Tidal Marsh Restoration Research Articles

Nature‐based shoreline protection in newly formed tidal marshes is controlled by tidal inundation and sedimentation rate

AbstractMany tidal marshes have been lost by past land use changes, but are nowadays increasingly restored and created to provide valuable ecosystem services such as nature‐based flood and erosion protection along estuarine shorelines. To be functional for flood and shoreline erosion protection, restored and created tidal marshes should develop erosion resistant sediment beds. Here, we investigated which factors drive the spatial variations in sediment strength and erosion resistance in a developing tidal marsh restoration site. Our results show that decreasing tidal inundation frequency, decreasing sedimentation rate, and better drainage led to stronger consolidation in deeper sediment layers. This consolidation resulted in greater sediment strength, quantified here by shear strength and penetration resistance. Generally, sediment strength was greater when sediment had higher bulk density, while a higher water and fine fraction (= clay and silt) content decreased sediment strength. Overall, all measurement locations were relatively erosion resistant, likely caused by the dense root network and cohesive sediment. To restore or create resilient tidal marshes for nature‐based flood and shoreline erosion protection, we should thus aim for sites with relatively low tidal inundation frequency, moderate sedimentation rates, and cohesive sediment mixtures of clay, silt, and sand, which are well drained and have potential for vegetation establishment. These conditions have a high likelihood of resulting in restored or created tidal marshes that contribute to nature‐based flood and shoreline erosion protection.

Testing strategies to enhance transplant success under stressful conditions at a tidal marsh restoration project

Tidal marsh restoration is becoming an increasingly common tool to plan for future sea level rise. Subsided marshes' elevation can be restored through sediment additions, which may necessitate the reestablishment of vegetation. Understanding key actions to increase vegetation cover at areas that remain persistently bare following elevation restoration is a critical component of a project's long‐term success. Dominant species can shape ecosystem function, as well as ameliorate stressful environments. We transplanted the dominant species, Salicornia pacifica, into bare areas of a restored tidal marsh in central California, United States, 3 years following a sediment addition. We tested salt hardening of plants before transplanting, targeted irrigation, transplant size, and planting configuration to identify management actions that could help vegetation persist in the most stressful areas of the high marsh. Weekly targeted irrigation until the first rains began was critical for small plant survivorship. We found that larger plants had increased survivorship and contributed higher amounts of growth and cover but did not facilitate the performance of nearby smaller plants. After 2 years, we determined that using lone, larger plants was more cost‐effective than multiple smaller plants at our tidal marsh. However, performance was highly site‐specific with dramatically less growth at a drier site with sandier soil. Our results highlight the importance of identifying site‐specific restoration strategies that either ameliorate or help plants tolerate stressful conditions, contributing to the continued success of tidal marsh restoration for climate resilience.

Recovery of planktonic invertebrate communities in restored and created tidal marshes along the northern Gulf of Mexico

A significant amount of tidal marsh restoration has occurred over the past two decades. However, restored marshes often fail to recover biological structure and ecosystem functions comparable to reference marshes. We implemented a 13-site inventory to evaluate the recovery of zooplankton and meroplankton abundance and community composition along the Mississippi and Alabama Gulf coasts. Understanding the recovery of zooplankton and meroplankton communities in restored marshes is critical, as many planktonic invertebrate species contribute to nutrient cycling and food web dynamics. We found that zooplankton and meroplankton communities in restored tidal marshes were comparable in total abundance, taxonomic richness, and taxonomic composition to communities observed in reference tidal marshes — with composition being driven mainly by surface water salinity. But zooplankton and meroplankton communities in restored marshes did have lower evenness and diversity than comparable reference marshes. These results suggest that zooplankton and meroplankton communities in restored marshes along the Mississippi and Alabama Gulf coast tend to recover after 7–34 years and support robust populations of prey items for larger, ecologically and economically-important species (e.g., fishes).

Habitat Use by Breeding Waterbirds in Relation to Tidal Marsh Restoration in the San Francisco Bay Estuary

The South Bay Salt Pond Restoration Project aims to restore many former salt production ponds, now managed for wildlife and water quality, to tidal marsh. However, because managed ponds support large densities of breeding waterbirds, reduction of pond habitat may influence breeding waterbird distribution and abundance. We investigated habitat use associated with breeding, feeding, and roosting behaviors during the breeding season for American Avocets (Recurvirostra americana), Black-necked Stilts (Himantopus mexicanus), Forster’s Terns (Sterna forsteri), and Caspian Terns (Hydroprogne caspia) in south San Francisco Bay in 2019 after substantial tidal marsh restoration, and compared results to a 2001 survey (before restoration). In 2019, managed ponds (26% of currently available habitat) were selected by waterbirds engaged in breeding behaviors (> 39% of observations), foraging (> 42%), and roosting (> 73%). Waterbirds avoided tidal habitats (43% of available habitat), comprising < 17% of observations of breeding behavior, < 28% of foraging observations, and < 13% of roosting observations. Waterbird densities increased in managed ponds between 2001 and 2019, and decreased in active salt ponds, especially among feeding Avocets (92% decrease) and Stilts (100% decrease). Islands were important for waterbirds observed breeding and roosting (45% of Avocet and 53% of Tern observations). Avocets and Stilts fed primarily on wet bare ground (65% and 58%, respectively), whereas feeding Forster’s Terns and Caspian Terns used mostly open water (82% and 93%, respectively). Within ponds, Avocets were associated with islands (131 m closer than expected). Stilts and Forster’s Terns were also associated with islands (68 m and 161 m closer than expected), except when feeding (1 m closer and 90 m farther than expected). Avocets and Stilts were associated with pond levees (39 m and 41 m closer than expected), but Forster’s Terns were not (9 m closer than expected). Our results emphasize the importance of managed ponds for breeding and foraging waterbirds, including islands for breeding and roosting and levees for foraging.

Silicon pools, fluxes and the potential benefits of a silicon soil amendment in a nitrogen-enriched tidal marsh restoration

Tidal marshes are important sites of silicon (Si) transformation, where dissolved Si (DSi) taken up by macrophytic vegetation and algal species is converted to biogenic silica (BSi), which can accumulate in the soil, be recycled within the marsh, or be exported to adjacent coastal waters. The role of restored and created tidal marshes in these processes is not well understood, nor is the impact of nutrient enrichment at either the plant or ecosystem level. Here, Si fluxes were examined to develop a Si mass balance in a nitrogen (N)-enriched marsh created with fine-grained dredged material from the Chesapeake Bay, United States. In addition, the effectiveness of Si soil amendments to ameliorate the negative effects of excess nitrogen on Spartina alterniflora was examined through laboratory and field experiments. Silicon was exported to the estuary as DSi (49 g m−2 y−1) and BSi (35 g m−2y−1) in stoichiometric excess of nitrogen and phosphorus. Rapid recycling of Si within both marsh and the tidal creeks appeared to be important in the transformation of Si and export from the marsh. Enhanced macrophyte SiO2 tissue concentrations were observed in the field experiment, with end-of-season mean values of 2.20–2.69% SiO2 in controls and 2.49–3.24% SiO2 in amended plots, among the highest reported for S. alterniflora; however, improved plant fitness was not detected in either experiment. Thus, tidal marshes created with a fine-grained, N-rich dredged material appear to function as a rich source of Si to the restored marsh and local estuarine environment, an overlooked ecosystem service. Soil Si amendments, however, did not appear likely to alleviate N-induced stress in S. alterniflora.

Multi-temporal high-resolution marsh vegetation mapping using unoccupied aircraft system remote sensing and machine learning

Coastal wetlands are among the most productive ecosystems in the world and provide important ecosystem services related to improved water quality, carbon sequestration, and biodiversity. In many locations, wetlands are threatened by coastal development and rising sea levels, prompting an era of tidal wetland restoration. The creation and restoration of tidal marshes necessitate the need for ecosystem monitoring. While satellite remote sensing is a valuable monitoring tool; the spatial and temporal resolution of imagery often places operational constraints, especially in small or spatially complex environments. Unoccupied aircraft systems (UAS) are an emerging remote sensing platform that collects data with flexible on-demand capabilities at much greater spatial resolution than sensors on aircraft and satellites, and resultant imagery can be readily rendered in three dimensions through Structure from Motion (SfM) photogrammetric processing. In this study, UAS data at 5 cm resolution was collected at an engineered wetland at Poplar Island, located in Chesapeake Bay, MD United States five times throughout 2019 to 2022. The wetland is dominated by two vegetation species: Spartina alterniflora and Spartina patens that were originally planted in 2005 in low and high marsh elevation zones respectively. During each survey, UAS multispectral reflectance, canopy elevation, and texture were derived and used as input into supervised random forest classification models to classify species-specific marsh vegetation. Overall accuracy ranged from 97% to 99%, with texture and canopy elevation variables being the most important across all datasets. Random forest classifications were also applied to down-sampled UAS data which resulted in a decline in classification accuracy as spatial resolution decreased (pixels became larger), indicating the benefit of using ultra-high resolution imagery to accurately and precisely distinguish between wetland vegetation. High resolution vegetation classification maps were compared to the 2005 as-built planting plans, demonstrating significant changes in vegetation and potential instances of marsh migration. The amount of vegetation change in the high marsh zone positively correlated with interannual variations in local sea level, suggesting a feedback between vegetation and tidal inundation. This study demonstrates that UAS remote sensing has great potential to assist in large-scale estimates of vegetation changes and can improve restoration monitoring success.

Tidal marsh restoration on Sapelo Island: A legacy of R.J. Reynolds, Jr., Eugene Odum and the University of Georgia Marine Institute

Restoration of tidal marshes throughout the 20th century have attempted to bring back important functions of natural tidal systems. In this study, vertical accretion, organic carbon (C) sequestration, and nitrogen burial were compared between a natural, never diked tidal salt marsh and a hydrologically restored tidal salt marsh on Sapelo Island, Georgia to examine the impacts of restoration years later. 64 years after hydrologic restoration in 1956, the restored marsh studied had higher rates of accretion based on 137Cs and 210Pb (4.8–5.1 mm/yr), C sequestration (118–125 g C/m2/yr) and N burial (8.3–8.8.g N/m2/yr) than the never diked marsh (2.9–3.4 mm/yr, 75–85 g C/m2/yr, 4.8–5.6 g N/m2/yr).Since maximum 137Cs deposition in 1964, approximately 30 cm of accretion has occurred in the restored marsh while the never diked marsh had approximately 10–30 cm of new soil deposited. The accumulated soil in the restored marsh was comparable to the natural marsh soil in terms of bulk density, percent C and N. However, below this depth, legacy effects from diking could be found through the higher soil bulk density and lower percent organic C and N relative to soils of the natural marsh.Vertical accretion in the natural marsh appears to be keeping pace with the current rate of sea level rise (SLR) (3.4 mm/yr) while accretion in the restored marsh exceeds SLR as the marsh compensates for subsidence that occurred when it was diked. Under current SLR and accretion rates, ecosystem functions of continual sequestration of C and burial of N will be supported. However, as SLR accelerates, the ability of both marshes to sequester C and bury N will depend on their ability to keep pace. If not, the marshes will eventually convert to mudflats or open water with a concurrent loss of these and other ecosystem services.

Coastal bird community response to dredge‐spoil tidal marsh restoration at New Round Island, Mississippi, U.S.A.

The northern Gulf of Mexico has been the focus of many coastal habitat restoration projects in the wake of new funding streams stemming from the settlement of the 2010 Deepwater Horizon oil spill litigation. One such project was the creation of New Round Island (RNDI) in Mississippi, a 86 ha island created using dredge material in 2017. The island design incorporated a novel U‐shaped sand berm with multiple interconnected containment sells. In this study we sought to document changes in relative abundance of various coastal bird species. We conducted surveys for breeding and nonbreeding birds from June 2017 to May 2021, and we conducted nonbreeding surveys at two reference sites for comparison. Breeding bird numbers were dominated by colonial nesting species in years 1 and 2, which subsequently declined as vegetation cover increased. Solitary nesting species increased over time, with Wilson's Plover (Charadrius wilsonia) nest count increasing from zero in year 1 to 29 in year 5. Nonbreeding shorebird counts peaked in years 1–2 and subsequently declined, although shorebird counts also decreased at the reference sites. Relative abundance of waders (Ardeidae), rallids (Rallidae), and passerines (Passeriformes and allies) increased in comparison to reference sites. This study demonstrates the short‐term benefits of this U‐shaped island design to early‐succession breeding species and nonbreeding shorebirds shortly after construction, with longer‐term benefits to breeding Wilson's Plover and to marsh birds as vegetation fills in.

Estimating the Effect of Tidal Marsh Restoration on Housing Prices: A Hedonic Analysis in the Nisqually National Wildlife Refuge, Washington, USA

This study employs the hedonic pricing method and a rich spatial and temporal dataset from two counties in Washington, USA to determine the effect of the 2009 Nisqually Restoration project (NRP) on housing prices in adjacent communities. The NRP restored 308 hectares of wetlands via dike removal in the Billy Frank Jr. Nisqually National Wildlife Refuge (NNWR), leading to improvements in salmon and bird abundance and recreational opportunities. We find that the ecological improvements made by the NRP increased the value of homes within 0.5 mile of the refuge by $37,631; homes 0.5 to 1 mile by $10,489; and homes 1 to 1.5 miles by $31,186. Our findings are consistent with previous wetland hedonic price analyses and may be useful inputs in natural resource management and policy decision-making.

Life in the Fast Lane: Feeding and Growth of Juvenile Steelhead and Chinook Salmon in Main‐Stem Habitats of the Columbia River Estuary

AbstractVery little is known about the ecology of juvenile Pacific salmon Oncorhynchus spp. that rapidly traverse estuaries. For these species and life history types, main‐stem habitats are thought to largely function as migratory corridors rather than as productive habitats that support feeding or growth, although little research has focused on this issue. This is especially true in the highly modified Columbia River estuary, where it is unclear whether fast‐migrating salmon benefit from extensive tidal marsh restoration. To address this deficit, we sampled migratory juvenile steelhead O. mykiss and Chinook Salmon O. tshawytscha at locations spread across nearly 200 km of the Columbia River estuary. Our results demonstrated that these juvenile salmon were actively feeding and growing as they moved downstream; dominant prey included chironomids, other insects, and corophiid and gammarid amphipods. We also observed variation in diet composition and quantity between years, which was likely associated with the highly contrasting river conditions. Insulin‐like growth factor 1 hormone levels and the size of juvenile salmon increased as the fish moved downstream, suggesting that prey quality and quantity were sufficient to fuel rapid growth, which may increase survival in marine waters. Our results have direct management implications for habitat restoration and suggest the potential for competition between hatchery and wild salmon. Overall, our results support a fundamental shift in the view of main‐channel estuarine habitats from serving primarily as a migration corridor to serving as productive habitat where rapidly moving salmon actively feed and grow.

Biogeomorphic modeling to assess the resilience of tidal-marsh restoration to sea level rise and sediment supply

Abstract. There is an increasing demand for the creation and restoration of tidal marshes around the world, as they provide highly valued ecosystem services. Yet restored tidal marshes are strongly vulnerable to factors such as sea level rise and declining sediment supply. How fast the restored ecosystem develops, how resilient it is to sea level rise, and how this can be steered by restoration design are key questions that are typically challenging to assess due to the complex biogeomorphic feedback processes involved. In this paper, we apply a biogeomorphic model to a specific tidal-marsh restoration project planned by dike breaching. Our modeling approach integrates tidal hydrodynamics, sediment transport, and vegetation dynamics, accounting for relevant fine-scale flow–vegetation interactions (less than 1 m2) and their impact on vegetation and landform development at the landscape scale (several km2) and in the long term (several decades). Our model performance is positively evaluated against observations of vegetation and geomorphic development in adjacent tidal marshes. Model scenarios demonstrate that the restored tidal marsh can keep pace with realistic rates of sea level rise and that its resilience is more sensitive to the availability of suspended sediments than to the rate of sea level rise. We further demonstrate that restoration design options can steer marsh resilience, as they affect the rates and spatial patterns of biogeomorphic development. By varying the width of two dike breaches, which serve as tidal inlets to the restored marsh, we show that a larger difference in the width of the two inlets leads to higher biogeomorphic diversity in restored habitats. This study showcases that biogeomorphic modeling can support management choices in restoration design to optimize tidal-marsh development towards sustainable restoration goals.

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.

Modelling blue carbon farming opportunities at different spatial scales

There is a growing interest in including blue carbon ecosystems (i.e., mangroves, tidal marshes and seagrasses) in climate mitigation programs in national and sub-national policies, with restoration and conservation of these ecosystems identified as potential activities to increase carbon accumulation through time. However, there is still a gap on the spatial scales needed to produce carbon offsets comparable with terrestrial or agricultural ecosystems. Here, we used the Coastal Blue Carbon InVEST 3.7.0 model to estimate future net carbon sequestration in blue carbon ecosystems along Australia's Great Barrier Reef (hereafter GBR) catchments, considering different management scenarios (i.e., reintroduction of tidal exchange through the removal of barriers, sea level rise, restoring low lying land) at three different spatial scales: whole GBR coastline, regional (14,000–16,300 ha), and local (335–370 ha) scales. The focus of the restoration (i.e., tidal marshes and/or mangroves) was dependent on data availability for each scenario. Furthermore, we also estimated the monetary value of carbon sequestration under each management scenario and spatial scale assessed in the study. We found that large scale restoration of tidal marshes could potentially sequester an additional ∼800,000 tonnes of CO2e by 2045 (potentially generating AU$12 million based on the average Australia carbon price), with greater opportunities when sea level rise is accounted for in the modelling. Also, we found that regional and local projects would generate up to 23 tonnes CO2e ha−1 by the end of the crediting period. Our results can guide future decisions in the blue carbon market and financing schemes, however, the return on investment is dependent on the carbon price and funding scheme available for project implementation.

Tidal marsh restoration enhances sediment accretion and carbon accumulation in the Stillaguamish River estuary, Washington.

Tidal marshes have been recognized globally for their ability to sequester “blue carbon” but there is still a need for studies investigating the marsh response to restoration, particularly in the Pacific Northwest United States. Here we report carbon stocks and accumulation rates for restored and natural tidal marshes in the Stillaguamish River estuary in Puget Sound, Washington, where a 60-hectare marsh was reintroduced to the tidal regime from its previous use as diked and drained farmland. We found that the restoration not only maximized carbon accumulation but also enhanced resilience to rising sea levels. Four years after restoration, mean sediment carbon stocks in the upper 30 cm within the restored marsh (4.43 kg C m-2) were slightly lower than those measured in the adjacent natural marshes (5.95 kg C m-2). Mean carbon accumulation rates, however, were nearly twice as high in the restored marsh (230.49 g C m-2 yr-1) compared to the natural marshes (123.00 g C m-2 yr-1) due to high rates of accretion in the restored marsh (1.57 cm yr-1). Mean elevation change rates were nearly twice that of corresponding 210Pb accretion rates, but all were greater than the current rate of sea level rise.

Monitoring Vegetation Dynamics at a Tidal Marsh Restoration Site: Integrating Field Methods, Remote Sensing and Modeling

Sea level rise threatens coastal wetlands worldwide, and restoration projects are implementing strategies that decrease vulnerability to this threat. Vegetation monitoring at sites employing new restoration strategies and determination of appropriate monitoring techniques improve understanding of factors leading to restoration success. In Central California, soil addition raised a degraded marsh plain to a high elevation expected to be resilient to sea level rise over the next century. We monitored plant survival and recruitment using area searches, transect surveys, and unoccupied aircraft systems (UAS) imagery. We used random forest modeling to examine the influence of nine environmental variables on vegetation colonization and conducted targeted soil sampling to examine additional factors contributing to vegetation patterns. Limited pre-construction vegetation survived soil addition, likely due to the sediment thickness (mean = 69 cm) and placement method. After 1 year, about 10% of the initially bare area saw vegetation reestablishment. Elevation and inundation frequency were particularly critical to understanding restoration success, with greatest vegetation cover in high-elevation areas tidally inundated < 0.85% of the time. Soil analysis suggested greater salinity stress and ammonium levels in poorly-vegetated compared to well-vegetated areas at the same elevation. We found that both transect and UAS methods were suitable for monitoring vegetation colonization. Field transects may provide the best approach for tracking early vegetation colonization at moderate-sized sites under resource limitations, but UAS provide a complementary landscape perspective. Beyond elucidating patterns and drivers of marsh dynamics at a newly restored site, our investigation informs monitoring of marsh restoration projects globally.

The Fate of Nitrogen in Dredged Material Used for Tidal Marsh Restoration

Tidal marsh restoration using dredged material is being undertaken in many coastal areas to replace lost habitat and ecosystem services due to tidal marsh loss. The fate of high levels of nitrogen (N) in fine-grained dredged material used as a substrate for marsh restoration is uncertain, but if exported tidally may cause subtidal habitat degradation. In this study, a mass balance was developed to characterize N fluxes in a two-year-old restored tidal marsh constructed with fine-grained dredged material at Poplar Island, MD, in Chesapeake Bay, and to evaluate the potential impact on the adjacent submersed aquatic vegetation (SAV) habitat. Denitrification and N accumulation in Spartina organic matter were identified as the major sinks (21.31 and 28.5 mg N m−2 d−1, respectively), while tidal export of TN was more modest (9.4 mg N m−2 d−1) and inorganic N export was low (1.59 mg N m−2 d−1). Internal cycling helped retain N within the marsh. Mineralization of N associated with labile organic matter in the dredged material was likely a large, but unquantified, source of N supporting robust plant growth and N exports. Exceedances of SAV water quality habitat requirements in the subtidal region adjacent to the marsh were driven by elevated Chesapeake Bay concentrations rather than enrichment by the marsh.

Waterfowl use of wetland habitats informs wetland restoration designs for multi‐species benefits

Abstract Extensive global estuarine wetland losses have prompted intensive focus on restoration of these habitats. In California, substantial tracts of freshwater, brackish and tidal wetlands have been lost. Given the anthropogenic footprint of development and urbanization in this region, wetland restoration must rely on conversion of existing habitat types rather than adding new wetlands. These restorations can cause conflicts among stakeholders and species that win or lose depending on identified restoration priorities. Suisun Marsh on the San Francisco Bay Estuary is the largest brackish marsh on the US Pacific coast. To understand how conversion of brackish managed wetlands to tidal marsh would impact waterfowl populations and whether future tidal marsh restorations could provide suitable habitat for dabbling ducks, we examined waterfowl wetland use with a robust GPS‐GSM tracking dataset (442,017 locations) from six dabbling duck species (N = 315). Managed wetlands, which comprise 47% of Suisun Marsh, were consistently and strongly selected by waterfowl over tidal marshes, with use ~98% across seasons and species. However, while use of tidal marsh (only 14% of Suisun Marsh) was generally &lt;2%, almost half our ducks (~44%) spent some time in this habitat and exhibited strong utilization of pond‐like features. Ponds only comprise ~10% of this habitat but attracted 44% use (~4.5 times greater than availability). Synthesis and applications. Managed wetlands were vital to dabbling ducks, but losses from conversion of these habitats may be partially mitigated by incorporating pond features that are more attractive to waterfowl, and likely to offer multi‐species benefits, into tidal marsh restoration designs. While waterfowl are presently a common taxon, previously seen calamitous population declines can be avoided through informed ecosystem‐based management that promotes species richness, biodiversity and helps ‘keep common species common’.

UAV to Inform Restoration: A Case Study From a California Tidal Marsh

Monitoring of environmental restoration is essential to communicate progress and improve outcomes of current and future projects, but is typically done in a very limited capacity due to budget and personnel constraints. Unoccupied aerial vehicles (UAVs) have been used in a variety of natural and human-influenced environments and have been found to be time- and cost-efficient, but have not yet been widely applied to restoration contexts. In this study, we evaluated the utility of UAVs as an innovative tool for monitoring tidal marsh restoration. We first optimized methods for creating high-resolution orthomosaics and Structure from Motion digital elevation models from UAV imagery by conducting experiments to determine an optimal density of ground control points (GCPs) and flight altitude for UAV monitoring of topography and new vegetation. We used elevation models and raw and classified orthomosaics before, during, and after construction of the restoration site to communicate with various audiences and inform adaptive management. We found that we could achieve 1.1 cm vertical accuracy in our elevation models using 2.1 GCPs per hectare at a flight altitude of 50 m. A lower flight altitude of 30 m was more ideal for capturing patchy early plant cover while still being efficient enough to cover the entire 25-hectare site. UAV products were valuable for several monitoring applications, including calculating the volume of soil moved during construction, tracking whether elevation targets were achieved, quantifying and examining the patterns of vegetation development, and monitoring topographic change including subsidence, erosion, and creek development. We found UAV monitoring advantageous for the ability to survey areas difficult to access on foot, capture spatial variation, tailor timing of data collection to research needs, and collect a large amount of accurate data rapidly at relatively low cost, though with some compromise in detail compared with field monitoring. In summary, we found that UAV data informed the planning, implementation and monitoring phases of a major landscape restoration project and could be valuable for restoration in many habitats.

Tidal Marsh Restoration Optimism in a Changing Climate and Urbanizing Seascape

Tidal marshes (including saltmarshes) provide remarkable value for many social (cultural, recreational) and environmental (fish production, water quality, shoreline protection, carbon sequestration) services. However, their extent, condition, and capacity to support these services are threatened by human development expansion, invasive species, erosion, altered hydrology and connectivity, and climate change. The past two decades have seen a shift toward working with managers to restore tidal marshes to conserve existing patches or create new marshes. The present perspective examines key features of recent tidal marsh restoration projects. Although optimism about restoration is building, not all marshes are the same; site-specific nuances require careful consideration, and thus, standard restoration designs are not possible. Restoration projects are effectively experiments, requiring clear goals, monitoring and evaluation, and adaptive management practices. Restoration is expensive; however, payment schemes for ecosystem services derived from restoration offer new ways to fund projects and appropriate monitoring and evaluation programs. All information generated by restoration needs to be published and easily accessible, especially failed attempts, to equip practitioners and scientists with actionable knowledge for future efforts. We advocate the need for a network of tidal marsh scientists, managers, and practitioners to share and disseminate new observations and knowledge. Such a network will help augment our capacity to restore tidal marsh, but also valuable coastal ecosystems more broadly.

A Lagrangian-to-Eulerian Metric to Identify Estuarine Pelagic Habitats

Estuaries are among the world’s most productive ecosystems, but recent natural and anthropogenic changes have stressed these ecosystems. Tools to assess estuarine pelagic habitats are important to support and maintain healthy ecosystem function. In this work, we demonstrate that estuarine pelagic habitats can be identified by a simple ratio, termed the LE ratio, that takes into account the tidal excursion along a channel (a Lagrangian length scale) and the distance along that channel (an Eulerian length scale). To develop and assess this concept, numerical simulations of the 1D advection–dispersion equation of a conservative tracer and tidal excursion estimates based on data were used to formulize a conceptual model and to define exchange zones within a tidal channel. This conceptual model was then used to predict the extent of pelagic habitats in a terminal channel network in the Sacramento–San Joaquin Delta. Exchange zones mapped onto these channels were found to be in good agreement with independent estimates of residence time. Sensitivity analyses of the numerical model suggest that productive pelagic habitats can be expanded by a factor of 2 by either increasing dispersion or increasing spring–neap variability in mean tidal velocity. Such changes can also enhance flushing in upper channel reaches. These findings are relevant for tidal marsh restoration projects that aim to expand beneficial aquatic habitats by varying exchange or residence time over the spring–neap cycle, because this variability may interact synergistically with varying rates of phytoplankton growth due to spatiotemporal changes in environmental conditions.