-restoration monitoring was completed in 2009–2010, the old dike was breached in October 2010, and post-breach monitoring commenced thereafter. Measurements of water level, velocities, and discharge at one breach, compared very well to model predictions. Likewise, patterns of sediment deposition were as predicted, and sedimentation rates were as expected based on empirical studies done in the area. The bioengineering species saltwater cordgrass (Spartina alterniflora) took 2 years to colonize the cells; it initially spread vegetatively and then by seeds. Plant cover became extensive in year 5 post-breach. Invertebrate and salt pool biological communities are lagging behind. Lessons learned include: (1) plan for future conditions and provide adequate accommodation space for development of a new marsh; (2) multi-level partnerships are critical to the success of such projects; (3) monitoring with a research focus ensures observation and quantification of unexpected phenomena; and (4) the design process used, including the hydrodynamic model, was successful and can be used again for similar situations.
... Marsh elevations can be measured with a digital elevation model (DEM) developed from DGPS or conventional surveying, but these methods are too time consuming and labor intensive to acquire data across large areas (Lohani and Mason, 2001). A commonly used alternative is to develop a DEM from discrete return (Mathew et al., 2010;Bowron et al., 2011;Millard et al., 2013;Krolik-Root et al., 2015;Kulawardhana et al., 2015;Stammermann and Piasecki, 2014) or full waveform LiDAR data (Rogers et al., 2015). Though not yet as common, LiDAR data have also been collected from an unmanned aerial vehicle (UAV) platform in other environments, primarily for tree canopy structure analyses (Wallace et al., 2016). ...
... Raw laser point clouds were processed using the LiDAR data post-processing software (TerraScan, TerraSolid, Ltd., Finland). Misclassified LiDAR data has the potential to cause significant errors in the LiDAR-derived DEM and vegetation structural parameters (Millard et al., 2013). Therefore, manual verifications and reclassifications were performed for reducing the misclassification errors caused by automatic classification routine. ...
Wetland biomass is essential for monitoring the stability and productivity of wetland ecosystems. Conventional field methods to measure or estimate wetland biomass are accurate and reliable, but expensive, time consuming and labor intensive. This research explored the potential for estimating wetland reed biomass using a combination of airborne discrete-return Light Detection and Ranging (LiDAR) and hyperspectral data. To derive the optimal predictor variables of reed biomass, a range of LiDAR and hyperspectral metrics at different spatial scales were regressed against the field-observed biomasses. The results showed that the LiDAR-derived H_p99 (99th percentile of the LiDAR height) and hyperspectral-calculated modified soil-adjusted vegetation index (MSAVI) were the best metrics for estimating reed biomass using the single regression model. Although the LiDAR data yielded a higher estimation accuracy compared to the hyperspectral data, the combination of LiDAR and hyperspectral data produced a more accurate prediction model for reed biomass (R2 = 0.648, RMSE = 167.546 g/m2, RMSEr = 20.71%) than LiDAR data alone. Thus, combining LiDAR data with hyperspectral data has a great potential for improving the accuracy of aboveground biomass estimation.
... daily) surface elevation changes because of a prohibitively high cost of labor and travelling involved. Elevation can also be assessed with great spatial coverage, using for example airborne laser altimetry (LIDAR) techniques, photogrammetric and Structure from Motion (SfM) techniques (Millard et al., 2013;Fonstad et al., 2013;Mancini et al., 2013). Restricted overpass frequency and limited vertical resolution, however, make such methods less suitable for monitoring individual erosion and deposition events (Table 4.1). ...
Tidal flat landscape formation and evolution are closely related to the biotic and abiotic processes that take place in the intertidal environments. Extensive studies have been carried out on the relevant agents such as hydrodynamics, sediment transport and the related ecosystem (vegetation and benthic communities) dynamics. However, the feedback mechanism among multi pleagents is complex and many key aspects are currently understudied. In ti mes of accelerating global change, knowledge of the mechanisms that drive tidal
flat evolution is of great importance to ecosystem conservation and restoration. This thesis addresses the currently understudied subjects related to intertidal hydrodynamic processes as well as the intertidal landscape developments, which are of great economic and ecological importance.
... Then, LiDAR point clouds were classified as vegetation and ground returns using the method proposed by Axelsson in the TerraScan software [37]. In addition, some manual reclassification were also conducted by visual inter- pretation because the misclassification of point clouds maybe lead to significant errors in the LiDAR-derived digital terrain [38]. In this study, a DTM was generated from the LiDAR ground returns through the inverse distance weighted interpolation algorithm with a grid cell size of 0.5 m × 0.5 m. ...
... daily) surface elevation changes because of a prohibitively high cost of labor and traveling involved. Elevation can also be assessed with great spatial coverage, using for example airborne laser altimetry (LIDAR) techniques, photogrammetric and Structure from Motion (SfM) techniques (Millard et al., 2013;Fonstad et al., 2013;Mancini et al., 2013). Restricted overpass frequency and limited vertical resolution, however, make such methods less suitable for monitoring individual erosion and deposition events (Table 1). ...
Tidal flat morphology is continuously shaped by hydrodynamic forces, resulting in a highly dynamic bed surface. The knowledge of short-term bed-level changes is important both for assessing sediment transport processes as well as for understanding critical ecological processes, such as vegetation recruitment on tidal flats. High frequency bed-level measurements with a high vertical resolution are generally needed for hypothesis testing and numerical model validation. However, conventional manual bed-elevation measurements tend to have a coarse temporal resolution (weeks to months) due to the labor involved. Existing automated methods for continuous monitoring of bed-level changes either lack a high vertical resolution or are very expensive and therefore limited in spatial application. In light of this, we developed a novel instrument called SED (Surface Elevation Dynamics) sensor for continuous monitoring with a high vertical resolution (2 mm). This sensor makes use of light sensitive cells (i.e. phototransistors) and operates stand-alone. The unit cost and the labor in deployments are reduced, facilitating spatial application with a number of units. In this study, a group of SED-sensors is tested on a tidal flat in the Westerschelde Estuary, the Netherlands. The obtained bed-level changes are compared with the data obtained with precise manual measurements using traditional Sedimentation Erosion Bars (SEB). An excellent agreement between the two methods was obtained, confirming the accuracy and precision of the SED-sensors. Furthermore, to demonstrate how the SED-sensors can be used for measuring short-term bed-level dynamics, two SED-sensors were deployed at two sites with contrasting wave exposure. Daily bed-level changes were obtained including a severe storm event. The difference in observed bed-level dynamics at both sites was statistically explained by their different hydrodynamic conditions. Thus, the stand-alone SED-sensor can be applied to monitor sediment surface dynamics with high vertical and temporal resolution, which provides opportunities to pinpoint morphological responses to various forces in intertidal environment. We expect that this sensor can also be applied in other morphological environments, such as rivers, salt-marsh, beaches and dunes, but the actual applicability remains to be tested. Furthermore, the SED-sensors may also offer opportunities for ground-truthing remote sensing techniques aimed at describing morphological changes. Finally, further improvements in future SED-sensors are discussed, including an inclination and compass sensor, wireless data retrieving function and additional IR-light bar for measurements with poor light availabilities.
... Some manual check and manual reclassification were also conducted because classification routine would most likely misclassify some points. The misclassification of point clouds could result in significant errors in the LiDAR derived DEM and vegetation structural parameters (Millard et al., 2013). ...
... The standard deviation of the elevation of both the all-hits (all of the LiDAR returns regardless of classification) and the ground-hits (the LiDAR returns that are classified as being returned from the ground surface) were calculated for each 8 m pixel. For the allhits , this derivative has been found to be correlated with the height of vegetation, especially in very short, dense vegetation (Millard et al., 2013). For the ground-hits, this represents the amount of variation in the ground over the 8 m pixel and is thought to be useful in peatlands for describing the hummocky nature of the landscape. ...
In this paper, we assess the use of Random Forest (RF) for mapping land cover classes within Mer Bleue bog, a large northern peatland in southeastern Ontario near Ottawa, Canada, using Synthetic Aperture Radar (SAR) and airborne Light Detection and Ranging (LiDAR). Not only has RF been shown to improve classification accuracies over more traditional classifiers, but it also provides useful information on the statistical importance of individual input image bands for land cover classification. Our specific objectives in this study were to: (i) assess the robustness of a RF approach to northern peatland classification; (ii) examine variable importance resulting from the RF classifications to identify which imagery types, derivatives, and analysis scales are most useful for mapping different classes of northern peatlands; (iii) assess if fusion of different LiDAR and SAR variables can improve classification accuracies at Mer Bleue; and (iv) assess physical interpretability of the multisensor image types and derivatives with respect to biophysical attributes associated with peatland classes. Our results show that the fusion of SAR with LiDAR imagery and derivatives at this study site did not provide additional classification accuracy over the use of LiDAR derivatives alone. Nevertheless, the RF-based approach presented here has strong potential to improve mapping and imagery classification of wetlands and may also help researchers and practitioners improve information extraction and land cover classification in other application areas benefitting from large volumes of multi-sensor imagery.
Vegetation cover is critical in supporting our lives by maintaining many ecological and environmental services. As part
of the vegetation cover, forests are the most essential components of the carbon cycle on the Earth. Canopy height is a
critical piece of data needed for calculating the ecological and silvicultural variables of the forest. Since the forest canopy
is the first/last frontier interacting with the atmosphere and incoming from space electromagnetic radiation, this study
investigates using Digital Elevation Models (DEMs) to map canopy heights. A comparison of the Canopy Height Models
(CHMs) with a reference CHM and Digital Terrain Model (DTM) was performed in this study. The investigated DEMs
include SRTM, ALOS World3D30 (AW3D30) and WorldDEM™. Results show an underestimation of CHMs and significant
variations between the DEMs used. Consistent for all DEMs, the spatial resolution of 30 m produced the CHMs’
RMSE of 15.35 m, 16.95 m, and 16.49 m for AW3D30, SRTM and WorldDEM™, respectively. In addition, the largest
CHM bias was for the SRTM. The ratio between the obtained CHMs and the reference CHM can provide a first-hand
method to estimate a suitable correction to the actual forest height. The study was conducted on a flat terrain covered by
pristine rainforest in Brunei Darussalam, Borneo. The forest is evergreen, and the phenological cycle is barely recognizable
throughout the year. These facts are essential for the research since the DEMs were collected at different months/
years.
The overwhelming spread of Spartina alterniflora (smooth cordgrass) has put many native plant communities and coastal environments at risk. A better understanding of how S. alterniflora responds to inundation and salinity gradients will help manage the invasion of this species. However, current spatial quantitative analyses are insufficient. Thus, unmanned aerial vehicles (UAVs) and field sampling data were integrated to assess the ecological response of S. alterniflora to inundation and salinity gradients. This study aimed to determine the optimum ecological range of flooding and saline for S. alterniflora in Dafeng Milu National Nature Reserve in Jiangsu, China. Our results showed that the optimum ecological amplitude of S. alterniflora to flooding depth was [−0.07 m, 0.82 m] and the optimum mean growing point was 0.38 m. Furthermore, the optimum flooding time was [0 h,11.87 h], and the optimum mean growing point was 4.13 h. Our analyses also showed that soil salinity had significant effects on the growth of S. alterniflora. The optimum ecological amplitude of S. alterniflora to soil salinity was [13.77 g/kg, 22.57 g/kg], and the optimum mean growing point was 18.19 g/kg. This is the first spatially quantitative analysis to study the eco-hydrological mechanism driving both the aboveground biomass and height of S. alterniflora over the intertidal zone to the best of our knowledge. Determining the optimal ecological range for flooding and salt will provide a scientific basis for measures to establish the ecological control of S. alterniflora and to predict the expansion of S. alterniflora in response to rising sea levels.
Background
The Yancheng coastal natural wetlands (YCNR) are well-preserved silty tidal flat wetlands in China. Due to the severe invasion of Spartina alterniflora , the native ecosystem has undergone great changes. The successful invasion of S. alterniflora reduced the biodiversity of the YCNR, changed the structure and function of the local ecosystem, and eventually led to the degradation of the ecosystem and the loss of ecosystem function and service. Fully understanding the impact of an alien species invasion on YCNR succession is an important prerequisite for protecting and restoring the wetlands.
Methods
In this study, remote sensing, GIS technology, and a cellular-automaton Markov model were used to simulate the natural succession process of native ecosystems without being affected by alien species. By comparing the landscape of the YCNR with the model simulation results, we gained a better understanding of how alien species affect native landscape-scale ecosystems.
Results
During the natural succession of the coastal native wetland ecosystem in the YCNR, the pioneer species S. alterniflora occupied the mudflats and expanded seaward. The whole area expanded and moved seaward with an average annual movement of 58.23 m. Phragmites australis seemed to dominate the competition with S. salsa communities, and the area gradually expanded with an average annual movement of 39.89 m. The invasion of S. alterniflora changed the native ecosystem’s spatial succession process, causing the S. salsa ecosystem to be stressed by ecosystems on the side of the sea ( S. alterniflora ) and that of land ( P. australis ). The area of the seaward-expanding P. australis ecosystem has been declining. Under a reasonable protected area policy, human activities have enhanced the succession rate of the P. australis ecosystem and have had a small impact on the ecological spatial succession of S. salsa and S. alterniflora .
Lidar-derived digital elevation models are widely used in modeling coastal marsh systems. However, the topographic error in these models can affect simulations of marsh coverage and characteristics. We investigated the relevance and impact of this error in micro- and meso-tidal systems. Lidar-derived and RTK-adjusted topography were each used in a dynamic marsh model, and the resulting marsh coverages were examined. For two microtidal sites (Apalachicola, FL, and Grand Bay, MS) using solely lidar-derived topography, the model produced Cohen Kappa values of 0.1 for both estuaries when compared to National Wetland Inventory data indicating a ‘very poor agreement’. Applying the RTK-adjusted topography improved the model marsh coverage results to ‘substantial agreement’ with the values to 0.6 and 0.77, respectively. The mesotidal site in Plum Island, MA, contained similar topographic errors, but the model produced a Cohen Kappa value of 0.73, which categorized it as ‘very good agreement’ with no need for further topographic adjustment given its present robust biomass productivity. The results demonstrate that marsh models are sensitive to topographic errors when the errors are comparable to the tidal range. The particular sensitivity of the modeling results to topographic error in microtidal systems highlights the need for close scrutiny of lidar-derived topography.
Determining the bathymetric properties of a river, lake or reservoir is important for many reasons because it identifies location of sections with sedimentation or erosion which indicate the key processes and biophysical habitat status. This study used observational data of a 5 km section of the Danube River (transformed into a reservoir after 1972) to determine the best GIS interpolation method and the optimal number of sampling points to get an accurate description of the riverbed. Nine interpolation methods were used to generate bathymetric maps of the Danube course, between km 955 and km 950, in the area of Iron Gates reservoir, using a variable number of points (n = 1943; n = 4328; n = 17139), obtained by single beam echo sounder. Six methods of deterministic interpolation have been used: Inverse Distance Weighting (IDW) – criteria automatically determined (CAD) and manually determined (MD); Local Polynomial Interpolation (LPI) – criteria automatically determined (CAD) and manually determined (MD); Radial Basis Function (RBF) – fully regularized spline CRS; Radial Basis Function RBF – spline with tension SWT, and three geo-statistics methods: Ordinary Kriging – OK, Simple Kriging – SK, Universal Kriging – UK. Cross-validation and bathymetric Digital Elevation Models (DEM s) analysis were used to evaluate the accuracy of the estimated data and maps. The two interpolation methods, Inverse Distance Weighting (IDW-MD) and Simple Kriging (SK), provide satisfactory results, even in the case of a small number of points (n = 1943). If the number of measured points grows and a section grid (perpendicular/longitudinal) is developed, the DEM s bathymetric accuracy improves significantly, especially in the case of complex morphology, even if the positive and negative forms of the bed lead to sudden changes in the measured values. The obtained results revealed differences between the interpolation methods used, particularly in the case of a small number of points measured per perpendicular trajectories, but by the addition of points on longitudinal paths, a significant improvement of the bathymetric maps is obtained.
The Mollicy Farms Unit of Upper Ouachita National Wildlife Refuge; LA; consists of former agricultural land replanted with traditional bottomland hardwood species. Much of it is surrounded by a containment levee built to hold back the annual floodwaters of the Ouachita River. In 2009, two extreme floods, with water levels over 4 in above the flood stage, breached the levee, leaving the area inside the levee inundated for an extended period of time. We investigated the mortality of trees and saplings following these floods. During the initial reforestation efforts, which began in 11998, trees were planted both inside and outside the levee, allowing us to compare tree and sapling mortality based on location, inside or outside the levee. The average mortality of all trees was 40.59%, and the average mortality of all saplings was 48.23%. Both tree and sapling mortality resulted from a significant interaction between elevation and location inside or outside the levee. Overall, results indicated increased mortality at lower elevations for the area inside the levee. Outside the levee, mortality was unaffected by elevation because floodwaters were able to recede naturally. Levee removal would restore a more traditional flooding regime, likely reducing tree and sapling mortality during future floods.
In New England salt marshes, Spartina alterniflora dominates the low-marsh habitat, which is covered daily by tides. The high-marsh habitat (not flooded daily) is dominated on its seaward border by S. patens, and on its terrestrial border by Juncus gerardi. While high-marsh perennials appear to be restricted to the high-marsh habitat by harsh physical conditions in the low-marsh habitat, S. alterniflora appears to be excluded from the high-marsh habitat by the high-marsh perennials. Throughout the high marsh, Distichlis spicata and Salicornia europaea are associated with phycial disturbance, in the form of mats of dead plant material (wrack) rafted by tides onto the marsh, which is most severe in the spring and early summer, and which decreases with increasing marsh elevation. D. spicata and S. alterniflora are most tolerant of wrack burial. Short-term disturbance increases the relative abundance of these species in the community. Longer lasting disturbance events kill the underlying vegetation, leaving bare patches throughout the high marsh. D. spicata rapidly colonizes these patches with runners; S. alterniflora and Sa. europaea recruit by seed. Over time these early colonizers are overgrown and displaced in high-marsh patches by S. patens and J. gerardi, which grow slowly, as dense turfs of roots, rhizomes, and tillers.-from Authors
The purpose of this research was to examine spatial patterns of changes in surface elevation in salt marshes and adjacent mudflats of the Cumberland Basin, Bay of Fundy. A series of transects were established and surveyed at 8 sites of varying age and morphology. Changes in surface elevation were measured annually at 7 sites from 1999 to 2003 using bedframes and co-located buried aluminium plates. Starting in 2000, detailed sampling was undertaken at 4 sites along 2 transects (3 of the original 7 sites plus 1 new site) using buried plates extending from the high marsh to the mudflat. Survival of the monitoring sites depends strongly on the amount of ice present and moving during winter. Many of the bedframe stations in low marsh areas and on the mudflats did not survive their first winter due to ice scour. The majority of plates on the marshes were re-located each year while plates on the mudflats disappeared every year. The results indicate a need to use measurement techniques that will survive winter. The data show considerable spatial and temporal variability in changes in surface elevation in these marsh/mudflat systems. For analysis, each profile was divided into marsh, margin, and mudflat zones. In general, the marsh zone was found to be stable or accreting, the margin zone was found to be accreting along the rivers and eroding in more exposed locations, and the mudflats were found to be eroding. However, the mudflats were also found to be very dynamic and thus identifying a trend from these data is questionable.
One of the world's largest tidal wetland restoration projects was conceived to offset the loss of nekton to once-through cooling at a power plant on Delaware Bay, USA. An aggregated food chain model was employed to estimate the area of tidal salt marsh required to replace these losses. The 5040 ha was comprised of two degraded marsh types – Phragmites-dominated marshes and diked salt hay farms – at eleven locations in oligo-mesohaline and polyhaline reaches of the estuary. At a series of `summits' convened with noted experts in the field, it was decided to apply an ecological engineering approach (i.e., `self design', and minimal intrusion) in a landscape ecology framework to the restoration designs while at the same time monitoring long-term success of the project in the context of a `bound of expectation'. The latter encompassed a range of reference marsh planforms and acceptable end-points established interactively with two advisory committees, numerous resource agencies, the permitting agency and multiple-stakeholder groups. In addition to the technical recommendations provided by the project's advisors, public health and safety, property protection and public access to the restored sites were a constant part of the dialogue between the utility, its consulting scientists and the resource/permitting agencies. Adaptive management was used to maintain the restoration trajectories, ensure that success criteria were met in a timely fashion, and to protect the public against potential effects of salt intrusion into wells and septic systems, and against upland flooding. Herbicide spray, followed by prescribed burns and altered microtopography were used at Phragmites-dominated sites, and excavation of higher order channels and dike breaching were the methods used to initiate the restorations at the diked salt hay farms. Monitoring consisted of evaluating the rate of re-vegetation and redevelopment of natural drainage networks, nekton response to the restorations, and focused research on nutrient flux, nekton movements, condition factors, trophic linkages, and other specific topics. Because of its size and uniqueness, the Estuary Enhancement Program as this project is known, has become an important case study for scientists engaged in restoration ecology and the application of ecological engineering principles. The history of this project, and ultimately the Restoration Principles that emerged from it, are the subjects of this paper. By documenting the pathways to success, it is hoped that other restoration ecologists and practitioners will benefit from the experiences we have gained.
Coastal marsh habitat and its associated vegetation are strongly linked to substrate elevation and local drainage patterns. As such, accurate representations of both the vegetation height and the surface elevations are requisite components for systematic analysis and temporal monitoring of the habitat. Topographic Light Detection and Ranging (LIDAR) data can provide high-resolution, high-accuracy elevation measurements of features both aboveground and at the surface. However, because of poor penetration of the laser pulse through the marsh vegetation, bare-earth LIDAR elevations can be markedly less accurate when compared with adjacent upland habitats. Consequently, LIDAR groundelevation errors (i.e., standard deviation [SD] and bias) can vary significantly from the standard upland land-cover classes quoted in a typical data provider's quality-assurance report. Custom digital elevation model (DEM) generation techniques and point classification processes can be used to improve estimates of ground elevations in coastal marshes.The simplest of these methods is minimum bin gridding, which extracts the lowest elevation value included within a user-specified search window and assigns that value to the appropriate DEM grid cell. More complex point-to-point classification can be accomplished by enforcing stricter slope limits and increasing the level of smoothing. Despite lowering the spatial resolution of the DEM, the application of these techniques significantly improves the vertical accuracy of the LIDAR-derived bare-earth surfaces. By employing the minimum bin technique to the bare-earth classified LIDAR data, the overall bias in the resultant surface was reduced by 12 cm, and the vertical accuracy was improved by 8 cm when compared with the "as-received" data.
Airborne laser scanning (ALS) provides more information about scanned surfaces than just elevation. Backscattered laser pulses are visually influenced by surficial reflectance properties of the terrain being mapped, such as the presence of water. In this study the impact of soil moisture and vegetation cover on laser pulse intensity was explored. The study area, an agricultural watershed in the Annapolis Valley of Nova Scotia, was scanned several times over an 18 month period using comparable survey settings. The intensity data for all acquisitions were normalized to account for range bias effects and scaled to an 8-bit range. Tests included comparing raw intensity data with range-normalized intensity data, comparing daily data to assess temporal changes in intensity, and correlating intensity data to spatially coincident soil surface volumetric moisture content measurements. The range-normalized intensity comparison revealed that while normalization removed the majority of systematic bias in the intensity some artefacts remained in overlapping scan areas. Temporal intensity variations were observed in agricultural fields, and while some of this change was attributable to changes in the surface wetness, crop cover and the confounding influence this had on laser pulse attenuation diminished the correlation. Ground sampled volumetric moisture content and intensity were not strongly correlated; however, it was shown that the two methods were measuring similar trends over some of the areas studied. This study concludes that while soil moisture conditions can influence laser return intensity over bare earth, vegetated ground cover has a greater overall control on the signal intensity.
A 1-D model for exploring the interaction between hydrodynamics, sedimentation, and plant community evolution on a salt marsh populated by Spartina alterniflora is developed. In the model tidally induced flows over marsh platforms are affected by S. alterniflora through drag forces. In general macrophyte characteristics are determined by a wide range of processes; here, based on field studies at North Inlet estuary, South Carolina, the biomass of the S. alterniflora on the marsh platform is simply related to their time of submergence under tidally induced flows. Additionally, field data collected at North Inlet are used to relate biomass to plant area per unit volume, stem diameter, and an empirical drag coefficient. Sedimentation is also related to biomass, through either organogenic deposition or trapping of suspended sediment particles. The morphologic evolution of simulated marshes is explored by varying the sedimentation process and the rate of sea level rise. Different sedimentation processes result in marshes with different morphologies. An organogenic marsh is predicted to evolve under a regime of steady sea level rise into a platform with a relatively flat surface, whereas a marsh developed primarily through a trapping mechanism is predicted to have a surface that slopes gently away from the salt marsh creek. As predicted by 0-D modeling studies, sea level rise may be accommodated up to a certain critical sea level rise rate, after which the salt marsh platform will drown. Marshes that accrete through sediment trapping adjust to changes in sea level more rapidly than marshes that accrete through organogenic deposition.
We examine rates of salt marsh accumulation in three marshes of the outer Bay of Fundy. At each marsh we selected a site in the high marsh with similar vegetation, and thus similar elevation. Accretion rates were estimated by 137Cs, 210Pb, and pollen stratigraphy to estimate rates of change over periods of 30, 100, and ∼ 170 years, respectively. These rates are compared with records from the two closest tide gauges (Saint John, New Brunswick, and Eastport, Maine) to assess the balance of recent marsh accretion and sea-level change. Averaged marsh accretion rates have ranged from 1.3 ± 0.4 to 4.4 ± 1.6 mm year-1 over the last two centuries. Recent rates are similar to the rate of sea-level change recorded at Eastport, Maine, suggesting that they are in step with recent sea-level change but very sensitive to short-term variation in relative sea level. Based on the pollen stratigraphy in the marsh sediments, the marsh accretion rate was higher during the late 18th to early 19th century. Higher rates probably were due to local increases in relative sea level as a result of neotectonic activity and may have been enhanced by increased sediment deposition through ice rafting.
This paper reviews the origin and development of New England salt marshes. The authors present vegetation patterns and dynamics in light of new data and evaluate the complex of interacting factors influencing the patterns. They consider man's impacts and make recommendations for maintaining marsh integrity.
Light Detection and Ranging (LIDAR) is a new technology that offers a potential alternative to field surveying and photogrammetric techniques for the collection of elevation data. It has the advantages of being rapid accurate and able to map areas that are difficult to access. LIDAR has demonstrated the capability to accurately estimate important vegetation structural characteristics such as forest canopy height. For these reasons. airborne LIDAR data were used to compare vegetation height determinations with field observations on one selected transect in the vicinity of Lake Hatchineha in Florida. USA. The approach was based on the LIDAR and field measurements. The results showed that the lowest height (0 cm) appeared to be open water and barren fields. Vegetation heights of 0-30 cm corresponded to short grassy areas and 90-180 cm corresponded to medium height plants. Tall plants were determined to be vegetation heights ranging from 180 to 365 cm and very tall plants were determined to range from 365 to 600 cm. In addition, vegetation heights ranging from 600 to 1200 cm and from 1200 to 1700 cm corresponded to low and medium-height trees, respectively. Sources of potential error in determining forest tree canopy height were found to evolve from the fact that medium-height tree branches were sometimes reflected and recorded as a first hit and so were incorrectly classified as either low tree or tall plant classes. The results showed that, in most cases. while field and photogrammetrlc methods fail to determine tree and other plant heights, they could be accurately detected by using LIDAR classification in the wetlands where the ground is not visible. The next step will be to try to find a correlation between LIDAR vegetation heights and water boundaries.
This paper reviews the status of research on the Atlantic salt marshes of eastern Canada. The floristics, habitats, and biophysical aspects of the Atlantic salt marshes are described and aspects relating to anthropogenic influences on the Atlantic marshes are discussed in the context of contemporary rural settlement and vulnerability to offshore oil development. Guidelines for environment management, protection, and rehabilitation research are proposed. Such guidelines are deemed important since more than half the 33 000 ha of salt marshes in Nova Scotia have been dyked for agriculture. Most of the salt-marsh habitats in Newfoundland have a high degree of domestic grazing, even though the marshes are small in size and rare in occurrence. The least disturbed in terms of domestic use are the Labrador salt marshes which, although grazed by migratory ducks and geese, have not yet been influenced by man's activities. In addition, the Labrador salt marshes are discussed and compared with the northern marshes of arctic Canada in terms of their ecology and formation.
Transformation of agricultural land to natural terrestrial vegetation has been suggested as a means to increase soil carbon storage. However, the capacity for carbon storage in terrestrial soils is limited as compared to soils of tidal salt marshes, the original vegetation of many coastal agricultural lands. In a number of countries, tidal salt marshes have been ''reclaimed,'' that is drained and diked to prevent tidal flooding and create suitable conditions for dry land agriculture. In this study we examine spatial and temporal patterns of carbon accumulation in tidal salt marshes of the Bay of Fundy and estimate the carbon storage potential of the bay's extensive area of reclaimed marsh. Rates of carbon accumulation vary from the upper to the outer Bay, over which there is a gradient of decreasing tidal range and suspended sediment supply. In the outer bay, high-marsh densities are highest (0.042 ± 0.009 g C cm À3), but carbon accumulation rates over the past 30 years are lowest (76 g C m À2 yr À1). The reverse pattern occurs in the upper bay where carbon densities in the high-marsh environment are lowest (0.036 ± 0.002 g C cm À3), but carbon accumulation rates over the past 30 years may be as high (184 g C m À2 yr À1). Compared to other ecosystems, the rates of carbon accumulation presented in this study were similar over timescales of years to centuries. Increases in relative sea level (over time) and suspended sediment supply (across the bay) positively affect the marsh soil accumulation rate and the rate of carbon sequestration. Parameters such as %C are not useful predictors of a marsh's potential for carbon sequestration. Soil carbon densities of functioning marshes and reclaimed marsh soils are similar, but marsh soils have a storage capacity that increases with rising sea level, while agricultural soils, such as those in reclaimed marshes, have a fixed (or possibly decreasing in reclaimed marshes) volume over time.
Saltmarshes in south‐east England have been eroding rapidly since 1960. Recently, Hughes & Paramor (2004 ) and Morris et al . (2004 ) have presented contrasting views on the extent to which physical and biological processes might contribute to the erosion. There are three contentious issues: (i) saltmarsh erosion is the result of coastal squeeze, where sea walls prevent a landward migration of a saltmarsh in response to sea level rise; (ii) saltmarsh erosion is linked to bioturbation and herbivory of seedlings by the ragworm Nereis diversicolor ; (iii) new saltmarshes will not develop on managed realignment sites where existing sea walls have been removed because of the effects of ragworms.
In this paper, we provide a literature review of physical and biological processes relevant to the above three issues, and discuss the relative importance of these processes at different spatial and temporal scales.
Our synthesis shows that, at a regional scale, the combination of strong winds, high tides and increased wave height appears to be responsible for the increased rate of marsh erosion and creek dissection recorded in the 1970s. There is also some laboratory evidence that bioturbation and herbivory from populations of Nereis can lead to sediment instability and loss of pioneer plant species, such as Salicornia spp. However, the field evidence is more equivocal and has been conducted at small spatial scales.
At a large number of different managed realignment sites there is strong evidence that even if bioturbation and herbivory by Nereis have occurred, overall the effects have been insufficient to restrict plant succession of exposed sediment.
Synthesis and applications. There is an urgent need for long‐term field studies that integrate and quantify physical and biological processes and the related feedbacks at different spatial and temporal scales. Until this is completed, terms such as coastal squeeze will remain contentious and management decisions will invite criticism.
Vegetation change in response to restriction of the normal tidal prism of six Connecticut salt marshes is documented. Tidal flow at the study sites was restricted with tide gates and associated causeways and dikes for purposes of flood protection, mosquito control, and/or salt hay farming. One study site has been under a regime of reduced tidal flow since colonial times, while the duration of restriction at the other sites ranges from less than ten years to several decades. The data indicate that with tidal restriction there is a substantial reduction in soil water salinity, lowering of the water table level, as well as a relative drop in the marsh surface elevation. These factors are considered to favor the establishment and spread ofPhragmites australis (common reed grass) and other less salt-tolerant species, with an attendant loss ofSpartina-dominated marsh. Based on detailed vegetation mapping of the study sites, a generalized scheme is presented to describe the sequence of vegetation change from typicalSpartina- toPhragmites-dominated marshes. The restoration of thesePhragmites systems is feasible following the reintroduction of tidal flow. At several sites dominated byPhragmites, tidal flow was reintroduced after two decades of continuous restriction, resulting in a marked reduction inPhragmites height and the reestablishment of typical salt marsh vegetation along creekbanks. It is suggested that large-scale restoration efforts be initiated in order that these degraded systems once again assume their roles within the salt marsh-estuarine ecosystem.
Salt marsh restoration practices based on the reintroduction of tides to hydrologically-altered wetlands may be hindered by
a lack of specific knowledge regarding plant community response to environmental change. Since saltmarsh plant communities
are controlled by physical stress tolerance and competition, we conducted a field experiment that measured effects of saltwater
flooding and competitive interactions on plants as a guide for predicting habitat response to tidal restoration. Six plant
species of New England salt marshes were studied: halophytes Spartina alterniflora, Spartina patens, and Juncus gerardii and brackish invasive species Phragmites australis, Typha angustifolia, and Lythrum salicaria. Plant shoots were transplanted across a gradient of three flooding and three salinity regimes and arranged into pair-wise
competitive combinations. After one growing season, saltwater flooding was found to decrease transplant survival, biomass
production, and/or relative growth for all species. Reduction in halophyte growth was largely due to increased flood duration;
brackish species were most reduced by increased salinity. Interspecific competition also influenced species growth, although
the short duration of the study may have weakened these effects. Transplants paired with S. alterniflora had reduced growth, but combinations with Juncus produced increased growth. Standardized factors of stress tolerance and relative competitive strength were derived for the
six study species as a framework for understanding community-level changes in marshes. As an aid to resource managers, experimental
results can be used to predict plant community response to existing and potential alterations in saltmarsh tidal hydrology.
Recent research has highlighted the valuable role that coastal and marine ecosystems play in sequestering carbon dioxide (CO2). The carbon (C) sequestered in vegetated coastal ecosystems, specifically mangrove forests, seagrass beds, and salt marshes, has been termed "blue carbon". Although their global area is one to two orders of magnitude smaller than that of terrestrial forests, the contribution of vegetated coastal habitats per unit area to long-term C sequestration is much greater, in part because of their efficiency in trapping suspended matter and associated organic C during tidal inundation. Despite the value of mangrove forests, seagrass beds, and salt marshes in sequestering C, and the other goods and services they provide, these systems are being lost at critical rates and action is urgently needed to prevent further degradation and loss. Recognition of the C sequestration value of vegetated coastal ecosystems provides a strong argument for their protection and restoration; however, it is necessary to improve scientific understanding of the underlying mechanisms that control C sequestration in these ecosystems. Here, we identify key areas of uncertainty and specific actions needed to address them.
We examine rates of salt marsh accumulation in three marshes of the outer Bay of Fundy. At each marsh we selected a site in the high marsh with similar vegetation, and thus similar elevation. Accretion rates were estimated by ¹³⁷Cs, ²¹⁰Pb, and pollen stratigraphy to estimate rates of change over periods of 30, 100, and ∼ 170 years, respectively. These rates are compared with records from the two closest tide gauges (Saint John, New Brunswick, and Eastport, Maine) to assess the balance of recent marsh accretion and sea-level change. Averaged marsh accretion rates have ranged from 1.3 ± 0.4 to 4.4 ± 1.6 mm year⁻¹ over the last two centuries. Recent rates are similar to the rate of sea-level change recorded at Eastport, Maine, suggesting that they are in step with recent sea-level change but very sensitive to short-term variation in relative sea level. Based on the pollen stratigraphy in the marsh sediments, the marsh accretion rate was higher during the late 18th to early 19th century. Higher rates probably were due to local increases in relative sea level as a result of neotectonic activity and may have been enhanced by increased sediment deposition through ice rafting.
Beginning in the 17th century many Bay of Fundy marshes were diked and drained for agricultural use, but storm breaching of dikes and failure of tidal gates has returned tidal flooding to some marshes. We investigated two breached and undiked salt marsh pairs in the Bay of Fundy to assess the potential for recovery of these reclaimed lands and improve our knowledge about salt marsh restoration. We examined the distribution of major species with respect to elevation and compared plant cover and production of reference and recovering marshes. The vertical range of both Spartina alterniflora and Spartina patens increased with tidal range - a condition recognized for S. alterniflora, but not previously reported for S. patens. Our results reveal that S. alterniflora and S. patens are inundated less frequently than in microtidal marshes and tolerate a large variation in inundation frequency and depth. The upper portions of the S. patens zone may not be submerged by tidal waters in some years, so hydroperiod (and its associated stresses) may play less of a role in limiting the lower elevation of a species' distribution in the high marsh. Our comparisons of reference and recovering diked marshes inform not only restoration activities on the Bay of Fundy, but also give a perspective on recovery trajectories of reclaimed salt marshes in general. Regionally, the broad elevation range of S. alterniflora and high sediment deposition rates impart Bay of Fundy marshes with a high resilience and prospects for success of deliberate restoration efforts are promising, without the addition of fill required for marsh restoration in some regions. While marsh loss occurs in other areas the Bay of Fundy provides an opportunity to regain this resource.
A scanning airborne topographic lidar was evaluated for its ability to quantify beach topography and changes during the Sandy Duck experiment in 1997 along the North Carolina coast. Elevation estimates, acquired with NASA's Airborne Topographic Mapper (ATM), were compared to elevations measured with three types of ground-based measurements - 1) differential GPS equipped all-terrain vehicle (ATV) that surveyed a 3-km reach of beach from the shoreline to the dune, 2) GPS antenna mounted on a stadia rod used to intensely survey a different 100 m reach of beach, and 3) a second GPS-equipped ATV that surveyed a 70-km-long transect along the coast. Over 40,000 individual intercomparisons between ATM and ground surveys were calculated. RMS vertical differences associated with the ATM when compared to ground measurements ranged from 13 to 19 cm. Considering all of the intercomparisons together, RMS ≃ 15 cm. This RMS error represents a total error for individual elevation estimates including uncertainties associated with random and mean errors. The latter was the largest source of error and was attributed to drift in differential GPS. The ≃ 15 cm vertical accuracy of the ATM is adequate to resolve beach-change signals typical of the impact of storms. For example, ATM surveys of Assateague Island (spanning the border of MD and VA) prior to and immediately following a severe northeaster showed vertical beach changes in places greater than 2 m, much greater than expected errors associated with the ATM. A major asset of airborne lidar is the high spatial data density. Measurements of elevation are acquired every few m2 over regional scales of hundreds of kilometers. Hence, many scales of beach morphology and change can be resolved, from beach cusps tens of meters in wavelength to entire coastal cells comprising tens to hundreds of kilometers of coast. Topographic lidars similar to the ATM are becoming increasingly available from commercial vendors and should, in the future, be widely used in beach surveying.
Tides are an ever-present reality in many coastal regions of the world, and their causes and influence have long been matters of intrigue. In few places do tides play a greater role in the economics and character of a region and its people than around the shores of the Bay of Fundy in eastern Canada. Indeed, the Bay of Fundy presents a wonderful natural laboratory for the study of tides and their effects. However, to understand these phenomena more fully, some large perspectives are called for on the general physics of the tides and their operation on an oceanic scale. The geologic history of the region too provides key insights into how and why the most dramatic tides in the world have come to be in the Bay of Fundy. Tidal characteristics along the eastern Canadian seaboard result from a combination of diurnal (daily) and semidiurnal (twice daily) tides, the latter mostly dominant. Tidal ranges in the upper Bay of Fundy commonly exceed 15 m, in large part a consequence of tectonic forces that initiated the Bay during the Triassic. The existence and position of the Bay is principally determined by a half-graben, the Fundy Basin, which was established at the onset of the opening of the Atlantic Ocean. Due to the proportions of the Bay of Fundy, differences in tidal range through the Gulf of Maine-Bay of Fundy-Georges Bank system are governed by near resonance with the forcing North Atlantic tides. Although Fundy tide curves are sinusoidal, tide prediction calls for consideration of distinct diurnal inequalities. Overlapping of the cycles of spring and perigean tides every 206 days results in an annual progression of 1.5 months in the periods of especially high tides. Depending on the year, these strong tides can occur at all seasons. The strongest Fundy tides occur when the three elements – anomalistic, synodical, and tropical monthly cycles – peak simultaneously. The closest match occurs at intervals of 18.03 years, a cycle known as the Saros. Tidal movements at Herring Cove, in Fundy National Park, illustrate the annual expected tidal variations. Vigorous quasi-equilibrium conditions characterize interactions between land and sea in macrotidal regions like the Bay of Fundy. Ephemeral on the scale of geologic time, estuaries progressively infill with sediments as relative sea level rises, forcing fringing salt marshes to grow to successively higher levels. Although closely linked to a regime of tides with large amplitude and strong tidal currents, Fundy salt marshes rarely experience overflow. Established about 1.2 m lower than the highest astronomical tide, only very large tides are able to cover the marshes with a significant depth of water. Peak tides arrive in sets at periods of 7 months, 4.53 years, and 18.03 years. For months on end no tidal flooding of the high marshes occurs. Most salt marshes are raised to the level of the average tide of the 18-year cycle. The exact locations of coastal zone water levels such as mean high water and mean low water is a recurring problem and the subject of much litigation. Marigrams constructed for selected river estuaries illustrate how the estuarine tidal wave is reshaped over its course, to form bores, and varies in its sediment-carrying and erosional capacity as a result of changing water surface gradients. Changing seasons bring about dramatic changes in the character of the estuaries, especially so as ice conditions develop during the second half of the 206-day cycle when the difference in height between Neap tide and Spring tide is increasing, the optimal time for overflow in any season. Maximum ice hazard, including build-up of "ice walls" in Fundy estuaries, occurs one or two months before perigean and spring tides combine to form the largest tide of the cycle. Although "ice walls" and associated phenomena pose hazards for man-made constructions, important natural purposes are served which need to be considered in coastal development and management schemes. Tides play a major role in erosion and in complex interactions among Fundy physical, biological, and chemical processes. Recent observations on mud flat grain size alterations, over deepening areas of the sea bed, and changes in the benthic community indicate changing environmental conditions in the Bay, caused possibly by increased hydrodynamic energy in the system. Résumé Les marées constituent une réalité omniprésente dans de nombreuses régions côtières du monde, et leurs causes et leur influence intriguent depuis longtemps. Il existe peu d'endroits où les marées jouent un rôle plus marquant au sein de l'économie et du caractère d'une région et de ses habitats que dans le secteur du rivage de la baie de Fundy, dans l'Est du Canada. La baie de Fundy représente effectivement un merveilleux laboratoire naturel pour l'étude des marées et de leurs effets. Il faut toutefois, pour mieux comprendre ces phénomènes, des perspectives élargies des caractéristiques physiques générales des marées et de leur fonctionnement à l'échelle océanique. Le passé géologique de la région fournit lui aussi des indices précieux sur la façon dont les marées les plus spectaculaires du globe sont apparues dans la baie de Fundy et sur les raisons de leur présence. Les caractéristiques des marées le long du littoral de l'Est du Canada découlent d'une combinaison de marées diurnes (quotidiennes) et semi-diurnes (biquotidiennes), parmi laquelle ces dernières prédominent principalement. Les amplitudes des marées dans la partie supérieure de la baie de Fundy dépassent communément 15 mètres, en grande partie en raison des forces tectoniques qui ont sculpté la baie au cours du Trias. L'existence et l'emplacement de la baie sont principalement déterminés par un semi-graben, le bassin de Fundy, dont l'établissement remonte au début de l'ouverture de l'océan Atlantique. Vu les proportions de la baie de Fundy, les différences d'amplitude des marées à l'intérieur du système du golfe du Maine, de la baie de Fundy et du Banc Georges sont régies par une quasi-résonance avec les marées de contrainte de l'Atlantique Nord. Même si les courbes des marées de Fundy sont sinusoïdales, les prévisions des marées nécessitent la considération d'inégalités diurnes distinctes. Le chevauchement des cycles des marées de vives-eaux et des marées de périgée tous les 206 jours entraîne une progression annuelle de 1,5 mois des périodes de marées particulièrement élevées. Selon l'année, ces marées de grande envergure peuvent survenir toutes les saisons. Les marées les plus fortes de Fundy apparaissent lorsque les trois éléments – les cycles mensuels anomalistique, synodique et tropique – culminent simultanément. Le jumelage le plus proche survient à des intervalles de 18,3 ans en vertu d'un cycle appelé le cycle Saros. Les mouvements des marées de l'anse Herring dans le parc national Fundy illustrent les variations annuelles des marées anticipées. Les interactions entre la terre et la mer dans les régions macrotidales comme la baie de Fundy sont caractérisées par des conditions de quasi-équilibre intenses. Des estuaires, éphémères à l'échelle des temps géologiques, se remplissent progressivement de sédiments au fur et à mesure que s'élève le niveau relatif de la mer, ce qui force les marais salés en bordure à passer à des niveaux successivement supérieurs. Même si les marais salés de Fundy sont étroitement liés à un régime de marées de grande amplitude et de courants périodiques puissants, ils débordent rarement. Comme ces marais sont établis à environ 1,2 mètre de moins que les marées astronomiques les plus élevées, seules les très grandes marées peuvent les recouvrir d'une couche d'eau d'une profondeur substantielle. Les marées les plus importantes se présentent en série à des périodes de sept mois, 4,53 ans et 18,03 ans. Aucune inondation des marais élevés due aux marées ne survient pendant des mois et des mois. La majorité des marais salés s'élèvent au niveau moyen du cycle de 18 ans. Les emplacements exacts des niveaux d'eau des zones côtières, comme le niveau moyen des hautes-eaux et le niveau moyen des basses-eaux, ne cessent de poser des problèmes et font l'objet de beaucoup de litiges. Les courbes de marées établies dans le cas de certains estuaires de rivières illustrent de quelle façon les vagues des marées estuariennes se transforment le long de leur trajet pour former des mascarets et dans quelle mesure varient leur capacité de transport de sédiments et capacité d'érosion par suite des variations des pentes de la ligne d'eau. Les saisons qui se succèdent entraînent des changements spectaculaires du caractère des estuaires, en particulier lorsque des glaces apparaissent au cours de la seconde moitié du cycle de 206 jours, quand la différence de hauteur entre la marée de mortes-eaux et la marée de vives-eaux s'accroît, moment optimal de débordement au cours de n'importe quelle saison. Le danger maximal de glaces, notamment l'apparition de « murs de glace » dans les estuaires de Fundy, survient un ou deux mois avant que les marées de périgée et de vives-eaux se combinent pour former la marée la plus importante du cycle. Même si les « murs de glace » et les phénomènes connexes posent des dangers aux constructions érigées, ils servent des fins naturelles importantes qu'il faut considérer dans les programmes d'aménagement et de mise en valeur des côtes. Les marées jouent un rôle marquant dans l'érosion et dans les interactions complexes au sein des processus physiques, biologiques et chimiques de Fundy. Les observations récentes des modifications des grosseurs des grains des vasières, les secteurs d'approfondissement marqué du plancher océanique et les changements survenus dans la communauté benthique révèlent que les conditions du milieu de la baie changent, possiblement en raison de l'énergie hydrodynamique accrue à l'intérieur du système. [Traduit par la rédaction]
In Carpinteria Salt Marsh, Salicornia virginica (pickleweed) grows at lower marsh elevations than does Arthrocnemum subterminalis (Parish's glasswort). Standing biomass of both species was greatest immediately adjacent to their abrupt border, suggesting that conditions for plant growth were best here. We utilized field experiments, in which growth rates of naturally occurring and transplanted individuals of both species were measured in four marsh zones, to investigate the role of edaphic factors and competition in maintaining this zonation pattern. The frequency of flooding, and hence soil waterlogging, was greatest at lower marsh elevations, whereas salinity was highest at higher marsh elevations. Consequently, it was not clear, a priori, which part of the marsh had the most severe physical conditions. In our field experiments, both Salicornia and Arthrocnemum grew better in the two middle marsh zones (high Salicornia zone and Arthrocnemum zone) than in either the low marsh (low Salicornia zone), where flooding was frequent and soils were waterlogged, or the high marsh (transition zone), where soil salinity was extremely high during much of the year and plant water potentials very low. However, Salicornia appeared better able to tolerate flooding, and so persisted in the low Salicornia zone, whereas Arthrocnemum appeared better able to tolerate high salinities, and so persisted in the transition zone. Interspecific competition was most important in the relatively benign middle marsh zones, where each species excluded the other from a portion of this prime habitat. In this marsh, flooding, soil salinity, and competition all interacted to determine plant zonation patterns, but the relative importance of these factors varied at different elevations.
An evaluation was completed to compare the accuracy of lidar (Light Detection and Ranging) against a statistically representative array of Real-Time Kinematic (RTK) GPS data in a low gradient, vegetated Southeastern U.S. salt marsh. In order to discern potential bias, analyses were
carried out separately on the platform-only data, the creek-only data and then the combined datasets. Lidar data were found to overestimate the RTK GPS topographic data by an overall average of only 7 cm. Additionally, these data showed little effect from the dominant macrophyte vegetation
within the lidar footprint. From this evaluation, 7 cm appears to be an appropriate vertical adjustment factor for using lidar data in low gradient salt marshes. However, local ground control will continue to be crucial in studies of intertidal environments incorporating airborne laser data
collection.
Ecogeomorphological modeling in salt marshes faces distinct challenges due to tidal oscillation and variability, fieldwork logistics, and the inherent dynamic nature of these environments. Recently developed technologies and methods introduce the capability to create fine-scale, system-wide databases to quantitatively characterize salt marsh geomorphology in support of improved understanding of the evolution of intertidal systems. This study combines the use of 20-cm AIMS-1 multispectral imagery flown at spring high and low tides with a LIDAR-derived digital elevation mode (DEM) of a New England estuarine system to quantify relationships among marsh features, their metrics, elevations, and tidal datums. The methods used to quantify features across an intertidal watershed in its entirety represent a significant advance in support of future development of process-driven models to explain these observations. Geomorphological analyses of the distribution of marsh features at the Great Marsh, Massachusetts, study area support field observations that water-filled ponds are concentrated in regions of the marsh around and above mean higher high water (MHHW), whereas drained ponds and pannes are distributed across the marsh platform; pannes are most abundant in the high marsh. These analyses are complicated by human interference in the form of ditches, which have the general effect of both draining ponds and inhibiting pond formation, altering the natural distribution of drained ponds, pannes, and water-filled ponds. However, the geomorphic distribution of pannes and ponds indicates strong elevational control on feature formation, most likely as a function of depth and duration of inundation.
Salt marsh grassland along the coasts of the Baltic sea in Germany is the result of several hundred years of agricultural activities, which replaced reeds of the brackish water zone gradually by grazing-resistent salt marsh plants. However, after diking and intensified agricultural landuse salt marsh grasslands along the Baltic Sea are very rare and most plant species in these areas are endangered. We report on a pilot project on a 350 ha area near Greifswald at the coast of the Greifswalder Bodden (Baltic sea). In this area, natural periodic flooding was re-introduced after the opening of the front dike line in 1993. Vegetation changes were recorded from 1994 to 1998, and were analyzed for changes in plant species diversity and composition. We established transects and permanent plots to monitor vegetational changes over five years. For three salt marsh species, Aster tripolium, Inula britannica and Puccinellia distans, number and size of populations were evaluated on the total area of 350 ha. Our analyses illustrate that the re-introduction of natural flooding, in combination with a traditional grazing regime, increases mean species diversity by a factor of four and total species diversity by a factor of 2.4. Five years after removing the dike line nearly 75% of the 350 ha were covered by typical salt marsh and salt grassland vegetation types, which also included 8.0% cover by pioneer vegetation. The three monitored salt marsh species had increased in number and size of colonised patches. We conclude that the restoration of formerly wide-spread salt marsh grassland is possible on a large scale.
An integrated remote sensing approach quantified saltmarsh dynamics in response to a sudden change in surface elevation due to a saltmarsh restoration scheme. The biogeomorphological relationship between surface elevation and saltmarsh presence occurs over the long-term so can be difficult to observe, though the ‘managed realignment’ of coastal defences provides a unique experimental opportunity to study this relationship. Realignment at Freiston Shore, Lincolnshire, UK in August 2002 caused a sudden and high-magnitude sediment input into the local coastal system, significantly increasing the intertidal surface elevation. The resulting impacts on the external, fronting saltmarsh were quantified by aerial photography and airborne multispectral imagery. Algal and pioneer saltmarsh boundary positions were calculated from 1984 to 2006, with the latter zone migrating slowly seaward pre-realignment (3.8 m a−1), but advancing significantly post-realignment (21.3 m a−1). Classification of five-year multispectral imagery accurately showed subtle changes in vegetation community composition within these boundaries. The realignment site was also colonized rapidly compared to other restoration sites, due to its high starting surface elevation. This study shows how, with sufficient sediment input and accommodation space, coastal management decisions can release intertidal surfaces from physical constraints to saltmarsh colonization.
Salt marshes, most now embanked, together with genetically related wetlands and high intertidal flats, make a major environmental contribution to the lowland coasts of Northwest Europe. They occur in many different contexts, but chiefly on open and barrier coasts and in estuaries and embayments, and range greatly in scale, from a modest total that measure hundreds of square kilometres in individual extent, to an enormous number each of an area no greater than tens to a few hundred hectares.These marshes and associated environments are under complex natural controls and experienced from the mid-Holocene onward human exploitation and, increasingly, interference. The main external controls are the sea-level, tidal and sediment-supply regimes. Intrinsic infuences are provided by the halophytic vegetation and sediment autocompaction. Upward sea-level movements and autocompaction combine to provide accomodation space within which marshes build upward. Field data and simulation modelling show that youthful mineralogenic marshes grow up rapidly and can mature within a few hundred years of inception. They consist of a vegetated platform dissected typically by extensive networks of blind-ended, branching tidal creeks and gullies. The flow-resistant surface vegetation, shaping the combined wave-tide boundary layer on the platforms, both traps and binds tidally introduced mineral sediment, but also contributes an organic component of indigenous origin to the deposit. When sea-level becomes stable or falls, however, in response to century-millennial scale fluctuations, the organic sediment component becomes dominant and mineralogenic marshes are transformed into organogenic ones. Organogenic marshes normally display a considerable range of sub-environments which create much spatial variation in the peat facies which accumulate. At an advanced stage, domed raised bogs, rising significantly above the general landscape, may appear on the marshes. Because peat is such a porous and permeable sediment, and there is little or no tidal inundation, organogenic marshes in Northwest Europe typically lack surface channels for internal drainage.The stratigraphic sequences accumulated during the Holocene beneath coastal marshes and high tidal flats typically present an alternation on a vertical scale of decimetres to metres of silts (mineralogenic marshes, high intertidal mudflats) and peats (organogenic highest intertidal-supratidal marshes). Coastal barriers and some channels are represented by local accumulations of sand and/or gravel. The silts and peats form couplets which are generally considered to be related to fluctuations of sea-level about the general upward trend. Field investigations and modelling show that, in areas where marshes are mature, the upward change from an organogenic to a sequence of mineralogenic marshes (transgressive overlaps) is accompanied by the initiation and invasive development of a branching network of tidal creeks. These decay and infill during the reversal of the environmental sequence and the approach, expressed as a series of regressive overlaps, of the next set of peat-forming conditions. The operation of the continuous, progressive, irreversible and asymptotic process of sediment autocompaction exerts a major, secondary control on depositional regimes and marsh behaviour. A variety of local responses are consequently possible in an extensive marsh, even though the marsh may be everywhere in dynamic equilibrium with environmental factors. Autocompaction also strongly shapes the character of Holocene coastal sequences as now perceived, introducing significant stratigraphic distortions and displacements which, for the time being, limit the accuracy of sea-level curves and rates of sea-level change based on dated intercalated peats.Prehistoric humans benefitted from the resources of coastal salt marshes, especially at the times when peat marshes begin to be transgressed. Peat domes not yet fully collapsed may have provided vantage points for seasonal ocupancy or even settlement from which the richer resource of the mineralogenic marshes developing on lower ground could be exploited. Increasing human interference on salt marshes over the last millennium, chiefly through wholesale land-claim and set-back, augmented by rising sea levels and continuing autocompaction, has led to a variety of poorly understood but generally deleterious effects in the lowland coastal zone. These include major changes to tidal and sedimentary regimes.
Coastal saltmarsh ecosystems occupy only a small percentage of Earth's land surface, yet contribute a wide range of ecosystem services that have significant global economic and societal value. These environments currently face significant challenges associated with climate change, sea level rise, development and water quality deterioration and are consequently the focus of a range of management schemes. Increasingly, soft engineering techniques such as managed realignment (MR) are being employed to restore and recreate these environments, driven primarily by the need for habitat (re)creation and sustainable coastal flood defence. Such restoration schemes also have the potential to provide additional ecosystem services including climate regulation and waste processing. However, these sites have frequently been physically impacted by their previous land use and there is a lack of understanding of how this ‘disturbance’ impacts the delivery of ecosystem services or of the complex linkages between ecological, physical and biogeochemical processes in restored systems. Through the exploration of current data this paper determines that hydrological, geomorphological and hydrodynamic functioning of restored sites may be significantly impaired with respects to natural ‘undisturbed’ systems and that links between morphology, sediment structure, hydrology and solute transfer are poorly understood. This has consequences for the delivery of seeds, the provision of abiotic conditions suitable for plant growth, the development of microhabitats and the cycling of nutrients/contaminants and may impact the delivery of ecosystem services including biodiversity, climate regulation and waste processing. This calls for a change in our approach to research in these environments with a need for integrated, interdisciplinary studies over a range of spatial and temporal scales incorporating both intensive and extensive research design.
Remote-sensing based cover mapping has a long history of use in natural resource management for a wide-range of applications. In order to be effectively employed, remote-sensing based cover maps must be accurate and meet the spatial scale inherent to the phenomena of interest. In this study, we employed the Random Forests algorithm in a supervised classification approach to construct a fine-scale (i.e., 1.0 meter pixel resolution) remote-sensing based cover map of coastal dune and salt marsh ecosystems at Cape Cod National Seashore, USA. We achieved high overall classification accuracies (i.e., 75.1% and 86.8% correct classification rate for the dune and salt marsh study areas, respectively) with a large proportion of the misclassified holdout validation assessment points being errors of commission between overlapping and/or ecologically similar cover classes. In addition, we were able to considerably reduce the predictor variable set by using a forward selection variable reduction method while achieving modestly higher classification accuracies compared to the global model. Our results suggest that coastal dune and salt marsh ecosystems can be mapped at a fine spatial resolution with reasonably high classification accuracy using a supervised Random Forests-based approach such as ours.
A new technique for quantifying the geomorphic form of northern forested wetlands from airborne LiDAR surveys is introduced, demonstrating the unprecedented ability to characterize the geomorphic form of northern forested wetlands using high-resolution digital topography. Two quantitative indices are presented, including the lagg width index (LWI) which objectively quantifies the lagg width, and the lateral slope index (LSI) which is a proxy measurement for the dome shape or convexity of the wetland ground surface. For 14 forested wetlands in central Ontario, Canada, northwestern Ontario, Canada, and northern Minnesota, United States, these indices were systematically correlated to metrics of topographic setting computed from LiDAR digital elevation models. In particular, these indices were strongly correlated with a Peatland Topographic Index (PTI, r2 = 0.58 and r2 = 0.64, respectively, p < = 0.001) describing the relative influence of upslope contributing area on the hydrology and biogeochemistry of individual wetlands. The relationship between PTI and the LWI and LSI indices was interpreted as geomorphic evolution in response to the spatially varying influence of upslope runoff on subsurface hydrochemistry. Spatial patterns of near-surface pore water chemistry were consistent with this interpretation. Specifically, at four wetland sites sampled extensively for pore water chemistry, the mean and variance of near-surface pore water methylmercury (MeHg) concentrations were higher within the zone of enhanced upland-wetland interactions, as inferred from the LiDAR-derived LWI estimates. Use of LiDAR surveys to measure subtle topographic gradients within wetlands may therefore help quantify the influence of upland-wetland interactions on biogeochemical cycling and export in northern forested landscapes.
Archaeological applications of airborne lidar topographic data are now well established and documented. However, less well explored by archaeologists and palaeoenvironmentalists are the potential applications of lidar intensity data. Here we explore this potential to remotely determine the differential preservation potential of valley floor sediments, within a temperate, lowland environment, especially where preserved within palaeochannels. We compare airborne lidar intensity data with simultaneously collected terrestrial records of sediment organic content, moisture and stratigraphy. Results suggest that while a correlation exists between lidar intensity values and sediment properties, it is neither linear nor robustly predictable. Nevertheless it is suggested that examination of lidar intensity data serve a useful purpose when assessing valley floor alluvial sediments.
The Cumberland Basin, a 118 km2 estuary at the head of the Bay of Fundy which has an average tidal range of about 11m, contains large tracts of salt marsh (15% of the area below highest high water). Low marsh (below about 0·9 m above mean high water) is composed almost exclusively of Spartina alterniflora while the vegetation on high marsh is more diverse but dominated by Spartina patens. Because of its higher elevation, high marsh is flooded infrequently for short periods by only extreme high tides. Low marsh is inundated much more frequently by water as much as 4m deep for periods as long as 4 h per tide. Temporal variability in the occurrence of extreme tides influences the flooding frequency of high marsh for any given month and year. Using a modification of Smalley's method, the mean annual net aerial primary production (NAPP) of low and high marsh is estimated to be 272 and 172 g C m−2, respectively. Vegetation turnover times average 1·0 and 2·0 y for low and high marsh, respectively. Because of abundant tidal energy, much of the low marsh production appears to be exported and distributed widely about the estuary. Since high levels of turbidity suppress phytoplankton production, salt marshes produce approximately half of the carbon fixed photosynthetically in the Cumberland Basin. It is concluded that salt marshes play a major ecological role in the Cumberland Basin.
Vertical elevation relative to mean sea level is a critical variable for the productivity and stability of salt marshes. This research classified a high spatial resolution Airborne Data Acquisition and Registration (ADAR) digital camera image of a salt marsh landscape at North Inlet, South Carolina, USA using an artificial neural network. The remote sensing-derived thematic map was cross- referenced with Light Detection and Ranging (LIDAR) elevation data to compute the frequency distribution of marsh elevation relative to tidal elevations. At North Inlet, the median elevation of the salt marsh dominated by Spartina alterniflora was 0.349 m relative to the North American Vertical Datum 1988 (NAVD88), while the mean high water level was 0.618 m (2001 to May, 2003) with a mean tidal range of 1.39 m. The distribution of elevations of Spartina habitat within its vertical range was normal, and 80% of the salt marsh was situated between a narrow range of 0.22 m and 0.481 m. Areas classified as Juncus marsh, dominated by Juncus roemerianus, had a broader, skewed distribution, with 80% of the distribution between 0.296 m and 0.981 m and a median elevation of 0.519 m. The Juncus marsh occurs within the intertidal region of brackish marshes and along the upper fringe of salt marshes. The relative elevation of the Spartina marsh at North Inlet is consistent with recent work that predicts a decrease in equilibrium elevation with an increasing rate of sea-level rise and suggests that the marshes here have not kept up with an increase in the rate of sea-level rise during the last two decades.
Tidal salt marshes provide a range of ecosystem services. The most recently recognized is their provision of highly effective sinks for atmospheric carbon dioxide, a characteristic they share with mangroves swamps which largely replace salt marshes in the intertidal zones of tropical regions. Efforts are emerging to use salt marsh preservation or restoration in carbon offset programs, similar to the REDD initiative for tropical forests, but a number of issues first must be addressed to determine if a site meets the requirements of these programs. As intertidal systems, both salt marshes and mangrove swamps are threatened by increasing rates of sea level rise, and it will be essential to determine their sustainability, thus meeting the requirement of permanence of the carbon sink. In many areas the vegetation responsible for marsh soil accretion may not survive increased flooding periods, resulting in submergence of the marsh in its present location or inability to restore a marsh at its previous elevation. However, the marsh and its carbon sink, may survive if allowed to migrate inland. Thus assessment of permanence requires a determination if inland migration will be hindered by barriers such as high slopes or development, i.e., if the ecosystem is in a coastal squeeze. Presently, the only technology that can provide elevation models at the required vertical accuracy is Lidar, which also is extremely valuable for assessing vulnerability of coastal communities to flooding. Yet, Lidar data is not available for all coastlines, even those in the developed world. To effectively plan for the future of our coastlines requires Lidar coverage on all sensitive coastlines and its free availability for impact assessments.
Two major aspects of tidal inundation and exposure, i.e., frequency and duration, were examined in relation to the abrupt demarcation between adjacent monotypic zones of Spartina alterniflora and Juncus roemerianus of salt marsh in Davis Bay, Mississippi. The marsh surface in the zone of S. alterniflora has a range in elevation from 0.24 m below mean low water (MLW) to 0.54 m above MLW. The J. roemerianus zone ranges from 0.54 m to 0.75 m above MLW. Spartina alterniflora occupies a seaward area on the tidal plane that spans an average of 0.76 m, an elevational spread three times that occupied by J. roemerianus (0.21 m). Analysis of annual tidal cycles for 1975 indicated that the entire zone of S. alterniflora is flooded much more frequently (139 times) than the entire J. roemerianus zone (16 times). Partial flooding occurs more often. Most (78%-98%) of the high tides occur within the lower three-fourths of the S. alterniflora zone. Correspondingly, the lower three-fourths of the S. alterniflora zone was flooded from 35-87% (hours innundated: 3,045 to 7,645) of annual total (8,750) in comparison to 10% (855 h) for the upper one-fourth. The zone of J. roemerianus is flooded from 0.8 to 5% (75 to 475 h) of the annual total, clearly indicating that this habitat is exposed most of the time. While major portions of the two monotypic stands have extremely different tidal relationships, frequency and duration of tidal flooding could not be related to the line of abrupt delineation between the plant zones, suggesting that factors other than the tide are involved.
Land cover mapping methodology should be governed by the attributes of the land cover types. Since land cover types usually have significantly different interpretation characteristics, they should be mapped separately according to the methodology suitable to their particular attributes. Land cover mapping requires the use of other interpretation elements than just reflectance, particularly position in the landscape, size and association. In addition, knowledge of the land use systems and their extent is essential for attributing spectral reflectance curves to land cover types. A bottom-up land cover mapping approach, using classical interpretation principles, but facilitated with modern remote sensing software, is recommended. The procedure has been applied to mapping land cover types of southern Sumatra from Landsat and Spot imagery.
Digital elevation models (DEMs) were compared to characterize how well airborne lidar (light detection and ranging) data depict the microtopography of a salt marsh. 72,000 GPS points and 700,000 lidar points from a 1 km2 salt marsh island were linearly interpolated using identical DEM configurations. Overall, 78% of lidar elevations were within ±0.15 m of the high precision GPS elevations. Spatial arrangement of difference values reveal that lidar performed best on the marsh platform, and poorly along tidal creeks and creek heads. Also, the overall shape of the salt marsh was poorly defined, even where lidar data were within the reported range of accuracy. These observations indicate that lidar appears to be a robust tool for mapping intertidal landscapes. However, lidar DEMs may not adequately resolve the microtopographic variations of a salt marsh, and for research questions that require accurate depiction of small-scale tidal creek networks and subtle terrain features lidar data should be augmented with other information. Copyright © 2011 John Wiley & Sons, Ltd.
Airborne Light Detection and Ranging (LiDAR), a remote sensing data collection technique, has many applications in the field of archaeology, including aiding in the planning of field campaigns, mapping features beneath forest canopy, and providing an overview of broad, continuous features that may be indistinguishable on the ground. LiDAR was used to create a high-resolution digital elevation model (DEM) in a heavily vegetated area at Fort Beauséjour–Fort Cumberland National Historic Site, Canada. Previously undiscovered archaeological features were mapped that were related to the siege of the fort in 1755. Features that could not be distinguished on the ground or through aerial photography were identified by overlaying hillshades of the DEM created with artificial illumination from various angles. LiDAR provides accurate digital topographic models with the additional benefit of mapping vertical surfaces in accurate detail below the forest canopy. © 2009 Wiley Periodicals, Inc.
A key question in designing any managed retreat site concerns the nature of the habitats which will be created, and their likely long-term sustainability and development. Studies of historical sea wall failures in Essex have shown that former reclaimed areas may respond to renewed tidal flooding in different ways depending on a number of factors, most importantly the elevation of the land at the time of breach, which governs the frequency and duration of tidal flooding. This paper demonstrates how digital terrain modelling using airborne lidar data can be used to calculate the elevation of the land behind a breach and to predict the likely habitats which will be created. When combined with data from sites of historical sea wall failure, predictions can also be made about the likely geomorphological and biological evolution of the created habitats in the longer term. At Abbotts Hall on the northern side of Salcott Creek, Essex, where a managed retreat scheme was activated in October 2002, the highest areas above 2·35 m OD were predicted to develop stable saltmarsh, intermediate areas between 2·1 and 2·34 m OD to develop potentially unstable saltmarsh which is likely undergo internal dissection, and the lowest areas below 2·1 m OD to remain as mudflat or lagoon. Approximately 38 per cent of the site was predicted to develop stable saltmarsh, and nearly 50 per cent to remain as lagoon or mudflat. Monitoring is now being undertaken but it will be several years before the accuracy of the predictions can be assessed. Copyright © 2004 John Wiley & Sons, Ltd.
A methodology combining ecological modelling with geographical information analysis and remote sensing was employed to determine the effects of sea-level rise in estuarine salt marshes, using the Tagus estuary (Portugal) as a case study. The development of salt marsh vegetation was simulated separately for C3 and C4 plants, using a combined biogeochemical and demographic model. This simulation, which provided small-scale (m 2) results of annual above-ground primary production, was upscaled to the whole salt marsh area, using bathymetry data, remote sensing and Geographic Information System (GIS) for assessing vegetation cover and determining areal distribution of C3 and C4 vegetation. Based on IPCC data, several sea-level rise scenarios were considered, and the coupled ecological model-GIS were applied to these in order to determine changes in global salt marsh productivity. The results indicate that the salt marshes of the mesotidal estuaries such as the Tagus are susceptible to sea-level rise only in a worst case scenario, which is more likely to occur if the terms set out by the Kyoto protocol are not met by several industrialised nations. The low vulnerability of salt marshes supports the suggestion that areas with high tidal ranges are less vulnerable to sea level change, due to greater sediment transport and accretion. Nevertheless, the precautionary principle should always be applied by coastal planners, due to the great uncertainty surrounding forecasts of sea-level rise. © 2001 Elsevier Science B.V. All rights reserved.
Assessing the response of salt marshes to tidal restoration relies on comparisons of ecosystem attributes between restored and reference marshes. Although this approach provides an objective basis for judging project success, inferences can be constrained if the high variability of natural marshes masks differences in sampled attributes between restored and reference sites. Furthermore, such assessments are usually focused on a small number of restoration projects in a local area, limiting the ability to address questions regarding the effectiveness of restoration within a broad region. We developed a hierarchical approach to evaluate the performance of tidal restorations at local and regional scales throughout the Gulf of Maine. The cornerstone of the approach is a standard protocol for monitoring restored and reference salt marshes throughout the region. The monitoring protocol was developed by consensus among nearly 50 restoration scientists and practitioners. The protocol is based on a suite of core structural measures that can be applied to any tidal restoration project. The protocol also includes additional functional measures for application to specific projects. Consistent use of the standard protocol to monitor local projects will enable pooling information for regional assessments. Ultimately, it will be possible to establish a range of reference conditions characterizing natural tidal wetlands in the region and to compare performance curves between populations of restored and reference marshes for assessing regional restoration effectiveness.
The purpose of this paper was to examine the vegetative, sedimentary, nekton and hydrologic conditions pre-restoration and the initial 2 years post-restoration at a partially restricted macro-tidal salt marsh site. Replacement of the culvert increased tidal flow by 88%. This was instrumental in altering the geomorphology of the site, facilitating the creation of new salt marsh pannes, expansion of existing pannes in the mid and high marsh zones, and expansion of the tidal creek network by incorporating relict agricultural ditches. In addition, the increase in area flooded resulted in a significant increase in nekton use, fulfilling the mandate of a federal habitat compensation program to increase and improve the overall availability and accessibility of fish habitat. The restoration of a more natural hydrological regime also resulted in the die-off of freshwater and terrestrial vegetation along the upland edge of the marsh. Two years post-restoration, Salicornia europea (glasswort) and Atriplex glabriuscula (marsh orache), were observed growing in these die-back areas. Similar changes in the vegetation community structure were not observed at the reference site; however, the latter did contain higher species richness. This study represents the first comprehensive, quantitative analysis of ecological response to culvert replacement in a hypertidal ecosystem. These data will contribute to the development of long-term data sets of pre- and post-restoration, and reference marsh conditions to determine if a marsh is proceeding as expected, and to help with models that are aimed at predicting the response of marshes to tidal restoration at the upper end of the tidal spectrum.
Airborne remote sensing offers high-density, spatially-averaged synoptic samples of radiation reflected from a surface which can be used to infer ecological processes and community composition. Unfortunately, the cost of the overheads in terms of time and resources, and scheduling constraints when deriving quantitative information have limited its use in operational monitoring programs. When the changes in reflected radiation related to the phenomenon under investigation are large, only minimal low-cost processing is required to identify ecosystem modification if high frequency multi-temporal imagery can be combined with expert knowledge. This methodology is likely to be of particular value in coastal environments where access for conventional measurements is restricted and changes in sensitive tidal wetlands may provide an early indicator of changing natural processes and/or human impact. Regularly acquired airborne remotely sensed imagery has been used in a reconnaissance study to identify and map seasonal vegetation patterns on intertidal surfaces in back barrier environments on the North Norfolk coast, England, U.K. The development of an operational system for coastal zone management is discussed.
Salt meadows are thought to be vulnerable to habitat loss under future sea-level rise (SLR) due to inundation and compression of coastal environments (coastal squeezing). The extent of this threat is poorly understood due to the lack of geographically comprehensive impact assessments. Here, we linked vegetation data for Danish salt meadows to novel very fine-resolution digital elevation models. We developed statistical models relating plant species richness and average salt tolerance to elevation at different spatial scales. The best models were used to quantify potential impacts of SLR on Danish salt-meadow vegetation under five potential 21st-century scenarios. Overall, species richness increased with elevation (average r
2 = 0.21), while average salt tolerance decreased (average r
2 = 0.45). Fine resolution (≤10-m) topography was required to fully represent vegetation-elevation relationships. At >50-m resolutions only feeble links were found. Under the worst scenarios 67–74% of the Danish salt-meadow area was projected to be lost. Notably, the relatively species-rich upper meadows were predicted to shrink drastically. If realized, these impacts may have severe consequences for salt-meadow biodiversity. We note that sedimentation, not accounted for here, may allow some salt meadows to partly keep up with SLR but the extent to which this will occur and where is uncertain.
Linking intertidal processes to their natural patterns within a framework of coastal erosion requires monitoring techniques providing high-resolution spatio-temporal data from the scale of processes to this of patterns. The Scanning Hydrographic Operational Airborne LiDAR Survey (SHOALS) consists of a ubiquitous topographic and bathymetric LiDAR (Light Detection And Ranging) system that has become an important technology for generating high-resolution Digital Terrain Models (DTM) and Digital Surface Models (DSM) over intertidal landscapes. The objectives of this project are i) to highlight the capacity of SHOALS Topography and intensity data (Red and Near-InfiraRed) to detect intertidal vegetation, ii) to assess the salt-marsh zonation, and iii) to map intertidal habitats and its adjacent coastal areas (Gulf of St. Lawrence, Canada). The study area was selected based on the spectrum of land cover types, encompassing beach, salt-marsh, arable farm and urban coastal environments. Surfaces constructed from the LiDAR survey included DSM, DTM, Normalized Surface Model (NSM), Digital Intensity Model for InfraRed (DIMI), Digital Intensity Model for Red (DIMR), and Normalized Difference LiDAR Vegetation Index Model (NDLVIM), derived from the two previous models. The correlation between the so-called NDLVI and the amount of salt-marsh vegetation, measured in situ, was 0.87 (p<0.01). Then, LiDAR-assessed salt-marsh ecological zonation allowed finding out intermediate and strong relationships between NDLVI and Topography (r(2) = 0.89, p<0.038) and Topographic heterogeneity (r(2) = 0.54, p<0.1394), respectively. Finally, NDLVI and Topography surfaces were classified using maximum likelihood algorithm into 17 classes. whose overall accuracy and kappa coefficient were 91.89% and 0.9088, respectively. These results support that (1) intertidal vegetation can be discriminated by NDLVI, (2) salt-marsh ecological zonation pattern, and (3) accurate coastal land cover maps can be satisfactorily generated from a single LiDAR survey using the NDLVIM and DTM approach. (C) 2009 Elsevier Inc. All rights reserved.
In order to explain biological zonation, shore height above the ordnance level is frequently used as an indicator of the abiotic gradient in intertidal ecosystems. This is based on the implicit assumption that shore height is directly correlated with inundation frequency and/or duration. Despite the importance of inundation for tidal ecosystems, measurements have rarely been taken directly by measuring inundation at the site of investigation. We measured mean high tide (MHT) and flooding frequency at three sites on the Dutch Barrier Island of Schiermonnikoog. To assess the scale dependence, we compared local measurements with the estimated inundation frequencies based on the official tide gauge (OTG) farther away. Locally measured MHT water levels differed among sites and were consistently higher than estimated MHT water levels. With this data, we subsequently estimated the inundation frequency of vegetation plots from our measurements and correlated it with species distribution. In a logistic regression inundation frequency accounted for twice the variance in explaining the dominance of three salt marsh species than shore height. The discrepancy in annual inundation frequency of the vegetation between sites was ≦300% for a given shore height. Within each site replicated estimates of inundation frequency proved to be consistent (scale 10–50 m). Estimated and measured inundation frequencies thus reliably correlated at a small-scale (tens of metres), but not at a larger scale (hundreds of metres to kilometres). If inundation frequency is used as an explanatory variable, it will therefore be advisable to consider the spatial heterogeneity of the measurements, in particular if different sites are to be compared. We give mean inundation frequencies of three dominant salt marsh species (Elymus athericus, Festuca rubra, Artemisia maritima) measured over 1 year.
A field study was conducted to determine the controls on spatial patterns of sediment deposition across a salt marsh surface in the Bay of Fundy. Approximately 670 surface-mounted sediment traps were deployed over 28 different tidal cycles in a variety of spatial configurations and environmental conditions. Spatial patterns of deposition were derived using spatial interpolation procedures in ArcView GIS 3.2. Suspended sediment concentration, flow characteristics and water depth were measured using co-located optical backscatterance sensors, electromagnetic current meters and a pressure transducer. Sediment deposition was a complex function of variables controlling the availability of sediment and the opportunity for this sediment to be deposited. The relative importance of inundation time, distance from source material, relative roughness and suspended sediment concentration varied across the marsh surface. Wave activity, however, exerted a significant influence on both the temporal and spatial patterns of sediment deposition, particularly through an increase in suspended sediment concentrations and through transport of suspended sediment further up into the mid and high marsh during spring tides. In addition, the region around the mean high water level appears to form a transition zone for processes of sediment transport and deposition, with most deposition taking place around this region. This study also emphasizes the importance of knowing precisely where one's sample stations are within the tidal frame. Modelling exercises must therefore consider spatial and temporal variability in sedimentary processes across a salt marsh surface. In addition, this study suggests sedimentation models developed for sheltered coastal marshes cannot necessarily be applied to open coastal marshes exposed to wave activity.
We used LiDAR topographic data, AVIRIS hyperspectral data, and locally measured tidal fluctuations to characterize patterns of plant distribution within a southern California salt marsh (Carpinteria Salt Marsh (CSM)). LiDAR data required ground truthing and correction before they were suitable for use. Twenty to forty percent of the uncertainty associated with LiDAR was due to variance in the elevation of the target surface, the balance was attributed to error inherent in the LiDAR system. The incidence of LiDAR penetration of plant canopy cover (i.e., registration of ground elevation) was only three percent. The depth of LiDAR penetration into the plant canopy varied according to plant species composition; plant species-specific corrections significantly improved LiDAR accuracy (58% reduction in overall uncertainty) and with the use of ground-based surveys, reduced overall RMSE to an average of 6.3 cm in vegetated areas. A supervised classification of AVIRIS data was used to generate a vegetation map with six classification types; overall classification accuracy averaged 59% with a kappa coefficient of 0.40. The vegetation classification map was overlaid with a LiDAR-based digital elevation model (DEM) to compute elevation distributions and frequencies of tidal inundation. The average elevations of the dominant plant classifications found in CSM (e.g., Salicornia virginica, Jaumea carnosa, and salt-grass mix, a mixture of multiple marsh plant species) occurred within a 17 cm range, a vertical change that resulted in a 7% difference in the period of tidal inundation.