Article

Marshes with and without sills protect estuarine shorelines from erosion better than bulkheads during a Category 1 hurricane

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Abstract

Acting on the perception that they perform better for longer, most property owners in the United States choose hard engineered structures, such as bulkheads or riprap revetments, to protect estuarine shorelines from erosion. Less intrusive alternatives, specifically marsh plantings with and without sills, have the potential to better sustain marsh habitat and support its ecosystem services, yet their shoreline protection capabilities during storms have not been evaluated. In this study, the performances of alternative shoreline protection approaches during Hurricane Irene (Category 1 storm) were compared by 1) classifying resultant damage to shorelines with different types of shoreline protection in three NC coastal regions after Irene; and 2) quantifying shoreline erosion at marshes with and without sills in one NC region by using repeated measurements of marsh surface elevation and marsh vegetation stem density before and after Irene. In the central Outer Banks, NC, where the strongest sustained winds blew across the longest fetch; Irene damaged 76% of bulkheads surveyed, while no damage to other shoreline protection options was detected. Across marsh sites within 25 km of its landfall, Hurricane Irene had no effect on marsh surface elevations behind sills or along marsh shorelines without sills. Although Irene temporarily reduced marsh vegetation density at sites with and without sills, vegetation recovered to pre-hurricane levels within a year. Storm responses suggest that marshes with and without sills are more durable and may protect shorelines from erosion better than the bulkheads in a Category 1 storm. This study is the first to provide data on the shoreline protection capabilities of marshes with and without sills relative to bulkheads during a substantial storm event, and to articulate a research framework to assist in the development of comprehensive policies for climate change adaptation and sustainable management of estuarine shorelines and resources in U.S. and globally.

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... The threshold of a marine ecosystem to provide effective coastal protection under extreme conditions is dependent on a range of variables including species, growth stage, spatial coverage and the incident wave conditions. However, contrary to conventional structures, marine ecosystems may be able to self-repair damage from a severe storm if there is sufficient time before the next storm event occurs 36 . This is one of the potential benefits of nature-based over traditional coastal protection (see Section 1.3: Benefits of Nature-Based Methods). ...
... In contrast, naturebased coastal defences can self-repair as they are a living, growing system. In the United States living shorelines using saltmarshes suffered less hurricane damage compared to bulkheads, and repaired themselves within one year with no reduction in shoreline elevation 36 . In Australia, defoliated mangroves can recover following cyclones 44 , and diebacks in response to these are patchy and expected to be counteracted by the landward expansion observed across Australia 45 . ...
... Broadly, for example, dunes and beaches are common features of open sandy coasts, whereas saltmarshes, mangroves, and shellfish reefs are found in comparatively sheltered estuaries and bays. These habitats alone can provide effective hazard risk reduction 36,64 . However, under higher-intensity hazards soft approaches are likely to require more maintenance, as the natural recovery processes can takes months to years depending on the frequency of recurrence of hazard events, as well as processes such as sediment volume and supply, and recruitment of new individuals 64,65 . ...
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Nature-based methods use the creation or restoration of coastal habitats for hazard risk reduction. This can be done through restoring the habitat alone (“soft” approach), or in combination with hard structures that support habitat establishment (“hybrid” approaches). The need to develop, test and apply more sustainable techniques to mitigate the impacts of coastal hazards has been identified as a national priority. One reason that nature-based methods have been underutilised in Australia is that decision-makers need clearer guidelines for when a soft, hybrid or hard coastal defence approach is most appropriate. International exemplars in nature-based methods have started this process, which include Ecoshape’s Building with Nature in Europe and the Army Corps of Engineers’ Engineering-with-Nature® in the United States. Here we build on this international knowledge and national research efforts to provide an Australian context for nature-based methods, as wider adoption of these techniques nationally requires accounting for the environmental, economic and socio-political contexts specific to Australia. This guideline summarises the physical processes that underpin nature-based methods, and the ecological and engineering considerations for their application based on the major coastal ecosystems found in Australia. It also provides frameworks for implementing nature-based methods and conducting a benefit-cost analysis, and the policy landscape within which nature-based methods can be applied. The aim of this document is to translate the known global and Australian research into a practical tool that can be used to support decisions by coastal practitioners to use nature-based methods.
... Previous studies have considered the vulnerability or response of barrier island and marsh shorelines to anthropogenic stressors [19][20][21], sea level rise [22][23][24], and episodic and long-term processes [25][26][27]. Many studies present marsh response parameters, such as the conversion to open water, erosion or accretion, or the change in elevation or shoreline position [22][23][24][25]27], based on aerial imagery [28], field observations [29,30], and/or computational modeling [31]. However, few studies have synthesized remotely sensed, field-based, and computationally modeled data to stochastically investigate the effects of erosive stressors on the marsh condition as healthy or eroded in varying degrees of severity. ...
... For Method 3, failure was defined based on empirical classification of the marsh as either "healthy", "eroded", or "severely eroded" ( Table 2). These classifications were developed based on a literature review [30,58,59] and field observations at the study area. A detailed classification of the marsh shoreline was performed by the research team in May 2021 and is used in the fragility derivations. ...
... One contribution of this study is the proposed methodology for characterizing the marsh shoreline as "healthy," "eroded," or "severely eroded" ( Table 2). While guidance exists for shoreline assessment that provides criteria for healthy or eroding marshes based on marsh slope or scarp height [58] and other studies have evaluated shoreline condition following extreme events [30,59,71], vulnerability to erosion [72][73][74][75][76][77], and recovery after storms [71,78], a standardized engineering methodology is required for assessing shoreline condition considering the status of erosion, vegetation persistence, and other landscape factors. Therefore, Table 2 may be refined, expanded, and generalized for evaluation of the condition of marsh shorelines or other nature-based shoreline-protection alternatives. ...
Article
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Coastal highways along narrow barrier islands are vulnerable to flooding due to ocean and bay-side events, which create hazardous travel conditions and may restrict access to surrounding communities. This study investigates the vulnerability of a segment of highway passing through the Pea Island National Wildlife Refuge in the Outer Banks, North Carolina, USA. Publicly available data, computational modeling, and field observations of shoreline change are synthesized to develop fragility models for roadway flooding and marsh conditions. At 99% significance, peak daily water levels and significant wave heights at nearby monitoring stations are determined as significant predictors of roadway closure due to flooding. Computational investigations of bay-side storms identify peak water levels and the buffer distance between the estuarine shoreline and the roadway as significant predictors of roadway transect flooding. To assess the vulnerability of the marsh in the buffer area, a classification scheme is proposed and used to evaluate marsh conditions due to long-term and episodic (storm) stressors. Marsh vulnerability is found to be predicted by the long-term erosion rate and distance from the shoreline to the 5 m depth contour of the nearby flood tidal channel. The results indicate the importance of erosion mitigation and marsh conservation to enhance the resilience of coastal transportation infrastructure.
... Hardened structures act as barriers to marsh migration landward, causing coastal squeeze (loss of coastal habitat in front of a landward boundary and the low water mark migrating landward due to SLR) and inevitable loss of intertidal habitat Pontee, 2013;Titus et al., 2009). Hard structures often result in reduced faunal and floral biodiversity and abundance, reduced sediment distribution along and adjacent to the structure, erosion and scouring of bottom habitat because of wave refraction, reduced storm protection (compared to marsh plantings with and without sills), and loss of critical intertidal ecosystem services (Bozek & Burdick, 2005;Gittman et al., 2014;Gittman, Smith, et al., 2016;Meyer & Posey, 2014;Riggs, 2001). ...
... Living shorelines provide a range of ecological cobenefits and have been implemented with documented instances of success in restoring habitat and ecosystem functions, such as habitat provisioning (compared to hardened structures; Gittman, Peterson, et al., 2016;Scyphers et al., 2011) and shoreline stabilization (Gittman et al., 2014;Polk & Eulie, 2018;Smith et al., 2018). With respect to habitat provisioning, various studies have observed the capacity of living shoreline sites to mimic or enhance biomass and species diversity relative to natural sites (Currin et al., 2008;Gittman, Peterson, et al., 2016). ...
... height, which is critical in fetch-limited environments], sediment supply, space for landward retreat) and design (e.g., height, width, and configuration) of sills is critical (Mitchell & Bilkovic, 2019), as the primary force causing lateral and vertical erosion of salt marsh edges is wind-wave attack (Tonelli et al., 2010). Although recent work has suggested that living shorelines with sills can prevent vertical erosion and shoreline damage from hurricanes (Gittman et al., 2014;Smith et al., 2018), more research is needed investigating the performance of a range of living shoreline sill designs in preventing lateral marsh erosion during highenergy and high-water conditions observed during hurricanes. Thus, the present study quantifies the lateral change in marsh position during a short-term period encompassing Category 1 storm event (Hurricane Florence, 2018) at living shorelines and natural marsh shorelines. ...
Article
A growing suite of research has demonstrated that nature‐based shoreline stabilization methods can increase resilience of coastal ecosystems by improving their capacity to return to pre‐disturbance states. Previous work suggests that during hurricanes, living shorelines promote vertical accretion and experience less damage than traditional shoreline stabilization alternatives. Nevertheless, there is limited research looking at the impacts of major storm events on living shorelines and most studies have investigated a small number of sites. This study used in situ real‐time kinematic (RTK)‐GPS surveys to quantify the resilience (via the lateral change in shore position) of 17 living shoreline sites before and after a Category 1 hurricane event (Hurricane Florence, 2018). By doing so, this study seeks to understand the capacity of living shorelines (marsh with seaward breakwater or sill) to provide storm protection as compared to unaltered natural fringing salt marshes. After Hurricane Florence, living shorelines on average experienced significantly less lateral erosion compared to unprotected control segments (shoreline change rates of 0.015 m y‐1 and ‐0.31 m y‐1, respectively). This study also explores how environmental siting variables (i.e. scarp presence, fetch, and bottom sediment) and sill design variables (i.e. sill material, width, and height) influence short‐ and long‐term erosion. Living shorelines were found to reduce erosion of fringing marsh edge among projects with a range of installation ages, structural materials, sill widths, and sill heights, and they were able to provide protection from erosion across a range of fetch, scarp, and bottom sediment conditions. Living shoreline siting and sill design may be suitable for broader environmental conditions than previously known. This study shows that living shorelines can increase resilience, by reducing erosion of fringing salt marshes, and even in some cases promoting lateral building up of shoreline zones during short‐term disturbance events and from their long‐term presence. This article is protected by copyright. All rights reserved.
... The anthropogenic view is based on widespread public perception that coastal change is primarily a hazard to property and infrastructure and that both hard and soft structural defenses are required to mitigate coastal hazards (Cooper and Jackson, 2019). There is a growing body of evidence, however, that indicates coastal ecosystems can, and often do, provide coastal protection and resilience to coastal communities (Shepard et al. 2011;Gittman et al. 2014;Narayan et al. 2017;Reguero et al. 2018) and that nature-based solutions, such as living shorelines, enhance the resilience of natural ecosystems and coastal communities (Smith et al. 2016). The ability of natural features to provide resilience is dependent on the health and integrity of the coastal ecosystem both now and in the future. ...
... The screening process applies an assessment scheme that identifies the preservation of existing coastal lands, and the restoration and the creation of new lands and natural features where possible ( Figure 1). The assessment scheme rational is founded on the results of a multitude of scientific studies that all conclude that the preservation of existing landforms and habitats provide the maximum ecosystem and community resilience benefits (e.g., Gittman et al. 2014;Zhao et al. 2016;Negandhi et al. 2019). ...
Technical Report
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A framework for determining the appropriate type and location of green infrastructure projects designed to improve the resilience of coastal communities and ecosystems through a high-level, landscape-scale screening of possible adaptations using geographical information system (GIS) data.
... Natural features that can attenuate waves (e.g., marshes) are being created to protect shorelines in many estuaries and coasts, and this practice has grown substantially over the past 20 yr (Sutton-Grier et al. 2015). When used for shore protection, these created features (living shorelines henceforth) often involve a combination of green-gray (hybrid) infrastructure, specifically restoring or creating a fringing marsh in combination with a stabilizing sill structure placed offshore and parallel to the marsh (Bilkovic et al. 2017a), which can be very effective at erosion protection (Shepard et al. 2011, Gittman et al. 2014, Morris et al. 2019) and more resilient than armoring (e.g., bulkheads) to storm events and sea level rise (Gittman et al. 2014, Smith et al. 2017, Mitchell and Bilkovic 2019. Living shorelines are being valued for not only protective services (e.g., wave energy reduction, mitigating storm surge impacts), but also non-protective services and cobenefits including water quality improvement, nutrient removal, and habitat provision (e.g., Sutton-Grier et al. 2015, Gittman et al. 2016, Beck et al. 2017. ...
... Natural features that can attenuate waves (e.g., marshes) are being created to protect shorelines in many estuaries and coasts, and this practice has grown substantially over the past 20 yr (Sutton-Grier et al. 2015). When used for shore protection, these created features (living shorelines henceforth) often involve a combination of green-gray (hybrid) infrastructure, specifically restoring or creating a fringing marsh in combination with a stabilizing sill structure placed offshore and parallel to the marsh (Bilkovic et al. 2017a), which can be very effective at erosion protection (Shepard et al. 2011, Gittman et al. 2014, Morris et al. 2019) and more resilient than armoring (e.g., bulkheads) to storm events and sea level rise (Gittman et al. 2014, Smith et al. 2017, Mitchell and Bilkovic 2019. Living shorelines are being valued for not only protective services (e.g., wave energy reduction, mitigating storm surge impacts), but also non-protective services and cobenefits including water quality improvement, nutrient removal, and habitat provision (e.g., Sutton-Grier et al. 2015, Gittman et al. 2016, Beck et al. 2017. ...
Article
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Coastal communities increasingly invest in natural and nature‐based features (e.g., living shorelines) as a strategy to protect shorelines and enhance coastal resilience. Tidal marshes are a common component of these strategies because of their capacity to reduce wave energy and storm surge impacts. Performance metrics of restoration success for living shorelines tend to focus on how the physical structure of the created marsh enhances shoreline protection via proper elevation and marsh plant presence. These metrics do not fully evaluate the level of marsh ecosystem development. In particular, the presence of key marsh bivalve species can indicate the capability of the marsh to provide non‐protective services of value, such as water quality improvement and habitat provision. We observed an unexpected low to no abundance of the filter‐feeding ribbed mussel, Geukensia demissa, in living shoreline marshes throughout Chesapeake Bay. In salt marsh ecosystems along the Atlantic Coast of the United States, ribbed mussels improve water quality, enhance nutrient removal, stabilize the marsh, and facilitate long‐term sustainability of the habitat. Through comparative field surveys and experiments within a chronosequence of 13 living shorelines spanning 2–16 years since construction, we examined three factors we hypothesized may influence recruitment of ribbed mussels to living shoreline marshes: (1) larval access to suitable marsh habitat, (2) sediment quality of low marsh (i.e., potential mussel habitat), and (3) availability of high‐quality refuge habitat. Our findings suggest that at most sites larval mussels are able to access and settle on living shoreline created marshes behind rock sill structures, but that most recruits are likely not surviving. Sediment organic matter (OM) and plant density were correlated with mussel abundance, and sediment OM increased with marsh age, suggesting that living shoreline design (e.g., sand fill, planting grids) and lags in ecosystem development (sediment properties) are reducing the survival of the young recruits. We offer potential modifications to living shoreline design and implementation practices that may facilitate self‐sustaining ribbed mussel populations in these restored habitats.
... There is growing acceptance that tidal marshes play a significant role in buffering communities from coastal storms (Wamsley et al. 2010, Gedan et al. 2011, Gittman et al. 2014, Bridges et al. 2015, Narayan et al. 2016. Therefore, their protection, management, and restoration are high priorities. ...
... boat traffic, wakes, and landings in the marsh, have had a greater adverse impact on shoreline stability, vegetation, and wildlife habitat than the impacts attributed to the storm in a number of areas where wetland vegetation recovered.The same study reported that marshes in areas previously compromised by ditching, open marsh water management, and diking appeared to have sustained more damage and were slower to recover than other more intact marsh areas(Bilinski et al. 2015). Another study found that tidal marshes in North Carolina survived Hurricane Irene better than bulkheads(Gittman et al. 2014), similar to the post-Hurricane Sandy results. ...
... Living shoreline approaches involve creating or restoring natural features that can attenuate waves, (e.g., fringing marshesnarrow bands of marsh vegetation typically less than 20 m wide along shorelines) and in higher energy settings may include an engineered feature to help break waves and support marsh establishment, such as a stone sill structure or oyster reef structures placed offshore and parallel to the marsh edge Fig. 1). Living shorelines are preferred because, unlike traditional armoring, they maintain coastal processes, restore shoreline habitats, and have greater potential to be resilient to sea level rise and storms, thus enhancing both community and ecosystem resilience (Gittman et al., 2014;Sutton-Grier et al., 2015;Bilkovic et al., 2017;Smith et al., 2017;Mitchell and Bilkovic, 2019). Living shorelines that include restoring or creating a marsh are made to emulate nearby natural fringing marsh habitats and processes, and when properly constructed, provide a plethora of ecological services through their biotic components, similar to their natural counterparts, including: refuge, nesting and feeding habitat (Davis et al., 2006;Gittman et al., 2015;Bilkovic et al., 2016;Gittman et al., 2016;Guthrie et al., in review); filtering of sediments and nutrients from waterways (Currin et al., 2010;Beck et al., 2017;Chambers et al., 2021); reduction of wave energy (Gedan et al., 2010;Gittman et al., 2014); and carbon storage (Davis et al., 2015;Chambers et al., 2021). ...
... Living shorelines are preferred because, unlike traditional armoring, they maintain coastal processes, restore shoreline habitats, and have greater potential to be resilient to sea level rise and storms, thus enhancing both community and ecosystem resilience (Gittman et al., 2014;Sutton-Grier et al., 2015;Bilkovic et al., 2017;Smith et al., 2017;Mitchell and Bilkovic, 2019). Living shorelines that include restoring or creating a marsh are made to emulate nearby natural fringing marsh habitats and processes, and when properly constructed, provide a plethora of ecological services through their biotic components, similar to their natural counterparts, including: refuge, nesting and feeding habitat (Davis et al., 2006;Gittman et al., 2015;Bilkovic et al., 2016;Gittman et al., 2016;Guthrie et al., in review); filtering of sediments and nutrients from waterways (Currin et al., 2010;Beck et al., 2017;Chambers et al., 2021); reduction of wave energy (Gedan et al., 2010;Gittman et al., 2014); and carbon storage (Davis et al., 2015;Chambers et al., 2021). Enhanced invertebrate and fish diversity and abundance along living shorelines compared to armored shorelines, as well as documented fish utilization of living shoreline habitats suggest that they are providing refuge and forage habitat (Davis et al., 2006;Currin et al., 2008;Scyphers et al., 2011;Gittman et al., 2016). ...
Article
Climate change and coastal development pressures have intensified the need for shoreline protection. Nature-first approaches that use natural habitats, particularly marshes, are being promoted globally as ecologically-beneficial alternatives to grey infrastructure. The ability of these novel shorelines to provide nursery habitat to blue crab (Callinectes sapidus), an ecologically and economically important species along the Atlantic and Gulf coasts of the United States, has not been fully evaluated. We quantified the abundance and size distribution of juvenile blue crabs from a chronosequence of living shorelines (created fringing marshes) spanning 2 to 16 years in age since construction compared with paired natural fringing marshes in the southern Chesapeake Bay. Both created and natural fringing marshes are used by blue crabs as primary nursery habitats. Despite interannual differences in abundance, young blue crabs (≤ 2.5 cm carapace width) were observed in similar densities and sizes at living shoreline and natural marshes. The age of the living shoreline was not related to blue crab density, indicating that even the youngest living shorelines (2 years) provided nursery habitat. The potential for living shorelines to serve as nursery habitat for an economically important species may provide additional incentive to implement these nature-based approaches for climate change adaptation.
... adding structural complexity or using eco-friendly materials; "hard ecoengineering"; Strain et al., 2019), replacement of infrastructure with rehabilitated or restored habitats ("soft eco-engineering"; French, 2006), or the combination of natural and restored habitat with built infrastructure ("hybrid eco-engineering; Borsje et al., 2011;Spalding et al., 2014;Schueler, 2017(Mitsch, 1996, 2012. Natural and constructed vegetated habitats can provide known coastal protection services (Doswald et al., 2014;Gittman et al., 2014;Van Cuong et al., 2015), and have the potential to provide other co-benefits such as maintenance of wildlife and raw materials or food relative to artificial structures (McLeod et al., 2011;Morris et al., 2018). ...
... Mangroves or saltmarsh combined with rock-sills are a commonly used hybrid eco-engineering solution for coastal defence (Bilkovic et al., 2016;Bilkovic and Mitchell, 2013;Gittman et al., 2016Gittman et al., , 2014, especially in areas exposed to greater hydrodynamic energy (Morris et al., 2020). Rock-sills reduce wave energy and allow for coastal vegetation to establish behind the structure. ...
Article
There is growing demand for novel coastal protection approaches that also provide co-benefits such as enhanced biodiversity. Rock-fillets, which are used to stabilise eroding banks in estuaries, can be colonised by mangroves, and may provide habitat for estuarine fauna. However, it is unknown whether hybrid mangrove/rock-fillet habitats are functionally equivalent to natural mangroves, for estuarine fauna. To determine whether hybrid mangrove habitats are functionally equivalent to natural mangroves, we used δ¹³C and δ¹⁵N stable isotope analyses to describe the isotopic niche space and overlap of estuarine species in these two habitats across three estuaries in NSW, Australia. Using a Bayesian standard ellipse analysis of isotopic niche area, over half the 12 species observed had larger isotopic niche areas in natural mangroves compared to hybrid habitats, however there were no clear patterns for species between habitats. Natural mangroves and hybrid rock-fillet habitats were isotopically distinct for all species sampled (low proportional overlap, 0–19%) suggesting they are not, at present, wholistically functionally equivalent. Estuarine communities from the two habitat types, however, had similar isotopic niches. Hybrid communities displayed a broader range of δ¹³C values compared to natural mangroves, suggesting mangrove/rock-fillet habitats have a more diverse range of basal food sources. These findings demonstrate the potential for defence solutions to provide unique co-benefits by supporting food webs, but also that natural habitats provide unique ecosystem services that should be protected and rehabilitated where possible. Future modelling and monitoring of habitat utilisation and species performance could provide further insight into the co-benefits and trade-offs of hybrid habitats.
... These approaches are considered to provide a balance between private shoreline erosion protection and the public benefits derived from natural shoreline features by having little adverse effect and the likely potential for increased ecosystem services . With the incorporation of newly created marsh, living shorelines can offset historical and projected marsh loss (Leo et al., 2019;Mitchell and Bilkovic, 2019) and have been shown to mimic services provided by natural marshes: erosion protection (Scyphers et al., 2011;Gittman et al., 2014;Narayan et al., 2016;Esteves and Williams, 2017), habitat services (Bacchiocchi and Airoldi, 2003;Bilkovic et al., 2016;Sharma et al., 2016;Browne and Chapman, 2017;Onorevole et al., 2018), biodiversity , fisheries benefits , and combined co-benefits to support coastal resilience (Morris et al., 2018;Currin, 2019). ...
... The SMM was used to produce recommendations for Virginia with living shorelines modeled as suitable for 73% of the shoreline. One of the major advantages of implementing these recommendations is that natural components, such as marsh vegetation, are self-sustaining and can expand or migrate given the right conditions (Gittman et al., 2014;Leo et al., 2019;Phase One, 2021. In this way, the SMM enables and supports decision-making consistent with public policy promoting the use of nature-based solutions (Phase One, 2021), or natural and nature-based features, for shoreline management. ...
Article
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The Shoreline Management Model (SMM) is a novel geospatial approach used to assess conditions along a shoreline, and recommend best management practices for defended and undefended shorelines. The SMM models available spatial data in order to identify areas where the use of living shorelines would be suitable to address shoreline erosion. The model was developed to support and inform decision-making by shoreline managers responsible for management of shoreline resources, shorefront property owners, and tidal habitat restoration actions. Recommended erosion control strategies are based on scientific knowledge of how shorelines respond to natural conditions and anthropogenic measures used to stabilize shorelines. The SMM uses input variables representing current conditions and recommends a strategy that falls into one of three general categories: living shorelines, traditional approaches, and special considerations. Areas of special consideration are areas where the model may not be able to provide an appropriate recommendation due to ecological, geological, or highly developed conditions. These areas are given recommendations that include the instruction to seek expert advice. Data required to run the model include presence of tidal marsh, beach, submerged aquatic vegetation (SAV), riparian land cover, bank height, nearshore bathymetry, fetch, and shoreline erosion control structures. The model has been calibrated and validated along Virginia's Chesapeake Bay shoreline, USA. The model results are largely consistent with field recommendations (i.e., shoreline management recommendations made by scientists based on on-site observations during shoreline evaluation visits). The SMM performed with an overall accuracy of 82.5%. The SMM is exportable; the model code can be adapted to other systems. This geospatial model provides a robust screening tool for local and state governments, coastal and environmental planners and engineers, as well as property owners, when considering best management practices, including living shorelines as an alternative for erosion control.
... Furthermore, most postevent field surveys focused on damage to the built environment or the capability of natural features to mitigate inland hydrodynamic conditions (e.g., Scyphers et al. 2011;Shepard et al. 2011;Zhang et al. 2012;Narayan et al. 2016). Few have investigated physical damage to shorelines (Gittman et al. 2014;Smith et al. 2017). Gittman et al. (2014) qualitatively evaluated the performance of bulkheads and marsh sites located on barrier islands in North Carolina during Hurricane Irene, a Category 1 hurricane. ...
... Few have investigated physical damage to shorelines (Gittman et al. 2014;Smith et al. 2017). Gittman et al. (2014) qualitatively evaluated the performance of bulkheads and marsh sites located on barrier islands in North Carolina during Hurricane Irene, a Category 1 hurricane. However, those authors acknowledged the need for quantitative evaluations of storm effects on shoreline-protection systems. ...
... These additional structural features potentially diversify the habitat complexity and may increase the ability of vegetated shorelines to keep pace with sea level rise (Smith et al., 2020;Waltham et al., 2021). Living shorelines tend to resist and recover from hurricanes and storm surges better than shoreline armoring (Gittman et al., 2014;Smith et al., 2018), demonstrating their expected resiliency under future climate regimes. The structural similarity of living shoreline marshes to natural marshes often is assumed to equate to similar ecological functions, such as nursery habitat and foraging opportunities for fish and crustaceans. ...
... Although the community composition abundances at living shorelines and reference marshes are similar, living shoreline marsh construction practices and differing habitat characteristics (rock sill, clean sand fill) can contribute to increased biomass for some marsh-dependent species. Compared to shoreline armoring, living shorelines are often more resilient during extreme storm events and can better protect shoreline properties as seas rise (Gittman et al., 2014;Smith et al., 2018). Living shorelines with rock sills may provide structural benefits similar to biogenic reefs, and have the potential to adapt better than natural marshes as they capture and retain sediment to accrete with sea level rise (Currin et al., 2008;Mitchell and Bilkovic, 2019;Waltham et al., 2021). ...
Article
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Salt marshes provide valued services to coastal communities including nutrient cycling, erosion control, habitat provision for crustaceans and fish (including juvenile and forage fish), and energy transfer from the detrital based food web to the greater estuarine system. Living shorelines are erosion control structures that recreate natural shorelines, such as fringing marshes, while providing other beneficial ecosystem services. Living shorelines are expected to provide fish and crustacean (nekton) habitat, but few comprehensive studies have evaluated nekton habitat use across a range of living shoreline settings and ages. We sampled the intertidal marsh and subtidal shallow water nekton community at 13 paired living shoreline and reference marsh sites, with living shorelines ranging in age from 2 to 16 years from construction. We compared nekton diversity, nekton community abundance, nekton community biomass, forage abundance, and juvenile abundance at reference marshes and living shorelines. Our results indicate that living shorelines are providing suitable marsh habitat for nekton communities, including juveniles and forage base species. The difference in living shoreline construction (rock sill, soil composition) did not appear to diminish habitat quality in the marsh or in nearshore waters, and rock sills may provide enhanced structural shoreline habitat. Living shorelines have the potential to combat marsh habitat loss and provide resilient nekton nursery habitat.
... There are several adaptation strategies to combat climate change effects on nearshore marine habitats and aquatic biota (Table 3). Protecting mudflats and marshes can help protect infrastructure and people during low-category hurricanes and coastal flooding (Gittman et al. 2014;Narayan et al. 2017). The dense vegetation combined with nature-based structures like oyster reefs can act as a coastal defense by attenuating wave energy, accreting sediment (which is also a large carbon sink), and stabilizing shorelines (Gittman et al. 2014;Narayan et al. 2017;Roberts et al. 2017). ...
... Protecting mudflats and marshes can help protect infrastructure and people during low-category hurricanes and coastal flooding (Gittman et al. 2014;Narayan et al. 2017). The dense vegetation combined with nature-based structures like oyster reefs can act as a coastal defense by attenuating wave energy, accreting sediment (which is also a large carbon sink), and stabilizing shorelines (Gittman et al. 2014;Narayan et al. 2017;Roberts et al. 2017). In addition, connecting freshwater sources to downstream deltas may provide sediment sources for marshes and mangroves, and provide buffering capacity to extreme events such as hurricanes (Ellison 2015). ...
Article
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Climate change is a global persistent threat to fish and fish habitats throughout North America. Climate‐induced modification of environmental regimes, including changes in streamflow, water temperature, salinity, storm surges, and habitat connectivity can change fish physiology, disrupt spawning cues, cause fish extinctions and invasions, and alter fish community structure. Reducing greenhouse emissions remains the primary mechanism to slow the pace of climate change, but local and regional management agencies and stakeholders have developed an arsenal of adaptation strategies to help partially mitigate the effects of climate change on fish. We summarize common stressors posed by climate change in North America, including (1) increased water temperature, (2) changes in precipitation, (3) sea level rise, and (4) ocean acidification, and present potential adaptation strategies that fishery professionals may apply to help vulnerable fish and fisheries cope with a changing climate. Although our adaptation strategies are primarily from North America, they have broader geographic applicability to fish and aquatic biota in other jurisdictions. These strategies provide opportunities for managers to mitigate the effects of climate change on fish and fish habitat while needed global policies to reduce greenhouse gas emissions emerge, which may offer more lasting solutions.
... Marsh platform and vegetation canopy are the critical factors mitigating tidal waves (Wamsley et al., 2010). Wave attenuating by marsh platform (i.e., the morphology) depends on platform elevation, tidal flat width, and the soil anti-erosion capability (Gittman et al., 2014;Vuik et al., 2016); while wave mitigating by vegetation canopy relies on the vegetation biosignature (Dalrymple et al., 1984;Cao et al., 2015). In terms of tidal morphology function, saltmarsh shows strong anti-erosion ability as long as it is in the seeding germination or seeding expansion stage (Leonardi et al., 2016;Vuik et al., 2019). ...
... The large-scale flume experiment showed a stem breakage up to 80% of the Elymus (Rupprecht et al., 2017) and a stem density reduction up to 50% of the Sp. alterniflora may occur after a Category-1 hurricane impact (Gittman et al., 2014). ...
Article
With climate change and rising sea levels, the coastal zone’s flood risk is deteriorating. Previous researches have shown a gradually degrading capacity of traditional hard engineering structures (e.g., seawall, dikes) on flood mitigation due to problems such as land subsidence and insufficient maintenance. To remedy the defects, the “building with nature concept” for coastal protection with saltmarshes was examined by combining field measurements and numerical simulations. The advantages of saltmarsh over traditional seawall on flood protection was demonstrated from the perspective of both flood area mitigation and economic gain, based on scenario simulations. Results show that tidal wetlands are essential in mitigating significant wave heights (Hs) and current velocities even during storm conditions. The storm wave and current velocity reduction ratio (RRw and RRc) by saltmarshes on Chongming Dongtan Shoal (CMDS) during Typhoon 9711 is approximately 11% and 51%, respectively. The wave and current mitigation by Scirpus mariqueter are more efficient than Spartina alterniflora and Phragmites australis during measurements in 2010, which were approximately 0.3 m and 0.2 m/s, 0.125 m and 0.155 m/s, 0.086 m and 0.128 m/s per kilometer width, respectively. The summer saltmarsh area 54.2 km2 on CMDS protects approximately 32 km2 land area behind the seawall from being flooded, equivalent to the seawall heightening of approximately 0.42 m on equivalent flood mitigation. The performance of cost-and-benefit analysis shows a relatively higher (by 3%–7%) net present value (NPV) and a higher (by 1.5 times) benefit-cost ratio (BC) of nature-based solution (i.e., saltmarsh restoration) compared with traditional hard engineering solution (i.e., seawall construction). Thus, building seawall with nature, such as a hybrid flood protection measure, should be implemented in the future coastal redesign and maintenance.
... While lots of questions about the resilience and benefits of these systems are not answered, few constructed ecosystem-based systems around the world, such as Scheldt estuary in Belgium and Chesapeake Bay program Generally, built infrastructure is well understood and has been used in coastal protection for decades, but it has a limited lifetime, weakens with time, and is constructed to specific parameters that cannot adapt to changing sea levels or other conditions. While an ecosystem-based system is not well understood, it has been shown that the system not only provides benefits for habitant, environment, coastline but can recover and resilient after extreme conditions (Gittman et al., 2014;Sutton et al., 2015). ...
... Salt marshes are one of the ecosystem-based systems which can be applied for protecting shorelines (Gittman et al., 2014); but still, there are a lot of uncertainties about the resilience of salt marshes in different climate and conditions. In this study, different salt marsh characteristics and the current condition of natural salt marshes in Connecticut are reviewed. ...
Preprint
Connecticut marshes, like other marshes in the world, are vulnerable to anthropogenic and climate change effects. However, assessment of current sea level rise and average marsh accretion rates in Connecticut demonstrate sea level rise is not the main vulnerable factor for salt marshes loss. The study on the feasibility of developing an ecosystem-based on two coastlines in Connecticut, Guilford and Stratford, shows that both coastlines, like other coastlines in Connecticut, have limited wave energy, which is a positive factor for marsh growth. The available data assessment represents that sediment supply is the most important parameter to guarantee the resilience and sustainability of a newly developed salt marsh system in Connecticut. In Stratford, conditions for establishing a new ecosystem seem to be better, as the fetch length is pretty small, and there is some sediment supply for the ecosystem. In Guilford, wave energy is limited, but it is more than in Stratford case. Besides, sediment availability is low and the coastline experienced considerable erosion during hurricane Sandy and has not recovered yet.
... While ecoengineering projects have commonly been driven from the conservation perspective (Dafforn et al., 2015;Mayer-Pinto et al., 2017), there is now sufficient evidence that such techniques can achieve both conservation and construction benefits when employed in civil/industrial projects in the coastal zone, such as coastal defense (protection of infrastructure on erosive coastlines), but also bunded walls for containing reclaimed land or stormwater, wharves and marinas. And hence represent viable alternatives to traditional construction techniques (Gittman et al., 2014;Narayan et al., 2016;Smallegan et al., 2016;Vuik et al., 2016;Smith et al., 2017;Morris et al., 2018). The reasons for the documented ecoengineering failures commonly stem from an incomplete appreciation of the physiological constraints and ecological traits of the target species (e.g., Samson and Rollon, 2008). ...
... Keystone, habitat forming species are an obvious target for restoration or novel ecosystem creation, and as such are commonly employed in ecoengineering projects of shoreline stabilization. These include reef-forming invertebrates such as corals (Ferrario et al., 2014), oysters (Scyphers et al., 2011), mussels and worms (Moody, 2012), intertidal vegetation such as mangroves and saltmarsh (Kumara et al., 2010;Gittman et al., 2014) or subtidal vegetation, such as seagrass or kelp (Dubi and Tørum, 1995;Ondiviela et al., 2014). The choice is based on which species provide the desired ecosystem services, and on whether their critical physiological and ecological requirements can reasonably be met (e.g., Ng et al., 2015;Ferrario et al., 2016;Perkol-Finkel et al., 2018). ...
Article
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As the artificial defenses often required for urban and industrial development, such as seawalls, breakwaters, and bund walls, directly replace natural habitats, they may produce population fragmentation and a disruption of ecological connectivity, compromising the delivery of ecosystem services. Such problems have increasingly been addressed through “Working with Nature” (WwN) techniques, wherein natural features such as species and habitats are included as additional functional components within the design of built infrastructure. There now exists a convincing body of empirical evidence that WwN techniques can enhance the structural integrity of coastal works, and at the same time promote biodiversity and ecosystem services. While these benefits have often been achieved through modification of the hard surfaces of the coastal defense structures themselves, the desired ecological and engineering goals may often demand the creation of new soft substrates from sediment. Here we discuss the design considerations for creating new sediment habitats in the intertidal zone within new coastal infrastructure works. We focus on the sediment control structures required to satisfy the physiological and ecological requirements of seagrass and mangroves – two keystone intertidal species that are common candidates for restoration – and illustrate the concepts by discussing the case study of soft habitat creation within a major multi-commodity port.
... However, the ongoing maintenance cost of gray infrastructure, valued at 105 million USD km −1 50 years −1 for seawalls is higher compared to maintenance of permeable walls in hybrid infrastructures -valued at 82.5 million USD km −1 50 years −1 ( Table 1 in: Cunniff and Schwartz 2015). Hybrid structures present lower construction and maintenance cost when compared to gray infrastructure, largely due to implementation of the naturebased solutions through enhanced conservation or restoration of coastal ecosystems (Gittman et al. 2014). Established ecosystems show self-regulating ability to withstand sea level rise by means of accreting above and belowground biomass (Stagg et al. 2018;Baustian, Mendelssohn, and Hester 2012). ...
Article
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Shoreline erosion and storm tide inundation increasingly threaten coastal populations, infrastructure and economies. Hard infrastructure, known as gray infrastructure (e.g. concrete seawalls), has commonly been used to protect coastal communities but is expensive to build, maintain, and deteriorates coastal vegetation. Green infrastructure (e.g. restored or conserved mangrove and marsh ecosystems) delivers nature-based coastal protection but in comparatively lower density coastal areas. Nowadays a more popularized approach to coastal protection is hybrid eco-engineering. In this study, we discuss lessons-learnt on how the hybridization of engineered structures and wetland restoration practices compared with traditional gray and green approaches. We contrast hybrid applications in mangrove and tidal marsh areas in the UK and south-east Asia. The majority (70%) of successful hybrid infrastructure cases were underpinned by understanding of ecological and hydrological changes in response to infrastructure and involved a wide range of stakeholders. In terms of construction and maintenance cost, limited data suggested that hybrid infrastructure may be more cost effective than gray infrastructure, but more expensive than green; however, data were very limited and therefore we suggest the need for further cost-benefit analyses to inform a robust comparison. Development of new technologies should see growing efficacy of future hybrid infrastructure in mitigating coastal flood risks.
... In particular, hard engineering structures often disrupt ecological connectivity by preventing organisms from migrating naturally across intertidal landscapes, and can further alter hydrodynamic and sediment transport processes, such as through the scouring of adjacent habitats that intercept refracted wave energy and dislodgement of the organisms that occur within these systems (e.g., Seitz et al., 2006;Bishop et al., 2019;Lee et al., 2018). As a result, ecological engineering and designing living shorelines that provide shoreline protection (strikingly better than hard engineering methods in some cases; e.g., Gittman et al., 2014), rejuvenate habitat-forming organisms, stimulate ecosystem services such as biodiversity enhancement, and stabilize sediment are sparking the interest of coastal managers and property owners around the world (e.g., Borsje et al., 2011;Temmerman et al., 2013;Cuong et al., 2015;Davis et al., 2015;Gittman et al., 2016b;Smith and Scyphers, 2019;Schotanus et al., 2020). Although increasing in popularity, living shorelines are highly variable in their efficacy in reducing shoreline erosion and restoring ecosystem structure and function (e.g., Morris et al., 2018). ...
Article
Interest and investment in constructing living shorelines rather than harder engineering structures are on the rise worldwide. However, the performance of these interventions in rejuvenating coastal habitats, depositing fine sediments with elevated organic content, and reducing erosion varies widely and is often low along energetic shorelines. In this study, we test the efficacy of a living shoreline design that couples breakwalls and oyster restoration structures, in protecting coastal estuarine ecosystems and their services along energetic shorelines. A field experiment was conducted between 2015 and 2019 along a section of the Atlantic Intracoastal Waterway in northeast Florida, which experiences commercial and recreational vessel traffic. We discovered that organic matter, silt and clay content all increased in sediments collected in the living shorelines compared to paired control treatments. In addition, oysters established and developed into robust reefs on the gabions – wire cages filled with seasoned oyster shells - that were used to facilitate oyster recovery within this living shorelines design, although oyster growth was highest where the gabions were placed at lower intertidal elevations. Additionally, salt marsh cordgrass along shoreline margins protected by the living shoreline structures remained stable or began advancing toward the Intracoastal Waterway channel at rates of ~1 m per year, whereas cordgrass in control treatments retreated at rates approaching 2 m per year. This study provides powerful evidence that vessel wake stress is indeed driving ecosystem loss and that simple nature-based living shoreline structures designed to dissipate this energy can slow or reverse ecosystem decline. More research is needed to optimize these nature-based solutions for shoreline protection in coastal and estuarine settings, and to improve their durability.
... This analysis finds that designation within CBRA coincides with reduced investments in shoreline armoring, which may increase the short-term risk of erosion for current residents. However, this is likely to have little effect on damages from hurricanes and tropical storms; strong evidence now demonstrates that maintaining natural shorelines can be more effective at reducing storm surge and flood risk, meaning fewer armored structures may decrease storm damages while also eliminating the need to repair damaged armored segments (Gittman et al., 2014;Arkema et al., 2013). Avoiding shoreline armoring can also reduce risk for potential future residents by eliminating the reinforcing feedbacks that incentivize rebuilding and further new development behind armored infrastructure after disasters (Woodruff et al., 2018;Burby, 2006). ...
Article
Shoreline armoring, which involves the installation of hardened structures to protect coastal property, dramatically alters shoreline composition and resulting ecological functions. Accelerating hazard threats to growing coastal communities compounds this problem, creating demand for more armoring. We examine whether designation by the U.S. Coastal Barrier Resources Act (CBRA) – enacted to disincentivize urban development on hazardous coastal barriers – is associated with lower propensities to armor shorelines. In designated areas, CBRA removes access to federally-subsidized flood insurance, infrastructure subsidies, and disaster assistance. Using logistic regression modeling, we examine armoring at the parcel scale across the State of Florida (USA), controlling for CBRA designation, land use, and local population density. Our findings reveal a significant negative relationship between CBRA designation and the odds of armoring, particularly for residential and vacant properties. As coastal areas grapple with increasing impacts from coastal hazards, removal of public subsidies may be an effective non-regulatory method for maintaining the ecological and protective benefits of natural shorelines.
... Similarly, Davis et al. (2006) found that this effect could be immediate for some species. Furthermore, living shorelines provide protection from storms (Gittman et al., 2014), sequester significant amounts of carbon (Davis et al., 2015), and reduce the amount of nutrient pollution entering adjacent waterways (Sparks et al., 2015;Onorevole et al., 2018). While this restoration of services can often be achieved with only living elements like plants and oyster shell, a "hybrid" design using rock or concrete structures to break waves is usually implemented in areas with high wave energy. ...
Article
In response to shoreline erosion and coastal wetland loss, living shorelines have been implemented as a natural alternative to shoreline hardening. In high wave energy systems, “hybrid” living shoreline designs incorporating large-scale breakwaters have been increasingly chosen to restore and conserve wetlands. However, evaluations of the effectiveness of breakwaters at preserving natural shorelines and promote the growth of shoreline plantings are limited. To evaluate the effectiveness of large-scale breakwaters at protecting or restoring marshes in high wave energy environments, we conducted an experimental planting and shoreline monitoring program landward of eight-year-old breakwaters and adjacent no breakwater sites along Bon Secour Bay, Alabama. Results showed that breakwaters help natural marsh to maintain its cover at a high level (70%), but have little impact on shoreline planting. Furthermore, breakwater presence reduced the pressure for upland migration, allowing natural marsh patches to expand seaward. Without breakwater protection, fringing marsh retreated upland significantly. Cumulatively, this study suggests that large-scale breakwaters could have an impact on preserving fringing marsh vegetation in high wave energy environments though their effectiveness into the future will require adaptive management in response to local sea-level rise.
... edade como reais alternativas às soluções mais tradicionais de defesa do litoral, para tal são necessários comparações e dados seguros sobre custos e efetividade dessas soluções.Há a indicação que a principal vantagem é que esses sistemas se adaptam às mudanças futuras e tendem a se auto recuperar após grandes tempestades. A seguir alguns exemplos.Gittman et al. (2014), na Carolina do Norte, EUA, mostram exemplo dos impactos do furacão Irene de 2011, nível 1, sobre estruturas longitudinais aderentes do tipo enrocamento e as comparam com os danos sofridos em áreas onde havia marismas (ou "pântanos salgados"). Os autores mostram que 76% das estruturas longitudinais rígidas sofreram algum tipo de dano ao ...
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... A seguir alguns exemplos. Gittman et al. (2014), na Carolina do Norte, EUA, mostram exemplo dos impactos do furacão Irene de 2011, nível 1, sobre estruturas longitudinais aderentes do tipo enrocamento e as comparam com os danos sofridos em áreas onde havia marismas (ou "pântanos salgados"). Os autores mostram que 6 das estruturas longitudinais rígidas sofreram algum tipo de dano ao passo em que as áreas ocupadas pelos marismas não foram afetadas significativamente. ...
Chapter
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Introdução A erosão costeira pode ser entendida como a resultante na paisagem da deficiência no balanço sedimentar em determinado segmento da linha de costa, durante determinado intervalo de tempo. Já o balanço sedimentar deve ser entendido como a diferença, em volume, entre o suprimento e a supressão de materiais sedimentares em determinado segmento costeiro, também em um intervalo de tempo definido. Os volumes de materiais sedimentares movimentados ao longo do litoral variam de acordo com a capacidade das fontes (ex. rios, falésias sedimentares, plataforma continental) em abastecer a linha de costa, e dos demais processos litorâneos-ondas, ventos, correntes de maré, células de circulação costeira, deriva litorânea, etc.-em os erodir e transportar, seja para outro segmento costeiro, seja para a plataforma continental, seja para um cânion submarino, seja para dentro de um estuário, ou para abastecer um campo de dunas. Na costa, quando o suprimento é maior do que a supressão, têm-se o balanço sedimentar positivo, resultando em acumulação ou acreção com o consequente avanço e elevação da posição da linha de costa, o que se denomina progradação. Quando há o predomínio da supressão em comparação ao suprimento, têm-se balanço sedimentar negativo, portanto, erosão com o consequente rebaixamento e recuo da posição da linha de costa. Tais processos são componentes naturais de evolução e dinâmica da paisagem litorânea, que ocorrem em intervalos de tempo bastante variados, mas no entanto, notadamente o termo erosão costeira tem sido utilizado quando o resultado da erosão é o recuo da linha de costa e o COMO CITAR: BULHÕES, E. Erosão costeira e soluções para a defesa do litoral. In MUEHE, D.; LINS-DE-BARROS, F. M.; PINHEIRO, L. (orgs.) Geografia Marinha oceanos e costas na perspectiva de geógrafos. Rio de Janeiro: PGGM, 2020. p. 655-6. ISBN-65-25 1-0-0
... Often added plants are used to augment existing or establish new vegetation (VIMS 2005). Living shorelines are not expected to significantly impair natural processes occurring at the land-water interface and they have been shown to attenuate wave energy better than armored shoreline structures (Gittman et al. 2014). ...
Article
This analysis uses data from a survey of shoreline property owners combined with data on shoreline modification permits to examine whether and how property owners modify their estuarine shorelines. We find that shoreline armoring is very popular among property owners that choose to modify their shoreline. While living shorelines are less common, applications for them are increasing both in absolute numbers and as a percentage of all shoreline modification requests. A number of different issues factor into the shoreline modification decision including effectiveness, cost, aesthetics, and property values. More valuable parcels are more likely to be modified, as are parcels that have been owned longer. Parcels with a high percentage of natural cover or agricultural use are less likely to be modified. Parcels with primary structures that are closer to the shoreline are more likely to have some sort of armoring. Regardless of their choice of shoreline modification, almost all survey respondents believe that their choices have had a neutral or positive impact on erosion and the health of the Chesapeake Bay.
... Separate branches indicate statistical differences at P ≤ .05 ecological outcomes than traditional armoring (NRC, 2007), and they may also be more resilient during storm events (Gittman, Popowich, Bruno, & Peterson, 2014;Smith, Puckett, Gittman, & Peterson, 2018). While the delivery of specific services will certainly vary across space and time (Koch et al., 2009), the potential for living shorelines to benefit people and nature is clear (Arkema et al., 2017). ...
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Shoreline armoring is a pervasive driver of habitat loss and ecosystem decline along coastlines. Nature‐based strategies for coastal protection, such as “living shorelines,” offer potential alternatives to armoring and are rapidly gaining traction among conservation scientists and practitioners. However, along residential coasts where armoring has often occurred at high rates, transitioning away from armoring has been generally slow. We studied the attitudes, beliefs, and decisions of waterfront homeowners with a goal of identifying effective incentives for living shorelines as a conservation tool for reversing coastal habitat loss. We show that while only 18% of homeowners with armored shorelines would willingly transition to living shorelines during a key window of opportunity, a modest economic incentive could increase the likelihood among 43% of all respondents and up to 61% of recent homeowners. Our study demonstrates potential pathways for navigating social, economic, and environmental influences on landowner decisions for coastal habitat conservation.
... Given sustained interest in living shorelines among researchers, practitioners, and policy makers, the need for common terminology is particularly pressing. The terminology used to refer to living shorelines in this study was extremely diverse; even the same authors used different terms to refer to the same projects (see Troch, 2013, 2015;Gittman et al., 2014Gittman et al., , 2016b. This could be because some papers pre-date the common use of the term living shoreline or it could reflect the fact that different terminology is used to appeal to different audiences (e.g., the term living shoreline is often used by non-governmental organizations, whereas the term marsh sill is commonly used by permitting agencies in the United States). ...
Article
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In an era of rapid coastal population expansion and habitat degradation, restoration is becoming an increasingly important strategy for combating coastal habitat loss and maintaining ecosystem services. In particular, techniques that use habitat restoration alone or restoration in combination with built infrastructure to provide coastal protective services are growing in popularity. These novel approaches, often called living shorelines, have the potential to expand the reach and applicability of coastal restoration projects. To understand how living shorelines research has expanded over time, we conducted a scoping review of English-language peer-reviewed articles. We included papers that self-identified as living shorelines research, as well as studies that used other related terminology, to investigate trends in publication rates, geography, site characteristics, and outcomes measured. Using a systematic search protocol, we compiled a database of 46 papers; the earliest study was published in 1981, and the earliest study to use the term living shoreline was published in 2008. Eighty-three percent of studies were conducted in North America, followed by 11% in Asia, and 7% in Europe, but the use of the term living shoreline was almost exclusively restricted to North America. Saltmarshes, oyster reefs, mangroves, and freshwater vegetation were used in living shoreline designs, but 91% of studies also incorporated structural materials like oyster shell and rock. Most living shorelines research was conducted at sites that were <5 years old. The vast majority of studies exclusively reported on ecological outcomes (89%), and of those, ecological processes were measured in 74% of studies. Processes related to coastal protection were measured most frequently (52% of ecological studies), followed by biological interactions, water filtration, nutrient cycling, and carbon sequestration. Altogether, our data suggest that living shorelines research is on the rise, but there is a need for more long-term data, socio-economic research, further consensus on the terminology used to describe different types of projects, and research on the types of living shorelines that are most effective in different environmental contexts. Future long-term and interdisciplinary research will help to elucidate the full effects of living shorelines.
... Even a small speed reduction may not be justified within all sections of the bay, as some shorelines can be reinforced using alternative green S.D. Meyers et al. shoreline protection. These are broadly categorized as 'living shorelines' and have received increasing recognition (Gittman et al., 2014;Herbert et al., 2018). Living shorelines provide wave attenuation, erosion protection, and (in many instances) increased resilience in the form of land accretion that decreases erosional susceptibility. ...
Article
Ship wakes generated by vessels moving through ecologically sensitive areas, or near poorly-protected infrastructure, can negatively impact these systems. This is especially true in regions hosting large seaports. Ship wakes in Tampa Bay, Florida, were calculated during two time periods using vessel movement data reported through the Automatic Identification System (AIS). The first period was for the years 2015–2017 using data from a government database. The second was during part of 2018 obtained by local monitoring. Only vessels operating at low Froude numbers were examined. Wake heights were estimated from each AIS record using an empirical equation and partitioned by functional vessel class. The largest estimated wakes were produced by the Passenger class. Cargo class vessels had the largest number of ships estimated to produce high wakes. Egmont Key, a long-eroding barrier island at the mouth of the Bay, was potentially subjected to the highest number of ship wakes and the highest cumulative wake energy. Differences in vessel representation in the two sets of AIS data yielded different distributions of wake energy by vessel class. Some strategies for managing wake energy are discussed.
... Living shoreline projects provide the same protection benefits as traditional coastal protection (i.e., wave attenuation, storm surge, and wave action buffering), maintain natural coastal processes, and provide valuable ecosystem services, while having reduced initial and maintenance costs (O'Donnell, 2017). In some cases, living shoreline projects are more protective than traditional shoreline protection (Gittman et al., 2014;Smith et al., 2018) while enhancing ecosystem services such as carbon sequestration, wave attenuation, and fish nursey habitat (Scyphers et al., 2011;Davis et al., 2015;Gittman et al., 2016). ...
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This study reports findings of an analysis of modifications to the incident wave field caused by constructed Oyster Castle® breakwater systems at Gandys Beach Preserve in Downe Township, NJ. The Nature Conservancy’s (TNC) Gandys Beach Preserve is a one-mile stretch of beach located along with intertidal mud flats, sandy beaches, tidal creeks, and salt marshes. Gandys Beach can be classified as a high-energy environment, with open water fetches exceeding 30 miles, and a tidal range on the order of 2 m. The Gandys Beach living shoreline project was designed and constructed by TNC in partnership with the United States Fish and Wildlife Service (USFWS) to investigate the effectiveness of various natural and nature-based features (NNBFs) in protecting and enhancing salt marshes and beaches in high (er) energy environments. Many of the NNBF techniques used at Gandys Beach, such as Oyster Castle® block breakwaters (Oyster Castles), had only been implemented at smaller scales in New Jersey prior to the project. Stevens was contracted by USFWS/TNC to evaluate the impact of the breakwater systems on incident waves. Four breakwater sections along the beach were selected to monitor wave attenuation. Month-long deployments of wave staffs and pressure sensors occurred in the summer and winter of 2019. Analysis of the data indicates that when crests of the Oyster Castles are exposed the breakwater system effectively attenuates waves. However, when the structures are submerged, wave height attenuation decreases, and under certain conditions wave heights behind Oyster Castles can be amplified more than 80%. These results are troubling, especially in areas experiencing sea level rise where the frequency of submergence will likely increase in the future. Due to the complex nature of Gandys Beach, exact mechanisms causing this amplification remain uncertain. Furthermore, transmission coefficients (K t ) above 1 are not typically modeled in existing empirical equations. Seabrook and Hall (Coast. Eng. Proc., 1998, 1 (26), 2000) is the only studied empirical formula that indicated an amplification of the H s as observed during these field deployments and therefore was used to model K t . However, poor agreement between the modeled and observed K t was found and a better predictive tool is needed.
... Instead, the living shoreline concept as applied to salt marshes moves the erosion-resistant material seaward to the base of the marsh and creates a gradual vegetated slope to the upland edge, using the vegetation to protect higher elevations from erosion (Morgan et al. 2009). As landowners become more concerned with erosion and conversion of their upland property to intertidal, the living shoreline approach could become a significant mechanism to promote marsh habitat that can effectively protect shorelines (Gittmann et al. 2014) and provide other benefits (e.g., habitat: Gittman et al. 2014; blue carbon: Davis et al. 2015). ...
... Less than 2% of marshes were damaged in Bay and Franklin counties, and less than 5% of marshes were damaged in Gulf County. This result suggests that the majority of marshes in the study counties can withstand the effects of a category 5 hurricane and continue to provide coastal protection ecosystem services 29 . This also identifies marshes as more resistant than most other coastal defenses, including bulkheads. ...
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Characterizing the fragility, resistance, and resilience of marshes is critical for understanding their role in reducing storm damages and for helping to manage the recovery of these natural defenses. This study uses high-resolution aerial imagery to quantify the impacts of Hurricane Michael, a category 5 hurricane, on coastal salt marshes in the Florida Panhandle, USA. Marsh damage was classified into several categories, including deposition of sediment or wrack, fallen trees, vegetation loss, and conversion to open water. The marshes were highly resistant to storm damages even under extreme conditions; only 2% of the 173,259 km2 of marshes in the study area were damaged—a failure rate much lower than that of artificial defenses. Marshes may be more resistant than resilient to storm impacts; damaged marshes were slow to recover, and only 16% of damaged marshes had recovered 6 months after landfall. Marsh management mattered for resistance and resilience; marshes on publicly-managed lands were less likely to be damaged and more likely to recover quickly from storm impacts than marshes on private land, emphasizing the need to incentivize marsh management on private lands. These results directly inform policy and practice for hazard mitigation, disaster recovery, adaptation, and conservation, particularly given the potential for more intense hurricane landfalls as the climate changes.
... Traditional approaches to coastal protection largely have relied on "gray" infrastructure, such as seawalls, levees, and breakwaters, which may reduce the risk of flooding but may have adverse ecological impacts (Bilkovic and Mitchell 2013) and alter physical dynamics resulting in downstream erosion (de Schipper et al., 2020). In response, management strategies in the United States (US) and elsewhere have evolved and often incorporate natural, or "green," approaches such as living shorelines (Gittman et al., 2014;Sutton-Grier et al., 2015). Interest in infrastructure projects with natural and naturebased features (NNBF) for tackling these coastal resilience challenges is rapidly expanding. ...
Article
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Coastal communities around the world are facing increased coastal flooding and shoreline erosion from factors such as sea-level rise and unsustainable development practices. Coastal engineers and managers often rely on gray infrastructure such as seawalls, levees and breakwaters, but are increasingly seeking to incorporate more sustainable natural and nature-based features (NNBF). While coastal restoration projects have been happening for decades, NNBF projects go above and beyond coastal restoration. They seek to provide communities with coastal protection from storms, erosion, and/or flooding while also providing some of the other natural benefits that restored habitats provide. Yet there remain many unknowns about how to design and implement these projects. This study examines three innovative coastal resilience projects that use NNBF approaches to improve coastal community resilience to flooding while providing a host of other benefits: 1) Living Breakwaters in New York Harbor; 2) the Coastal Texas Protection and Restoration Study; and 3) the South Bay Salt Pond Restoration Project in San Francisco Bay. We synthesize findings from these case studies to report areas of progress and illustrate remaining challenges. All three case studies began with innovative project funding and framing that enabled expansion beyond a sole focus on flood risk reduction to include multiple functions and benefits. Each project involved stakeholder engagement and incorporated feedback into the design process. In the Texas case study this dramatically shifted one part of the project design from a more traditional, gray approach to a more natural hybrid solution. We also identified common challenges related to permitting and funding, which often arise as a consequence of uncertainties in performance and long-term sustainability for diverse NNBF approaches. The Living Breakwaters project is helping to address these uncertainties by using detailed computational and physical modeling and a variety of experimental morphologies to help facilitate learning while monitoring future performance. This paper informs and improves future sustainable coastal resilience projects by learning from these past innovations, highlighting the need for integrated and robust monitoring plans for projects after implementation, and emphasizing the critical role of stakeholder engagement.
... Along the coast, some communities with armored shorelines may face higher damages from storm surges and coastal erosion than those with natural saltmarshes and mangrove forests. For example, in coastal North Carolina during Hurricanes Irene and Matthew, properties with bulkheads sustained more damage and experienced greater shoreline erosion compared to properties with natural shorelines (Gittman et al. 2014). And communities within the so-called "wildland-urban interface" (WUI), which is the area where houses are in or near wildland vegetation, may face increased risks from wildfires as more extreme heat and drought, insect outbreaks, expansion of fire-tolerant invasive species such as cheatgrass, and historical management practices that have excluded naturally-occurring fire in historically fire-adapted systems. ...
Technical Report
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“Nature-based Solutions” (NbS) can play an important role in community adaptation and resilience by not only ameliorating climate-related risks but also through enhancing the quality of life for community residents. This guide delves into the opportunities for integrating NbS into community adaptation planning processes with a special focus on the U.S. Climate Resilience Toolkit's “Steps to Resilience” framework.
... Pete was ahead of his times, practicing marine spatial planning before it was an established practice (Foley et al., 2010). Throughout his career, Pete conducted research related to siting and understanding ecological functions of artificial structures, ranging from wind turbines (Taylor et al., 2016;Voss et al., 2013) and hardened shorelines (Gittman et al., 2014(Gittman et al., , 2015 to artificial reefs (Lemoine et al., 2019;Paxton et al., 2017Paxton et al., , 2018Paxton, Newton, et al., 2020;Paxton, Peterson, et al., 2019;Peterson et al., 2003;Powers et al., 2003;Rosemond et al., 2018); so, this manuscript prescribes a path forward for incorporating ecological principles into planning for artificial reefs that is in line with Pete's visions. We thank Pete for his invaluable mentorship. ...
Article
Humans use the coastal ocean and its resources as a source of food and energy, as well as for a variety of other purposes, including transportation and recreation. Over the past several decades, uses of the coastal ocean have been increasingly accompanied by the installation of artificial structures. These artificial structures come in different shapes and sizes, ranging from energy and aquaculture infrastructure that incidentally form habitat for marine organisms to artificial reefs that are often deployed intentionally to become habitat. Marine spatial planning has offered a robust framework for siting artificial structures to minimize conflicts with other uses and maximize societal and economic benefits with other intended uses of the seascape, but ecological criteria are seldom considered in the planning process. In contrast, artificial reefs are intentionally sunk to form structured habitat and provide a variety of ecological functions, yet ecological principles are not often incorporated into the siting and planning process. Instead, artificial reefs are sited largely to advance societal and economic benefits and minimize conflicts with other uses, such as shipping traffic, military use, or impacts to sensitive areas. We outline a framework to further incorporate ecological principles into artificial reef siting, design and construction, and evaluation that features place‐based and adaptive management coupled with tenets from experimental field ecology. This framework accounts for complexities of and interactions among ecological, societal, and economic criteria associated with artificial reefs to ensure they meet defined goals.
... The ecological effects of shoreline armoring are welldocumented, as are the environmental benefits of nature-based alternatives such as living shorelines (Bilkovic and Mitchell, 2013;Mitchell and Bilkovic, 2019). Living shorelines' ability to reduce erosion has also been studied (Gittman et al., 2014;Bilkovic and Mitchell, 2017). However, the lack of side-by-side comparisons of the physical protective capabilities of natural or nature-based vs. hardened shoreline management strategies has been identified as a major hurdle in the wider promotion and adoption of naturebased shoreline management (Arkema et al., 2017;Morris et al., 2018). ...
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Rising sea levels, extreme weather events, and unsustainable coastal zone development pose serious threats to growing coastal communities. Human actions, such as shoreline development and hardening in at-risk areas, can damage nearshore ecosystems and exacerbate existing risks to coastal populations. A comprehensive understanding of shoreline changes in response to development, storm events, and sea-level rise is needed to effectively mitigate coastal hazards and promote adaptive and resilient coastlines. To determine whether human modification of shorelines can be accurately quantified and assessed over time, we evaluated past and present shoreline mapping and classification efforts in the United States. We coupled a review of available US shoreline data with a survey of coastal planners and managers involved with US state shoreline mapping programs. Using these data, we estimated the current extent of shoreline modification along the Atlantic, Pacific, and Gulf US coasts. However, we found that quantifying shoreline modifications over time nationally—or even within a single state—is currently infeasible due to changes in shoreline resolution associated with advances in shoreline mapping methodologies and a lack of regularly updated shoreline maps. State-level analysis from surveys revealed that 20 US coastal states have undertaken shoreline mapping projects, with sixteen tracking shoreline type and/or condition. However, of the 36 shoreline maps and databases identified, only half (18) were updated regularly or had planned updates. Lacking shoreline change data, coastal communities risk accepting increasingly degraded coastal zones and making poor management decisions based on shifted baselines. Thus, we recommend increasing the scale and funding for several ongoing innovative shoreline mapping efforts. These efforts are particularly focused on improving and standardizing shoreline mapping techniques, as well as establishing accurate baselines for shoreline conditions in the United States. Without accurate baselines and regular, consistent updates to shoreline data, managers cannot manage shorelines in a way that effectively mitigates coastal hazards while also promoting socio-ecological resilience in a changing climate.
... All of these types of nature-based solutions can support coastal resilience and risk reduction by using natural processes and landforms to provide protection for both ecosystems and the built environment 10,11 . They can provide not only protection from sea-level rise and storms [12][13][14] , but also climate change mitigation through carbon sequestration, opportunities for recreation, habitat for key species, and other benefits [15][16][17][18][19][20] . These benefits-ecosystem services or nature's contributions to people-help connect healthy, functioning ecosystems to human wellbeing 21,22 . ...
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Globally, rising seas threaten massive numbers of people and significant infrastructure. Adaptation strategies increasingly incorporate nature-based solutions. New science can illuminate where these solutions are appropriate in urban environments and what benefits they provide to people. Together with stakeholders in San Mateo County, California, USA, we co-developed nature-based solutions to support adaptation planning. We created six guiding principles to shape planning, summarized vulnerability to sea-level rise and opportunities for nature-based solutions, created three adaptation scenarios, and compared multiple benefits provided by each scenario. Adaptation scenarios that included investments in nature-based solutions deliver up to eight times the benefits of a traditionally engineered baseline as well as additional habitat for key species. The magnitude and distribution of benefits varied at subregional scales along the coastline. Our results demonstrate practical tools and engagement approaches to assessing the multiple benefits of nature-based solutions in an urban estuary that can be replicated in other regions.
... Previous studies of flexible vegetation such as sea grasses (Manis et al. 2015, Lei andNepf 2019) and marsh or wetland vegetation (Coops et al. 1996, Anderson et al. 2011, Smith and Anderson 2011, Ozeren et al. 2014, Gittman et al. 2014) have shown that these systems provide essential habitat, sequester carbon, and improve water quality as well as perform engineering services, including flood storage, wave attenuation, and erosion mitigation. Therefore, these systems have potential as sustainable, resilient shoreline protection alternatives. ...
... In the past, shoreline armoring (riprap revetment (riprap, hereafter) and bulkhead) was the primary means to stabilize a shoreline. Whereas both riprap and bulkheads are effective at reducing tidally-driven shore erosion, hardened shorelines are unable to naturally adapt to rising seas, are less resilient during storms, and scour the nearshore sediment through wave refraction (Gittman et al., 2014;Smith et al., 2017). Ecological studies have consistently found that shoreline armoring negatively impacts the intertidal and nearshore benthic and nekton communities relative to unmodified sections of shoreline via habitat fragmentation (Peterson & Lowe, 2009), changes in nearshore erosion processes (Bozek & Burdick, 2005), increased depth of nearby waters (Toft et al., 2013), reduced species abundance and diversity (Bilkovic et al., 2006;Bilkovic & Roggero, 2008;Kornis et al., 2017;Seitz et al., 2006) at both local and landscape scales (Isdell et al., 2015), and prevention of landward migration of intertidal habitats (Bilkovic, 2011;Titus et al., 2009). ...
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Nature-based shoreline protection provides a welcome class of adaptations to promote ecological resilience in the face of climate change. Along coastlines, living shorelines are among the preferred adaptation strategies to both reduce erosion and provide ecological functions. As an alternative to shoreline armoring, living shorelines are viewed favorably among coastal managers and some private property owners, but they have yet to undergo a thorough examination of how their levels of ecosystem functions compare to their closest natural counterpart: fringing marshes. Here, we provide a synthesis of results from a multi-year, large-spatial-scale study in which we compared numerous ecological metrics (including habitat provision for fish, invertebrates, diamondback terrapin, and birds, nutrient and carbon storage, and plant productivity) measured in thirteen pairs of living shorelines and natural fringing marshes throughout coastal Virginia, USA. Living shorelines were composed of marshes created by bank grading, placement of sand fill for proper elevations, and planting of S. alterniflora and S. patens , as well as placement of a stone sill seaward and parallel to the marsh to serve as a wave break. Overall, we found that living shorelines were functionally equivalent to natural marshes in nearly all measured aspects, except for a lag in soil composition due to construction of living shoreline marshes with clean, low-organic sands. These data support the prioritization of living shorelines as a coastal adaptation strategy.
... While site orientation is a fixed variable on coastal properties, several alternative options exist for standard armoring materials. Choosing materials that satisfy engineering criteria and reduce thermal extremes has the potential to enhance intertidal species survivorship directly Mcafee et al., 2016) and indirectly by reducing secondary risks from thermal stress like increased susceptibility to disease (Petton et al., 2013;Gittman et al., 2014;Strain et al., 2018b). ...
Article
Ecological engineering approaches have been shown to enhance the abundance and species diversity of intertidal organisms living on urban shoreline infrastructure (i.e., bulkheads and seawalls). Ecological studies have long shown the overarching importance of temperature in driving the physiology and survival of these organisms, yet we often do not fully understand what these temperatures are on engineered surfaces, as they can be very different from air or water temperature. The current study used a heat budget model to estimate surface temperature on bulkheads of different construction materials and surface orientations as a potential factor controlling the abundance and distribution of algal and invertebrate species living on armored shorelines. A Land Surface Model previously adapted for mussel beds was modified to incorporate the physical and thermal properties of three construction materials commonly used in shoreline armoring: concrete, granite and steel. Hourly temperature, tide and solar elevation data for Boston, MA, USA were used to simulate temperatures on a total of twelve model surfaces representing each construction material with north, east, south, and west surface orientations, respectively, over a period of 5 years (2014–2018). A rapid species assessment of intertidal epibiota on bulkheads in Boston Harbor provided baseline data about ecological communities that might be targeted in enhancement efforts, and information on physiological sensitivities of key species was determined from published literature. Comparisons between these sensitivities and exposures estimated from the model showed that simulated surface temperatures can exceed the physiological limits of local species but that this depends on surface orientation and material properties of the structure. Results further highlight the influence of material properties (density, specific heat capacity and thermal conductivity) of engineered structures on the incidence and severity of thermal extremes when exposed to direct solar radiation at low tide. Significant differences in the duration and intensity of high temperature values among model surfaces demonstrate that the potential effectiveness of choices in bulkhead construction materials designed to mitigate thermal extremes are likely most effective on south- and west-facing surfaces where incident solar radiation is highest. The ability to predict thermal extremes on existing or planned coastal development projects can improve and further refine ecological enhancement initiatives on shoreline infrastructure. Such collaborations would enable coastal zone managers, shorefront property owners, ecologists, and designers to co-design structures that create physiologically tolerable temperatures as a basis for ecological enhancement.
... A second category is structural integrity and hazard mitigation, referring to the ability of a shoreline feature to resist breaking or deforming under various pressures (e.g., wave energy, drought, sea level rise) and reducing or eliminating risks to life and property from hazard events (e.g., storms or droughts). Whereas hard structural features tend to suffer costly damage under severe storm events, certain NNBF can naturally recover (Gittman et al. 2014) and adapt to sea level rise (Morris et al. 2002(Morris et al. , 2018. A third category consists of social and economic outcomes, which include direct and indirect effects of shoreline features on people and their livelihoods. ...
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There is growing interest in the application of nature-based solutions to adapt to climate change and promote resilience, yet barriers exist to their implementation. These include a perceived lack of evidence of their functioning in comparison to conventional solutions and an inability for existing design, policy, and assessment processes to capture the multiple benefits of these solutions. Positing this as a challenge of operationalizing and measuring resilience, we argue that the concept of resilience needs to be given concrete meaning in applied management contexts. Starting with shoreline vulnerability as a policy problem and natural and nature-based shoreline features as a promising solution, we present a case study of a co-creative process to produce an interdisciplinary and locally relevant approach to understanding and capturing the benefits of natural and nature-based solutions. We develop the notion of resilience service to enable a concreteness to resilience that simultaneously takes into account ecological, technical, and social dimensions. Through the co-creative process, our researcher-practitioner network developed a monitoring framework for shoreline features in New York State to facilitate the comparison of natural and nature-based features with conventional shoreline approaches. We describe the process and assess the advantages and drawbacks of integrating scientific input and local knowledge. We present the monitoring framework, showing how the co-creative character of the process is consequential in the formulation of the final framework through the selection of parameters, indicators, and protocols. We argue that interdisciplinarity, co-creation, pragmatism, multi-scalar applicability, and policy relevance are critical principles to understand the functioning and facilitate the implementation of nature-based solutions, while recognizing that this work necessitates compromise and as such will lead to continued deliberation. We posit this is a strength of the process for it acknowledges the creation of resilience as a social process in which values are central and subject to change.
... Few studies, however, have compared the actual performance of ecosystem-based coastal protection to conventional measures. Gittman et al. (2014) compared the performance of North Carolina shoreline protection measures during Hurricane Irene (a category 1 hurricane) and found that marshes with and without sills suffered less erosion than bulkheads. More direct studies are needed to build the evidence base of where and under what circumstances ecosystem-based approaches can outperform or supplement their conventional counterparts. ...
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An increasing abundance of projects demonstrate that coastal management strategies that align engineering and ecological objectives can deliver a wide range benefits. Better understanding how these strategies fare under stress is crucially important, including in comparison to more conventional coastal engineering approaches, in order to inform where they might be a viable alternative or complement to conventional coastal storm risk management. In particular, the prospect that these strategies may be able to recover from disturbances and adapt to better survive future disturbances with minimal or no intervention is compelling. However, no formal accounting method exists to assess how ecosystem-based approaches contribute to the resilience of coastal systems, that is, their ability to prepare, absorb, recover, and adapt from stressors. An assessment rubric is developed and demonstrated for Engineering With Nature® projects and limitations and ways forward are discussed.
Chapter
Islands in estuaries, major river deltas, and open-coast environments reduce the severity of hazards, including erosion and flooding from wind-driven waves and extreme water levels, on the nearby habitats and shorelines. Islands may also provide critical ecosystem function for threatened and endangered species and migratory birds while providing access to recreational opportunities and navigation co-benefits. This chapter (Chapter 11) of the International Guidelines on Natural and Nature-Based Features (NNBF) for Flood Risk Management focusses on islands as NNBFs that support coastal resilience. Three types of islands are discussed—barrier islands, deltaic islands (including spits), and in-bay or in-lake islands. These islands may be new construction or, as in most cases, the restoration of island remnants. The degradation and loss of islands through combined processes such as sea-level rise, subsidence, and inadequate sediment input (e.g., upstream impoundments, navigation channels, evolving natural processes) are reducing the coastal resilience benefits of these features.
Article
Over the past decade, the scientific community has studied, experimented, and published a notable body of literature on ecological enhancement of coastal and marine infrastructure (CMI). The Nature‐Inclusive Design (NID) approach refers to methods and technologies that can be integrated into the design and construction of CMI to create suitable habitat for native species (or communities) whose natural habitat has been degraded or reduced. To examine the compliance of new environmentally sensitive technologies with structural requirements and fiscal restraints, while providing ecosystem and habitat value, this paper presents the findings of a structural‐economical‐biological analysis of ecologically engineered Articulated Concrete Block Mattresses (ACBM). To evaluate the structural and biological performance of the ECO ACBM's, a pilot project was deployed in April 2017 at Port Everglades, FL, USA and evaluated against controls of adjacent artificial structures and smooth‐surface concrete blocks and monitored over a period of 2 years. The elements of ecological enhancement implemented in the fabrication and design of the ecologically enhanced ACBM’s were comprised of bio‐enhancing concrete additives and science‐based designs. Based on the results of this study, these design alterations have increased the richness and diversity of sessile assemblages compared to control blocks and adjacent artificial structures, and supported a higher abundance of mobile species. This ecological improvement was achieved within the operational limitations of conventional manufacturing and installation technologies, while complying with strict structural requirements for standard concrete marine construction. The results supported the working hypothesis, and demonstrated that modifications of concrete composition, surface texture, and macro‐design, have the potential to elevate the ecological value of concrete‐based CMI and promote a more sustainable and adaptive approach to coastal and marine development in an era of climate resilience building. This article is protected by copyright. All rights reserved.
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Small reef islands provide habitable land for coastal communities in many parts of the world. However, the small, low lying reef islands are commonly considered among the most geomorphically sensitive landforms to changes in sea level, wave processes, sediment supply and anthropogenic impacts. Kepulauan Seribu in the Java Sea comprise of numerous reef islands. By 2019, the islands chain is host to more than 24 thousand people. Kepulauan Seribu is affected by monsoon wind cycle. The monsoon wind also known to interact with an interannual phenomenon such as Indian Ocean Dipole (IOD) which affecting regional and local wind circulation. This study aims to examine the reef shoreline response to seasonal and interannual climate variability using satellite data that encompasses yearly monsoon cycle and IOD event. Strengthens (weakens) of winds speed in the study area during the East (West) Monsoon, which in some year also coincides with a positive (negative) IOD event, are observed from 2009 to 2018 ERA - Interim by The European Centre for Medium - Range Weather Forecasts (ECMWF) data. This variability influences the shoreline shifting in the uninhabited reef islands of Kepulauan Seribu as identified based on satellite imagery analysis. More pronounce shifted of large sediment flux are perceptible on opposing monsoon which coincides with positive/negative IOD event. Small uninhabited reef islands have ecological and economical value. Hence, enhancing coastal resilience from erosion by using conservation-types approach should be taking into consideration. Ultimately, a good understanding of climate variability that controlled changes in beach systems of reef islands is important for adequate coastal management decisions.
Article
The use of natural habitats for coastal protection (a.k.a. Nature Based Solutions or NBS) in place of engineered structures like breakwaters and seawalls can yield a wide range of ecological and economic benefits. Despite these advantages, NBS are not commonly implemented for shoreline protection due to uncertainty over the amount of protection afforded by each unique feature and how protective capacity and ecological benefits are likely to change over time as NBS mature and adapt to changing environmental drivers. Here we highlight the recent restoration of Swan Island in the Chesapeake Bay, and the collaborative approach used to evaluate post‐construction performance, as a framework for quantitative evaluation of NBS projects. At Swan Island, 60,000 cubic yards of dredged sediment were used to elevate and restore the island's footprint with an emphasis on increasing its protective and ecological benefits and long‐term resilience to sea level rise. Five entities have leveraged resources to quantify the benefits and efficacy of island restoration by conducting pre‐ and post‐restoration monitoring which supports development of an integrated, simulation model that includes three 'measured' system parameters: wave height, vegetation biomass and island profiles (i.e., elevations). The model will be used to predict island performance under a range of different system scenarios and used to inform adaptive management options. Results will demonstrate the efficacy of leveraging natural and engineered processes to restore island systems while providing a framework for quantifying NBS. This article is protected by copyright. All rights reserved.
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This study uses data from shoreline modification permit applications in Gloucester County, Virginia to provide insights into how coastal managers can encourage the use of living shorelines over shoreline armoring. The data show that shorelines are more likely to be modified on properties with high neighboring property values and properties threatened by hurricane storm surge and high wave energy, while modifications are less likely in conservation areas and areas with high percentages of natural cover and agricultural use. Compared to armoring, living shorelines are more likely in FEMA Special Flood Hazard Areas and following recent flooding experiences but are less likely to be installed following an FEMA disaster declaration. Property owners are also significantly more likely to install a specific modification if their neighbors have already installed that modification. Based on these results, coastal managers may be able to increase the effectiveness of interventions to reduce shoreline modification by targeting unmodified high value properties in residential areas with high wave energy. To encourage property owners to install living shorelines over armoring, the results suggest that coastal managers should target properties with armored neighbors or properties in business zones and should develop interventions directly following significant storm events.
Chapter
Despite its importance in supporting the global economy and to accommodate an ever-growing population at the coast, many of the coastal ecosystems such as mangroves, reefs, seagrass meadows, salt marshes and dunes had in the recent years an accentuated decrease in their coverage. The loss of coastal ecosystems, among other problems, leads to the loss of natural capacity for flood mitigation and coastal erosion. Since a considerable share of the coastal population is living in flood-prone areas, the loss of capacity of the ecosystems to mitigate the impacts of floods and coastal erosion can increase the vulnerability to natural hazards such as storm surges, hurricanes and typhoons. This is especially relevant in a context of increasing sea-level rise and intensity and frequency of extreme weather events, both increasing the risk to lose lives and assets. Coastal flood mitigation has been done primarily through the use of hard grey infrastructures. However, these types of structures can have long-term impacts on coastal ecosystems, require continuous maintenance and, in the face of extreme events, may represent an inefficient way to prevent coastal degradation. This called the attention of scientists and decision-makers towards the role of nature to mitigate the impacts of coastal floods through nature-based solutions (NBS). NBS, under the framework of ecosystem-based management, are interventions that aim to reduce the impacts of coastal flooding and erosion and simultaneously enhance ecosystems, biodiversity and natural resources. NBS can use (1) natural solutions (e.g. marine protected areas), (2) soft engineering and ecological restoration (e.g. beach nourishment) and (3) hybrid solutions, which integrate natural and grey infrastructures. Recently, NBS are gaining popularity and are part of coastal management strategies in many countries. Despite their efficiency, it is still a new practice, and therefore concerns are raised regarding their environmental and anthropogenic impacts. Also, there are some drawbacks and pitfalls that need to be overcome to increase NBS implementation. In this chapter we make an overview on the need for NBS for coastal flood mitigation, its implementation in a worldwide context, their impacts on the coastal social ecological economics systems, drawbacks and opportunities to improve their acceptance.
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Climate change and coastal development pressures have intensified the need for shoreline protection. Nature-first approaches that use natural habitats, particularly marshes, are being promoted globally as ecologically-beneficial alternatives to grey infrastructure. The ability of these novel shorelines to provide nursery habitat to blue crab, an ecologically and economically important species along the Atlantic and Gulf coasts of the United States, has not been quantified. We quantified the abundance and size distribution of juvenile blue crabs from a chronosequence of living shorelines (created fringing marshes) spanning 2 to 16 years in age (since construction) and compared with paired natural fringing marshes in the southern Chesapeake Bay. Both created and natural fringing marshes are being used by blue crabs as primary nursery habitats. While there were interannual differences in abundance, young blue crabs (≤ 2.5 cm carapace width) were observed in similar densities and sizes at living shoreline and natural marshes. There was no relationship between the age of the living shoreline and blue crab density, indicating that even the youngest living shorelines (2 years) were providing primary nursery habitat. Young blue crabs were more abundant in more isolated marshes and those that were inundated for longer periods of time each tidal cycle, which may be evidence for habitat-limitation. Synthesis and applications: We provide evidence that juvenile blue crabs are comparably using natural and created fringing salt marshes as primary nursery habitat. Although the relative importance of salt marshes as young crab nursery habitat is not fully understood and likely varies by system, the value of marshes within a suite of available structural nursery habitats may increase under a changing climate. The potential for living shorelines to serve as nursery habitat for an economically important species may provide additional incentives to implement these climate adaptation strategies.
The need for sustainable and resilient long-term strategies for coastal restoration and development projects is largely due to pressures brought by changing climate conditions and growing human populations along coastal boundaries. As anthropogenic impacts along our coasts increase, the demand for sustainable, nature-based solutions (NbS) will grow commensurately. Trusted approaches are needed for successful implementation of NbS, especially in regions hardest hit by environmental changes. Nearshore strategies for new construction and protection of existing coastal infrastructure are shifting rapidly from hardened approaches to more ecologically aligned techniques that work with natural forces and enhance natural habitat. This paper highlights the benefits of living shorelines composed of ecotypic native plants, wave attenuation structures for coastal protection, and managed retreat to restore coastal environments while supporting and maintaining natural habitats. We review several NbS and present two case studies to illustrate the value of incorporating nature-based approaches to vulnerable coastal environments and highlight the importance of maximizing synergies and understanding tradeoffs in their use long-term. This article is protected by copyright. All rights reserved.
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The Protective Value of Nature summarizes the latest science on the effectiveness of natural infrastructure in lowering the risks to communities from weather- and climate-related hazards. Over the past two decades, the body of research evaluating and quantifying the protective performance of natural infrastructure has increased significantly. Both model-based assessments and empirical evidence from recent floods, hurricanes, wildfires, and other natural disasters underscore the considerable risk reduction services that natural systems such as wetlands, reefs, dunes, floodplains, and forests provide. At the same time, natural infrastructure offers numerous additional benefits to society, from provision of food and clean water for people and habitat for fish and wildlife, to recreational opportunities, and cultural and spiritual fulfillment. As we highlight throughout the report, evidence suggests that both natural and nature-based approaches for hazard mitigation can be equally or more effective than conventional structural approaches, and they are often more cost-effective. Since healthy, intact ecosystems are often adapted to natural disturbances such as floods and wildfires, they may have the capacity to withstand or recover from extreme weather- and climate-related hazards and adjust to ongoing environmental changes. Conventional structural approaches (i.e., “gray infrastructure”), on the other hand, often require ongoing maintenance, and may need costly repairs when they fail or are damaged. Thus, natural defenses can play a critical role in enhancing the resilience of human and ecological systems to natural disasters and climate change. To advance the use of natural infrastructure across the country, the report offers key policy recommendations in the following areas: --Protect and restore existing features providing natural defenses --Mainstream use of natural infrastructure across sectors --Improve risk assessment and encourage smart development --Dramatically scale up investments in community resilience and supporting research
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Traditional coastal protection methods that rely on built, hard structures like seawalls may not be effective to keep pace with a changing climate. Nature-based coastal defences based on habitat restoration can be an adaptive coastal protection alternative.
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Coastal ecosystems provide numerous services, such as nutrient cycling, climate change amelioration, and habitat provision for commercially valuable organisms. Ecosystem functions and processes are modified by human activities locally and globally, with degradation of coastal ecosystems by development and climate change occurring at unprecedented rates. The demand for coastal defense strategies against storms and sea-level rise has increased with human population growth and development along coastlines worldwide, even while that population growth has reduced natural buffering of shorelines. Shoreline hardening, a common coastal defense strategy that includes the use of seawalls and bulkheads (vertical walls constructed of concrete, wood, vinyl, or steel), is resulting in a "coastal squeeze" on estuarine habitats. In contrast to hardening, living shorelines, which range from vegetation plantings to a combination of hard structures and plantings, can be deployed to restore or enhance multiple ecosystem services normally delivered by naturally vegetated shores. Although hundreds of living shoreline projects have been implemented in the U.S. alone, few studies have evaluated their effectiveness in sustaining or enhancing ecosystem services relative to naturally vegetated shorelines and hardened shorelines. We quantified the effectiveness of (1) sills with landward marsh (a type of living shoreline that combines marsh plantings with an offshore low-profile breakwater), (2) natural salt marsh shorelines (control marshes), and (3) unvegetated bulkheaded shores in providing habitat for fish and crustaceans (nekton). Sills supported higher abundances and species diversity of fishes than unvegetated habitat adjacent to bulkheads and even control marshes. Sills also supported higher cover of filter-feeding bivalves (a food resource and refuge habitat for nekton) than bulkheads or control marshes. These ecosystem-service enhancements were detected on shores with sills three or more years after construction, but not before. Sills provide added structure and may provide better refuges from predation and greater opportunity to use available food resources for nekton than unvegetated bulkheaded shores or control marshes. Our study shows that unlike shoreline hardening, living shorelines can enhance some ecosystem services provided by marshes, such as provision of nursery habitat. Read More: http://www.esajournals.org/doi/abs/10.1890/14-0716.1
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Coastal development affects estuarine resources by severing terrestrial-aquatic link- ages, reducing shallow water habitats, and degrading ecosystem services, which is predicted to result in measurable declines in nekton community integrity. We assessed the effects of landscape features on nearshore habitats and biological communities, relating subtidal habitat, shoreline condition, upland land use and nearshore fish communities in a Chesapeake Bay tributary, the James River, Virginia. Both upland development and the placement of erosion control structures on the shoreline were associated with reduced fish community integrity, and shoreline alterations were linked with the amount of subtidal structural habitat in the nearshore. Ecological thresholds in nek- ton community integrity were evident at ≥23% developed land use within 200 and 1000 m buffer increments. Nekton assemblages at sites with low development (
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Within the coastal zone, waterfront development has caused severe loss of shallowwater habitats, such as salt marshes and seagrass beds. Although the effects of habitat degradation on community structure within intertidal marshes have been well studied, little is known about the impact of habitat degradation on, and the ecological value of, subtidal shallow-water habitats, despite the prevalence of these habitats in coastal ecosystems. In coastal habitats, bivalves are dominant benthic organisms that can comprise over 50% of benthic prey biomass and are indicative of benthic production. We quantified bivalve diversity, density, and biomass in deep and shallow (<1.5 m MLW) unstructured subtidal habitats in 2 tributaries of lower Chesapeake Bay (Elizabeth- Lafayette River system and York River). We also examined the effects of shoreline alteration in shallow habitats by contrasting the benthos of the subtidal areas adjacent to natural marsh, bulkhead, and rip-rap shorelines. Bivalve diversity, density, and biomass were significantly higher in shallow than in deep benthic habitats in both systems. Benthic abundance and diversity were higher in subtidal habitats adjacent to natural marsh than those adjacent to bulkhead shorelines; abundance and diversity were intermediate in rip-rap shorelines, and appeared to depend on landscape features. Predator density and diversity tended to be highest adjacent to natural marsh shorelines, and density of crabs was significantly higher in natural marsh than in bulkhead habitats. There is thus a crucial link between natural marshes, infaunal prey in subtidal habitats, and predator abundance. Consequently, the indirect effects of coastal habitat degradation upon secondary production in the shallow, subtidal habitats adjacent to salt marshes may be as great as or greater than direct habitat effects.
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The coastal zone has changed profoundly during the 20th century and, as a result, society is becoming increasingly vulnerable to the impact of sea-level rise and variability. This demands improved understanding to facilitate appropriate planning to minimise potential losses. With this in mind, the World Climate Research Programme organised a workshop (held in June 2006) to document current understanding and to identify research and observations required to reduce current uncertainties associated with sea-level rise and variability. While sea levels have varied by over 120m during glacial/interglacial cycles, there has been little net rise over the past several millennia until the 19th century and early 20th century, when geological and tide-gauge data indicate an increase in the rate of sea-level rise. Recent satellite-altimeter data and tide-gauge data have indicated that sea levels are now rising at over 3mmyear−1. The major contributions to 20th and 21st century sea-level rise are thought to be a result of ocean thermal expansion and the melting of glaciers and ice caps. Ice sheets are thought to have been a minor contributor to 20th century sea-level rise, but are potentially the largest contributor in the longer term. Sea levels are currently rising at the upper limit of the projections of the Third Assessment Report of the Intergovernmental Panel on Climate Change (TAR IPCC), and there is increasing concern of potentially large ice-sheet contributions during the 21st century and beyond, particularly if greenhouse gas emissions continue unabated. A suite of ongoing satellite and in situ observational activities need to be sustained and new activities supported. To the extent that we are able to sustain these observations, research programmes utilising the resulting data should be able to significantly improve our understanding and narrow projections of future sea-level rise and variability.
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Narrow fringing salt marshes dominated by Spartina alterniflora occur naturally along estuarine shorelines and provide many of the same ecological functions as more extensive marshes. These fringing salt marshes are sometimes incorporated into shoreline stabilization efforts. We obtained data on elevation, salinity, sediment characteristics, vegetation and fish utilization at three study sites containing both natural fringing marshes and nearby restored marshes located landward of a stone sill constructed for shoreline stabilization. During the study, sediment accretion rates in the restored marshes were approximately 1.5- to 2-fold greater than those recorded in the natural marshes. Natural fringing marsh sediments were predominantly sandy with a mean organic matter content ranging between 1.5 and 6.0%. Average S. alterniflora stem density in natural marshes ranged between 130 and 222 stems m−2, while mean maximum stem height exceeded 64 cm. After 3 years, one of the three restored marshes (NCMM) achieved S. alterniflora stem densities equivalent to that of the natural fringing marshes, while percentage cover and maximum stem heights were significantly greater in the natural than in the restored marshes at all sites. There was no significant difference in the mean number of fish, crabs or shrimp captured with fyke nets between the natural and restored marshes, and only the abundance of Palaemonetes vulgaris (grass shrimp) was significantly greater in the natural marshes than in the restored ones. Mean numbers of fish caught per 5 m of marsh front were similar to those reported in the literature from marshes adjacent to tidal creeks and channels, and ranged between 509 and 634 fish net−1. Most of the field data and some of the sample analyses were obtained by volunteers as they contributed 223 h of the total 300 h spent collecting data from three sites in one season. The use of fyke nets required twice as many man-hours as any other single task. Vegetation and sediment parameters were sensitive indicators of marsh restoration success, and volunteers were capable of contributing a significant portion of the labor needed to collect these parameters.
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Seagrass beds have declined in Chesapeake Bay, USA as well as worldwide over the past century. Increased seston concentrations, which decrease light penetration, are likely one of the main causes of the decline in Chesapeake Bay. It has been hypothesized that dense populations of suspension-feeding bivalves, such as eastern oysters (Crassostrea virginica), may filter sufficient seston from the water to reduce light attenuation and enhance seagrass growth. Furthermore, eastern oyster populations can form large three-dimensional reef-like structures that may act like breakwaters by attenuating waves, thus decreasing sediment resuspension. We developed a quasi-three-dimensional Seagrass-Waves-Oysters-Light-Seston (SWOLS) model to investigate whether oyster reefs and breakwaters could improve seagrass growth by reducing seston concentrations. Seagrass growth potential (SGP), a parameter controlled by resuspension-induced turbidity, was calculated in simulations in which wave height, oyster abundance, and reef/breakwater configuration were varied. Wave height was the dominant factor influencing SGP, with higher waves increasing sediment resuspension and decreasing SGP. Submerged breakwaters parallel with the shoreline improved SGP in the presence of 0.2 and 0.4m waves when sediment resuspension was dominated by wave action, while submerged groins perpendicular to the shoreline improved SGP under lower wave heights (0.05 and 0.1m) when resuspension was dominated by along-shore tidal currents. Oyster-feeding activity did not affect SGP, due to the oysters’ distance from the seagrass bed and reduced oyster filtration rates under either low or high sediment concentrations. Although the current implementation of the SWOLS model has simplified geometry, the model does demonstrate that the interaction between oyster filtration and along-shore circulation, and between man-made structures and wave heights, should be considered when managing seagrass habitats, planning seagrass restoration projects, and choosing the most suitable methods to protect shorelines from erosion.
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Shore protection and habitat enhancement along a residential island werethe main goals of this shoreline study. The physical and geological factorsnecessary to design shoreline stabilization structures capable of confidentlysupporting suitable and stable habitat enhancement/restoration substrate areemphasized since this area of study generally may be unfamiliar to wetlandresource managers. Erosion along the targeted shoreline is influenced by aunidirectional wave field from the south-southwest. Results of our analysesshowthat a headland control system comprised of headland breakwaters could be usedsuccessfully to stabilize the existing shoreline and provide resource managersflexibility in habitat restoration decisions. Headland breakwaters are designedto diffract wave energy so that shore planform equilibrium is attained and canbe sized and positioned to maximize the length of stabilized shoreline.Maximization of the new shoreline length provides increased subaerial,intertidal, and subaqueous environments for flexible habitat restorationalternatives. The final restoration design developed through this study willcreate approximately 69,000 m2 of new habitat includingstable beach, dune, tidal marsh, scrub shrub, and submersed aquatic vegetation.An additional 2,000 m2 of rock substrate habitat isprovided directly by the headland control structures.
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Background: Salt marshes lie between many human communities and the coast and have been presumed to protect these communities from coastal hazards by providing important ecosystem services. However, previous characterizations of these ecosystem services have typically been based on a small number of historical studies, and the consistency and extent to which marshes provide these services has not been investigated. Here, we review the current evidence for the specific processes of wave attenuation, shoreline stabilization and floodwater attenuation to determine if and under what conditions salt marshes offer these coastal protection services. Methodology/principal findings: We conducted a thorough search and synthesis of the literature with reference to these processes. Seventy-five publications met our selection criteria, and we conducted meta-analyses for publications with sufficient data available for quantitative analysis. We found that combined across all studies (n = 7), salt marsh vegetation had a significant positive effect on wave attenuation as measured by reductions in wave height per unit distance across marsh vegetation. Salt marsh vegetation also had a significant positive effect on shoreline stabilization as measured by accretion, lateral erosion reduction, and marsh surface elevation change (n = 30). Salt marsh characteristics that were positively correlated to both wave attenuation and shoreline stabilization were vegetation density, biomass production, and marsh size. Although we could not find studies quantitatively evaluating floodwater attenuation within salt marshes, there are several studies noting the negative effects of wetland alteration on water quantity regulation within coastal areas. Conclusions/significance: Our results show that salt marshes have value for coastal hazard mitigation and climate change adaptation. Because we do not yet fully understand the magnitude of this value, we propose that decision makers employ natural systems to maximize the benefits and ecosystem services provided by salt marshes and exercise caution when making decisions that erode these services.
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Shorelines at the interface of marine, estuarine and terrestrial biomes are among the most degraded and threatened habitats in the coastal zone because of their sensitivity to sea level rise, storms and increased human utilization. Previous efforts to protect shorelines have largely involved constructing bulkheads and seawalls which can detrimentally affect nearshore habitats. Recently, efforts have shifted towards "living shoreline" approaches that include biogenic breakwater reefs. Our study experimentally tested the efficacy of breakwater reefs constructed of oyster shell for protecting eroding coastal shorelines and their effect on nearshore fish and shellfish communities. Along two different stretches of eroding shoreline, we created replicated pairs of subtidal breakwater reefs and established unaltered reference areas as controls. At both sites we measured shoreline and bathymetric change and quantified oyster recruitment, fish and mobile macro-invertebrate abundances. Breakwater reef treatments mitigated shoreline retreat by more than 40% at one site, but overall vegetation retreat and erosion rates were high across all treatments and at both sites. Oyster settlement and subsequent survival were observed at both sites, with mean adult densities reaching more than eighty oysters m(-2) at one site. We found the corridor between intertidal marsh and oyster reef breakwaters supported higher abundances and different communities of fishes than control plots without oyster reef habitat. Among the fishes and mobile invertebrates that appeared to be strongly enhanced were several economically-important species. Blue crabs (Callinectes sapidus) were the most clearly enhanced (+297%) by the presence of breakwater reefs, while red drum (Sciaenops ocellatus) (+108%), spotted seatrout (Cynoscion nebulosus) (+88%) and flounder (Paralichthys sp.) (+79%) also benefited. Although the vertical relief of the breakwater reefs was reduced over the course of our study and this compromised the shoreline protection capacity, the observed habitat value demonstrates ecological justification for future, more robust shoreline protection projects.
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Global sea levels have risen through the 20th century. These rises will almost certainly accelerate through the 21st century and beyond because of global warming, but their magnitude remains uncertain. Key uncertainties include the possible role of the Greenland and West Antarctic ice sheets and the amplitude of regional changes in sea level. In many areas, nonclimatic components of relative sea-level change (mainly subsidence) can also be locally appreciable. Although the impacts of sea-level rise are potentially large, the application and success of adaptation are large uncertainties that require more assessment and consideration.
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Rising sea level threatens existing coastal wetlands. Overall ecosystems could often survive by migrating inland, if adjacent lands remained vacant. On the basis of 131 state and local land use plans, we estimate that almost 60% of the land below 1 m along the US Atlantic coast is expected to be developed and thus unavailable for the inland migration of wetlands. Less than 10% of the land below 1 m has been set aside for conservation. Environmental regulators routinely grant permits for shore protection structures (which block wetland migration) on the basis of a federal finding that these structures have no cumulative environmental impact. Our results suggest that shore protection does have a cumulative impact. If sea level rise is taken into account, wetland policies that previously seemed to comply with federal law probably violate the Clean Water Act.
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A common assumption is that ecosystem services respond linearly to changes in habitat size. This assumption leads frequently to an "all or none" choice of either preserving coastal habitats or converting them to human use. However, our survey of wave attenuation data from field studies of mangroves, salt marshes, seagrass beds, nearshore coral reefs, and sand dunes reveals that these relationships are rarely linear. By incorporating nonlinear wave attenuation in estimating coastal protection values of mangroves in Thailand, we show that the optimal land use option may instead be the integration of development and conservation consistent with ecosystem-based management goals. This result suggests that reconciling competing demands on coastal habitats should not always result in stark preservation-versus-conversion choices.
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The Supreme Court's 2001 decision in Solid Waste Agency of Northern Cook County v. United States Army Corps of Engineers (SWANCC) cast a pall over the Army Corps of Engineers' wetlands regulation program. The Court threatened to lessen the scope of the Clean Water Act and infused virtually exercise of the Corps's jurisdiction with doubt. In the consolidated cases Rapanos v. US and Carabell v. US, the Supreme Court granted a partial reprieve to the CWA. The Court's divided opinion left substantial uncertainty about the scope of federal jurisdiction, the court rejected strict limits on the corps's authority under the CWA.
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Oyster cultch was added to the lower intertidal fringe of three created Spartina alterniflora marshes to examine its value in protecting the marsh from erosion. Twelve 5-m-wide plots were established at each site, with six randomly selected plots unaltered (noncultched) and cultch added to the remaining (cultched) plots. Within each cultched plot, cultch was placed along the low tide fringe of the marsh during July 1992, in a band 1.5 m wide by 0.25 m deep. Marsh-edge vegetation stability and sediment erosion were measured for each plot from September 1992 to April 1994. Significant differences (p < 0.05) in marsh-edge vegetation change were detected at the only south-facing site after a major southwester storm. Significantly different rates of sediment erosion and accretion also were observed at this same site. Areas upland of the marsh edge in the cultched areas showed an average accretion of 6.3 cm, while noncultched treatment areas showed an average loss of 3.2 cm. A second site, with a northern orientation, also experienced differential sediment accretion and erosion between treatment type, caused instead by boat wakes that were magnified by the abutment of a dredge effluent pipe across the entire front fringe of the site. During this period we observed significant differences in sediment accumulation, with the areas upland of the marsh edge in the cultched treatment having an average accretion of 2.9 cm and the noncultched an average loss of 1.3 cm.
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Along densely populated coasts, the armoring of shorelines is a prevalent cause of natural habitat loss and degradation. This article explores the values and decision making of waterfront homeowners and identifies two interlinked and potentially reversible drivers of coastal degradation. We discovered that: (1) misperceptions regarding the environmental impacts and cost-effectiveness of different shoreline conditions was common and may promote armoring; and (2) many homeowners reported only altering their shorelines in response to damage caused by armoring on neighboring properties. Collectively, these findings suggest that a single homeowner's decision may trigger cascading degradation along a shoreline, which highlights the necessity of protecting existing large stretches of natural shoreline. However, our study also found that most homeowners were concerned with environmental impacts and preferred the aesthetics of natural landscapes, both of which could indicate nascent support and pathways for conservation initiatives along residential shorelines.
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A strong northeast storm that lasted several days and culminated on Halloween Eve 1991 caused extensive erosion and structural damage along Massachusetts' North and South Shores. The passage of Hurricane Bob six weeks earlier had resulted in a significant decrease of the beach/barrier buffer zone which had made the coast extra vulnerable to this new storm. Both erosion and structural damage were controlled primarily by the beach and dune morphology, sediment composition, exposure to waves and wind, and the presence or absence of coastal structures. The most widespread and severe damage to dwellings occurred along the South Shore in areas where storm buffer zones are narrow to nonexistent and where houses were subjected to gravel overwash. Areas heavily impacted by the Halloween Eve storm were the same ones that were most severely damaged during the February Blizzard of 1978.
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Many birds, alligators, and turtles spend their entire lifetimes communing between wetlands and adjacent bodies of water, while land animals that normally occupy dry land visit the wetlands to feed. Herons, eagles, sandpipers, ducks, and geese winter in marshes or rest there while migrating. The larvae of shrimp, crab, and other marine animals find shelter in the marsh from larger animals. Bluefish, flounder, oysters, and clams spend all or part of their lives feeding on other species supported by the marsh. Some species of birds and fish may have evolved with a need to find a coastal marsh or swamp anywhere along the coast (Teal and Teal 1969). Wetlands also act as cleansing mechanisms for ground and surface waters. The importance of coastal wetlands was not always appreciated. For over three centuries, people have drained and filled marshes and swamps to create dry land for agriculture and urban development. Flood control levees and navigation channels have prevented fresh water, nutrients, and sediment from reaching wetlands, resulting in their conversion to open water. Marshes have often been used as disposal sites for channel dredging, city dumps, and hazardous waste sites. In the 1960s, however, the public began to recognize the importance of environmental quality in general and these ecosystems. In 1972, the U.S. Congress added Section 404 to the federal Clean Water Act, which strengthened the requirement that anyone wishing to fill a coastal wetland obtain a permit from the Army Corps of Engineers, and added the requirement of approval by the Environmental Protection Agency. Several coastal states enacted legislation to sharply curtail destruction of coastal wetlands. These restrictions have substantially reduced conversion of wetlands to dry land in coastal areas. The rate of coastal wetland loss declined from 1000 to 20 acres per year in Maryland (Redelfs 1983), from 3100 to 50 acres per year in New Jersey ( Tiner 1984), and from 444 to 20 acres per year in Delaware (Hardisky and Klemas 1983). The rate of conversion to dry land in South Carolina has been reduced to about 15 acres per year (South Carolina Coastal Council
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Increasing concentrations of carbon dioxide and other gases are expected to warm the earth several degrees in the next century by a mechanism known as the greenhouse effect. Such a warming could cause sea level to rise two to five feet by expanding ocean water, melting mountain glaciers, and perhaps eventually causing polar glaciers to melt and slide into the oceans.A rise in sea level of even three feet could cause substantial erosion of beaches and coastal wetlands, increased flooding, and intrusion of saltwater into rivers, bays, and aquifers. Fortunately, many of the adverse consequences can be avoided by taking timely measures in anticipation of sea level rise. Nevertheless, many coastal zone managers are reluctant to take these measures until the prospect of sea level rise becomes more certain.This article examines the implications of future sea level rise and identifies anticipatory measures that may be appropriate today in spite of current uncertainties.
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Tidal marshes are valued, protected and restored in recognition of their ecosystem services: (1) high productivity and habitat provision supporting the food web leading to fish and wildlife, (2) buffer against storm wave damage, (3) shoreline stabilization, (4) flood water storage, (5) water quality maintenance, (6) biodiversity preservation, (7) carbon storage and (8) socio‐economic benefits. Under US law, federal and state governments have joint responsibility for facilitating restoration to compensate quantitatively for ecosystem services lost because of oil spills and other contaminant releases on tidal marshes. This responsibility is now met by choosing and employing metrics (proxies) for the suite of ecosystem services to quantify injury and scale restoration accordingly. Most injury assessments in tidal marshes are triggered by oil spills and are limited to: (1) documenting areas covered by heavy, moderate and light oiling; (2) estimating immediate above‐ground production loss (based on stem density and height) of the dominant vascular plants within each oiling intensity category and (3) sampling sediments for chemical analyses and depth of contamination, followed by sediment toxicity assays if sediment contamination is high and likely to persist. The percentage of immediate loss of ecosystem services is then estimated along with the recovery trajectory. Here, we review potential metrics that might refine or replace present metrics for marsh injury assessment. Stratifying plant sampling by the more productive marsh edge versus the less accessible interior would improve resolution of injury and provide greater confidence that restoration is truly compensatory. Using microphytobenthos abundance, cotton‐strip decomposition bioassays and other biogeochemical indicators, or sum of production across consumer trophic levels fails as a stand‐alone substitute metric. Below‐ground plant biomass holds promise as a potential proxy for resiliency but requires further testing. Under some conditions, like chronic contamination by organic pollutants that affect animals but not vascular plants, benthic infaunal density, toxicity testing, and tissue contamination, growth, reproduction and mortality of marsh vertebrates deserve inclusion in the assessment protocol. Additional metrics are sometimes justified to assay microphytobenthos, use by nekton, food and habitat for reptiles, birds and mammals, or support of plant diversity. Empirical research on recovery trajectories in previously injured marshes could reduce the largest source of uncertainty in quantifying cumulative service losses.
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Detection and attribution of past changes in cyclone activity are hampered by biased cyclone records due to changes in observational capabilities. Here, we relate a homogeneous record of Atlantic tropical cyclone activity based on storm surge statistics from tide gauges to changes in global temperature patterns. We examine 10 competing hypotheses using nonstationary generalized extreme value analysis with different predictors (North Atlantic Oscillation, Southern Oscillation, Pacific Decadal Oscillation, Sahel rainfall, Quasi-Biennial Oscillation, radiative forcing, Main Development Region temperatures and its anomaly, global temperatures, and gridded temperatures). We find that gridded temperatures, Main Development Region, and global average temperature explain the observations best. The most extreme events are especially sensitive to temperature changes, and we estimate a doubling of Katrina magnitude events associated with the warming over the 20th century. The increased risk depends on the spatial distribution of the temperature rise with highest sensitivity from tropical Atlantic, Central America, and the Indian Ocean. Statistically downscaling 21st century warming patterns from six climate models results in a twofold to sevenfold increase in the frequency of Katrina magnitude events for a 1 °C rise in global temperature (using BNU-ESM, BCC-CSM-1.1, CanESM2, HadGEM2-ES, INM-CM4, and NorESM1-M).
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Oyster cultch was added to the lower intertidal fringe of three created Spartina alterniflora marshes to examine its value in protecting the marsh from erosion. Twelve 5-m-wide plots were established at each site, with six randomly selected plots unaltered (non-cultched) and cultch added to the remaining (cultched) plots. Within each cultched plot, cultch was placed along the low tide fringe of the marsh during July 1992, in a band 1.5 m wide by 0.25 m deep. Marsh-edge vegetation stability and sediment erosion were measured for each plot from September 1992 to April 1994. Significant differences (p < 0.05) in marsh-edge vegetation change were detected at the only south-facing site after a major southwester storm. Significantly different rates of sediment erosion and accretion also were observed at this same site. Areas upland of the marsh edge in the cultched areas showed an average accretion of 6.3 cm, while noncultched treatment areas showed an average loss of 3.2 cm. A second site, with a northern orientation, also experienced differential sediment accretion and erosion between treatment type, caused instead by boat wakes that were magnified by the abutment of a dredge effluent pipe across the entire front fringe of the site. During this period we observed significant differences in sediment accumulation, with the areas upland of the marsh edge in the cultched treatment having an average accretion of 2.9 cm and the noncultched an average loss of 1.3 cm.
Article
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.
Article
Seawalls are often built along naturally dynamic coastlines, including the upland edge of salt marshes, in order to prevent erosion or to extend properties seaward. The impacts of seawalls on fringing salt marshes were studied at five pairs of walled and natural marshes in the Great Bay Estuary of New Hampshire, USA. Marsh plant species and communities showed no difference in front of walls when compared with similar elevations at paired controls. However, seawalls eliminated the vegetative transition zone at the upper border. Not only did the plant community of the transition zone have high plant diversity relative to the low marsh, but it varied greatly from site to site in the estuary. The effects of seawall presence on other marsh processes, including sediment movement, wrack accumulation, groundwater flow, and vegetation distribution and growth, were examined. Although no statistically significant effects of seawalls were found, variation in the indicators of these processes were largely controlled by wave exposure, site-specific geomorphology and land use, and distance of the sampling station from the upland. Trends indicated there was more sediment movement close to seawalls at high energy sites and less fine grain sediment near seawalls. Both trends are consistent with an increase in energy from wave reflection. The distribution of seawalls bordering salt marshes was mapped for Great and Little Bays and their rivers. Throughout the study area, 3.54% of the marshes were bounded by shoreline armoring (5876m of seawalls along 165.8km of marsh shoreline). Localized areas with high population densities had up to 43% of marshes bounded by seawalls. Coastal managers should consider limiting seawall construction to preserve plant diversity at the upper borders of salt marshes and prevent marsh habitat loss due to transgression associated with sea level rise.
Article
Coastal areas are among the world's most vulnerable landscapes to impacts related to climate change, including inundation from sea-level rise (SLR), increased exposure to shoreline erosion, and greater frequency and intensity of storms. The status of research on the physical, ecological, and socio-economic effects of vulnerability to SLR and progress toward planning for its consequences varies from region to region worldwide. Here, we synthesize the results of three decades of SLR research and the development of coastal management policies in North Carolina, USA. We identify the major factors responsible for opening new policy ‘windows’ that address SLR, including how stakeholders have developed an increased understanding of the risks, the extent of public dialogue about potential response strategies, and advances in political receptivity to policy change. Research and policy progress in North Carolina continue to provide a model for other regions to help guide and evaluate the development of coastal policies.
Article
Tidal marshes are valued, protected and restored in recognition of their ecosystem services: (1) high productivity and habitat provision supporting the food web leading to fish and wildlife, (2) buffer against storm wave damage, (3) shoreline stabilization, (4) flood water storage, (5) water quality maintenance, (6) biodiversity preservation, (7) carbon storage and (8) socio-economic benefits. Under US law, federal and state governments have joint responsibility for facilitating restoration to compensate quantitatively for ecosystem services lost because of oil spills and other contaminant releases on tidal marshes. This responsibility is now met by choosing and employing metrics (proxies) for the suite of ecosystem services to quantify injury and scale restoration accordingly. Most injury assessments in tidal marshes are triggered by oil spills and are limited to: (1) documenting areas covered by heavy, moderate and light oiling; (2) estimating immediate above-ground production loss (based on stem density and height) of the dominant vascular plants within each oiling intensity category and (3) sampling sediments for chemical analyses and depth of contamination, followed by sediment toxicity assays if sediment contamination is high and likely to persist. The percentage of immediate loss of ecosystem services is then estimated along with the recovery trajectory. Here, we review potential metrics that might refine or replace present metrics for marsh injury assessment. Stratifying plant sampling by the more productive marsh edge versus the less accessible interior would improve resolution of injury and provide greater confidence that restoration is truly compensatory. Using microphytobenthos abundance, cotton-strip decomposition bioassays and other biogeochemical indicators, or sum of production across consumer trophic levels fails as a stand-alone substitute metric. Below-ground plant biomass holds promise as a potential proxy for resiliency but requires further testing. Under some conditions, like chronic contamination by organic pollutants that affect animals but not vascular plants, benthic infaunal density, toxicity testing, and tissue contamination, growth, reproduction and mortality of marsh vertebrates deserve inclusion in the assessment protocol. Additional metrics are sometimes justified to assay microphytobenthos, use by nekton, food and habitat for reptiles, birds and mammals, or support of plant diversity. Empirical research on recovery trajectories in previously injured marshes could reduce the largest source of uncertainty in quantifying cumulative service losses.
Sea-level rise and its impact on coastal Zones. Science 328, 1517e1520. North Carolina Division of Coastal Management, 2011. Weighing Your Options. North Carolina Division of Coastal Management, 2012. Estuarine Shoreline Mapping Project
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Nicholls, R.J., Cazenave, A., 2010. Sea-level rise and its impact on coastal Zones. Science 328, 1517e1520. North Carolina Division of Coastal Management, 2011. Weighing Your Options. North Carolina Division of Coastal Management, 2012. Estuarine Shoreline Mapping Project. http:dcm2.enr.state.nc.us/estuarineshoreline/mapping.html. North Carolina One Map, 2013. Orthoimagery of North Carolina.
National estuaries. In: Adaptation Options for Climate-sensitive Eco-systems and Resources. U.S. Climate Change Science Program
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Peterson, C., Barber, R., Christian, R., Cottingham, K., Lotze, H., Simenstad, C., et al., 2008b. National estuaries. In: Adaptation Options for Climate-sensitive Eco-systems and Resources. U.S. Climate Change Science Program, Washington, D.C. Poulter, B., Feldman, R.L., Brinson, M.M., Horton, B.P., Orbach, M.K., Pearsall, S.H., Reyes, E., Riggs, S.R., Whitehead, J.C., 2009. Sea-level rise research and dialogue in North Carolina: creating windows for policy change. Ocean. Coast. Manag. 52, 147e153.
Coastal ecosystem-based management with nonlinear ecological functions and values Effects of coastal development on nearshore estu-arine nekton communities Understanding global sea levels: past, present and future Mitigating Shore Erosion along Sheltered Coasts
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