Much uncertainty exists about the vulnerability of valuable tidal marsh ecosystems to relative sea level rise. Previous assessments of resilience to sea level rise, to which marshes can adjust by sediment accretion and elevation gain, revealed contrasting results, depending on contemporary or Holocene geological data. By analyzing globally distributed contemporary data, we found that marsh sediment accretion increases in parity with sea level rise, seemingly confirming previously claimed marsh resilience. However, subsidence of the substrate shows a nonlinear increase with accretion. As a result, marsh elevation gain is constrained in relation to sea level rise, and deficits emerge that are consistent with Holocene observations of tidal marsh vulnerability.

The generality of ecological patterns depends inextricably on the scale at which they are examined. We investigated patterns of crab distribution and the relationship between crabs and vegetation in salt marshes at multiple scales. By using consistent monitoring protocols across 15 U.S. National Estuarine Research Reserves, we were able to synthesize patterns from the scale of quadrats to the entire marsh landscape to regional and national scales. Some generalities emerged across marshes from our overall models, and these are useful for informing broad coastal management policy. We found that crab burrow distribution within a marsh could be predicted by marsh elevation, distance to creek and soil compressibility. While these physical factors also affected marsh vegetation cover, we did not find a strong or consistent overall effect of crabs at a broad scale in our multivariate model, though regressions conducted separately for each site revealed that crab burrows were negatively correlated with vegetation cover at 4 out of 15 sites. This contrasts with recent smaller-scale studies and meta-analyses synthesizing such studies that detected strong negative effects of crabs on marshes, likely because we sampled across the entire marsh landscape, while targeted studies are typically limited to low-lying areas near creeks, where crab burrow densities are highest. Our results suggest that sea-level rise generally poses a bigger threat to marshes than crabs, but there will likely be interactions between these physical and biological factors. Beyond these generalities across marshes, we detected some regional differences in crab community composition, richness, and abundance. However, we found striking differences among sites within regions, and within sites, in terms of crab abundance and relationships to marsh integrity. Although generalities are broadly useful, our findings indicate that local managers cannot rely on data from other nearby systems, but rather need local information for developing salt marsh management strategies.

Measures of extreme climate variability around Chesapeake Bay have changed over the past century (1895–2014), resulting in the need to establish new baselines for understanding future change. Here, observed climate variability is compared with Coupled Model Intercomparison Project fifth assessment climate models to evaluate ensemble model skill in this region. Observed trends include annual and seasonal declines in the percentage of cold days. Similarly, increases in the annual and seasonal percentages of warm days occurred in all seasons of the North Chesapeake (>38.2°N) but were only significant in spring and summer in the South (<38.2°N) demonstrating regional differences even at local scales. Precipitation intensity increased over the past century. Models using emissions scenarios RCP4.5 and 8.5 project these trends will continue, though they have little skill in precipitation extremes. Pacific and Atlantic climate modes are generally more correlated with climate extremes than mean temperature and precipitation suggesting potential predictability in the synoptic patterns underlying the extremes. However, they also drive the need for time series at least 60‐years long for establishing climate trends. This local analysis differs from regional, state level, and local 2.5° × 3.75° grid analyses, highlighting the importance of local climate assessments that consider topographic and regional weather patterns.

No abstract

Terrestrial-aquatic interfaces such as salt marshes, mangroves, and similar coastal wetlands occupy only a small fraction of the Earth's surface but account for at least 50% of the total carbon sequestration to ocean ecosystems (Duarte et al., 2005). Carbon sequestered and stored in coastal ecosystems and oceans is known as blue carbon (Mcleod et al., 2011) and there is a need to improve Earth system models across such coastal interfaces (Ward et al., 2020). These ecosystems are carbon-rich and play important roles in greenhouse gas biogeochemistry and the cycling of nutrients, including nitrogen (N) and phosphorus (Mcleod et al., 2011). The rapid loss (1%-3%/yr) of these coastal ecosystems, due to a variety of natural and anthropogenic disturbances, results in substantial impacts on carbon sequestration, carbon storage capacity, and nutrient cycling Abstract Measurements of atmospheric ammonia (NH 3 ) concentrations and fluxes are limited in coastal regions in the eastern U.S. In this study, continuous and high temporal resolution measurements (5s) of atmospheric NH 3 concentrations were recorded using a cavity ring-down spectrometer in a temperate tidal salt marsh at the St Jones Reserve (Dover, DE). Micrometeorological variables were measured using an eddy covariance system which is part of the AmeriFlux network (US-StJ). Soil, plant, and water chemistry were also analyzed to characterize the sources and sinks of atmospheric NH 3 . A new analytical methodology was used to estimate the average ecosystem-scale diurnal cycle of NH 3 fluxes by replicating the characteristics of a chamber experiment. This virtual chamber approach estimates positive surface fluxes in continuing strongly stable conditions when mixing with the air above is minimal. Our findings show that tidal water level may have a significant impact on NH 3 emissions from the marsh. The largest fluxes were observed at low tide when more soil was exposed. While it is expected that NH 3 fluxes will peak when the air temperature maximizes, high tide occurred concurrently with midday peaks in solar irradiance led to a decrease in NH 3 fluxes. Furthermore, soil, plant, and water chemistry measurements underpinning the NH 3 concentrations and fluxes lead us to conclude that this coastal wetland ecosystem can act as either a sink or a source of NH 3 . Such measurements provide novel data on which we can base reliable parameterizations to simulate NH 3 emissions from coastal salt marsh ecosystems using surface-atmosphere transfer models. Plain Language SummaryCoastal wetlands such as salt marshes, mangroves, and seagrasses provide a natural environment for the sequestration and long-term storage of carbon dioxide (CO 2 ) from the atmosphere. As a fertilizer, nitrogen (N) increases the vegetative growth and thus more CO 2 may be fixed in plants as biomass representing the short-term storage pool of carbon, therefore reducing its atmospheric level. Salt marshes, in particular, have been identified as being highly effective at carbon sequestration as well as a...