Seasonal Hydrology at the Salt Marsh‐Upland Interface

Abstract Sea level rise and storm surges are salinizing coastal areas, transforming forests and agricultural fields into salt marshes. This study examines seasonal variations in soil and groundwater hydrology at the transition zone between salt marshes and upland areas along the Mid‐Atlantic coast of the USA. We apply Linear Discriminant Analysis to data sets of soil moisture, soil conductivity, soil temperature, water table depth, groundwater salinity, and groundwater temperature to identify and categorize patterns within hydrological data. We further used Canonical Correlation Analysis to determine relationships between vegetation characteristics (greenness and Basal Area (BA)), soil composition (fraction of clay and sand), and hydrological parameters (groundwater level, groundwater specific conductivity, soil water content, and soil conductivity). Our analysis indicates that storm surges increase spatial variations in seasonal subsurface hydrological conditions among sites, as each location responds differently to disturbance. This heightened inter‐site variability contrasts with previous findings of storm‐driven homogenization within individual sites. By summer, sites become more homogeneous as hydrological variability decreases, indicating that vegetation gradients along the marsh–forest ecotone are mainly governed by winter and spring conditions. Vegetation characteristics (BA and greenness) are more strongly associated with soil water than with groundwater characteristics. Vegetation greenness also correlates closely with soil water conditions in fall and winter, when site differences are more pronounced. Groundwater salinity and water table depth are related to clay content in the soil. This regional‐scale comparison highlights the hydrological variability of the marsh‐upland boundary, how it is influenced by soil characteristics, and its relation to vegetation cover, offering insights for effective adaptation strategies to mitigate salinization and preserve coastal biodiversity.