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One of the world's largest "blue carbon" ecosystems, Louisiana's tidal wetlands on the US Gulf of Mexico coast, is rapidly being lost. Louisiana's strong legal, regulatory, and monitoring framework, developed for one of the world's largest tidal wetland systems, provides an opportunity for a programmatic approach to blue carbon accreditation to support restoration of these ecologically and economically important tidal wetlands. Louisiana's coastal wetlands span ∼1.4 million ha and accumulate 5.5–7.3 Tg yr−1 of blue carbon (organic carbon), ∼6%–8% of tidal marsh blue carbon accumulation globally. Louisiana has a favorable governance framework to advance blue carbon accreditation, due to centralized restoration planning, long term coastal monitoring, and strong legal and regulatory frameworks around carbon. Additional restoration efforts, planned through Louisiana's Coastal Master Plan, over 50 years are projected to create, or avoid loss of, up to 81,000 ha of wetland. Current restoration funding, primarily from Deepwater Horizon oil spill settlements, will be fully committed by the early 2030s and additional funding sources are required. Existing accreditation methodologies have not been successfully applied to coastal Louisiana's ecosystem restoration approaches or herbaceous tidal wetland types. Achieving financial viability for accreditation of these restoration and wetland types will require expanded application of existing blue carbon crediting methodologies. It will also require expanded approaches for predicting the future landscape without restoration, such as numerical modeling, to be validated. Additional methodologies (and/or standards) would have many common elements with those currently available but may be beneficial, depending on the goals and needs of both the state of Louisiana and potential purchasers of Louisiana tidal wetland carbon credits. This study identified twenty targeted needs that will address data and knowledge gaps to maximize financial viability of blue carbon accreditation for Louisiana's tidal wetlands. Knowledge needs were identified in five categories: legislative and policy, accreditation methodologies and standards, soil carbon flux, methane flux, and lateral carbon flux. Due to the large spatial scale and diversity of tidal wetlands, it is expected that progress in coastal Louisiana has high potential to be generalized to similar wetland ecosystems across the northern Gulf of Mexico and globally. [ABSTRACT FROM AUTHOR]

Salt marshes in the northeastern United States provide critical breeding habitat for tidal marsh specialist birds like the Ammospiza caudacuta (Saltmarsh Sparrow). The Ammospiza caudacuta population declined by 9% annually from 1998 to 2012, necessitating immediate conservation actions for this vulnerable species. However, estimating species vital rates across a large geographic region is logistically challenging and cost prohibitive. Therefore, we developed and tested a rapid assessment monitoring protocol focused on reproductive metrics to enhance future conservation planning. We used 3 years (2018, 2019, and 2021) of intensive demographic data from 12 sites to estimate daily nest survival, nest period success, fledglings produced per female, and successful broods per female. We implemented the rapid assessment protocol co-located at intensive sites in the same years to estimate the number of captured females and juveniles. We used Pearson's correlation analyses to determine the association of intensive metrics with rapid metrics. We found that the sum of Ammospiza caudacuta female and juvenile captures was positively correlated with daily nest survival (r  = 0.61, P  = 0.01), nest period success (r  = 0.70, P  = 0.002), fledglings produced per female (r  = 0.82, P  < 0.001), and successful broods per female (r  = 0.82, P  < 0.001). Our results demonstrate that fixed-effort mist-netting from our rapid assessment protocol is an informative and time-efficient sampling method that can aid in making informed management decisions related to Ammospiza caudacuta conservation. [ABSTRACT FROM AUTHOR]

Estuarine systems that provide valuable ecosystem services to society and important foraging and rearing habitat for fish and wildlife species continue to undergo degradation. In Puget Sound, WA, as much as 70–80% of historic estuarine habitat has been lost to anthropogenic development, and continued losses are expected through the end of the twenty-first century due to rising sea levels. To evaluate whether Puget Sound's estuarine habitats will keep pace with current and projected sea-level rise (SLR), we assessed vertical rates of elevation change from a regional network of surface elevation tables and marker horizons (SET-MH). Over the past two decades, SET-MH equipment has been installed throughout a variety of habitats in five Puget Sound estuaries: the Nisqually, Snohomish, Stillaguamish, and Skagit River estuaries, and Padilla Bay. These data provide a unique opportunity to assess elevation change and habitat resilience across a spatiotemporal and environmental gradient. We observed different rates of surface elevation change among estuaries and habitats (Nisqually = 4.64 ± 2.81 mm/year, Snohomish = 5.71 ± 5.83 mm/year, Stillaguamish = 12.82 ± 10.29 mm/year, Skagit = 16.13 ± 7.57 mm/year, Padilla = − 1.25 ± 1.58 mm/year). The highest rates were found at restoring sites with regular sediment input in the Stillaguamish and Skagit estuaries, whereas rates were consistently negative at low elevation sites in sediment starved Padilla Bay. Many sites in Puget Sound appear to be keeping pace with current rates of relative SLR, and some areas are on track to exceed projected rates through the end of the century. These findings indicate that Puget Sound's estuarine habitats can be resilient to rising tidal levels—as long as sediment delivery is maintained. [ABSTRACT FROM AUTHOR]

Australian tidal wetlands differ in important respects to better studied northern hemisphere systems, an artefact stable to falling sea levels over millennia. A network of Surface Elevation Table-Marker Horizon (SET-MH) monitoring stations has been established across the continent to assess accretionary and elevation responses to sea-level rise. This network currently consists of 289 SET-MH installations across all mainland Australian coastal states and territories. SET-MH installations are mostly in mangrove forests but also cover a range of tidal marsh and supratidal forest ecosystems. Mangroves were found to have higher rates of accretion and elevation gain than all the other categories of tidal wetland, a result attributable to their lower position within the tidal frame (promoting higher rates of accretion) higher biomass (with potentially higher rates of root growth), and lower rates of organic decomposition. While Australian tidal marshes in general show an increase in elevation over time, in 80% of locations, this was lower than the rate of sea-level rise. High rates of accretion did not translate into high rates of elevation gain, because the rate of subsidence in the shallow substrate increased with higher accretion rates (r2 = 0.87). The Australian SET-MH network, already in many locations spanning two decades of measurement, provides an important benchmark against which to assess wetland responses to accelerating sea-level rise in the decades ahead. [ABSTRACT FROM AUTHOR]

The scale at which New Zealand is currently storing and sequestering blue carbon, and could create additional blue carbon via restoration, has been unclear. Here, we calculate a preliminary estimate for the current extent of three key blue carbon ecosystems (saltmarshes, mangrove forests and seagrass meadows), their carbon stocks and their carbon sequestration rates using the best available data to provide a preliminary estimate of blue carbon in New Zealand. We also use local examples to explore opportunities to create additional blue carbon. Based on the available literature, we estimate the current extent of New Zealand's blue carbon ecosystems to be 76,152 ha, which is 1.0% of the area of terrestrial native forests. Our preliminary estimate of New Zealand's blue carbon stock is 2.66–3.76 Mt of carbon, with a current carbon sequestration rate of 0.12 (0.05–0.26) Mt/CO2/yr, which is equivalent to 0.16% of New Zealand's 2021 gross emissions. Restoration of saltmarshes could enhance their carbon sink capacity, mangrove forests are naturally expanding and seagrass meadow restoration techniques at scale are still in development. Developing a national framework for blue carbon protection, monitoring and restoration is important as part of New Zealand's climate change mitigation and adaptation efforts. [ABSTRACT FROM AUTHOR]

Aim: Tidal marsh ecosystems are heavily impacted by human activities, highlighting a pressing need to address gaps in our knowledge of their distribution. To better understand the global distribution and changes in tidal marsh extent, and identify opportunities for their conservation and restoration, it is critical to develop a spatial knowledge base of their global occurrence. Here, we develop a globally consistent tidal marsh distribution map for the year 2020 at 10‐m resolution. Location: Global. Time period: 2020. Major taxa studied: Tidal marshes. Methods: To map the location of the world's tidal marshes at 10‐m resolution, we applied a random forest classification model to Earth observation data from the year 2020. We trained the classification model with a reference dataset developed to support distribution mapping of coastal ecosystems, and predicted the spatial distribution of tidal marshes between 60° N and 60° S. We validated the tidal marsh map using standard accuracy assessment methods, with our final map having an overall accuracy score of 0.85. Results: We estimate the global extent of tidal marshes in 2020 to be 52,880 km2 (95% CI: 32,030 to 59,780 km2) distributed across 120 countries and territories. Tidal marsh distribution is centred in temperate and Arctic regions, with nearly half of the global extent of tidal marshes occurring in the temperate Northern Atlantic (45%) region. At the national scale, over a third of the global extent (18,510 km2; CI: 11,200–20,900) occurs within the USA. Main conclusions: Our analysis provides the most detailed spatial data on global tidal marsh distribution to date and shows that tidal marshes occur in more countries and across a greater proportion of the world's coastline than previous mapping studies. Our map fills a major knowledge gap regarding the distribution of the world's coastal ecosystems and provides the baseline needed for measuring changes in tidal marsh extent and estimating their value in terms of ecosystem services. [ABSTRACT FROM AUTHOR]

Sorption processes at the soil-water interface are observed to be rapid and dominant pathways of dissolved organic carbon (DOC) exchange. However, kinetics data for sorption in any ecosystem are sparse, and specifically non-existent for temperate tidal marshes. In this study, sorption rate kinetics experiments were designed to constrain new formulations of a sediment flux model coded to include explicit sorption between soil organic carbon and DOC pools. Batch incubations for marsh soil samples from Taskinas Creek (VA, USA) and Jug Bay Wetlands Sanctuary (MD, USA) were performed anaerobically under four sets of initial conditions: permutations of two salinities (0, 35) and two DOC concentrations (0 mg L-1, 275 mg L-1). Rates were measured at seven time points over 24 h. These results are the first DOC sorption kinetics data for tidal marsh soils, revealing that 76% of total sorption occurred within 15 min. The results also revealed higher capacity for adsorption under high DOC concentrations and salinity, with differences in magnitude between soil types. Numerical models simulating processes from these experiments provided a range of rates by fitting linear first order and non-linear ordinary differential equations to the kinetic change in DOC concentration curves over time. The outputs suggested that introducing soil adsorption capacity improved model fits across all cases. These results provide a deeper understanding of the biogeochemical controls on sorption kinetics and suggest that it is crucial to incorporate sorption processes into sediment flux models to accurately represent DOC fluxes from tidal marshes. [ABSTRACT FROM AUTHOR]

Coastal wetlands, especially tidal marshes, play a crucial role in supporting ecosystems and slowing shoreline erosion. Accurate and cost-effective identification and classification of various marsh types, such as high and low marshes, are important for effective coastal management and conservation endeavors. However, mapping tidal marshes is challenging due to heterogeneous coastal vegetation and dynamic tidal influences. In this study, we employ a deep learning segmentation model to automate the identification and classification of tidal marsh communities in coastal Virginia, USA, using seasonal, publicly available satellite and aerial images. This study leverages the combined capabilities of Sentinel-2 and National Agriculture Imagery Program (NAIP) imagery and a UNet architecture to accurately classify tidal marsh communities. We illustrate that by leveraging features learned from data abundant regions and small quantities of high-quality training data collected from the target region, an accuracy as high as 88% can be achieved in the classification of marsh types, specifically high marsh and low marsh, at a spatial resolution of 0.6 m. This study contributes to the field of marsh mapping by highlighting the potential of combining multispectral satellite imagery and deep learning for accurate and efficient marsh type classification.

Coastal flood risk is expected to increase due to climate change and population growth. Much of our coastlines is protected by “grey” infrastructure such as a dike. Dike maintenance and strengthening requires ever increasing capital and space, putting their economic viability in question. To combat this trend, more sustainable alternatives are explored, also known as Nature based Solutions. A promising option has shown to be tidal marshes. Tidal marshes are coastal wetlands with high ecological and economic value. Also, they protect dikes through wave attenuation and in case of a dike breach reduce its development. However, the effectiveness of a tidal marsh on reducing dike breach development rates highly depends on the stability of the tidal marsh itself. Not much is known about the stability of a tidal marsh under dike breach conditions, which are accompanied with flow velocities that can reach 4–5ms−1. In this study we tested the vegetation response and erodibility of a mature tidal marsh, in-situ, under high flow velocities ( > 0.5 m s−1). Our results confirm that tidal marshes similar to the one tested in this study are highly erosion resistant with low erodibility. More research is necessary to confirm this for tidal marshes with different soil and vegetation properties. For tidal marshes similar to what is tested thus far, erosion under dike breach conditions is negligible and other erosion mechanisms such as headcut erosion probably dominate the erosion process [ABSTRACT FROM AUTHOR]

More than 100 tidal marsh creation projects were constructed throughout the Fraser River Estuary, British Columbia, Canada from the 1980s to present. Past studies described and evaluated many of these projects and found varied success, but the underlying factors that determine project outcomes remain uncertain. Combining field sampling, spatial analysis, and statistical modeling of plant communities, we aim to address this knowledge gap by asking what factors influence the resilience of created marshes, as measured by (1) persistence of marsh vegetation, (2) native species dominance, and (3) species richness. We observed marsh recession in 40 of the 78 projects visited, representing 23,666 m2 (9.3%) of the 254,357 m2 of created marsh surveyed. Increases in mean site elevation had a negative effect on percent recessed area, while sites in the north branch of the river and sites further upriver were more prone to recession. From field observations and data interpretation we suggest that wake erosion and Canada Goose (Branta canadensis) herbivory may be drivers behind these losses and warrant further investigation. Dominance of native species declined with distance upriver, though invasive cattail (Typha angustifolia, T. × glauca) defied this trend, dominating outer estuary sites, particularly closed embayments, when present. Native and non-native richness shared similar patterns and were comparable between reference and created marshes, increasing on average with elevation and distance upriver. These findings offer insight into how site design and location influence the outcome of marsh creation projects, and the challenges presented by stressors and environmental change in estuaries. [ABSTRACT FROM AUTHOR]

One of the world’s largest “blue carbon” ecosystems, Louisiana’s tidal wetlands on the US Gulf of Mexico coast, is rapidly being lost. Louisiana’s strong legal, regulatory, and monitoring framework, developed for one of the world’s largest tidal wetland systems, provides an opportunity for a programmatic approach to blue carbon accreditation to support restoration of these ecologically and economically important tidal wetlands. Louisiana’s coastal wetlands span ∼1.4 million ha and accumulate 5.5–7.3 Tg yr−1 of blue carbon (organic carbon), ∼6%–8% of tidal marsh blue carbon accumulation globally. Louisiana has a favorable governance framework to advance blue carbon accreditation, due to centralized restoration planning, long term coastal monitoring, and strong legal and regulatory frameworks around carbon. Additional restoration efforts, planned through Louisiana’s Coastal Master Plan, over 50 years are projected to create, or avoid loss of, up to 81,000 ha of wetland. Current restoration funding, primarily from Deepwater Horizon oil spill settlements, will be fully committed by the early 2030s and additional funding sources are required. Existing accreditation methodologies have not been successfully applied to coastal Louisiana’s ecosystem restoration approaches or herbaceous tidal wetland types. Achieving financial viability for accreditation of these restoration and wetland types will require expanded application of existing blue carbon crediting methodologies. It will also require expanded approaches for predicting the future landscape without restoration, such as numerical modeling, to be validated. Additional methodologies (and/or standards) would have many common elements with those currently available but may be beneficial, depending on the goals and needs of both the state of Louisiana and potential purchasers of Louisiana tidal wetland carbon credits. This study identified twenty targeted needs that will address data and knowledge gaps to maximize financial viability of blue carbon accreditation for Louisiana’s tidal wetlands. Knowledge needs were identified in five categories: legislative and policy, accreditation methodologies and standards, soil carbon flux, methane flux, and lateral carbon flux. Due to the large spatial scale and diversity of tidal wetlands, it is expected that progress in coastal Louisiana has high potential to be generalized to similar wetland ecosystems across the northern Gulf of Mexico and globally.

Spatial quantification of blue carbon ecosystem stocks is crucial for developing policies to mitigate climate change, especially in regions experiencing ongoing wetland disturbance from biological invasions. We integrated multiple machine learning models with the space-for-time substitution method to quantify the spatiotemporal impact of Spartina alterniflora invasion on tidal marsh sediment blue carbon (soil organic carbon – 'SOC') stocks at 100 cm depth in the Yangtze Estuary. Our results show that the invasive S. alterniflora contributed more than half of the total SOC stocks (2,056 ± 379 Gg C, 1 Gg = 106 kg) in the 27,600 ha tidal marshes of the Yangtze Estuary, which were estimated to be 1,107 ± 176 Gg C. S. alterniflora increased the SOC stocks in the Yangtze Estuary within the first 15 years, but this gain was not sustained in the long term, with a gradual decline (by 13.14 Mg C/ha) observed after 15 years of S. alterniflora growth. We found that sediment salinity, tidal range, and human accessibility were strong indicators for modeling and predicting SOC stocks, with Random Forest providing the best simulation of tidal marsh SOC stocks (R2 = 0.894, RMSE=7.646 Mg C/ha, and MAPE=9.469 %). Our study provides much needed information on blue carbon stocks in the Yangtze Estuary under biological invasion stress, and offers guidance for targeted S. alterniflora management actions in the future.

Coastal wetlands encompass diverse ecosystems such as tidal marshes, mangroves, and seagrasses, which harbor substantial amounts of carbon (C) within their vegetation and soils. Despite their relatively small global extent, these wetlands exhibit carbon sequestration rates on par with those observed in terrestrial forests. The application of remote sensing technologies offers a promising means of monitoring aboveground biomass (AGB) in wetland environments. However, the scarcity of field data poses a significant challenge to the utilization of spaceborne data for accurate estimation of AGB in coastal wetlands. To address this limitation, this study presents a novel multi-scale approach that integrates field data, aerial imaging, and satellite platforms to generate high-quality biomass maps across varying scales. At the fine scale level, the AVIRIS-NG hyperspectral data were employed to develop a model for estimating AGB with an exceptional spatial resolution of 5 m. Subsequently, at a broader scale, large-scale and multitemporal models were constructed using spaceborne Sentinel-1 and Sentinel-2 data collected in 2021. The Random Forest (RF) algorithm was utilized to train spring, fall and multi-temporal models using 70% of the available reference data. Using the remaining 30% of untouched data for model validation, Root Mean Square Errors (RMSE) of 0.97, 0.98, and 1.61 Mg ha−1 was achieved for the spring, fall, and multi-temporal models, respectively. The highest R-squared value of 0.65 was achieved for the multi-temporal model. Additionally, the analysis highlighted the importance of various features in biomass estimation, indicating the contribution of different bands and indices. By leveraging the wetland inventory classification map, a comprehensive temporal analysis was conducted to examine the average and total AGB dynamics across various wetland classes. This analysis elucidated the patterns and fluctuations in AGB over time, providing valuable insights into the temporal dynamics of these wetland ecosystems. [ABSTRACT FROM AUTHOR]

Coastal flood risk is expected to increase due to climate change and population growth. Much of our coastlines is protected by “grey” infrastructure such as a dike. Dike maintenance and strengthening requires ever increasing capital and space, putting their economic viability in question. To combat this trend, more sustainable alternatives are explored, also known as Nature based Solutions. A promising option has shown to be tidal marshes. Tidal marshes are coastal wetlands with high ecological and economic value. Also, they protect dikes through wave attenuation and in case of a dike breach reduce its development. However, the effectiveness of a tidal marsh on reducing dike breach development rates highly depends on the stability of the tidal marsh itself. Not much is known about the stability of a tidal marsh under dike breach conditions, which are accompanied with flow velocities that can reach 4–5 m s−1. In this study we tested the vegetation response and erodibility of a mature tidal marsh, in-situ, under high flow velocities (>0.5 m s−1). Our results confirm that tidal marshes similar to the one tested in this study are highly erosion resistant with low erodibility. More research is necessary to confirm this for tidal marshes with different soil and vegetation properties. For tidal marshes similar to what is tested thus far, erosion under dike breach conditions is negligible and other erosion mechanisms such as headcut erosion probably dominate the erosion process.

Field studies are necessary for understanding natural processes in spite of the human‐induced disturbances they cause. While researchers acknowledge these effects, no studies have empirically tested the direct (e.g., harvesting plants) and indirect (i.e., trampling) effects of researcher activities on biological structure and edaphic conditions. We leveraged field studies in Alabama and California to monitor the recovery of tidal marshes following research activities. Researcher effects on animals, plants, and sediment conditions remained prevalent almost one year after the disturbance ended. For instance, trampled plots had 14%–97% lower plant cover than undisturbed plots after >10 months of recovery. Researcher effects also impacted plant composition, leading to increased subordinate species abundance. We encourage field researchers to adopt strategies that reduce their scientific footprints, including reducing field visits, limiting field team size, and considering ways to limit potential environmental impacts during study design. [ABSTRACT FROM AUTHOR]

Although the promotion of biodiversity has been recognized as an important conservation goal, salt marsh restoration typically focuses on reestablishing dominant foundation species. Salt marsh restoration projects that add or remove sediment to optimize marsh elevation often result in a bare landscape following construction. Restoration managers must decide whether to plant and, if so, which species. This decision can be difficult because few studies have examined the ecological functions of individual species, especially those that are less abundant. Within a major salt marsh restoration project in Elkhorn Slough, California, where 17,000 plants of five high marsh species were planted, we investigated how rarer species and the naturally recruiting dominant (Salicornia pacifica) differ in ecosystem function. We evaluated 31 different metrics related to blue carbon, plant productivity, environmental effects, and community interactions. No single species had the greatest ecological function across this suite of metrics, and measured effects were mainly independent, with only 16 of 435 pairwise comparisons revealing a strong correlation. We found significant differences among species for 18 metrics, revealing key contrasts in ecosystem function, with significant effects of marsh elevation and interaction between effects of species and elevation on some of these functions. S. pacifica scored highest for metrics such as recruitment and canopy height but other species outperformed Salicornia in other metrics. Frankenia salina had the greatest ecological function in the highest number of metrics, including cover and belowground biomass carbon content, but other species had higher rates of photosynthesis and harbored fewer individuals of invasive arthropods. We recommend planting a suite of less common species at restoration sites to provide more diverse functions across the landscape. F. salina in particular is recommended for its tolerance of hypersalinity and low moisture conditions. Our demonstration of the value of complementing restoration of the dominant foundation species with restoration of less common species is applicable to restoration of other ecosystems beyond salt marshes. The approach we implemented, evaluating a large suite of functions for multiple species across a restored landscape, can serve as a model for investigations of the importance of biodiversity for enhancing multifunctionality in other restored ecosystems. [ABSTRACT FROM AUTHOR]

Understanding the drivers of variability in plant diversity from local to landscape spatial scales is a challenge in ecological systems. Environmental gradients exist at several spatial scales and can be nested hierarchically, influencing patterns of plant diversity in complex ways. As plant community dynamics influence ecosystem function, understanding the drivers of plant community variability across space is paramount for predicting potential shifts in ecosystem function from global change. Determining the scales at which stress gradients influence vegetation composition is crucial to inform management and restoration of tidal marshes for specific functions. Here, we analyzed vegetation community composition in 51 tidal marshes from the San Francisco Bay Estuary, California, USA. We used model-based compositional analysis and rank abundance curves to quantify environmental (elevation/tidal frame position, distance to channel, and channel salinity) and species trait (species form, wetland indicator status, and native status) influences on plant community variability at the marsh site and estuary scales. While environmental impacts on plant diversity varied by species and their relationships to each other, overall impacts increased in strength from marsh to estuary scales. Relative species abundance was important in structuring these tidal marsh communities even with the limited species pools dominated by a few species. Rank abundance curves revealed different community structures by region with higher species evenness at plots higher in the tidal frame and adjacent to freshwater channels. By identifying interactions (species-species, species-environment, and environment-trait) at multiple scales (local, landscape), we begin to understand how variability measurements could be interpreted for conservation and land management decisions. [ABSTRACT FROM AUTHOR]

Understanding the drivers of variability in plant diversity from local to landscape spatial scales is a challenge in ecological systems. Environmental gradients exist at several spatial scales and can be nested hierarchically, influencing patterns of plant diversity in complex ways. As plant community dynamics influence ecosystem function, understanding the drivers of plant community variability across space is paramount for predicting potential shifts in ecosystem function from global change. Determining the scales at which stress gradients influence vegetation composition is crucial to inform management and restoration of tidal marshes for specific functions. Here, we analyzed vegetation community composition in 51 tidal marshes from the San Francisco Bay Estuary, California, USA. We used model-based compositional analysis and rank abundance curves to quantify environmental (elevation/tidal frame position, distance to channel, and channel salinity) and species trait (species form, wetland indicator status, and native status) influences on plant community variability at the marsh site and estuary scales. While environmental impacts on plant diversity varied by species and their relationships to each other, overall impacts increased in strength from marsh to estuary scales. Relative species abundance was important in structuring these tidal marsh communities even with the limited species pools dominated by a few species. Rank abundance curves revealed different community structures by region with higher species evenness at plots higher in the tidal frame and adjacent to freshwater channels. By identifying interactions (species–species, species–environment, and environment–trait) at multiple scales (local, landscape), we begin to understand how variability measurements could be interpreted for conservation and land management decisions.

Tidal wetlands are important blue carbon reservoirs, but it is unclear how sea-level rise (SLR) may affect carbon cycling and soil microbial communities either by increased inundation frequency or via shifting plant species dominance. We used an in-situ marsh organ experiment to test how SLR-scenarios (0, + 7.5, + 15 cm) and vegetation treatments (Spartina alterniflora, Spartina patens, Phragmites australis, unvegetated controls) altered CO2 fluxes (net ecosystem exchange, ecosystem respiration), soil carbon mineralization rates, potential denitrification rates, and microbial community composition. Increasing inundation frequency with SLR treatments decreased the carbon sink strength and promoted carbon emissions with + 15-cm SLR. However, SLR treatments did not alter soil chemistry, microbial process rates, or bacterial community structure. In contrast, our vegetation treatments affected all carbon flux measurements; S. alterniflora and S. patens had greater CO2 uptake and ecosystem respiration compared to P. australis. Soils associated with Spartina spp. had higher carbon mineralization rates than P. australis or unvegetated controls. Soil bacterial assemblages differed among vegetation treatments but shifted more dramatically over the three-month experiment. As marshes flood more frequently with projected SLR, marsh vegetation composition is predicted to shift towards more flood-tolerant S. alterniflora, which may lead to increased CO2 uptake, though tidal marsh carbon sink strength will likely be offset by increased abundance of unvegetated tidal flats and open water. Our findings suggest that plant species play a central role in ecosystem carbon dynamics in vegetated tidal marshes undergoing rapid SLR. [ABSTRACT FROM AUTHOR]

Oryzomys palustris (Harlan, 1837), the common marsh rice rat, is an Oryzomyine rodent with a tail nearly as long as the head and body, grayish above and white below with long-toed white feet. This account is an update of Mammalian Species 176 on the subject species by James L. Wolfe (1982a), incorporating 103 new references, most published since 1982. Oryzomys palustris, one of six living and two extinct species in this Neotropical genus, is semiaquatic and omnivorous, being highly carnivorous in some populations. It is parapatric with O. texensis in the western portion of its distribution in the southern United States. Oryzomys palustris is classified as "Least Concern" (LC) on the International Union for Conservation of Nature Red List. [ABSTRACT FROM AUTHOR]

Saltmarsh (Ammospiza caudacuta) and Nelson's (A. nelsoni) sparrows are sister taxa that breed in tidal marshes along the coast of the Northeastern United States and Canada. The Saltmarsh Sparrow breeds from mid‐coast Maine south to Virginia, while the Acadian Nelson's Sparrow breeds from the Canadian maritime provinces south to northern Massachusetts. Here, we present three extralimital observations of breeding Saltmarsh (n = 2) and Nelson's (n = 1) sparrows. In 2021 and 2022, we observed Saltmarsh Sparrow females attending nests at Mendall Marsh, ME, and Milbridge, ME, respectively, approximately 60 and 110 km beyond the documented northern extent of the Saltmarsh Sparrow breeding range. In 2022, we observed a breeding‐condition male Nelson's sparrow singing in the upriver portion of a marsh on Cape Cod, Massachusetts, approximately 115 km beyond the previously documented southern extent of the Nelson's Sparrow breeding range. We confirmed morphological species identification using a panel of microsatellite DNA loci. Due to both the well‐documented population declines of these species in the region and the intensity of sampling effort undertaken in recent years, we suggest that these observations likely are not indicative of range expansion. However, they do indicate that these 2 taxa have the capacity to use and successfully reproduce in marshes well beyond their established breeding limits. Our findings provide novel insight into the potential for these taxa to occur and successfully breed outside their documented breeding ranges. Given increased interest in their conservation, these results support the idea that management actions aimed at creating or maintaining nesting habitat across both species ranges could benefit both taxa. [ABSTRACT FROM AUTHOR]

Climate change is fundamentally altering marine and coastal ecosystems on a global scale. While the effects of ocean warming and acidification on ecology and ecosystem functions and services are being comprehensively researched, less attention is directed toward understanding the impacts of human‐driven ocean salinity changes. The global water cycle operates through water fluxes expressed as precipitation, evaporation, and freshwater runoff from land. Changes to these in turn modulate ocean salinity and shape the marine and coastal environment by affecting ocean currents, stratification, oxygen saturation, and sea level rise. Besides the direct impact on ocean physical processes, salinity changes impact ocean biological functions with the ecophysiological consequences are being poorly understood. This is surprising as salinity changes may impact diversity, ecosystem and habitat structure loss, and community shifts including trophic cascades. Climate model future projections (of end of the century salinity changes) indicate magnitudes that lead to modification of open ocean plankton community structure and habitat suitability of coral reef communities. Such salinity changes are also capable of affecting the diversity and metabolic capacity of coastal microorganisms and impairing the photosynthetic capacity of (coastal and open ocean) phytoplankton, macroalgae, and seagrass, with downstream ramifications on global biogeochemical cycling. The scarcity of comprehensive salinity data in dynamic coastal regions warrants additional attention. Such datasets are crucial to quantify salinity‐based ecosystem function relationships and project such changes that ultimately link into carbon sequestration and freshwater as well as food availability to human populations around the globe. It is critical to integrate vigorous high‐quality salinity data with interacting key environmental parameters (e.g., temperature, nutrients, oxygen) for a comprehensive understanding of anthropogenically induced marine changes and its impact on human health and the global economy. [ABSTRACT FROM AUTHOR]

We used a numerical model to investigate the effects of sea‐level rise (SLR) on the biogeochemical processes in the York River Estuary with extensive tidal marshes. The fully‐coupled hydrodynamic‐water quality‐marsh model accounts for the spatial and temporal variations of physical‐biogeochemical interactions between the tidal marshes and surrounding waters. This study focuses on an SLR scenario where the vertical accretion of tidal marshes keeps pace with the rising sea levels. Results show that SLR amplifies the tidal range and prolongs flooding duration, which results in enhanced porewater exchanges of materials between the tidal marshes and the surrounding waters. The increased availability of shallow‐water habitats and enhanced light utilization in the shallow areas under SLR promote phytoplankton production (PP) in the shallow‐water regions of the York River. Consequently, the organic carbon in the open water is fueled by the contributions from shallow waters and the enhanced export of organic carbon from the marshes. The change in the dissolved oxygen (DO) budget in the York River Estuary is attributed to changes in water column respiration, net metabolism of the benthic layer, reaeration, PP, and increased stratification under SLR. The net DO flux out of the York River increases at the York River mouth. Diel DO variation, especially in the marshes in the upper estuary, promotes phosphorus release from the sediment. The changes in dissolved nitrogen under SLR are relatively minimal. Plain Language Summary: As one of the consequences of climate change, sea‐level rise (SLR) has a wide‐ranging impact on the estuarine environment. SLR has a significant impact on tidal marshes, which are located at the interface between estuarine water and inner land. Despite the possibility of marsh retreat, many tidal marshes will keep up with the SLR through vertical accretion if sufficient sediment sources are available. SLR will result in deeper water and elevated tidal marshes in the estuary. The biogeochemical processes under this condition were predicted using a numerical modeling approach in this study. The tidal range is estimated to increase, encouraging more material exchange between marshes and estuarine water. More organic carbon is produced in this system, resulting in increased oxygen consumption. In this condition, there is a greater likelihood of low‐DO events occurring during the diel cycle, which will further affect nutrient dynamics. Key Points: A coupled tidal marsh and eutrophication model is applied to study the impacts of sea‐level rise (SLR) on estuarine biogeochemical processesThe tidal marshes that keep up with SLR are predicted to have more porewater‐surface water exchange and dissolved material exportsThe York River Estuary is predicted to have lower bottom dissolved oxygen and more hypoxia events under SLR [ABSTRACT FROM AUTHOR]

Reduced sediment loading contributes to tidal marsh loss, making evaluations of sediment dynamics useful in assessing marsh resilience to sea-level rise. Tidal marsh construction can offset these losses, but sediment dynamics are less commonly assessed in these systems. Some studies suggest sediment dynamics should develop over time; however, these studies often focus on accumulation at a single time and/or place, without considering sediment composition (i.e., organic vs. inorganic). We compared seasonal sediment dynamics between a natural and 34-year-old constructed tidal marsh with limited hydrologic connectivity. In July 2021, we established permanent sampling points along one tidal creek in each marsh and made monthly measurements of sedimentation, organic matter accumulation, and surface scour for one year. We found that sedimentation and organic matter accumulation were lower in the constructed marsh, while surface scour was similar between sites. Additionally, the relationship between distance from the tidal creek mouth and sedimentation differed between marshes (positive in natural, negative in constructed), as did organic matter accumulation (no relationship in natural, positive in constructed). However, we found that both marshes followed similar seasonal trends in sediment accumulation (highest in summer, lowest in winter). Observed differences in sedimentation between marshes appear to be marsh-specific (due to limited hydrologic connectivity in the constructed marsh), as sedimentation rates between other natural and restored marshes in the region did not differ. Collectively, these results suggest that consideration of sedimentation rates, including spatial and temporal variation, is critical to develop adequate sedimentary dynamics in restored and constructed marshes. [ABSTRACT FROM AUTHOR]

Abstract Accelerating sea‐level rise combined with the stresses of human land use threatens the persistence of tidal marshes. The proper management of existing marshes and the conservation of lands for marsh migration require a synthesis of factors affecting future marsh evolution. There are a number of existing marsh models, with different parameters and run at different scales, that can assist in this type of assessment. However, as with many models forecasting future conditions, there is no clearly identified ‘best’ model and they all perform slightly differently across different scenarios and with different suites of available data inputs. In this paper, we worked with local and regional managers to inform the development of an ensemble methodology that uses results from multiple marsh models in conjunction with social, land use and environmental data to inform marsh management, conservation and restoration under sea‐level rise. The methodology was developed and tested in three locations in the Virginia portion of the Chesapeake Bay, United States, using existing marsh migration models already run throughout the Bay. Stakeholder groups of local decision makers and a steering committee composed of regional managers were engaged in the process to ensure that the resulting methodology met current management needs. The need for a multimodel approach to identifying marsh migration pathways was supported by the marsh migration comparison done during methodology development which showed disparate results from multiple marsh migration models. Five existing marsh model outputs were combined into a single Marsh Migration Corridor Envelope (MMCE), which encompasses the potential area of current upland expected to become marsh under a selected sea‐level rise scenario. Within the identified MMCE, land covers were assessed for suitability for marsh support and the socio‐economic context of the parcels of land was considered. Last, the current condition of existing marsh on the properties was assessed to determine preservation activities that can increase their longevity. Together, these pieces of information inform a physical and sociological understanding of tidal marshes that can allow for a management framework that incorporates both current and future concerns.

Thin-layer sediment placement (TLP) is a promising management tool for enhancing tidal marsh resilience to rising seas. We conducted a 3-year experiment at eight US National Estuarine Research Reserves using a standardized implementation protocol and subsequent monitoring to evaluate effects of sediment placement on vegetation in low and high marsh, and compared this to control and reference plots. Sediments added to experimental plots were sourced from nearby quarries, were sandier than ambient marsh soils, and had more crab burrowing, but proved effective, suggesting that terrestrial sources can be used for tidal marsh restoration. We found strong differences among sites but detected general trends across the eight contrasting systems. Colonization by marsh plants was generally rapid following sediment addition, such that TLP plot cover was similar to control plots. While we found that 14-cm TLP plots were initially colonized more slowly than 7-cm plots, this difference largely disappeared after three years. In the face of accelerated sea-level rise, we thus recommend adding thicker sediment layers. Despite rapid revegetation, TLP plots did not approximate vegetation characteristics of higher elevation reference plots. Thus, while managers can expect fairly fast revegetation at TLP sites, the ultimate goal of achieving reference marsh conditions may be achieved slowly if at all. Vegetation recovered rapidly in both high and low marsh; thus, TLP can serve as a climate adaptation strategy across the marsh landscape. Our study illustrates the value of conducting experiments across disparate geographies and provides restoration practitioners with guidance for conducting future TLP projects. [ABSTRACT FROM AUTHOR]

Abstract Saltmarsh (Ammospiza caudacuta) and Nelson's (A. nelsoni) sparrows are sister taxa that breed in tidal marshes along the coast of the Northeastern United States and Canada. The Saltmarsh Sparrow breeds from mid‐coast Maine south to Virginia, while the Acadian Nelson's Sparrow breeds from the Canadian maritime provinces south to northern Massachusetts. Here, we present three extralimital observations of breeding Saltmarsh (n = 2) and Nelson's (n = 1) sparrows. In 2021 and 2022, we observed Saltmarsh Sparrow females attending nests at Mendall Marsh, ME, and Milbridge, ME, respectively, approximately 60 and 110 km beyond the documented northern extent of the Saltmarsh Sparrow breeding range. In 2022, we observed a breeding‐condition male Nelson's sparrow singing in the upriver portion of a marsh on Cape Cod, Massachusetts, approximately 115 km beyond the previously documented southern extent of the Nelson's Sparrow breeding range. We confirmed morphological species identification using a panel of microsatellite DNA loci. Due to both the well‐documented population declines of these species in the region and the intensity of sampling effort undertaken in recent years, we suggest that these observations likely are not indicative of range expansion. However, they do indicate that these 2 taxa have the capacity to use and successfully reproduce in marshes well beyond their established breeding limits. Our findings provide novel insight into the potential for these taxa to occur and successfully breed outside their documented breeding ranges. Given increased interest in their conservation, these results support the idea that management actions aimed at creating or maintaining nesting habitat across both species ranges could benefit both taxa.

Coastal wetlands encompass diverse ecosystems such as tidal marshes, mangroves, and seagrasses, which harbor substantial amounts of carbon (C) within their vegetation and soils. Despite their relatively small global extent, these wetlands exhibit carbon sequestration rates on par with those observed in terrestrial forests. The application of remote sensing technologies offers a promising means of monitoring aboveground biomass (AGB) in wetland environments. However, the scarcity of field data poses a significant challenge to the utilization of spaceborne data for accurate estimation of AGB in coastal wetlands. To address this limitation, this study presents a novel multi-scale approach that integrates field data, aerial imaging, and satellite platforms to generate high-quality biomass maps across varying scales. At the fine scale level, the AVIRIS-NG hyperspectral data were employed to develop a model for estimating AGB with an exceptional spatial resolution of 5 m. Subsequently, at a broader scale, large-scale and multitemporal models were constructed using spaceborne Sentinel-1 and Sentinel-2 data collected in 2021. The Random Forest (RF) algorithm was utilized to train spring, fall and multi-temporal models using 70% of the available reference data. Using the remaining 30% of untouched data for model validation, Root Mean Square Errors (RMSE) of 0.97, 0.98, and 1.61 Mg ha−1 was achieved for the spring, fall, and multi-temporal models, respectively. The highest R-squared value of 0.65 was achieved for the multi-temporal model. Additionally, the analysis highlighted the importance of various features in biomass estimation, indicating the contribution of different bands and indices. By leveraging the wetland inventory classification map, a comprehensive temporal analysis was conducted to examine the average and total AGB dynamics across various wetland classes. This analysis elucidated the patterns and fluctuations in AGB over time, providing valuable insights into the temporal dynamics of these wetland ecosystems.

Seed burial under wrack, mats of water-transported plant debris, can limit recruitment of seedlings in wetlands. In a greenhouse experiment, we studied the effects of wrack burial (0, 1, 2, 4, 8 cm depths) on germination and emergence of the macrophyte Iris pseudacorus, native to Europe, Mediterranean Basin, and western Asia, that has invaded wetlands in nearly every global ecozone. We recorded the percentages of germinating, senescent, and quiescent seeds and evaluated seedling establishment and growth relative to substrate environmental variables. Seedling emergence of I. pseudacorus was reduced from >80% in controls without burial to <40% even at minimal wrack depths of 1 cm. Few I. pseudacorus seedlings were able to emerge from wrack burial of up to 8 cm in depth. We also found greater numbers of both quiescent seeds and germinated seeds that did not emerge from wrack burial. Reduced seedling emergence and increased seed quiescence with wrack burial were primarily explained by a reduction in daily temperature variation within the substrate. No senescent seedlings were observed with any depth of wrack burial. In view of our results, the management of I. pseudacorus invasion will be a long-term challenge, requiring continued control due to persistent seeds in wrack-buried seed banks. [ABSTRACT FROM AUTHOR]

A key value of saltmarshes is their role in providing trophic subsidies, notably in the form of prey pulses of crab zoeae (CZ). No studies to date, however, have investigated quantitatively the patterns between crab zoeae pulses and saltmarsh tidal connectivity in tropical estuaries. In this study, CZ densities were examined over successive tides and months using a zooplankton sampling pump to examine links between tidal fluctuations and pulses of CZ in a tropical Australian estuary with a complex of tidal saltmarshes, mangroves, and unvegetated flats. CZ densities were linked to spatially explicit information on tidal wetland inundation that was derived from Unattended-Aerial-Vehicle (UAV) Structure from motion (SfM) photogrammetry and two-dimensional hydrodynamic modelling. The study found that: (1) tidal connectivity is a key trigger to prey pulse export; (2) while tidal connectivity was critical in the export of CZ, not all tidal connections resulted in meaningful ecological connectivity; and (3) succulent saltmarsh was one of the tidal wetland types contributing to the export of CZ. Surprisingly, we reveal that not all succulent saltmarshes were uniformly participating in CZ export. These findings highlight the significance of quantitative eco-hydrological approaches to assess saltmarsh and tidal connectivity values. This study supports the need for management and restoration approaches to integrate a contextual understanding of the synergies between hydrology, ecology, and habitat heterogeneity. These data emphasise the need to move beyond generalisations that "similar" habitat type share similar ecological functions and should be managed equally. • Tidal connectivity is a key trigger to the export of pulses of intertidal crab zoeae. • Tropical succulent saltmarsh inundation is contributing to crab zoea pulses. • Not all connections and saltmarsh patches were important in supporting crab zoea export. • The importance of contextual-based understanding of saltmarsh function is highlighted. [ABSTRACT FROM AUTHOR]

Conservation of estuaries is strengthened by an understanding of past and current estuary extent, which helps stakeholders envision resilient estuarine habitats in the future. We used spatial analyses to improve understanding of estuarine habitat and extent in and around 30 US National Estuarine Research Reserves using two approaches, elevation-based mapping and historical mapping. We collaborated with stakeholders to incorporate local knowledge, and found that our methodologies were effective across disparate geographies. Elevation-based mapping proved to be a powerful tool for mapping areas within reach of tides, yielding a better understanding of the past, present, and potential estuary. This approach revealed that US estuaries are or were bigger – often vastly so – than what is shown in most maps. In particular, at over 80 % of studied estuaries, elevation-based mapping detected temperate forested tidal wetlands missed by maps generated primarily from aerial photographs. Historical mapping, conducted consistently across diverse regions, provided a valuable window into past ecological conditions. Our change analysis using historical maps revealed that tidal marsh has undergone dramatic losses on the Pacific coast (average > 60 % loss). On other US coasts, tidal marsh extent has changed less (average < 10 % loss), with marsh losses offset by landward migration; however, marsh migration may have caused net loss of vegetated tidal wetlands due to loss of forested tidal wetlands. Comparing mapping methods revealed important changes that could not be detected using a single method. Each mapping approach had limitations, so combining multiple methods will enhance understanding of both past and present conditions at estuaries worldwide. • Combining mapping methods enhances understanding of estuary boundaries and change. • Elevation-based mapping reveals estuaries are larger than shown by previous maps. • Elevation-based maps detect many tidal forests missing from current estuary maps. • For best insight into the past estuary, combine historical and elevation-based maps. • The Pacific coast has lost vastly more tidal marsh than other US regions. [ABSTRACT FROM AUTHOR]

• Total nitrogen was a key driver in soil CH 4 and CO 2 production in tidal marshes. • Nitrate enrichments tended to decrease CH 4 and CO 2 production. • Nitrate but not ammonium addition decreased mcr A gene abundance. • Salinity was not a mitigating factor in either nitrogen eutrophication scenarios. Eutrophication is an important environmental stressor in coastal wetlands that alters ecosystem processes including primary production and the carbon cycle. However, how different nitrogen eutrophication scenarios may affect CH 4 and CO 2 production along a salinity gradient in coastal wetlands is poorly known. We collected the surface soil samples from both tidal freshwater and mesohaline Phragmites australis marshes in six main estuaries in China and conducted inorganic nitrogen enrichment anaerobic incubation experiments. Background soil CH 4 and CO 2 production rates were strongly correlated with total nitrogen but not salinity. On average, nitrate enrichment decreased soil CH 4 and CO 2 production rates by ca. 20 % in freshwater marsh and 16–43 % in mesohaline marshes, whereas ammonium enrichment decreased CO 2 production by ca. 26–30 % but had no effect on CH 4 production. Salinity was not an important mitigating factor in either eutrophication scenario. In most cases, nitrogen addition decreased the extracellular enzyme activities of β-1,4-glucosidase and cellobiohydrolase, but increased the activity of β-N-acetyl glucosaminidase, phenol oxidase and peroxidase. Nitrate addition decreased the mcr A gene abundance on average by 34–35 % but ammonium addition had insignificant effect. Total nitrogen availability was an important driver of CH 4 and CO 2 production rates in these tidally influenced coastal wetlands. Our results showed that tidal marshes with salinity < 15 ppt had similar soil CH 4 production rates, and increasing inorganic nitrogen eutrophication might lower soil microbial carbon gas production in both tidal freshwater and mesohaline marshes. [ABSTRACT FROM AUTHOR]

Seed banks play an important role in determining the spatial and temporal distribution of halophytes in salt marshes. We tested the ability of native Spartina maritima and invasive S. densiflora spikelets to disperse by flotation on water with different salinity concentrations, and the longevity of spikelet viability relative to environmental conditions including dry or wet storage at low or moderate temperatures, and aqueous salinity concentrations from fresh to sea water. We quantified pre-dispersal seed production and pre- and post-dispersal focal Spartina spp. presence in seed banks along intertidal gradients within salt marshes at the Gulf of Cádiz (Southwest Iberian Peninsula). Spartina densiflora spikelets, especially from middle and high elevation marshes, showed greater ability than S. maritima to remain afloat, which suggests this species could be dispersed over longer distances. Wet-stored Spartina seeds were able to maintain viability for months, while seeds under dry storage rapidly lost viability. This decline was most significant for S. maritima, and for seeds stored at moderate temperatures. Storage of spikelets under wet and cold conditions optimized spikelet viability. Native S. maritima did not establish transient or persistent seed banks, while invasive S. densiflora established transient seed banks mainly at higher marsh elevations. Our results on the dynamics of seed dispersal and seed banks and seedling recruitment provide fundamental knowledge that can be applied for conservation of native S. maritima, management of invasive S. densiflora, and ecological restoration of tidal salt marshes. [ABSTRACT FROM AUTHOR]

Terminal channels were historically a common feature of tidal delta ecosystems but have become increasingly rare as landscapes have been modified. Tidal hydrodynamics are a defining feature in tidal terminal channel ecosystems from which native aquatic communities have evolved. However, few studies have explored the relationship between fish community structure and hydrodynamics in these tidal terminal channel ecosystems. We sampled fish communities throughout a network of terminal channels within the northeasternmost region of the San Francisco Estuary to determine the relationship between fish community structure and hydrodynamics within these environments. We collected two years (2017 and 2018) of fish community samples using gill nets and analyzed data using multivariate community analyses and count models. We found metrics of fish diversity and counts of native fishes to be greatest upstream (farthest from tidal influence) of the tidal excursion within terminal channels. Counts of non‐native fishes were less affected by this hydrodynamic feature of terminal channels and more tightly correlated to local habitat conditions (e.g., water temperature, depth). Our results suggest that channel hydrodynamics plays a role in structuring fish communities within terminal channels, particularly native fishes. These results indicate that hydrodynamics in tidal delta ecosystems may be able to be altered in ways that benefit native fishes without the cost of water pumping. [ABSTRACT FROM AUTHOR]

Tidal marshes are among the world's most valuable ecosystems; however, they are increasingly threatened by rising sea levels and a decline in fluvial sediment supply. The survival of a tidal marsh under these twin threats depends upon the net input of tidal sediments, because this will determine the deposition rate. The rate of relative sea level rise currently affecting the Yangtze Delta is rapid (~4 mm/a), and the sediment discharge from the Yangtze River has decreased by >70% over recent decades. In order to improve our understanding of the response of the marshes in the turbid zone of the Yangtze Estuary to these changing environmental conditions, we measured sediment transport in and out of a tidal basin and calculated the deposition rate over eight tidal cycles covering different tidal ranges during the summer and winter seasons. The suspended sediment concentration (SSC) during the flood phase of the tidal cycle (average = 0.395 kg/m3) was markedly higher than that during the ebb (average = 0.164 kg/m3), although water transport during the flood tide was almost equivalent to that during the ebb. As a result, ~40% of the sediment inflow during the flood phase was retained within the marsh. This reason is mainly attributable to the dense marsh vegetation, which attenuates waves and currents and to which the sediments adhere. The annual deposition rate in the marsh was approximately 6.7 mm/a. These findings indicate that under the combined influence of sea level rise and river sediment supply reduction, the sediment transport through the turbidity maximum zone of the Yangtze River estuary could maintain the relative stability of the marsh area to a certain extent. [ABSTRACT FROM AUTHOR]

Quantitative, broadly applicable metrics of resilience are needed to effectively manage tidal marshes into the future. Here we quantified three metrics of temporal marsh resilience: time to marsh drowning, time to marsh tipping point, and the probability of a regime shift, defined as the conditional probability of a transition to an alternative super-optimal, suboptimal, or drowned state. We used organic matter content (loss on ignition, LOI) and peat age combined with the Coastal Wetland Equilibrium Model (CWEM) to track wetland development and resilience under different sea-level rise scenarios in the Sacramento-San Joaquin Delta (Delta) of California. A 100-year hindcast of the model showed excellent agreement (R2 = 0.96) between observed (2.86 mm/year) and predicted vertical accretion rates (2.98 mm/year) and correctly predicted a recovery in LOI (R2 = 0.76) after the California Gold Rush. Vertical accretion in the tidal freshwater marshes of the Delta is dominated by organic production. The large elevation range of the vegetation combined with high relative marsh elevation provides Delta marshes with resilience and elevation capital sufficiently great to tolerate centenary sea-level rise (CLSR) as high as 200 cm. The initial relative elevation of a marsh was a strong determinant of marsh survival time and tipping point. For a Delta marsh of average elevation, the tipping point at which vertical accretion no longer keeps up with the rate of sea-level rise is 50 years or more. Simulated, triennial additions of 6 mm of sediment via episodic atmospheric rivers increased the proportion of marshes surviving from 51% to 72% and decreased the proportion drowning from 49% to 28%. Our temporal metrics provide critical time frames for adaptively managing marshes, restoring marshes with the best chance of survival, and seizing opportunities for establishing migration corridors, which are all essential for safeguarding future habitats for sensitive species.

Thalassosols developing on the accumulative coasts of the East Siberian Sea include initial soils of regularly flooded tidal flats with sparse vegetation, episodically flooded marsh soils with different degrees of salinization, and maritime soils that are morphologically close to the zonal soils but are affected by salts transferred by wind with seawater drops and organomineral matter from the non-vegetated seashores. Weakly developed marsh soils have the initial features and structure of the marine sediments combined with the processes of salinization; sulfate reduction; gleyzation; cryogenic mass exchange; as well as the transfer, accumulation, and weak biochemical transformation of the raw organic matter. Soils with different degrees of salinization are formed on tidal marshes and are characterized by some redistribution of salts in the soil profile with weak accumulation of salts in the uppermost organic horizons and in the suprapermafrost layers along with pronounced sulfate reduction. Slightly saline organogenic and peaty gleyic soils predominate in the areas of sedge marshes. The majority of studied marsh soils form under the conditions of distinct cryogenic polygonal microtopography, waterlogging, and relatively shallow permafrost. [ABSTRACT FROM AUTHOR]

[Display omitted] • Machine learning reveals spatiotemporal dynamics of SOC stocks in tidal marshes. • Sediment salinity and tidal range are key factors influencing SOC stocks prediction. • Invasive S. alterniflora contributes over half of SOC stocks in Yangtze Estuary. • S. alterniflora increased SOC stocks within the first 15 years of its invasion. • S. alternifloras high SOC storage capacity is not sustained in the long term. Spatial quantification of blue carbon ecosystem stocks is crucial for developing policies to mitigate climate change, especially in regions experiencing ongoing wetland disturbance from biological invasions. We integrated multiple machine learning models with the space-for-time substitution method to quantify the spatiotemporal impact of Spartina alterniflora invasion on tidal marsh sediment blue carbon (soil organic carbon – 'SOC') stocks at 100 cm depth in the Yangtze Estuary. Our results show that the invasive S. alterniflora contributed more than half of the total SOC stocks (2,056 ± 379 Gg C, 1 Gg = 106 kg) in the 27,600 ha tidal marshes of the Yangtze Estuary, which were estimated to be 1,107 ± 176 Gg C. S. alterniflora increased the SOC stocks in the Yangtze Estuary within the first 15 years, but this gain was not sustained in the long term, with a gradual decline (by 13.14 Mg C/ha) observed after 15 years of S. alterniflora growth. We found that sediment salinity, tidal range, and human accessibility were strong indicators for modeling and predicting SOC stocks, with Random Forest providing the best simulation of tidal marsh SOC stocks (R2 = 0.894, RMSE=7.646 Mg C/ha, and MAPE=9.469 %). Our study provides much needed information on blue carbon stocks in the Yangtze Estuary under biological invasion stress, and offers guidance for targeted S. alterniflora management actions in the future. [ABSTRACT FROM AUTHOR]

Spatial heterogeneity of species (beta diversity) is an important attribute of ecological communities, but is less frequently considered when assessing restoration success than other aspects of diversity (gamma and alpha). Differences in beta diversity between restored and natural sites may arise due to differences in environmental heterogeneity.We used a nested sampling design to survey plant communities and environmental conditions (elevation, redox potential and metrics of topography) on four pairs of restored and natural saltmarshes. We assessed whether there were differences in both alpha and beta diversity between natural and restored sites and analysed their environmental drivers.Topography was an important driver of plant alpha diversity and beta diversity on saltmarshes. The effects of topography were partly indirect, mediated though changes in redox potential, but topography also influenced plant communities independently of both elevation and redox.Restored saltmarshes were less heterogeneous in topography than natural marshes. This reduced topography was reflected in lower beta diversity; plant communities 1 m apart in natural marshes were as dissimilar as those found 20 m apart in restored marshes.Large‐scale topographic manipulation carried out at one site a decade after initial restoration successfully increased topographic heterogeneity and increased beta diversity when surveyed 3 years after manipulation. These changes were still evident when resurveyed after a further 2 years.Synthesis and applications. Increasing environmental heterogeneity can improve restoration outcomes by increasing beta diversity on restored sites. The effect of environmental heterogeneity is likely to be particularly strong within intertidal habitats such as saltmarshes, where small changes in topography can determine whether a species can occur at a given location. Topographic manipulation is a feasible post‐restoration technique that can be applied to ensure restored saltmarshes better meet policy targets of biological, physical and functional equivalence with natural marshes. [ABSTRACT FROM AUTHOR]

Non-native predatory fish strongly affect aquatic communities, and anthropogenic habitat alterations can exacerbate their effects. Loss of natural habitat, and restoration actions that reverse habitat loss, can modify relationships between non-native predators and prey. Predicting how these relationships will change is often difficult because insufficient information exists on the habitat-specific feeding ecology of non-native predators. To address this information gap, we examined diets of non-native Striped Bass (Morone saxatilis; 63 to 671 mm standard length; estimated age 1 to 5 yrs) in the San Francisco Estuary during spring and summer in three habitat types--marsh, shoal, and channel--with the marsh habitat type serving as a model for ongoing and future restoration. Based on a preyspecific index of relative importance, Striped Bass diets were dominated by macroinvertebrates in spring and summer (amphipods in spring, decapods and isopods in summer). In spring, diets were relatively consistent across habitats. In summer, marsh diets were dominated by sphaeromatid isopods and shoal/channel diets by idoteid amphipods and decapods. Striped Bass consumed a variety of native and non-native fishes, primarily Prickly Sculpin (Cottus asper) and Gobiidae. The highest importance of fish prey was in the marsh in spring (~ 40% prey weight), and fish prey comprised less than 25% prey weight in all other season/habitat combinations. Linear discriminant analyses suggested that marsh foraging was prevalent in Striped Bass collected in other habitats, mostly because of the predominance of marsh-associated invertebrates found in the stomachs of individual Striped Bass collected outside the marsh. Striped Bass diets differ across habitats, with marsh foraging important to Striped Bass regardless of collection location. This information can be used to forecast the potential utilization of restored habitats by this non-native piscivore. [ABSTRACT FROM AUTHOR]

Globally, mangrove range limits are expanding, often at the cost of adjacent coastal ecosystems including saltmarshes, potentially leading to a change in ecosystem services such as organic carbon (OC) sequestration. Studies in the southeastern US have focused almost exclusively on Avicennia germinans range expansion, the most cold-tolerant mangroves in North America. The Apalachicola Bay region of north Florida represents the northern range limit of mangroves in the Gulf of Mexico, and uniquely also includes Rhizophora mangle. The objective of this research was to quantify soil OC density beneath both mangrove species and compare results to the soils beneath two contiguous native tidal saltmarsh species: Juncus roemerianus and Spartina alterniflora in a barrier island setting. Dominant plant taxa were not a significant predictor of soil OC density, highlighting the relative importance of site-specific environmental attributes as controls on soil properties. Soil profile δ13C compositions included a range of values reflective of C3 and C4 plant inputs, suggesting that shifts in plant taxa, both from marsh to mangroves and between marsh species, have been occurring at all sites in this study. These findings support much of the literature on mangrove encroachment, which indicates mangrove soil OC concentrations, densities, or stocks are less than or equal to that of co-located tidal marsh habitats. Through a systematic review, the potential of several proposed explanatory variables (climate, environmental setting, plant physiology and productivity, and duration of encroachment) were identified to evaluate how soil OC density in mangrove habitats might increase over time, which is critical to forecasting how continued mangrove expansion might affect blue C storage as these habitats evolve.

Climate change is intensifying the effects of multiple interacting stressors on aquatic ecosystems worldwide. In the San Francisco Estuary, signals of climate change are apparent in the long-term monitoring record. Here we synthesize current and potential future climate change effects on three main ecosystems (floodplain, tidal marsh, and open water) in the upper estuary and two representative native fishes that commonly occur in these ecosystems (anadromous Chinook Salmon, Oncorhynchus tshawytscha and estuarine resident Sacramento Splittail, Pogonichthys macrolepidotus). Based on our review, we found that the estuary is experiencing shifting baseline environmental conditions, amplification of extremes, and restructuring of physical habitats and biological communities. We present priority topics for research and monitoring, and a conceptual model of how the estuary currently functions in relation to climate variables. In addition, we discuss four tools for management of climate change effects: regulatory, water infrastructure, habitat development, and biological measures. We conclude that adapting to climate change requires fundamental changes in management. [ABSTRACT FROM AUTHOR]

The biogeochemistry of tidal marsh sediments facilitates the transformation of mercury (Hg) into the biologically available form methylmercury (MeHg), resulting in elevated Hg exposures to tidal marsh wildlife. Saltmarsh and Acadian Nelson's sparrows (Ammospiza caudacutua and A. nelsoni subvirgatus, respectively) exclusively inhabit tidal marshes, potentially experiencing elevated risk to Hg exposure, and have experienced range-wide population declines. To characterize spatial and temporal variation of Hg exposure in these species, we sampled total mercury (THg) in blood collected from 9 populations spanning 560 km of coastline, including individuals resampled within and among years. Using concurrent nesting studies, we tested whether THg was correlated with nest survival probabilities, an index of fecundity. Blood THg ranged from 0.074–3.373 µg/g ww across 170 samples from 127 individuals. We detected high spatial variability in Hg exposure, observing differences of more than 45-fold across all individuals and 8-fold in mean blood THg among all study plots, including 4-fold between study plots within 4 km. Intraindividual changes in blood Hg exposure did not vary systematically in time but were considerable, varying by up to 2-fold within and among years. Controlling for both species differences and maximum water level, the dominant driver of fecundity in this system, nest survival probability decreased by 10% across the full range of female blood THg concentrations observed. We conclude that Hg has the potential to impair songbird reproduction, potentially exacerbating known climate-change driven population declines from sea-level rise in saltmarsh and Acadian Nelson's sparrows. [ABSTRACT FROM AUTHOR]

Seed burial under wrack, mats of water-transported plant debris, can limit recruitment of seedlings in wetlands. In a greenhouse experiment, we studied the effects of wrack burial (0, 1, 2, 4, 8 cm depths) on germination and emergence of the macrophyte Iris pseudacorus, native to Europe, Mediterranean Basin, and western Asia, that has invaded wetlands in nearly every global ecozone. We recorded the percentages of germinating, senescent, and quiescent seeds and evaluated seedling establishment and growth relative to substrate environmental variables. Seedling emergence of I. pseudacorus was reduced from >80% in controls without burial to I. pseudacorus seedlings were able to emerge from wrack burial of up to 8 cm in depth. We also found greater numbers of both quiescent seeds and germinated seeds that did not emerge from wrack burial. Reduced seedling emergence and increased seed quiescence with wrack burial were primarily explained by a reduction in daily temperature variation within the substrate. No senescent seedlings were observed with any depth of wrack burial. In view of our results, the management of I. pseudacorus invasion will be a long-term challenge, requiring continued control due to persistent seeds in wrack-buried seed banks.

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 <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'. [ABSTRACT FROM AUTHOR]

Tidal marshes are one of the world's most economically valuable habitats; yet, they have experienced large and persistent declines globally. Increased knowledge of the ecosystem services delivered by marshes has become a powerful tool to conserve and restore them. But hesitancies regarding valuations and their application in decision-making remain. Here we draw on the literature and collective experience of participants in the "Concepts and controversies in tidal Marsh ecology revisited" workshop, November 2 and 3, 2019, Mobile, AL, to provide a concise snapshot of the current field of salt marsh ecosystem service valuation, discuss the possible risks in salt marsh valuation, and the importance of stakeholder engagement to mitigate them. We provide examples of the application of valuation in conservation-related decision-making, illustrating the growing operationalization of ecosystem services in incentivizing salt marsh conservation and restoration. Ecosystem service quantification and valuation is already playing an important role in decision-making by coastal risk managers, insurers, engineers, and policy makers. While there are legitimate criticisms of valuation techniques and remaining uncertainties in ecosystem service delivery that arise both through natural variability across space and time and through differing and shifting cultural values, our perspective is that the rise of big data, the development of valuation techniques, a growing understanding and application of environmental justice practices, and increasing interdisciplinarity to tackle these complex issues are paving the way for valuation to play a critical role in decision-making around salt marshes. [ABSTRACT FROM AUTHOR]

Widespread invasion by non-native, submerged aquatic vegetation (SAV) may modify the sediment budget of an estuary, reducing the availability of inorganic sediment required by marshes to maintain their position in the tidal frame. The instantaneous trapping rate of suspended sediment in SAV patches in an estuary has not previously been quantified via field observations. In this study, flows of water and suspended sediment through patches of invasive SAV were measured at three tidally forced, freshwater sites, all located within the Sacramento-San Joaquin Delta in California. An acoustic Doppler current profiler deployed from a roving vessel provided velocity and backscatter data used to quantify fluxes of both water and suspended sediment. Sediment trapping efficiency, defined as instantaneous net trapped flux divided by incident flux, was positive in 24 of 29 cases, averaging + 5%. Coupled with 3 years of measured sediment flux data at one site, this suggests that trapping averages 3.7 kg m−2 year−1. This estimate compares favorably with the mean mass accumulation rate of 3.8 kg m−2 year−1 estimated from dated sediment cores collected at the study sites. Long-term measurements made upstream reveal a strong negative trend (− 1.8% year−1) in suspended sediment concentration, and intra-annual changes in both suspended sediment concentration and percent fines. The large footprint and high spatial density of invasive SAV coupled with declining sediment supply are diminishing downstream suspended sediment concentrations, potentially reducing the resiliency of marshes in the Delta and lower estuary to future sea-level rise. [ABSTRACT FROM AUTHOR]

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.

Wetlands export chromophoric dissolved organic matter (CDOM) to estuaries, where CDOM is removed and transformed through biotic and abiotic process, subsequently impacting nutrient cycling, light availability, ecosystem metabolism, and phytoplankton activity. We examined the bioavailability and photoreactivity of CDOM exported from four Chesapeake Bay tidal marshes across three seasons and along an estuarine salinity gradient using three incubation treatments: 14‐day microbial (MD), 7‐day combined photochemical/microbial (PB + MD), and 7‐day microbial incubation after photobleaching (MD after PB). CDOM absorption at 300 nm (aCDOM300) and dissolved organic carbon (DOC) concentrations showed strong seasonality, with minima in winter, but CDOM quality (absorption spectral slopes, fluorescence component ratios) was less variable seasonally. PB + MD over 7 days decreased aCDOM300 (−56.0%), humic‐like fluorescence (−67.6%), and DOC (−17.8%), but increased the spectral slope ratio SR (=S275–295/S300–350) (+94.8%), suggesting a decrease in CDOM molecular weight. Photochemistry dominated the PB + MD treatment. Photoreactivity was greater during the winter and in marsh/watershed versus down‐estuary sites, likely due to less previous light exposure. Prior photobleaching increased the bioavailability of marsh‐exported CDOM, resulting in a greater loss of aCDOM300 and DOC, and a greater increase in humic‐like fluorescence (−6.0%, −5.9%, and +18.4% change, respectively, over 7‐day MD after PB incubations, vs. −2.8%, −5.5%, and +2.6% change, respectively, over 14‐day MD incubations). CDOM exported from a marsh downstream of a major wastewater treatment plant showed the greatest photoreactivity and bioavailability. This highlights the significance of human activity on estuarine CDOM quality and biogeochemical cycles. Plain Language Summary: Marshes are sources of colored dissolved organic matter (CDOM) to estuaries, where CDOM can be transformed or removed by ultraviolet (UV) radiation or microbes. We examined CDOM susceptibility to UV radiation and microbial degradation from four Chesapeake Bay marshes and along a down‐estuary salinity gradient, using incubation experiments with samples collected in the summer, fall, and winter. Our results showed that although more CDOM is exported by marshes in the summer, the quality of this material (based on optical proxies for CDOM composition) was consistent seasonally and interannually. Microbial processing removed a small, but significant, amount of CDOM and increased the contribution of humic‐like CDOM typically associated with terrestrial sources. Microbial degradation combined with UV exposure decreased the amount of CDOM and the contribution of humic‐like CDOM. Microbial degradation after exposure to UV light resulted in a greater loss of DOC and more production of humic‐like CDOM compared to microbial degradation alone, suggesting exposure to light enhances the microbial utilization of marsh‐exported CDOM. A marsh downstream of a major wastewater treatment plant exported CDOM that was more susceptible to UV and microbial degradation, suggesting that human activity can have significant effects on estuarine biogeochemical cycles, water quality, and ecosystem productivity. Key Points: Marsh dissolved organic matter export showed strong seasonal dependence, but seasonal variability in its quality was significantly lowerExposure to light increased the bioavailability of marsh‐exported chromophoric dissolved organic matter (CDOM)Photobleaching decreased humic‐like CDOM fluorescence, but increased microbial production of humic‐like CDOM fluorescence [ABSTRACT FROM AUTHOR]

Tidal marsh restoration and creation is growing in popularity due to the many and diverse sets of services these important ecosystems provide. However, it is unclear what conditions within constructed settings will lead to the successful establishment of tidal marsh. Here we provide documentation for widespread and rapid development of tidal freshwater wetlands for a major urban estuary as an unintended result of early industrial development. Anthropogenic backwater areas established behind railroad berms, jetties, and dredge spoil islands resulted in the rapid accumulation of clastic material and the subsequent initiation of emergent marshes. In one case, historical aerial photos document this transition occurring in less than 18 years, offering a timeframe for marsh development. Accretion rates for anthropogenic tidal marshes and mudflats average 0.8–1.1 and 0.6–0.7 cm year−1, respectively, equivalent to two to three times the rate of relative sea level rise as well as the observed accretion rate at a 6000+ year‐old reference marsh in the study area. Paired historical and geospatial analysis revealed that more than half of all the tidal wetlands on the Hudson River were likely triggered by anthropogenic development since the onset of the industrial era, including two‐thirds of the emergent cattail marsh. These inadvertently constructed tidal wetlands currently trap roughly 6% of the Hudson River's sediment load. Results indicate that when sediment is readily available, freshwater tidal wetlands can develop relatively rapidly in sheltered settings. The study sites serve as useful examples to help guide future tidal marsh creation and restoration efforts. [ABSTRACT FROM AUTHOR]