Marsh Restoration Research Articles

Economic Evaluation and Systematic Review of Salt Marsh Restoration Projects at a Global Scale

Restoring degraded and damaged salt marshes has become an important initiative in the coastal wetlands management around the world. Evaluating the economic output of salt marsh restoration is of great significance for identifying the current state of knowledge gaps related to conservation activities and economic benefits. To address this question, we conducted an overview of global salt marsh restoration projects, and their financial expenses and restoration benefits in the past 40 years. The results showed that most of the saltmarsh restoration projects are near megacities and larger rivers, and restoration techniques of different regions depend on the types of disturbance factors such as climate change, extreme weather events, and land use change. With limited resources, fund allocation between protected areas and unprotected areas in middle-income countries is often unbalanced, indicating a mismatch between conservation efforts and regional needs. Although restoration projects are expensive, the evidence in this article implies that most salt marsh restoration projects could recover their financial expense in the finite time, especially for large-scale restoration activities. Besides, the great carbon sequestration potential would make salt marsh restoration projects more profitable under current efforts to promote carbon sequestration for combating global warming.

Mapping three-dimensional morphological characteristics of tidal salt-marsh channels using UAV structure-from-motion photogrammetry

Tidal channels (TCs) are geomorphological features of coastal and tidal landscapes. They provide a pathway for the exchange of material and energy between marshes and adjacent water bodies and thereby control the hydrodynamic, morphological, and ecological processes on marsh platforms. Due to difficulties in terms of accessibility, limitations on the duration of exposure during low-water stages, and variations in morphology over time, rapid and accurate mapping of such intertidal morphological features at a high frequency is extremely challenging. Here, we present an efficient method integrated unmanned aerial vehicles (UAVs) structure-from-motion (SfM) photogrammetry, and spatial morphological fitting and delineation for accurately quantifying channel three-dimensional (3D) morphological features in terms width, depth, width-to-depth ratio, and cross-sectional area. We also relate these measured proxies to salt marsh species distributions. A two-step thresholding approach combining elevation and slope is developed in order to determinate TC boundaries from salt marsh and tidal flat area, and a Gaussian fit is used to estimate water-bearing channel depth and cross-sectional area. Salt marsh species are identified from fine-resolution multispectral satellite data and a field training dataset using a Random Forest classifier. Our results indicate that (1) UAV-based SfM photogrammetry can achieve centimeter-level accuracy in mapping the topography of TCs, with a root mean square error (RMSE) of 5.7 cm — mainly from the strong reflection of light from smooth TC water surfaces and the presence of water-bearing layers; (2) the morphological features of TCs, ranging from tidal flats to salt marsh areas, demonstrate a similar tendency, which increases at first and then decreases. The maximum depth and cross-sectional area of TCs is in sparse salt-marsh area, up to 4 m and 150 m2, respectively; and (3) TC morphology has a major impact on the distribution of salt marsh plants and such effects vary across different plant species. These results greatly contribute deep understanding of feedbacks between TCs and salt marsh plant species distribution and have significant implications for developing ecological and morphological salt marsh restoration guidelines.

Modeling the Dynamics of Salt Marsh Development in Coastal Land Reclamation

AbstractThe valuable ecosystem services of salt marshes are spurring marsh restoration projects around the world. However, it is difficult to determine the final vegetated area based on physical drivers. Herein, we use a 3D fully coupled vegetation‐hydrodynamic‐morphological modeling system to simulate the final vegetation cover and the timescale to reach it under various forcing conditions. Marsh development in our simulations can be divided in three distinctive phases: A preparation phase characterized by sediment accumulation in the absence of vegetation, an encroachment phase in which the vegetated area grows, and an adjustment phase in which the vegetated area remains relatively constant while marsh accretes vertically to compensate for sea level rise. Sediment concentration, settling velocity, sea level rise, and tidal range each comparably affect equilibrium coverage and timescale in different ways. Our simulations show that the Unvegetated‐Vegetated Ratio also relates to sediment budget in marsh development under most conditions.

Solving hindered groundwater dynamics in restored tidal marshes by creek excavation and soil amendments: A model study

Groundwater fluxes in tidal marshes largely control key ecosystem functions and services, such as vegetation growth, soil carbon sequestration, and nutrient cycling. In tidal marshes restored on formerly embanked agricultural land, groundwater fluxes are often limited as compared to nearby natural marshes, as a result of historical agricultural soil compaction. To improve the functioning of restored tidal marshes, knowledge is needed on how much certain design options can optimize soil-groundwater interactions in future restoration projects. Based on measured data on soil properties and tidally induced groundwater dynamics, we calibrated and evaluated a 2D vertical model of a creek-marsh cross-section, accounting for both saturated and unsaturated groundwater flow and solute transport in a variably saturated groundwater flow model. We found that model simulations of common restoration practices such as soil amendments (increasing the depth of porous soil on top of the compact layer) and creek excavation (increasing the creek density) increase the soil aeration depth and time, the drainage depth and the solute flux, and decrease the residence time of solutes in the porewater. Our simulations indicate that increasing the depth to the compact layer from 20 cm to 40 cm, or increasing the creek density from 1 creek to 2 creeks along a 50 m marsh transect (while maintaining the total creek cross-sectional area), in both cases more than doubles the volume of water processed by the marsh soil. We discuss that this may stimulate nutrient cycling. As such, our study demonstrates that groundwater modelling can support the design of marsh restoration measures aiming to optimize groundwater fluxes and related ecosystem services.

Coastal marshes provide valuable protection for coastal communities from storm-induced wave, flood, and structural loss in a changing climate

Wetlands such as tidal marshes and mangroves are known to buffer coastal communities from wave, flood, and structural loss during storms. Coastal communities and resource managers seek to understand the ecosystem service value of coastal wetlands for reducing storm-induced flood loss in a changing climate. A recent modeling study found that a tall and dense Phragmites-dominated Piermont Marsh reduced the flood loss in the Village of Piermont, New York, U.S.A. during Superstorm Sandy and the 1% annual chance flood and wave event by 8% and 11%, respectively. Here we used the same modeling approach to examine the marsh’s buffering capacity in a changing climate (from 2020 to 2100), considering a potential marsh restoration plan (from 2020 to 2025) and potential marsh loss due to sea-level rise. Results showed that from 2020 to 2100, the 1% annual chance flood, wave, and structural loss would increase due to sea-level rise, storms, and marsh loss. However, the marsh will buffer ~ 11–12% of structural loss until 2050. Under the extreme SLR scenario of 2.89 m and a low accretion rate, Piermont Marsh is expected to lose its buffering capacity by 2080–2100 but will retain some buffering capacity with a high accretion rate of 10 mm/year and marsh growth. The marsh’s buffering capacity will remain during extra-tropical storms during winter and spring unless the wind has a significant northerly component. Lessons learned from this study can be used by coastal communities and marsh managers to develop coastal resiliency and marsh restoration plan.

Hitchhiking halophytes in wrack and sediment-laden ice blocks contribute to tidal marsh development in the Upper Bay of Fundy

Salt marshes are a type of coastal wetland that are affected by dynamic coastal processes. Ice blocks and wrack (mats of plant debris) regularly float onto northern marshes and become stranded, affecting vegetation and soil accretion. There is little research regarding the capacity of ice and wrack to transport viable plant propagules onto marshes where they can colonize, which may be particularly important at barren new salt marsh restoration sites. Contributions of sediment by ice may also be important to raise the marsh platform to elevations appropriate for plant colonization. We collected ice (n = 27) and wrack (n = 18) samples at marshes in the Bay of Fundy, ran germination trials with the contents, and measured the quantity of sediment in the ice. We found viable propagules from halophytic and non-halophytic species in wrack, and viable propagules of Sporobolus pumilus in ice. Additionally, we found sediment densities between 0.01 and 4.75 g/cm3 in ice blocks that translated to 26.61–21,483.59 kg of total sediment per block, representing a large source of sediment. We found that the number of germinating propagules could not be predicted by wrack size, and that pH, sediment density, sediment weight in ice blocks were variable across the marsh surface, while ice salinity was negatively correlated with elevation and distance from creek. Our results indicate that ice and wrack represent a potential source for vegetation colonization at salt marsh sites and highlights their contributions to facilitating vegetation colonization through building marsh soils.

Re‐meander, rewet, rewild! Overwhelming public support for restoration of small rivers in the three Baltic Sea basin countries

Baltic Sea is one of the World's most oxygen‐depletes seas, so the region requires urgent mitigation measures to significantly reduce nitrogen and phosphorus inputs from land through rivers, which cannot be achieved without large‐scale restoration of wetland buffer zones. The manuscript summarizes the findings of the discrete choice experiment aimed at assessment of the preferences of Danish, German, and Polish citizens toward ecosystem services of lowland small rivers of the Baltic Sea basin. Our results suggest that respondents in all the studied countries are willing to pay substantial amounts to improve water quality in rivers and the Baltic Sea, as well as to restore naturally meandering rivers and natural riparian vegetation. Wild marshes and Wetland agriculture were equally valued as the most desirable options. Respondents systematically cared about the appearance of small rivers in their neighborhood. We conclude that re‐meandering, rewetting of floodplains, and restoration of wild marshes (i.e. natural wetland vegetation) or development of wetland agriculture could gain a lot of public support in Europe.

The response of foraminifera to rapid sea-level rise from tidal restoration of Ni-les'tun marsh, Oregon, U.S.A

Foraminifera preserved in saltmarshes are widely used to reconstruct relative sea-level change (RSL), and inferred from this, coseismic vertical coastal motions following an earthquake. However, how quickly foraminifera respond to rapid changes in RSL is poorly understood. Here, we present a six-year foraminiferal study of the tidal restoration of Ni-les'tun marsh and a comparison of modern and fossil assemblages. We installed eight stations on the marsh and sampled these stations for live foraminifera prior to and during the first six years after tidal restoration (2011–2017), and we extruded one short core at station 1 in 2016. At stations 1 to 7, tidal flat/low marsh assemblages, dominated by Miliammina fusca, colonized 10 months to 2.5 years after tidal restoration. At station 8, the first living mixed assemblage of foraminifera, dominated by Haplophragmoides wilberti, was found 2 years after tidal restoration. Our observations suggest that M. fusca, and to some extent H. wilberti, are opportunistic species (r-strategists), able to increase their standing crop rapidly after invading a new habitat (to up to ~3600 specimens per 10 cm3 sediment volume). Potential causes for the delay in foraminifera colonization include their reproductive cycle and/or limited food availability due to the slow response of the vegetation community and soil development to tidal restoration. However, the similarity among assemblages and concentrations of agglutinated foraminifera between the fossil and modern sediments, indicate that post-depositional taphonomic processes have minimal influence when incorporated in the stratigraphic record. Although foraminifera have shown a delayed response to tidal restoration in the Ni-les'tun marsh, the similarities between the modern and fossil assemblages indicate that the delayed response of foraminifera to tidal restoration is undetectable in study areas with low sedimentation rates (in this case 3.3 mm/yr) after tidal restoration. In the case of high post-earthquake sedimentation rates, sampling a few cm higher rather than immediately above an earthquake contact could avoid uncertainties of coseismic vertical motions when foraminifera have a delayed colonization.

How Much Marsh Restoration Is Enough to Deliver Wave Attenuation Coastal Protection Benefits?

As coastal communities grow more vulnerable to sea-level rise and increased storminess, communities have turned to nature-based solutions to bolster coastal resilience and protection. Marshes have significant wave attenuation properties and can play an important role in coastal protection for many communities. Many restoration projects seek to maximize this ecosystem service but how much marsh restoration is enough to deliver measurable coastal protection benefits is still unknown. This question is critical to guiding assessments of cost effectiveness and for funding, implementation, and optimizing of marsh restoration for risk reduction projects. This study uses SWAN model simulations to determine empirical relationships between wave attenuation and marsh vegetation. The model runs consider several different common marsh morphologies (including systems with channels, ponds, and fringing mudflats), vegetation placement, and simulated storm intensity. Up to a 95% reduction in wave energy is seen at as low as 50% vegetation cover. Although these empirical relationships between vegetative cover and wave attenuation provide essential insight for marsh restoration, it is also important to factor in lifespan estimates of restored marshes when making overall restoration decisions. The results of this study are important for coastal practitioners and managers seeking performance goals and metrics for marsh restoration, enhancement, and creation.

Facilitating Salt Marsh Restoration: The Importance of Event-Based Bed Level Dynamics and Seasonal Trends in Bed Level Change

Intertidal salt marshes provide a range of valuable ecosystem services which typically increase with marsh width. Understanding the drivers for salt marsh expansion versus retreat is thus key to managers. Previous research highlights the influence of short-term (daily/event) bed level dynamics on germination and establishment and subsequent vegetation presence. However, more recent literature suggests the importance of medium-term seasonal bed level dynamics on viable seed availability and subsequent vegetation presence. This study aims to assess event-based and seasonal bed level dynamics for vegetation presence in natural and semi-natural salt marshes and to provide generic thresholds for vegetation presence. To gain insight into bed level dynamics, data was used from autonomous Optical and Acoustic Surface Elevation Dynamics sensors (O-SED and A-SED) around the edge of natural and semi-natural salt marshes. Sensors were installed at vegetated and unvegetated measurement station Field observations from 22 O-SEDs deployed at 4 well-established natural salt marshes in the Western Scheldt estuary and 4 O-SEDs at a well-established semi-natural salt marsh in the Wadden Sea were reanalyzed. Six novel A-SEDs were deployed at a pioneer semi-natural salt marsh in the Ems-Dollard Estuary. The measurement duration at all salt marshes was at least 1 year. The A-SED sensor was successfully validated against manual measurements. Furthermore, vegetation data and water level data were obtained. No significant difference was observed between natural and semi-natural salt marshes. However, a significant difference between vegetated and unvegetated measurement stations for short-term bed level dynamics was observed. Vegetation was found to be present at locations restricted by short-term bed level variability smaller than or equal to 12 mm, emphasizing the presence of a short-term threshold. Although trends in the non-growing season were significantly different between vegetated and unvegetated stations, seasonal thresholds for vegetation presence were not found. The findings imply that knowledge of bed level-dynamics in well-established natural marshes can be used to predict vegetation presence in constructed semi-natural marshes. The importance of local short-term dynamics for vegetation presence instead of longer-term dynamics highlights possibilities for developing favorable conditions for vegetation presence in marsh restoration projects and the construction of new salt marsh ecosystems.

Coastal salt marsh restoration drives element composition of soils toward its original state by recovering soil organic matter

AbstractLarge areas of coastal wetlands have been restored recently throughout the world; it is important to know if restoration practice recovers original levels of biogeochemical functioning in coastal wetlands. We did samplings in five sites in the Liaohe River Delta, China. Each site had three salt marsh types: natural, restored, and degraded. We measured the concentrations of 43 elements and environmental variables including soil organic matter, soil electrical conductivity, soil pH, soil salinity, and soil water content. Concentrations of 39 elements differed significantly between salt marsh types. The values of the concentrations of 39 elements in the restored salt marshes were all in between those of natural and degraded salt marshes. Soil organic matter and the relative abundance of most elements including nutrients and metals increased simultaneously during restoration. Redundancy analysis indicated that soil organic matter explained 72.1% of the total variation in element composition. Our findings indicated that the recovery of soil biogeochemical functioning in salt marshes was driven by the accumulation of soil organic matter during restoration. It may take a very long time for the soil composition and biogeochemistry to reach the original levels prior to disturbance.

Salt marsh restoration: an overview of techniques and success indicators.

Coastal wetlands including salt marshes are among the most productive ecosystems on Earth. They are known for improving the quality of coastal water and provisioning coastal fisheries. However, this ecosystem is under potential threat due to urban coastal land reclamation, limited sediment supply, increased nutrient/eutrophication, and sea level rise. Therefore, restoration efforts to protect the degraded salt marsh habitat are considerably increasing worldwide. In this paper, we present an overview of salt marsh restoration techniques and success indicators. Published scientific literature in English language was collected by searching the most relevant keywords from popular search engines, namely, Google Scholar, Scopus, and Mendeley to get the information about salt marsh restoration techniques and success indicators. This study comprehensively reviewed data from 78 peer-reviewed papers. Results indicated that much of the salt marsh was restored through assisted abiotic strategies (e.g., recovery of tidal exchange, managed realignment, and sediment level amendment). A total of 214 indicators were found, spanning over six major ecological attributes such as structural diversity, ecosystem functions, physical conditions, species composition, external exchange, and absence of threat. Author keywords analysis revealed several hotspots for recent research (e.g., 16s rRNA, fungi, microbial communities, carbon accumulation, and blue carbon). This paper proposes a model for restoring degraded salt marsh, as well as tracking their success.The information presented here will assist the marine ecosystem restoration practitioners in getting a comprehensive understanding of salt marsh restoration success evaluation.

Restoration of small marsh and evaluation of its effectiveness: A case study of nature restoration at Tsuguro Highland's marsh which aiming local community re-vitalization

西南日本には人為の影響で成立・維持されてきたと見られる小規模な湿原が各地に散在し，生物多様性のホットスポットとなっている．しかし，その多くは里山利用の停止に伴う遷移の進行で劣化や消滅の危機に瀕している．筆者らは，岡山県北部の中国山地に位置する津黒高原湿原を事例研究地として小規模湿原の再生を試行し，①施工前後で環境と植生のデータを比較し，再生事業の効果を検証すること，②調査，評価，目標設定，計画設計，施工，モニタリングという一連の流れを手順化し，一定の一般化を図ること，③小規模湿原の再生に関連した生態系サービスの享受を地域づくりに結び付けることを企図し，その評価を行うこと，の3つを目的とした．まず，2013年に，測量，植生調査，水質・水文調査，日射量調査を行い，現存植生図，地下水位図，日射量分布図などを作成した．その結果，①湿原の一部での地下水位の低下，②湿原とその近接地での高木林による日射阻害，③水質などの富栄養化による高茎草本の繁茂，が明らかとなり，これらが湿原劣化の主要因と考えられた．そこで，流水のかけ流しによる地下水位の上昇，高木伐採による光環境の改善，富栄養化した表土の除去による低茎・中茎の湿生草本群落の成立促進，および環境の多様化を図るための止水域の造成，を主な内容とする湿原再生計画を立案した．この計画は2014年に実施に移された．再生事業で伐採された樹木は近隣の温泉施設で加温用熱源として利用され，また，自然再生士研修会を兼ねた作業により事業が推進された．2015年には，2013年と同内容の調査を行い，施工前後のデータが比較された．その結果，光環境の劇的な改善と，地下水位と水質の一定の改善が認められた．また，湿生草本植物の種数が増加し，目標とするヨシ群落クサレダマ下位単位などが拡大した．一連の事業実践にもとづいて，小規模湿原の再生手順を記述した．また，湿原再生の過程で生じた森林バイオマスの有効利用と，都市部からの参加者を巻き込んだ湿原の再生作業を通じた地域づくりへの貢献について評価した．

Eastern Black Rail (Laterallus jamaicensis jamaicensis) Home Range and Habitat Use in Late Winter and Early Breeding Season in Coastal Texas, USA

Habitat use by the Eastern Black Rail (Laterallus jamaicensis jamaicensis) in coastal Texas, USA is poorly understood. To provide data for effective management of the subspecies in Texas, home range size was estimated and habitat use was examined. From February-May of 2017 and 2018, regular locations of 13 radio-transmitted Eastern Black Rails were obtained at San Bernard National Wildlife Refuge, Texas. The mean fixed kernel home range for birds with ≥ 24 relocations was 2.3 ha, with a mean core area of 0.43 ha. Average 95% MCP home range was 0.98 ha with a mean core area of 0.12 ha. During radio tracking, an Eastern Black Rail nest was found on 19 March 2018, the earliest on record for the state. Birds used the Salt and Brackish High Tidal Marsh, Salty Prairie, and Baccharis (Baccharis spp.) Shrubland, and avoided Salt and Brackish Low Tidal Marsh. Home ranges contained a gently sloping elevation gradient suggesting the importance of on-foot access to higher ground. Protection and restoration of Salty Prairie, and Salt and Brackish High Tidal Marsh is recommended for maintaining Eastern Black Rail populations in coastal Texas.

Salt Marsh Restoration for the Provision of Multiple Ecosystem Services

Restoration of salt marsh is urgent, as these ecosystems provide natural coastal protection from sea-level rise impacts, contribute towards climate change mitigation, and provide multiple ecosystem services including supporting livelihoods. This study identified potential restoration sites for intervention where agricultural and degraded land could be returned to salt marsh at a national scale in South African estuaries. Overall, successful restoration of salt marsh in some estuaries will require addressing additional pressures such as freshwater inflow reduction and deterioration of water quality. Here, we present, a socio-ecological systems framework for salt marsh restoration that links salt marsh state and the well-being of people to guide meaningful and implementable management and restoration interventions. The framework is applied to a case study at the Swartkops Estuary where the primary restoration intervention intends to route stormwater run-off to abandoned salt works to re-create aquatic habitat for waterbirds, enhance carbon storage, and provide nutrient filtration. As the framework is generalized, while still allowing for site-specific pressures to be captured, there is potential for it to be applied at the national scale, with the largest degraded salt marsh areas set as priorities for such an initiative. It is estimated that ~1970 ha of salt marsh can be restored in this way, and this represents a 14% increase in the habitat cover for the country. Innovative approaches to restoring and improving condition are necessary for conserving salt marshes and the benefits they provide to society.

Tidal and Nontidal Marsh Restoration: A Trade‐Off Between Carbon Sequestration, Methane Emissions, and Soil Accretion

AbstractSupport for coastal wetland restoration projects that consider carbon (C) storage as a climate mitigation benefit is growing as coastal wetlands are sites of substantial C sequestration. However, the climate footprint of wetland restoration remains controversial as wetlands can also be large sources of methane (CH4). We quantify the vertical fluxes of C in restored fresh and oligohaline nontidal wetlands with managed hydrology and a tidal euhaline marsh in California's San Francisco Bay‐Delta. We combine the use of eddy covariance atmospheric flux measurements with 210Pb‐derived soil C accumulation rates to quantify the C sequestration efficiency of restored wetlands and their associated climate mitigation service. Nontidal managed wetlands were the most efficient in burying C on‐site, with soil C accumulation rates as high as their net atmospheric C uptake (−280 ± 90 and −350 ± 150 g C m−2 yr−1). In contrast, the restored tidal wetland exhibited lower C burial rates over decadal timescales (70 ± 19 g C m−2 yr−1) that accounted for ∼13%–23% of its annual C uptake, suggesting that the remaining fraction is exported via lateral hydrologic flux. From an ecosystem radiative balance perspective, the restored tidal wetland showed a > 10 times higher CO2‐sequestration to CH4‐emission ratio than the nontidal managed wetlands. Thus overall, tidal wetland restoration resulted in a negative radiative forcing (cooling) through increased soil C accumulation, while nontidal wetland restoration led to an early positive forcing (warming) through increased CH4 emissions potentially lasting between 2.1 ± 2.0 to 8 ± 4 decades.

Evaluating direct and strategic placement of dredged material for marsh restoration through model simulations

Dredged material can be used for marsh restoration by depositing it on the marsh surface (thin-layer placement), by releasing it at the mouth of channels and allowing tidal currents to transport it onto the marsh platform (channel seeding), or by creating new marshes over shallow areas of open water. We investigate the efficacy of these different methods using a comprehensive 2D marsh evolution model that simulates tidal dynamics, vegetation processes, bank and wave erosion, and ponding. Total marsh area is assessed over 50 years in an idealized microtidal marsh under different relative sea level rise (RSLR) scenarios. For a given volume of total sediment added, the frequency of deposition is relatively unimportant in maximizing total marsh area, but the spatial allocation of the dredged material is crucial. For a given volume of sediment, thin-layer deposition is most effective at preserving total marsh area, especially at high rates of RSLR. Channel seeding is less efficient, but it could still provide benefits if larger amounts of sediment are deposited every 1-2 years. Marsh creation is also beneficial, because it not only increases the marsh area, but additionally slows the erosion of the existing marsh. The 2D model is highly computationally efficient and thus suited to explore many scenarios when evaluating a restoration project. Coupling the model with a cost assessment of the different restoration techniques would provide a tool to optimize marsh restoration.

Incorporation of coarse-grained dredged material into marsh and shoreline restoration projects in coastal New Jersey

Millions of cubic yards of sediment are dredged every year in coastal New Jersey for the operation and maintenance of an extensive marine transportation system stretching from the New Jersey Harbor south along the Atlantic Coast from Sandy Hook to Cape May and north up the Delaware River. Dredged material from these public and private projects has been managed using a variety of placement approaches and technologies, from open-water disposal to landfilling to construction materials. For the past several decades, the State of New Jersey has advocated for and implemented a policy of beneficial use of dredged material rather than its disposal. The New Jersey Department of Transportation’s Office of Maritime Resources (NJDOT/OMR) is the lead state agency for research and implementation of beneficial use statewide. NJDOT/ OMR is also responsible for the recovery of the 200-mile network of shallow-draft navigation channels along the Atlantic coast of New Jersey that was damaged by a series of severe coastal storms, most notably Superstorm Sandy in 2012. For the past decade, considerable effort has been made to develop methods that use clean dredged material from the Atlantic region to rebuild and improve coastal features such as marshes, dunes, and beaches, thereby retaining the sediment in the ecosystem. Although there have been a number of successful beneficial use projects, concerns remain about the long-term sustainability of the program due to high cost, timelines, scalability, habitat sensitivity, resiliency, aesthetics, and other factors. This paper explores some of these issues and proposes solutions. It focuses on the use of available coarse-grained material as a way to provide resiliency to these restored features while increasing scale and efficiency, protecting aesthetics, and providing increased habitat value.

Tidal marsh restoration at Blackwater National Wildlife Refuge, Maryland: A case study in thin-layer placement

Tidal marsh loss at Blackwater National Wildlife Refuge (NWR) has been a major concern of refuge managers in recent decades. The approximately 2,035 hectares (5,028 acres) of tidal marsh that have converted to open water in Blackwater NWR since 1938 (Scott et al. 2009) represent one of the most significant areas of marsh conversion within the Chesapeake Bay. In 2013, a suite of climate adaptation strategies focused on sea level rise was developed for Blackwater NWR and surrounding areas of Dorchester County by the Blackwater Climate Adaptation Project (BCAP). The BCAP is a collaboration of The Conservation Fund, Audubon Maryland-DC, and the U.S. Fish and Wildlife Service, assisted by the Maryland Department of Natural Resources (MD DNR), U.S. Geological Survey, and others. In 2016, the BCAP implemented a thin-layer placement (TLP) project at Shorter’s Wharf in Blackwater NWR on 16 hectares (40 acres) of subsiding and fragmenting tidal marsh dominated by Schoenoplectus americanus, Spartina alterniflora, and Spartina patens. The purpose of the project was to increase the 16 hectares’ (40 acres’) resiliency to climate-driven sea level rise and storm impacts. The project built up the marsh elevation by applying thin layers of sediment dredged from the adjacent Blackwater River. The sediment enhancement was designed to extend the longevity of the marsh and increase its resiliency by raising its surface elevation in relation to the tidal regime and to return the habitat to its prior high-marsh condition with S. patens dominating. The colonization of this site by saltmarsh sparrow would be an indicator of success in reaching this goal. Dredging operations in November and December 2016 placed approximately 19,900 cubic meters (26,000 cubic yards) of sediment on the project site. Post-restoration elevations obtained one year after material placement indicated that, although the target elevations were achieved in 78% of the surveyed placement area, the material was not distributed uniformly. Coarser material tended to stack up at the discharge location while the grain size declined and the slopes flattened toward the periphery of the discharge area. In 2017, natural vegetation had regenerated through the placed sediment with vigorous regrowth of S. americanus and S. alterniflora . This regrowth was supplemented with hand-planting of more than 200,000 plugs of S. patens. Vegetation monitoring is ongoing to determine the plant composition evolution within the placement site. Pre-dredge and post-dredge bathymetric surveys reveal 70% accretion nearly two years after dredging within the borrow area footprint.

Advancing salt marsh restoration for coastal resilience: a learning exchange

A multidisciplinary group of salt marsh professionals from Maine to Virginia participated in a collaborative learning exchange to improve restoration for the overall health and resilience of coastal wetlands. This was an unprecedented forum through which participants representing different geographies, backgrounds, and roles in salt marsh management were able to share and learn from one another to develop the best available restoration methods for on-the-ground projects that address multiple benefits. By including mosquito control agencies, restoration practitioners, regulatory agencies, academic researchers, and conservation organizations in the learning exchange, we developed an understanding and acceptance of different approaches. Regulators learned about project ideas and contributed to project designs in early development stages. Collaborating while engaged in on-the ground projects enabled participants to implement lessons learned in real time. Field trips to restoration sites at different stages of development allowed a greater and more fluid exchange of ideas and practical implementation advice. Practitioners leveraged resources and developed new collaborations. Lessons learned and shared through this faster and more flexible forum will inform the design, implementation, and monitoring of restoration projects across the region and improve overall marsh health and resilience in the face of climate change. Learning exchanges like this should be used more frequently to improve the efficiency and effectiveness of coastal restoration particularly when there is a windfall of cash and a short window of opportunity such as with post-disaster federal spending.