Tidal marshes serve as important “blue carbon” ecosystems that sequester large amounts of carbon with limited area. While much attention has been paid to the spatial variability of sedimentation within salt marshes, less work has been done to characterize spatial variability in marsh soil carbon density. Soil properties in marshes vary spatially with several parameters, including marsh platform elevation, which controls inundation depth, and proximity to the marsh edge and tidal creek network, which control variability in relative sediment supply. We used lidar to extract these morphometric parameters from tidal marshes to map soil organic carbon at the meter scale. Fixed volume soil samples were collected in 2021 at four northeast U.S. tidal marshes with distinctive morphologies to aid in building predictive models. Tidal creeks were delineated from 1-m resolution topobathy lidar data using a semi-automated workflow in GIS. Log-linear multivariate regression models were developed to predict soil organic content, bulk density, and carbon density as a function of predictive metrics at each site and across sites. Results show that modeling salt marsh soil characteristics with morphometric inputs works best in marshes with single connected creek network morphologies. Distance from tidal creeks was the most significant model predictor. Addition of distance to the inlet and tidal range as regional metrics significantly improves cross-site modeling. Our mechanistic approach results in predicted total marsh carbon stocks comparable to previous studies but captures important meter level variation. Further, we provide motivation to continue rigorous mapping of soil carbon at fine spatial resolutions.

Non-linear turbidity-discharge relationships are explored in the context of sediment sourcing and event-driven hysteresis using long-term (≥12 year) turbidity observations from the tidal freshwater and saline estuary of the Hudson River. At four locations spanning 175 km, turbidity generally increased with discharge but did not follow a constant log-log dependence, in part due to event-driven adjustments in sediment availability. Following major sediment inputs from extreme precipitation and discharge events in 2011, turbidity in the tidal river increased by 20-50% for a given discharge. The coherent shifts in the turbidity-discharge relationship along the tidal river over the subsequent 2 years suggest that the 2011 events increased sediment availability for resuspension. In the saline estuary, changes in the sediment-discharge relationship were less apparent after the high discharge events, indicating that greater background turbidity due to internal sources make event-driven inputs less important in the saline estuary at interannual time scales.

Barrier inlets and marshes behind them are often viewed and managed as separate systems with independent controls because they are affected by different boundary conditions. Here, we make use of a 120-year-old storm-driven change in inlet location to illustrate how barrier beaches and wetland processes are intricately linked. Further, we show that tidal marshes can be resilient to a rapid increase in inundation given sufficient sediment supply and discuss implications for coastal management along sediment-deficient coastlines. In 1898, a coastal storm eroded a new inlet through the barrier beach that fronts the North-South Rivers Estuary in Massachusetts, USA. The old inlet silted in after the storm, and the change in inlet location shortened the North River channel by 5.6 km. After the inlet location change, historical records indicated increased high tide levels along the North River. We make use of this increase in water levels and associated marsh response to examine conditions that have allowed for marsh resilience after a rapid increase in inundation depth. Sediment cores show that increased mineral sediment deposition after 1898 played a dominant role in allowing marshes along the North River channel to adjust to greater inundation. To accommodate greater tidal flow after the change in inlet location, the North River channel widened by an average of 18%. Edge erosion from channel widening likely provided sediment to the marsh platform. Modern water level monitoring along the channel shows that mean high water declines landward by at 4.8 cm/km up to 10 km from the inlet. North River channel shortening thereby likely increased mean high water by at least 27 cm within the lower estuary. At present, the marsh platform elevation along both channels has largely reequilibrated to the effective change in sea level, with similar marsh inundation depths along both channels of the estuary. The role of mineral sediment in allowing for rapid marsh sediment deposition and resilience of this marsh to an abrupt increase in inundation depth points to the importance of management strategies that maintain sediment supplies to coastal regions.