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Salt marshes are globally important ecosystems and thus their resilience to climate change holds societal importance. To date, studies addressing salt marsh responses to climate change have focused on sea‐level rise and biogeochemical feedbacks with increasing inundation. Less is known about how salt marsh sediment temperatures, which impact physical, biological, and chemical ecosystem processes, will respond to climate change. In this study, we present multi‐depth sediment temperature and porewater level data from low‐, mid‐, and high‐marsh sites at a New England salt marsh for a 1‐year period and investigate how salt marsh sediment temperatures respond to atmospheric and oceanic forcing. We use spectral analyses to identify the frequencies at which sediment temperatures vary and link the temperature variations to specific forcing mechanisms. We find that all sites across the marsh responded to air temperature with roughly equal amplitude whereas the responses to radiative heating and ocean tides varied spatially. The high‐marsh site is more sensitive to radiative heating than the mid‐ and low‐marsh sites. The low‐marsh is affected by tidal processes and inundation whereas the high‐ and mid‐marsh sites are not. In addition, we find that the bulk thermal diffusivity of the saturated sediments decreases with distance from the tidal channel. These factors contribute to considerable temporal and spatial variability in sediment temperatures with elevation, distance from the tidal channel, and time of year (season) being most important. [ABSTRACT FROM AUTHOR]

The availability and delivery of an external clastic sediment source is a key factor in determining salt marsh resilience to future sea level rise. However, information on sources, mechanisms, and timescales of sediment delivery are lacking, particularly for wave‐protected mesotidal estuaries. Here we show that marine sediment mobilized and delivered during coastal storms is a primary source to the North and South Rivers, a mesotidal bar‐built estuary in a small river system impacted by frequent, moderate‐intensity storms that is typical to New England (United States). On the marsh platform, deposition rates, clastic content, and dilution of fluvially‐sourced contaminated sediment by marine material all increase down‐estuary toward the inlet, consistent with a predominantly marine‐derived sediment source. Marsh clastic deposition rates are also highest in the storm season. We observe that periods of elevated turbidity in channels and over the marsh are concurrent with storm surge and high wave activity offshore, rather than with high river discharge. Flood tide turbidity also exceeds ebb tide turbidity during storm events. Timescales of storm‐driven marine sediment delivery range from 2.5 days to 2 weeks, depending on location within the estuary; therefore the phasing of storm surge and waves with the spring‐neap cycle determines how effectively post‐event suspended sediment is delivered to the marsh platform. This study reveals that sediment supply and the associated resilience of New England mesotidal salt marshes involves the interplay of coastal and estuarine processes, underscoring the importance of looking both up‐ and downstream to identify key drivers of environmental change. Plain Language Summary: Salt marshes need an external supply of mineral sediment to survive. Understanding sources and physical mechanisms of sediment delivery is therefore critical to effective salt marsh management. Sediment can be sourced from land and delivered to marshes through rivers, or it can come from the ocean during high tides and storm surges; however, the relative importance of these sediment sources is uncertain for most marshes. Here, we show that ocean sediment mobilized and delivered during coastal storms is the primary source to the North/South River estuary, a typical New England salt marsh system. Within the marsh platform, mineral sediment is most abundant near the ocean, and we find little river‐derived sediment beyond the most landward region of the estuary. In estuary channels, we also observe the greatest amounts of suspended sediment when incoming tides flood the estuary during coastal storms. In contrast, we do not observe elevated suspended sediment when river flow is high. Our work shows that coastal and marine processes influence sediment supply and the associated resilience of New England salt marshes, underscoring the importance of looking both up‐ and downstream to identify key drivers of environmental change. Key Points: Marine sediment mobilized and delivered during coastal storms is a primary source to a typical New England mesotidal salt marshSuspended sediment in the estuary is highly non‐stationary, with timescales of marine sediment delivery ranging from 2.5 days to 2 weeksFindings provide insight into sediment sources for small mesotidal estuaries and the more routine compounding impacts of annual storms [ABSTRACT FROM AUTHOR]

Thin Layer Placement (TLP) is an increasingly used management technique to promote coastal resilience to accelerated sea level rise, but it is unclear how differential thickness of dredged sediment application alters plant-soil carbon dynamics in northeastern Atlantic coast salt marshes. We initiated a field experiment in a microtidal Spartina alterniflora (smooth cordgrass) dominated salt marsh in Connecticut (USA) to examine how a silt-loam dredge applied at different thicknesses (low: +5 cm, medium: +10 cm, and high: +15 cm) altered biological and biogeochemical responses. Over two growing seasons we monitored plant responses (above and belowground biomass, stem height, stem density, leaf area) and soil-biogeochemical parameters (EC, pH, redox, NH 4 +, sulfides, C:N, decomposition, bulk density, carbon fluxes). We found adding 5–7 cm of dredged sediment promoted rapid revegetation, alleviated phytotoxic sulfides, enhanced CO 2 uptake, and reduced CH 4 emissions. Low treatments reached similar vegetation cover to controls after one growing season, though sediment treatments greater than 10-cm thick showed delayed growth. Low levels of sediment addition stimulated the highest root biomass in the underlying soil, promoting CO 2 efflux, but this was offset by aboveground biomass productivity, promoting net CO 2 uptake. Phytotoxic sulfides were reduced in all sediment addition treatments, but our data indicate that coastal managers aiming to promote rapid vegetative recovery while increasing elevation in the short term should target conservative depths (< 10 cm) when using fine-grained dredged material. Collectively, our work will guide wetland managers as they develop restoration specifications for perpetuating coastal marshes in the face of rising seas. [Display omitted] [ABSTRACT FROM AUTHOR]