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Marsh restoration using thin layer sediment addition: Initial soil evaluation

Authors:
  • US Army Corps of Engineers

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Current efforts are utilizing thin layer applications of dredged materials to address concerns regarding marsh degradation and enhancement of marsh resilience and habitat within a large wetland complex located near Avalon, New Jersey, USA. The S. alterniflora-dominated marsh displayed several signs of instability including erosion, expansion of open water areas, and fragmentation. Sediment placement occurred between November 2015 and March 2016. Dredged sediments were obtained during channel maintenance from the federally-maintained New Jersey Intracoastal Waterway following Superstorm Sandy. Sediment placement depths ranged from 5-20 cm in vegetated areas and up to 50 cm in open water portions of the marsh. Primary project goals include stabilization of the marsh platform, increasing the elevation of recently developed open water areas to promote vegetation establishment, and evaluating the potential benefits of thin layer sediment application for other restoration activities. Stabilization of the degraded Avalon marsh will also provide continued benefits to the barrier island community of Avalon by maintaining protection from waves and erosion. Monitoring efforts to document restoration outcomes began in 2016 and will continue during 2017 and beyond.
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Wetland Science & Practice March 2017 13
INTRODUCTION
Many coastal wetlands
display degradation
attributable to various factors
including land development,
erosion, salinization, and a
lack of sediment inputs (Bar-
ras et al. 2003; Baumann et al.
1984). Additionally, condi-
tions may worsen as impacts
associated with sea level rise
as well as increases in storm
frequency and intensity exac-
erbate marsh stressors (Hauser
et al. 2015). Marshes naturally
exhibit a mosaic of vegetated
and open water areas (Adamo-
wicz and Roman 2005). How-
ever, studies document marsh
fragmentation and subsequent degradation by examining an
increase in the conversion of vegetated areas to open water
(Figure 1; Turner 1997; Day et al. 2000).
Conceptual models of marsh degradation describe three
processes: 1) drowning - whereby accretionary processes
are outpaced by sea level rise, 2) edge retreat - caused
primarily by wave erosion at lower marsh margins, and 3)
marsh pond (sometimes referred to as pools or pannes) col-
lapse - in which open water areas fail to maintain elevation
relative to rising sea level and expand through continued
edge erosion (Mariotti 2016). DeLaune and others (1994)
described the process as pond initiation, in which newly
formed open water areas allow for marsh degradation via
erosion, collapse, and other mechanisms. In response,
wetland restoration projects have been implemented over
the past three decades to stabilize and enhance marsh eco-
systems (Warren et al. 2002). Techniques include erosion
control, invasive species removal, and re-establishment of
natural wetland vegetation and tidal ow regimes (GM-
CHRS 2004; Jackson 2009). Notably, in a recent article
Smith and Niles (2016) highlights the need for improved
approaches to documenting marsh degradation and deter-
mining the potential benets and/or risks associated with
marsh restoration.
Broome and others (1988) identied important compo-
nents in marsh restoration including elevation of the site in
relation to tidal regime, slope, exposure to wave action, soil
chemical and physical characteristics, nutrient supply, sa-
linity and availability of viable propagules for revegetation.
These factors highlight the need for restoration strategies
that counterbalance subsidence, support a stable platform
for plant growth, and keep pace with expected sea level rise
while maintaining natural patterns of wetland hydrology
and vegetation. The intentional application of sediments
into marsh habitats has the potential to help achieve resto-
ration goals by allowing the marsh to maintain elevation
despite ongoing subsidence or sea level rise.
Dredged materials have been utilized for many years
in wetland creation and restoration projects (Faulkner and
Poach 1996; Craft 1999; Cahoon and Cowan 1988). Com-
monly, materials are deposited within diked containment
areas, adjacent to shorelines, or in open water until target
elevations are reached (Landin et al. 1989; USACE 1983;
Berkowitz et al. 2015). The placement of dredged material
RESEARCH FOR SALT MARSH RESTORATION
1Correspondence author: Jacob.F.Berkowitz@usace.army.mil, 601-634-5218
Marsh Restoration Using Thin Layer Sediment Addition: Initial Soil Evaluation
Jacob Berkowitz1, Christine VanZomeren, and Candice Piercy
U.S. Army Corps of Engineers (USACE), Engineer Research and Development Center (ERDC), Vicksburg, MS
FIGURE 1. Site conditions in a degrading marsh near Avalon, New Jersey, USA in which portions of the marsh
have shifted from vegetated areas to shallow open features that display signs of erosion and subsidence
(left). Within vegetated sections of the marsh, Spartina alterniora roots form a dense root mat that helps to
stabilize marsh soils (right).
14 Wetland Science & Practice March 2017
directly onto the marsh surface remains challenging due to
the need to achieve target elevations while maintaining or
rapidly establishing the native plant communities that sta-
bilize marsh soils (DeLaune et al. 1994). As a result, much
interest has focused on the application of thin layers of
dredged materials within existing marshes to support marsh
elevation while enhancing existing habitat.
Wilbur (1992) dened thin layer placement techniques
as the application of dredged materials to a thickness that
does not transform the receiving habitat’s ecological func-
tions. Others have dened thin layer placement utilizing
a layer thickness criteria ranging from as little as a few
centimeters up to 50 cm. Sediment application typically
occurs via the spraying of uidized dredged materials onto
the marsh surface (Figure 2). Ray (2007) provided a review
of thin layer placement case studies. For example, Reimold
and others (1978) performed initial small-scale studies in
which Spartina alterniora successfully recovered follow-
ing the placement of 23 cm of dredged materials on the
marsh surface. Placement of thick layers reduced or pre-
vented plant recovery by rhizomes (Ford et al. 1999; Schrift
et al. 2008). Other studies examined thin layer placement
techniques designed to restore or enhance
degraded marshes through evaluation of plant
communities (Pezeshki et al. 1992; Ford et al.
1999), invertebrates (Croft et al. 2006), soil
organic matter and bulk density (Slocum et
al. 2005), and marsh resilience following a
disturbance (Stagg and Mendelssohn 2011).
TESTING THIN LAYER SEDIMENT TO RESTORE
DEGRADING SALT MARSH IN NEW JERSEY
Current efforts are utilizing thin layer applica-
tions of dredged materials to address concerns
regarding marsh degradation and enhance-
ment of marsh resilience and habitat within a
large wetland complex located near Avalon,
New Jersey, USA (Figure 3). The S. alternio-
ra-dominated marsh displayed several signs
of instability including erosion, expansion of
open water areas, and fragmentation. Sedi-
ment placement occurred between November
2015 and March 2016. Dredged sediments
were obtained during channel maintenance
from the federally-maintained New Jersey
Intracoastal Waterway following Superstorm
Sandy. Sediment placement depths ranged
from 5-20 cm in vegetated areas and up to
50 cm in open water portions of the marsh.
Primary project goals include stabilization of
the marsh platform, increasing the elevation
of recently developed open water areas to pro-
mote vegetation establishment, and evaluating
the potential benets of thin layer sediment
application for other restoration activities. Sta-
bilization of the degraded Avalon marsh will
also provide continued benets to the barrier
island community of Avalon by maintaining
protection from waves and erosion. Monitor-
ing efforts to document restoration outcomes
began in 2016 and will continue during 2017
and beyond.
FIGURE 2. Site preparation prior to thin layer sediment application included placement
of coir logs to target areas receiving sediment additions (top). Thin layer placement of
dredged materials involves spraying a dredged sediment slurry onto the marsh surface
(bottom). (Photo courtesy of Tim Welp)
Wetland Science & Practice March 2017 15
Project partners will be monitoring responses of veg-
etation, fauna, and other factors to the thin layer placement
effort, while our team is focused on soil physical, nutrient
and biogeochemical properties. Soils provide the physical
substrate supporting plant growth and soil microbial com-
munities have been shown to respond quickly to changes in
the environment (Slocum et al. 2005; Harris 2009). As a re-
sult, we believe that examining soil physical, nutrient, and
microbial properties associated with restoration techniques
remains an important component in evaluating restoration
trajectory and success (Table 1; Berkowitz 2013; Berkowitz
and White 2013). Prior to dredged material placement, soil
core samples were collected in vegetated and open water
areas within the restoration footprint and in adjacent control
regions of the marsh (Figure 4). The combination of pre-
application data with subsequent soil collections will allow
investigation of baseline soil property differences between
vegetated and open water features in the marsh as well as
change detection within control and treatment areas where
thin layer applications have occurred.
Figure 3. Location of the tidal marsh in coastal New Jersey, USA.
Note the location of the New Jersey Intracoastal Waterway, the source
for dredged materials utilized in the thin layer application. The areas
highlighted in white outline the portions of the marsh receiving thin layer
sediment application.
FIGURE 4. Sampling conditions differed between open water areas and S.
alterniora-dominated sections of the marsh as indicated by the lack of
soil stability in the open water areas. (Photo courtesy of Bobby McComas)
Physical properties Anticipated marsh response
Bulk density
Root distribution
Particle size
Moisture content
Soil horizon development; bulk
density decrease; dredge material
incorporated into the original soil
material
Nutrient status
Soil organic matter
Total phosphorus
Extractable nitrate
Total dissolved nitrogen
Dissolved organic carbon
Total carbon
Total nitrogen
Extractable ammonium
Soluble reactive phosphorus
Accumulation of organic C, N, and P;
C sequestration; improved nutrient
cycling over time
Microbial activity
Microbial biomass carbon
Potentially mineralizable nitrogen
Microbial biomass nitrogen Microbial communities become
established; marsh functions
dependent on microbes return to
comparable marsh levels
TABLE 1. Soil parameters being evaluated following thin layer sediment application and anticipated marsh response
16 Wetland Science & Practice March 2017
We anticipate the partial recovery of marsh functions
following dredged material placement based upon previous
studies. For example, Craft and others (1999) examined
constructed and planted S. alterniora marshes over a 25-
year period reporting accumulation of soil organic C and
soil N and decreases in bulk density. However, soil proper-
ties did not correspond with values observed in a natural
marsh. Thin layer placement applications may increase
recovery timelines, due to the presence of potential seed
sources for vegetation and microbial populations. Microbial
communities represent a small but active nutrient pool in
the soil environment, regulating biogeochemical cycling
and bioavailability of nutrients (White and Reddy 2001). As
marsh functions develop over time we expect soil horizon
development, organic C, N, and P accumulation, as well as
bulk densities and nutrient cycling to approach levels iden-
tied in the control marsh areas. Analysis of pre-treatment
and initial post-treatment samples collected after thin layer
placement of dredged materials are ongoing and should
lend insight into the implications and potential benets of
restoration techniques utilizing thin layer sediment applica-
tion (Figure 5).
For further information on this project, please feel free
to contact the senior author or the project leads Monica
Chasten from the USACE Philadelphia District and Dave
Golden from the New Jersey Department of Environmental
Protection Division of Fish and Wildlife. n
ACKNOWLEDGMENT
Research funding for this portion of the Avalon monitoring
effort was provided by the USACE Environmental Manage-
ment and Restoration Research Program (Trudy Estes – Pro-
gram Manager). Jason Pietroski and Kevin Philley assisted
with eld data collection and sample preparation. The Avalon
marsh restoration project was the result of a collaboration
with the USACE Philadelphia District, the New Jersey De-
partment of Environmental Protection Division of Fish and
Wildlife, The Nature Conservancy, and Green Trust Alliance
FIGURE 5. S. alterniora emerging from dredged materials utilized for marsh restoration via thin layer sediment application. The photos were taken
approximately six months (a, b), nine months (c), and 18 months (d) after placement of dredged material.
a.
c.
b.
d.
Wetland Science & Practice March 2017 17
funded jointly through the 2013 Disaster Relief Appropria-
tions Act (Superstorm Sandy recovery) and National Fish
and Wildlife Foundation Hurricane Sandy Coastal Resiliency
Competitive Grant. The authors would also like to acknowl-
edge the project leads Monica Chasten from the USACE
Philadelphia District and Dave Golden from the New Jersey
Department of Environmental Protection Division of Fish
and Wildlife and the dedicated team including Ms. Metthea
Yepsen from The Nature Conservancy and Ms. Jackie Jahn
from GreenVest LLC., and all the other staff from the Green
Trust Alliance and the Stone Harbor Wetlands Institute who
assisted with these projects. Special acknowledgements
are also offered for the dredging contractor, Barnegat Bay
Dredging, Inc. dredge captains and crew whose innovation,
teamwork and dedication contributed greatly to making this
project successful. The authors would like to acknowledge
the assistance of the USACE ERDC Program Managers, Ms.
Linda Lillycrop and Dr. Todd Bridges for continual support
of USACE Philadelphia District efforts to bring the Avalon
marsh restoration project to fruition.
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Coastal wetlands are experiencing accelerated rates of fragmentation and degradation due to sea-level rise, sediment deficits, subsidence, and saltwater intrusion. This reduces their ability to provide ecosystem benefits, such as wave attenuation, habitat for migratory birds, and a sink for carbon and nitrogen cycles. A deteriorated back barrier wetland in New Jersey, USA was nourished through thin layer placement (TLP) of dredged sediment in 2016. A field investigation was conducted in 2019 using a cone penetrometer (CPT) to quantify the establishment of soil strength post sediment nourishment compared to adjacent reference sites in conjunction with traditional wetland performance measures. Results show that the nourished area exhibited weaker strengths than the reference sites, suggesting the root system of the vegetation is still establishing. The belowground bio-mass measurements correlated to the CPT strength measurements, demonstrating that shear strength measured from the cone penetrometer could serve as a surrogate to monitor wetland vegetation trajectories. In addition, heavily trafficked areas underwent com-paction from heavy equipment loads, inhibiting the development of vegetation and highlighting how sensitive wetlands are to anthropogenic disturbances. As the need for more expansive wetland restoration projects grow, the CPT can provide rapid high-resolution measurements across large areas supplying government and management agencies with vital establishment trajectories.
... Berkowitz et al. 2017). Recent interest has focused on restoring coastal marshes in order to provide habitat, improve resiliency, and maximize ecological services that benefit society (Berkowitz et al. 2016). ...
Technical Report
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Wetland restoration activities utilizing sediments, including dredged material, may induce formation of solid phase iron sulfide (FeS) materials. Under certain conditions subsequent oxidation of FeS materials can negatively impact soil pH, posing a risk to restoration success. As a result, procedures have been developed to document the presence of FeS using both field and laboratory techniques. This technical report evaluated conditions at three restoration sites, identifying FeS materials at a subset of sample locations. Guidance for evaluating FeS materials in a restoration context and associated management strategies are also discussed.
Chapter
Tidal marshes are common in temperate regions of the world. They are characterized by mixing of seawater and freshwater and by hydrologic pulsing driven by the astronomical tides and are among the most productive of wetlands, supporting high levels of plant and animal biomass. Many tidal marshes have been lost to shoreline development and urbanization and, sometimes, agriculture. Efforts to restore them consist of reintroducing tidal inundation by removing fill, dikes, levees, and tide gates and by managed realignment where coastal defenses are removed and marsh vegetation is allowed to reestablish. Because of the vigorous energy associated with tidal inundation, reestablishment of vegetation by natural colonization or seeding is slow and planting is often required. Development of heterotrophic food webs depends on establishing good coverage of vegetation and accumulation of soil organic matter and nitrogen (N). Keys to successful restoration include selecting sites with large tidal range to support a wide expanse of vegetation, gentle slope to limit waterlogging, and enhancing connectivity by creating tidal creeks and abundant vegetated edge to facilitate access and use by nekton and wading birds.
Preprint
Coastal wetlands are experiencing accelerated rates of fragmentation and degradation due to sea level rise, sediment deficits, subsidence, and salt-water intrusion. This reduces their ability to provide ecosystem benefits, such as wave attenuation, habitat for migratory birds, and a sink for carbon and nitrogen cycles. A deteriorated back barrier wetland near Avalon, New Jersey was nourished through thin layer placement (TLP) of dredged sediment in 2016. A field investigation was conducted in 2019 using a cone penetrometer (CPT) to quantify the establishment of soil strength in a restored site compared to control sites in conjunction with traditional wetland establishment markers. Results show that the nourished area exhibited weaker strengths than the reference sites, suggesting the root system is still growing. The belowground biomass measurements correlated to the CPT strength measurements, demonstrating that shear strength measured from the cone penetrometer could serve as a surrogate to monitor wetland trajectories. During the construction process, heavily trafficked areas underwent compaction from heavy equipment loads, inhibiting the development of vegetation and highlighting how sensitive wetlands are to anthropogenic disturbances. As the need for more expansive wetland restoration projects grow, the CPT provides rapid high-resolution measurements across large sites supplying government and management agencies with vital establishment trajectories.
Technical Report
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Guidance relevant to the maintenance and restoration of coastal salt marshes in the face of sea level rise is limited and sometimes conflicting; an understanding of ecological considerations and best management practices are needed to inform restoration and management that is appropriate, timely, successful, and sustainable. A literature search was conducted to assess the severity of current and projected impacts of sea level rise on salt marshes throughout the coastal regions of the United States, to identify other stressors contributing to relative sea level rise, to assess and consolidate current practices in marsh management, and to identify knowledge gaps that are impediments to development of consistent best management practices for restoring or maintaining marshes exhibiting degradation due to relative sea level rise. Literature identified in this search is synthesized, organized by stressor type, relevant metrics, management actions, and adaptive management. The citations are presented in such a way as to be easily utilized by managers of marshes degraded by relative sea level rise. The results of this literature search will inform data acquisition efforts to address data gaps and uncertainties necessary to support development of a holistic approach to identifying, sustaining, and restoring impacted marsh areas.
Article
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The signs and causes of marsh degradation must be correctly identified in order to plan restoration actions that (1) do no harm to functioning ecosystems, (2) produce lasting results, and (3) use scarce restoration dollars effectively. There are many ways to productively use dredged material to conserve, manage and restore tidal wetlands. The broad acceptance of dredged sediment use for tidal marsh conservation is an important step forward in the management of marshes. However, sediment must be used in a way that does not adversely impact systems that are currently functioning well, such as unaltered marshes with dynamic pool systems.
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The U.S. Army Corps of Engineers (USACE) conducts dredging activities to maintain navigation channels in the lower Atchafalaya River (Figure 1). These dredging activities remove sediment from navigation channels, which is then available for the creation and/or expansion of wetlands (Boustany 2010). During the 1990s, placement of shoal material dredged from the Horseshoe Bend section of the river occurred at eight wetland development sites located along the river's banklines (Berkowitz et al. 2014). Capacity of these placement sites was nearly exhausted by 1999. Thus, to meet the anticipated disposal requirements for future channel maintenance, in 2002 USACE began mounding dredged material in an open water placement site upriver of a small naturally forming shoal. Open channel displacement reduces transport costs associated with moving sediment to traditional disposal areas or open ocean disposal. The strategic placement of sediments upstream of the natural shoal area created a 35-ha wetland island (Figure 2). As a result, this project adheres to USACE Engineering With Nature (EWN) principles by utilizing natural processes in support of navigation and environmental goals (Bridges et al., 2014; Gerhardt-Smith and Banks 2014; http://el.erdc.usace.army.mil/ewn/). In 2014, USACE constructed a new navigation channel route on the east side of the island. The new route is anticipated to increase flow velocities in the navigation channel, encouraging the channel to "self maintain" and reducing dredging maintenance requirements. Any required future activities will adhere to EWN principles by mounding dredged material upriver of the island or in the former navigation channel. This article presents results from an initial ecological survey of the 12-year old created wetland island to quantify the ecological functions and benefits of strategic open water placement of dredged material. Ongoing and future research initiatives are also discussed.
Article
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Wetland creation and restoration are frequently used to replace ecological functions and values lost when natural wetlands are degraded or destroyed. On many sites, restoration of ecological attributes such as secondary production, habitat/species diversity, and wetland soil characteristics do not occur within the first decade, and no long-term studies exist to document the length of time required to achieve complete restoration of wetland dependent functions and values. Characteristics of community structure (macrophyte aboveground biomass, macro-organic matter [MOM], benthic invertebrates) and ecosystem processes (soil development, organic C, N, and P accumulation) of two constructed Spartina alterniflora (Loisel) marshes (established 1971 and 1974) and paired natural S. alterniflora marshes in North Carolina were periodically measured during the past 25 yr. On constructed marshes, the macrophyte community developed quickly, and within 5 to 10 yr, aboveground biomass and MOM were equivalent to or exceeded corresponding values in natural marshes. After 15-25 yr, benthic infauna density and species richness were greater than in the natural marshes. Soil bulk density decreased, and organic C and total N increased over time in constructed marshes, but after 25 yr, soil organic C and N reservoirs were much smaller than in a 2000-yr-old natural marsh. Organic C accumulation was similar in constructed and natural marshes with 12-24% of the net primary production buried annually. Nitrogen accumulation was much higher in constructed marshes (7-12 g.m(-2).yr(-1)) than in natural marshes (2-5 g.m(-2).yr(-1)), reflecting the open biogeochemical cycles and paucity of N in these young ecosystems. Different ecological attributes develop at different rates, with primary producers achieving equivalence during the first 5 yr, followed by the benthic infauna community 5-10 yr later. Accumulation of soil nutrients to levels similar to those of reference marshes may require more time.
Article
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The capabilities of a new wetland dredging technology were assessed along with associated newly developed state and federal regulatory policies to determine if policy expectations realistically match the technological achievement. Current regulatory practices require amelioration of spoil bank impacts upon abandonment of an oil/gas well, but this may not occur for many years or decades, if at all. Recently, a dredging method (high‐pressure spray spoil disposal) was developed that does not create a spoil bank in the traditional sense. Its potential for reducing environmental impacts was recognized immediately by regulatory agencies for whom minimizing spoil bank impacts is a major concern. The use of high‐pressure spray disposal as a suitable alternative to traditional dredging technology has been adopted as policy even though its value as a management tool has never been tested or verified. A qualitative evaluation at two spoil disposal sites in saline marsh indicates that high‐pressure spray disposal may indeed have great potential to minimize impacts, but most of this potential remains unverified. Also, some aspects of current regulatory policy may be based on unrealistic expectations as to the ability of this new technology to minimize or eliminate spoil bank impacts.
Article
Ponds are un-vegetated rounded depressions commonly present on marsh platforms. The role of ponds on the long-term morphological evolution of tidal marshes is unclear – at times ponds expand but eventually recover the marsh platform, at other times ponds never recover and lead to permanent marsh loss. Existing field observations indicate that episodic disturbances of the marsh vegetation cause the formation of small (1-10 m) isolated ponds, even if the vegetated platform keeps pace with Relative Sea Level Rise (RSLR), and that isolated ponds tend to deepen and enlarge until they eventually connect to the channel network. Here I implement a simple model to study the vertical and planform evolution of a single connected pond. A newly connected pond recovers if its bed lies above the limit for marsh plant growth, or if the inorganic deposition rate is larger than the RSLR rate. A pond that cannot accrete faster than RSLR will deepen and enlarge, eventually entering a runaway erosion by wave edge retreat. A large tidal range, a large sediment supply, and a low rate of RSLR favor pond recovery. The model suggests that inorganic sediment deposition alone controls pond recovery, even in marshes where organic matter dominates accretion of the vegetated platform. As such, halting permanent marsh loss by pond collapse requires to increase inorganic sediment deposition. Because pond collapse is possible even if the vegetated platform keeps pace with RSLR, I conclude that marsh resilience to RSLR is less than previously quantified.
Article
The effects of Hurricane Sandy storm surge on wetland degradation and consequent loss of ecosystem services were estimated for coastal wetlands in New Jersey. Research in this field has qualitatively determined the effects of hurricanes on wetlands; however, there has been little quantification of wetland degradation and absolutely no assessment of impact to ecosystem services following a hurricane. Wetland degradation was mapped and quantified by comparing pre- and post-Sandy aerial photography from 2012. Loss of ecosystem services was estimated based on degree of wetland degradation. Our wetland degradation analysis found that the main mechanisms behind degradation were erosion, deposition and marsh salinization. Moderate flooding and marsh dieback were the most prevalent types of damage, and saline marshes and herbaceous wetlands were the most degraded wetland types. Severe degradation was most prevalent, occurring in 41.38 % of the wetlands. In addition, we found that 51.05 % of the degradation was long-term damage. In our ecosystem service loss analysis, we created a range of monetary values to show the distribution of damage. Monetary loss within New Jersey ranged up to $4.4 billion of the total $9.4 billion provided by wetlands (47 %). Our wetland degradation quantification and ecosystem service loss analysis provide insight into the impacts from storm surge damage and offers a novel methodology for remediation and restoration efforts.
Article
Large scale wetland restoration and reforestation efforts continue to expand throughout the Lower Mississippi Valley. Monitoring of restoration performance and the development of restoration trajectories pose challenges to resource managers and remain problematic due to (1) temporal patterns in forest succession, (2) budget constraints and short project monitoring timeframes, (3) disparity in the extent of pre-restoration hydrologic and landscape manipulations, and (4) lack of coherent restoration performance standards. The current work establishes a framework for identifying restoration trajectory metrics within project-relevant timescales. The study examined 17 variables commonly applied in rapid assessments. Four variables yielded positive restoration trajectories within a few years to 20 years. These include shrub-sapling density, ground vegetation cover, and development of organic and A soil horizons. Remaining variables including flood frequency and tree density provide limited useful information within critical early years following reforestation due to the time required for measurable changes to occur. As a result, assessment components are classified into three categories of rapid response, response, and stable variables. Restoring entities should maximize stable variables (e.g., afforestation species composition) during project implementation through site selection and planting techniques; while development of restoration milestones should focus on rapid response variables. Data collected at mature bottomland hardwood control sites displays the non-linearity of trajectory curves over decadal time scales.
Article
The need for practical, repeatable, and technically sound ecosystem assessment methods remains essential to natural resource management. Rapid assessment methodologies determining ecosystem condition and function continue expansion, especially within wetlands. Few studies determine the accuracy of rapid assessment approaches by applying quantitative parameters, especially with respect to biogeochemical functions. Functional measurements require extensive sampling and analytical expertise, beyond financial and time constraints of most restoration projects. Further, measuring biogeochemical ecosystem functions requires the coupling of abundance measures (e.g., soil nutrient concentrations) with processing or transport mechanisms (e.g., microbial activity, flood frequency). This work assessed nutrient cycling, organic C export, and water quality improvement functions applied to >300 km2 of restored bottomland hardwood forests, Mississippi River Valley. Assessment parameters (e.g., sapling shrub density, organic soil horizon thickness) and biogeochemical measures (e.g., microbial biomass C, potentially mineralizable N) were determined at 45 reforested areas and 21 control locations representing an 80-yr restoration chronosequence. Significantly higher rapid assessment outcomes were associated with increased ecosystem functionality (P = 0.001–0.029). These findings suggest that rapid assessment tools serve as reliable proxies for measurements of nutrient and biogeochemical cycling; validating the procedure examined. Assessment scores were also associated with increased restoration stand age (ps < 0.001) supporting further development of similar rapid assessments using ecosystem classification, qualitative data collection, and scaling based on reference data. The wide variety of rapid assessments in use underscores the need for validation with biogeochemical and hydrological measurements.
Article
regulates the size and activity of the microbial pool will also affect the biogeochemical cycling of N. Organic N mineralization can regulate the bioavailability of N in The redox status of a wetland soil system can exert wetland soils and be controlled by the availability of inorganic electron substantial control over the cycling of N (Reddy and acceptors. During the past 40 yr, the northern Everglades has been Patrick, 1975). Mineralization of organic N can proceed affected by nutrient loading as a consequence of the diversion of surface water runoff from agricultural lands. The greatest hydraulic under both aerobic and anaerobic conditions. Due to loading occurs in the summer season when precipitation is highest. the restricted supply of O2 in wetland soils, the influence Fluctuations in water levels and loading of alternate electron acceptors of alternate electron acceptors on microbial catabolic (NO 2 3 and SO 22 4 ) could result in variable N turnover rates. The effect processes can mediate the rate at which organic matter of aerobic, NO 2 3 reducing, SO 22 4 reducing, and methanogenic condi-