Marsh Loss Research Articles

Improved mapping of coastal salt marsh habitat change at Barnegat Bay (NJ, USA) using object-based image analysis of high-resolution aerial imagery

Tidal wetlands are valued for the ecosystem services they provide yet are vulnerable to loss due to anthropogenic disturbances such as land conversion, hydrologic modifications, and the impacts of climate change, especially accelerating rates of sea level rise. To effectively manage tidal wetlands in face of multiple stressors, accurate studies of wetland extent and trends based on high-resolution imagery are needed. We provide salt marsh delineations for Barnegat Bay, New Jersey, by means of object-based image analysis of high-resolution aerial imagery and digital elevation models. We performed trends analyses of salt marsh extent from 1995 to 2015 and estimated drivers of marsh area change. We found that in 1995, 8830 ± 390 ha were covered with marsh vegetation, while in 2015 only 8180 ± 380 ha of salt marsh habitat remained. The resulting net loss rate of 0.37% yr−1 is equivalent to historic loss rates since the 1970s, indicating that despite regionally accelerating relative sea level rise and purported eutrophication, salt marsh loss rates at Barnegat Bay remain steady. The main drivers of salt marsh loss are excavations for mosquito control (409 ha), edge erosion (303 ha) and ponding (240 ha). Upland migration of salt marsh did not completely mitigate these losses but accounted for a gain of 147 ha of tidal marsh habitat. The methodology presented herein yielded accurate salt marsh delineations (>90%) and trend detection (85%), outperforming low-resolution wetland delineations used in coastal management. This study demonstrates the suitability of high-resolution imagery for the detection of open water features. For the purposes of salt marsh change detection and the identification of change drivers, management and conservation agencies should make use of high-resolution imagery whenever feasible.

Global hotspots of salt marsh change and carbon emissions

Salt marshes provide ecosystem services such as carbon sequestration1, coastal protection2, sea-level-rise (SLR) adaptation3 and recreation4. SLR5, storm events6, drainage7 and mangrove encroachment8 are known drivers of salt marsh loss. However, the global magnitude and location of changes in salt marsh extent remains uncertain. Here we conduct a global and systematic change analysis of Landsat satellite imagery from the years 2000–2019 to quantify the loss, gain and recovery of salt marsh ecosystems and then estimate the impact of these changes on blue carbon stocks. We show a net salt marsh loss globally, equivalent to an area double the size of Singapore (719 km2), with a loss rate of 0.28% year−1 from 2000 to 2019. Net global losses resulted in 16.3 (0.4–33.2, 90% confidence interval) Tg CO2e year−1 emissions from 2000 to 2019 and a 0.045 (−0.14–0.115) Tg CO2e year−1 reduction of carbon burial. Russia and the USA accounted for 64% of salt marsh losses, driven by hurricanes and coastal erosion. Our findings highlight the vulnerability of salt marsh systems to climatic changes such as SLR and intensification of storms and cyclones.

Feeling Modernist Patronage: Edward Marsh, Rupert Brooke, and Modernism's Intimate Ecologies

Feeling Modernist Patronage:Edward Marsh, Rupert Brooke, and Modernism's Intimate Ecologies Jodie Medd (bio) On April 24, 1915, the day after Henry James learned that Rupert Brooke, the World War I poet and naval officer, had succumbed to septicemia on the Aegean en route to Gallipoli, he sent a letter of condolence. "This is too horrible and heartbreaking," James begins, "If there was a stupid and hideous disfigurement of life and outrage to beauty left for our awful conditions to perpetrate, those things have been now supremely achieved, and no other brutal blow in the private sphere can better them for making one just stare through one's tears." As he continues to lament this loss, James issues a pause that is as empathetic as it is rhetorical: "But why do I speak of my pang, as if it had a right to breathe in presence of yours?—which makes me think of you with the last tenderness of understanding. I value extraordinarily having seen him here in the happiest way (in Downing St., &c.) two or three times before he left England, and I measure by that the treasure of your own memories and the dead weight of your own loss." He advises his bereft correspondent "to entertain the pang and taste the bitterness for all they are 'worth'—to know to the fullest extent what has happened to you and not miss one of the hard ways in which it will come home. You won't have again any relation of that beauty, won't know again that mixture of the elements that made him." The only consolation he can offer: that this loss gives a greater "price and a refinement of beauty and poetry" to Brooke's last "splendid" war sonnets, "which will enrich our whole collective consciousness," and that "his legend and his image will hold."1 [End Page 785] This reads as a letter to a bereaved mother, a devastated brother, a mourning widow. And in a way, it is a letter to all three—and more—for it is addressed to Edward Marsh (1872–1953), Brooke's patron, supporter and, in James's own words, "intimate and devoted friend."2 This devoted friendship first took root while Brooke was at King's College Cambridge and, like Marsh nearly fifteen years before him, a member of the Apostles. That James could claim the "last tenderness of understanding" for Marsh's loss attests not only to James's extraordinary capacity for eloquent feeling, but also to his unique capability to empathize with this particular loss, of a beautiful, young, glamorous, semi-talented young man, whom Marsh had supported, admired, housed, and promoted. James's depth of attachments to artistically ambitious younger men, particularly later in his life—attachments that have informed and enriched queer considerations of James's life and work—uniquely qualified him in identifying with Marsh's wartime loss.3 Certainly, Marsh received an outpouring of consolation letters, particularly from the other poets and artists he had supported, many of whom had been published with Brooke in the Georgian Poetry anthologies, which Marsh and Brooke had masterminded together. But few, if any, could come close to James in appreciating the particular "pang" of this loss. At the same time, the only comfort that James's letter can offer—the value of Brooke's sonnets and the persistence of "his legend and image"—were not yet guaranteed resources at Marsh's disposal; in fact, they are phenomena that Marsh would actively produce and promote as his own means of mourning. The public endurance of Brooke's work, legend, and image were the direct result of Marsh's efforts, not only in his support of Brooke's early career, but most powerfully through his elegiac efforts in Brooke's posthumous memorialization. Theirs was a patronage relation extending far beyond death. Just how are we to understand this relation, its peculiar strain of intimacy that James intuitively recognized and honored, and its place within the cultural economy of modernist production and patronage? Approaching it requires rethinking the terms of the production and promotion of modernist literature and authors, structures of patronage, and their intersection with the...

High nutrient loads amplify carbon cycling across California and New York coastal wetlands but with ambiguous effects on marsh integrity and sustainability.

Eutrophic conditions in estuaries are a globally important stressor to coastal ecosystems and have been suggested as a driver of coastal salt marsh loss. Potential mechanisms in marshes include disturbance caused by macroalgae accumulations, enhanced soil sulfide levels linked to high labile carbon inputs, accelerated decomposition, and declines in belowground biomass that contribute to edge instability, erosion, and slumping. However, results of fertilization studies have been mixed, and it is unclear the extent to which local environmental conditions, such as soil composition and nutrient profiles, help shape the response of salt marshes to nutrient exposure. In this study, we characterized belowground productivity and decomposition, organic matter mineralization rates, soil respiration, microbial biomass, soil humification, carbon and nitrogen inventories, nitrogen isotope ratios, and porewater profiles at high and low marsh elevations across eight marshes in four estuaries in California and New York that have strong contrasts in nutrient inputs. The higher nutrient load marshes were characterized by faster carbon turnover, with higher belowground production and decomposition and greater carbon dioxide efflux than lower nutrient load marshes. These patterns were robust across marshes of the Atlantic and Pacific coasts that varied in plant species composition, soil flooding patterns, and soil texture. Although impacts of eutrophic conditions on carbon cycling appeared clear, it was ambiguous whether high nutrient loads are causing negative effects on long-term marsh sustainability in terms of studied metrics. While high nutrient exposure marshes had high rates of decomposition and soil respiration rates, high nutrient exposure was also associated with increased belowground production, and reduced levels of sulfides, which should lead to greater marsh sustainability. While this study does not resolve the extent to which nutrient loads are negatively affecting these salt marshes, we do highlight functional differences between Atlantic and Pacific wetlands which may be useful for understanding coastal marsh health and integrity.

Revised global estimates of resilience to sea level rise for tidal marshes

Earth system models are widely used to estimate future changes in wetland extent but do not incorporate surface elevation change (SEC) into predicting wetland's real responses to sea level rise (SLR). A machine learning model (MLM) was used to investigate the impact of multiple drivers on SEC and sediment accretion rate (SAR) in tidal marshes, and an earth system model (i.e. integrated climate and wetland migration model) was developed to predict the response of tidal marshes to SLR. The earth system model incorporates factors influencing SEC found by the MLM. Firstly, global data on SAR and SEC for tidal marshes was synthesised and the MLM was used to examine the drivers for SEC and SAR, including tidal range and frequencies, sediment loadings, precipitation, elevation, latitude, sea ice and/or relative SLR (RSLR). Human disturbance resulted in less sediment accretion and existing conservation activities were inefficient in promoting sediment accretion. Secondly, an integrated climate and wetland migration model was developed to assess the resilience of global tidal marshes responding to future SLR in Matlab by incorporating SEC, RSLR, climatic zones, tidal inundation, elevation and latitude into the model. The model was implemented under representative concentration pathways (RCPs) 2.6, 4.5 and 8.5, as well as nature-based human adaptation scenarios. Under the RCPs and nature-based human adaptation scenarios, tidal marshes will gain 53%-58% of the current global area by 2100 if sufficient sediment loadings and accommodation space allow landward migration. If current accommodation space is maintained, net global areal losses of 23%-30% are possible. Hotspots of future marsh loss are largely in North America, Australia and China. Projections for most SLR scenarios see marsh area peaking in the mid rather than late 21st century. Ecogeomorphic feedbacks affect rates of sediment accumulation but cannot be incorporated into the earth system model. The importance of nature-based adaptation was highlighted in enhancing the resilience of tidal marshes to future SLR.

Vegetation zones as indicators of denitrification potential in salt marshes.

Salt marsh vegetation zones shift in response to large‐scale environmental changes such as sea‐level rise (SLR) and restoration activities, but it is unclear if they are good indicators of soil nitrogen removal. Our goal was to characterize the relationship between denitrification potential and salt marsh vegetation zones in tidally restored and tidally unrestricted coastal marshes, and to use vegetation zones to extrapolate how SLR may influence high marsh denitrification at the landscape scale. We conducted denitrification enzyme activity assays on sediment collected from three vegetation zones expected to shift in distribution due to SLR and tidal flow restoration across 20 salt marshes in Connecticut, USA (n = 60 sampling plots) during the summer of 2017. We found lower denitrification potential in short‐form Spartina alterniflora zones (mean, 95% CI: 4, 3–6 mg N h−1 m−2) than in S. patens (25, 15–36 mg N h−1 m−2) and Phragmites australis (56, 16–96 mg N h−1 m−2) zones. Vegetation zone was the single best predictor and explained 52% of the variation in denitrification potential; incorporating restoration status and soil characteristics (soil salinity, moisture, and ammonium) did not improve model fit. Because denitrification potential did not differ between tidally restored and unrestricted marshes, we suggest landscape‐scale changes in denitrification after tidal restoration are likely to be associated with shifts in vegetation, rather than differences driven by restoration status. Sea‐level‐rise‐induced hydrologic changes are widely observed to shift high marsh dominated by S. patens to short‐form S. alterniflora. To explore the implications of this shift in dominant high marsh vegetation, we paired our measured mean denitrification potential rates with projections of high marsh loss from SLR. We found that, under low and medium SLR scenarios, predicted losses of denitrification potential due to replacement of S. patens by short‐form S. alterniflora were substantially larger than losses due to reduced high marsh land area alone. Our results suggest that changes in vegetation zones can serve as landscape‐scale predictors of the response of denitrification rates to rapid changes occurring in salt marshes.

Loss of Coastal Wetlands in Lake Burullus, Egypt: A GIS and Remote-Sensing Study

Lake Burullus is the second largest lake at the northern edge of the Nile Delta, Egypt, and has been recognized as an internationally significant wetland that provides a habitat for migrating birds, fish, herpetofauna, and mammals. However, the lake is experiencing severe human impacts including drainage and conversion to agricultural lands and fish farms. The primary goal of this study was to use multispectral, moderate-spatial-resolution (30 m2) Landsat satellite imagery to assess marsh loss in Lake Burullus, Egypt, in the last 35 years (1985–2020). Iterative Self-Organizing Data Analyses (ISODATA) unsupervised techniques were applied to the Landsat 5 Thematic Mapper (TM) and Landsat 8 Operational Land Imager–Thermal Infrared Sensor (OLI–TIRS) satellite images for classification of the Lake Burullus area into four main land-use classes: water, marsh, unvegetated land surfaces (roads, paths, sand sheets and dunes), and agricultural lands and fish farms. The overall classification accuracy was estimated to be 96% and the Kappa index was 0.95. Our results indicated that there is a substantial loss (44.8% loss) in the marsh aerial coverage between 1985 and 2020. The drainage and conversion of wetlands into agricultural lands and/or fish farms is concentrated primarily in the western and southern part of the lake where the surface area of the agricultural lands and/or fish farms doubled (103.2% increase) between 2000 and 2020. We recommend that land-use-policy makers and environmental government agencies raise public awareness among the local communities of Lake Burullus of the economic and environmental consequences of the alarming loss of marshland, which will likely have adverse effects on water quality and cause a reduction in the invaluable wetland-ecosystem services.

A rapid method to assess salt marsh condition and guide management decisions

Salt marshes are increasingly vulnerable to degradation and loss from accelerating sea-level rise and other pervasive disturbances, spurring a need for broad, science-based information to guide management. The Salt Marsh Rapid Assessment Method, MarshRAM, was designed to address this need by documenting information characterizing salt marsh type, setting, ecological value, disturbance, integrity, and opportunity for landward migration at the site scale. We used the method to collect information from onsite and remote observations of thirty-one (31) salt marshes in Rhode Island, USA. MarshRAM's Wetland Disturbance Index is a checklist that ranks the intensity of individual and cumulative human disturbances, while the Index of Marsh Integrity (IMI) is generated using a novel walking-transect approach to rapidly characterize site-wide vegetation-community composition. The IMI was designed to reflect ecological response to direct disturbances and inundation stress, and our finding that IMI strongly correlates with cumulative disturbance + marsh platform elevation indicates it works as intended. A strong correlation between IMI components and historic marsh loss suggests that salt marsh community cover can also serve as an indicator of salt marsh resilience. Our study marshes diverge from accounts of historic New England salt marsh conditions in that meadow high marsh species no longer dominate the high marsh zone, Spartina alterniflora is now the dominant high marsh species, and severe edge erosion and invasion by Phragmites australis are ubiquitous. We demonstrate how MarshRAM data can be analyzed to inform restoration and conservation strategies and policy decision-making. For example, our findings suggest that inundation stress is strongly impacting marsh platform integrity, high-marsh vegetation loss is a strong indicator of degradation and vulnerability, and unassisted landward marsh migration may already be promoting resilience to inundation stress. We suggest adapting MarshRAM to meet the management needs of other regions or broader applications.

Relationships between ecosystem properties and sea-level rise vulnerability of tidal wetlands of the U.S. Mid-Atlantic.

Tidal wetlands in the Mid-Atlantic, USA, are experiencing high rates of relative sea level rise, and it is unclear whether they will be resilient in the face of future flooding increases. In a previous study, we found 80% of our study areas in tidal freshwater and salt marshes in the Delaware Estuary and Barnegat Bay had elevation change rates lower than the 19-year increase in mean sea level. Here, we examine relationships between marsh elevation dynamics and abiotic and biotic parameters in order to assess their utility as indicators of vulnerability to relative sea level rise. We further apply a range of marsh vulnerability indicators including elevation change rates to evaluate their ability to corroborate marsh habitat change over the last 30years. Of the field measurements, soil bulk density and belowground plant biomass were among the strongest predictors of elevation change and accretion dynamics across all marsh types and settings. Both tidal freshwater and salt marshes tended to have higher rates of elevation increase and surface accretion in areas where soil bulk density and live belowground biomass were higher. Nine of the ten marshes experienced a net loss of area from the 1970s to 2015 ranging from 0.05 to 14%. Although tidal freshwater marshes were low in elevation and experienced variable elevation change rates, marsh area loss was low. Conversely, salt marshes closest to the coast and perched high in the tidal frame with a higher degree of human modification tended to experience the greatest marsh loss, which incorporated anthropogenic impacts and edge erosion. Thus, our regional assessment points to the need for a comprehensive understanding of factors that influence marsh resilience including human modifications and geomorphic settings.

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.

Soil microbial community development across a 32-year coastal wetland restoration time series and the relative importance of environmental factors

Soil microbes play key roles in ecosystem functioning through processes such as organic matter decomposition, nutrient and carbon cycling, and regulating vegetation structure and productivity. Coastal marshes are situated at the confluence of terrestrial and marine ecosystems; thus, their soils support abundant and diverse microbiota which facilitate globally important biogeochemical processes including nutrient cycling and greenhouse gas fluxes. With coastal marsh ecosystems threatened by relative sea level rise, subsidence, and development, mitigation for the loss of marshes is becoming commonplace. Despite the widespread implementation of marsh construction projects, little is known about the development and variability of microbial communities in created marshes. For this study, we tested the hypothesis that microbial community composition differs across created marshes of different ages and between created and natural marshes. We also hypothesized that the microbial community would be correlated with soil properties including soil organic carbon and nitrogen content, which were predicted to increase with marsh age. To test these hypotheses, we determined dominant microbial groups and environmental characteristics from six constructed marshes ranging in age from 0 to 32 years old, as well as an adjacent natural marsh. Our results revealed that microbial biomass estimates increased with marsh age except for the high elevation 20-year old marsh, yet each marsh contained a distinct microbial community composition. Across marshes, microbial community composition was significantly related to soil C:N ratio with an increase in total microbial abundance and actinomycetes and GM+ bacteria with an increase in soil C to N ratio. Additionally, shifts in dominant microbial groups were associated with differences in vegetation, elevation, and marsh age. The natural marsh community grouped more closely with younger rather than older marshes suggesting age is less important than environmental conditions. This study shows that microbial communities are not homogenized across restoration sites and do not necessarily converge to be similar to natural marshes over time. Local biotic and environmental conditions were correlated with microbial compositions, yet in seemingly similar conditions, microbial groups also differed. The effect of differences in microbial compositions on ecological functions are yet to be fully understood.

Burrowing crabs and physical factors hasten marsh recovery at panne edges.

Salt marsh loss is projected to increase as sea-level rise accelerates with global climate change. Salt marsh loss occurs along both lateral creek and channel edges and in the marsh interior, when pannes expand and coalesce. Often, edge loss is attributed to erosive processes whereas dieback in the marsh interior is linked to excessive inundation or deposition of wrack, but remains poorly understood. We conducted a two-year field investigation in a central California estuary to identify key factors associated with panne contraction or expansion. Our study explored how an abundant burrowing crab, shown to have strong negative effects on marsh biomass near creek edges, affects panne dynamics. We also explored which physical panne attributes best predicted their dynamics. To our knowledge, ours is the first study of panne dynamics in a California marsh, despite how ubiquitous pannes are as a feature of marshes in the region and how often extensive marsh dieback occurs via panne expansion. Overall, we found that pannes contracted during the study period, but with variable rates of marsh recovery across pannes. Our model incorporating both physical and biological factors explained 86% of the variation in panne contraction. The model revealed a positive effect of crab activity, sediment accretion, and a composite of depth and elevation on panne contraction, and a negative effect of panne size and distance to nearest panne. The positive crab effects detected in pannes contrast with negative effects we detected near creek edges in a previous study, highlighting the context-dependence of top-down and bioturbation effects in marshes. As global change continues and the magnitude and frequency of disturbances increases, understanding the dynamics of marsh loss in the marsh interior as well as creek banks will be critical for the management of these coastal habitats.

Buying Time with Runnels: a Climate Adaptation Tool for Salt Marshes

A prominent form of salt marsh loss is interior conversion to open water, driven by sea level rise in interaction with human activity and other stressors. Persistent inundation drowns vegetation and contributes to open water conversion in salt marsh interiors. Runnels are shallow channels originally developed in Australia to control mosquitoes by draining standing water, but recently used to restore marsh vegetation in the USA. Documentation on runnel efficacy is not widely available; yet over the past 10 years dozens of coastal adaptation projects in the northeastern USA have incorporated runnels. To better understand the efficacy of runnels used for restoration, we organized a workshop of 70 experts and stakeholders in coastal resource management. Through the workshop we developed a collective understanding of how runnels might be used to slow or reverse open water conversion, and identified unresolved questions. In this paper we present a synthesis of workshop discussions and results from a promising case study in which vegetation was restored at a degraded marsh within a few years of runnel construction. Despite case study outcomes, key questions remain on long-term runnel efficacy in marshes differing in elevation, tidal range, and management history. Runnel construction is unlikely to improve long-term marsh resilience alone, as it cannot address underlying causes of open water conversion. As a part of holistic climate planning that includes other management interventions, runnels may “buy time” for salt marshes to respond to management action, or adapt to sea level rise.

Vegetation interactions with geotechnical properties and erodibility of salt marsh sediments

Salt marshes provide diverse ecosystem services including coastal protection, habitat provision and carbon sequestration. The loss of salt marshes is a global scale phenomenon, of great socio-economic concern due to the substantial benefits that they provide. However, the causes of spatial variability in marsh loss rates are inadequately understood for the purposes of predicting future ecosystem distributions and functions under global environmental change. This study investigated the relationship between the presence of different saltmarsh plants and the mechanical properties of the underlying substrate that relate to its vulnerability to erosion. Relationships between three halophytes (Puccinellia spp., Spartina spp. and Salicornia spp.) and sediment stability were assessed and compared to unvegetated substrates using in-situ and laboratory tests of substrate geotechnical properties and sediment characteristics. Sampling was conducted at two UK sites with contrasting sedimentology, one sand-dominated and one clay-rich. Sediment samples, collected simultaneously with measurements of shear strength, were analysed for moisture content, particle size and organic, carbonate and mineral compositions. These data were then used to explore the contribution of plant type, alongside the sedimentological parameters, to measured shear strength.Shear strength of the sediment varied between and, to a lesser extent, within sites, with the four cover types having a similar effect on shear strength within sites relative to each other. Sediments covered by Puccinellia spp exhibit the highest shear strength, while bare sediments exhibit the lowest. The effect of vegetation type on shear strength was greater in the coarser sediments of Warton Sands. Surface cover type made a significant contribution to exploratory statistical models developed for the prediction of sediment shear strength. The findings support existing recognition that vegetation can enhance sediment shear strengths but extend the insight to reveal differences in this effect that show generality between sedimentological settings. Further, the combination of methods provides insight into the fundamental mechanics by which various measures of sediment stability may be affected by different surface cover types. Cohesion appears to be a more appropriate descriptor of sediment erodibility than shear strength or friction angle and is most greatly enhanced by the presence of a fine, fibrous root system such as that of Puccinellia. A more detailed understanding of the multi-scale mechanisms by which plants confer strength to substrates is needed to better anticipate their impact on sediment erodibility, and therefore salt marsh vulnerability.

Exploring open-source multispectral satellite remote sensing as a tool to map long-term evolution of salt marsh shorelines

From an ecological and socio-economic perspective, salt marshes are one of the most valuable natural assets on Earth. As external pressures are causing their extensive degradation and loss globally, the ability to monitor salt marshes on a long-term scale and identify drivers of change is essential for their conservation. Remote sensing has been demonstrated to be one of the most adept methods for this purpose and open-source multispectral satellite remote sensing missions have the potential to provide worldwide long-term time-series coverage that is non-cost-prohibitive. This study derives the long-term lateral evolution of four salt marsh patches in the Ria Formosa coastal lagoon (Portugal) using data from the Sentinel-2 and Landsat missions as well as from aerial photography surveys to quantitatively examine the accuracy and associated uncertainty in using open-source multispectral satellite remote sensing for this purpose. The results show that these open-source satellite archives can be a useful tool for tracking long-term salt marsh extent dynamics. During 1976–2020, there was a net loss of salt marsh in the study area, with erosion rates reaching an average of −3.3 m/yr opposite a tidal inlet. The main source of error in the satellite results was the dataset spatial resolution limits, but the specific salt marsh shoreline environment contributed to the relative magnitude of that error. The study notes the influence of eco-geomorphological dynamics on the mapping of sedimentary environments, so far not extensively discussed in scientific literature, highlighting the difference between mapping a morphological process and a sedimentary environment.

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.

A process-based assessment of landscape change and salmon habitat losses in the Chehalis River basin, USA.

Identifying necessary stream and watershed restoration actions requires quantifying natural potential habitat conditions to diagnose habitat change and evaluate restoration potential. We used three general methods of quantifying natural potential: historical maps and survey notes, contemporary reference sites, and models. Historical information was available only for the floodplain habitat analysis. We used contemporary reference sites to estimate natural potential habitat conditions for wood abundance, riparian shade, main channel length, and side channel length. For fine sediment, temperature, and beaver ponds we relied on models. We estimated a 90% loss of potential beaver pond area, 91% loss of side-channel length, and 92% loss or degradation of floodplain marshes and ponds. Spawning habitat area change due to wood loss ranged from -23% to -68% across subbasins. Other changes in habitat quantity or quality were smaller-either in magnitude or spatial extent-including rearing habitat areas, stream temperature, and accessible stream length. Historical floodplain habitat mapping provided the highest spatial resolution and certainty in locations and amounts of floodplain habitat lost or degraded, whereas use of the contemporary reference information provided less site specificity for wood abundance and side-channel length change. The models for fine sediment levels and beaver pond areas have the lowest reach-specific certainty, whereas the model of temperature change has higher certainty because it is based on a detailed riparian inventory. Despite uncertainties at the reach level, confidence in subbasin-level estimates of habitat change is moderate to high because accuracy increases as data are aggregated over multiple reaches. Our results show that the largest habitat losses were floodplain and beaver pond habitats, but use of these habitat change results in salmon life-cycle models can illustrate how the potential benefits of alternative habitat restoration actions varies among species with differing habitat preferences.

Is shoreline armoring a response to marsh migration? Modeling relationships between coastal marshes and private adaptation decisions

The value and vulnerability of salt marshes has led to efforts to ensure their preservation, including the preservation of marsh transgression zones (uplands onto which marshes can migrate) and restrictions on shoreline armoring. Coastal armoring involves the placement of hardened structures such as revetments and bulkheads along the shoreline. These structures can prevent coastal marshes from migrating onto adjacent uplands as sea levels rise, thereby causing marsh loss over time. Hence, efficient targeting of efforts to ensure marsh sustainability requires an understanding of where and why coastal armoring is likely to occur. This article develops a random utility model that characterizes residential landowners’ shoreline armoring decisions for beachfront and non-beachfront residential property, focusing on whether armoring is influenced by features related to marsh migration. The model is illustrated using parcel-level data from Accomack County, Virginia with armoring observations on each parcel for two time periods, 2002 and 2013. Independent models for the two time periods suggest that landowners in the case study area do not tend to construct armoring in ways that impede marsh migration—all else equal armoring is less likely to occur in areas suitable for marsh migration. Rather, armoring appears to be motivated primarily by factors associated with shoreline erosion risk such as high wave energy. • Ensuring marsh preservation requires an understanding of coastal armoring patterns. • A Random Utility Model characterizes residential homeowners' armoring decisions. • Results indicate that armoring does not occur in order to impede marsh migration. • Results indicate that armoring occurs to prevent shoreline erosion.

Mechanisms of Pond Expansion in a Rapidly Submerging Marsh

The development and expansion of ponds within otherwise vegetated coastal marshes is a primary driver of marsh loss throughout the world. Previous studies propose that large ponds expand through a wind wave-driven positive feedback, where pond edge erosion rates increase with pond size, whereas biochemical processes control the formation and expansion of smaller ponds. However, it remains unclear which mechanisms dominate at a given scale, and thus how, and how fast, ponds increase their size. Here, we use historical photographs and field measurements in a rapidly submerging microtidal marsh to quantify pond development and identify the processes involved. We find that as small ponds emerge on the marsh platform, they quickly coalesce and merge, increasing the number of larger ponds. Pond expansion rates are maximized for intermediate size ponds and decrease for larger ponds, where the contribution of wave-driven erosion is negligible. Vegetation biomass, soil shear strength, and porewater biogeochemical indices of marsh health are higher in marshes adjacent to stable ponds than in those adjacent to unstable ponds, suggesting that pond growth rates are negatively related to the health of the surrounding marsh. We find that the model of Vinent et al. (2021) correctly predicts measured pond growth rates and size distribution, which suggest the different mechanisms driving pond growth are a result of marsh drowning due to sea level rise (SLR) and can be estimated by simplified physical models. Finally, we show that all relevant processes increasing pond size can be summarized by an empirical power-law equation for pond growth which predicts the temporal change of the maximum pond size as a lower bound for the total pond area in the system. This gives a timescale for the growth of ponds by merging and thus the critical time window for interventions to prevent the irreversible pond expansion associated with large scale pond merging.

Coastal setting determines tidal marsh sustainability with accelerating sea-level rise

There is an increasing concern over how accelerated rates of sea-level rise (SLR) will impact tidal marsh ecosystems. The present study evaluates the potential impacts of SLR on marsh sustainability using the Tidal Marsh Model (TMM) with the addition of a new vegetation algorithm within the SCHISM (Semi-implicit Cross-scale Hydroscience Integrated System Model) framework. This new functionality contributes to an improved understanding of how vegetation affects the mean flow velocity and turbulence, and consequently, the sedimentation processes. Using two SLR scenarios (intermediate and extreme SLR rates), we projected the changes in marsh extent over the next 50 years in two representative marsh systems within a subestuary of Chesapeake Bay. Each study site has marshes associated with different physical settings and anthropogenic components: Carter Creek (developed, high topography) vs. Taskinas Creek (natural, low topography, steep banks). Carter Creek experienced a net marsh loss of 7.3% and 60% in the intermediate and extreme SLR scenario, respectively. In some places, due to the local geomorphic settings, marshes were able to migrate inland and offset part of the total loss, whereas marsh transgression was truncated near development and hardened shoreline structures. In Taskinas Creek, marshes are associated with natural lands with steep upland slopes (inhibitor for marsh transgression due to SLR). Marsh net decline was 23.1% (intermediate SLR scenario), and 89.6% (extreme SLR scenario). Marsh transgression was not substantial in this site, suggesting that marsh loss can be primarily attributed to upland bank conditions which prevented marsh migration with accelerated SLR rates. The enhanced TMM provides the highly-resolved simulations of multi-scale processes needed to inform restoration, strategic planning, and monitoring activities to support marsh sustainability in an evolving system.