Marsh Migration into Forests and Farms: Effects on Soil Biogeochemistry Along the Salinity Gradients

jabbrv-ltwa-all.ldf jabbrv-ltwa-en.ldf Sea level rise (SLR) and increased storm intensity cause landward expansion of intertidal zones in the low-lying Delmarva Peninsula, allowing marsh migration into forests and agricultural (ag) fields. Transitional zones along the marsh-forest and marsh-ag transects are visible aboveground as ghost forests and crop die-off, respectively. While the aboveground impacts of marsh migration are clear, how marsh migration affects belowground biogeochemistry is understudied. To characterize the impacts of marsh migration on soil biogeochemistry, we collected soil cores from marsh-forest and marsh-ag transects at 6 different sites (i.e., 3 marsh-ag and 3 marsh-forest) along the Delmarva Peninsula. Soil cores were analyzed for both porewater chemistry and solid-phase characterization. Marsh end members support sulfate reduction; transitional zones support iron reduction; and upland end members support aerobic metabolisms at the surface, with Fe reduction occurring at depth. In addition, the quality and quantity of dissolved organic matter changed across the transects, indicating differences in carbon source and cycling dynamics. Furthermore, our results show that soil carbon concentration varies drastically from lowland marsh to adjacent forest and ag uplands. Marshes have 4-50 times more soil carbon than their upland endmembers. The migrating marsh layer of soil was characteristic of a typical anaerobic wetland (i.e., low EH, high silt, high C), but was relatively thin and is underlain by typical upland aerobic soil (i.e., high EH, low silt, low C). These findings have important implications for better understanding the incremental and belowground effects of sea level rise on coastal forests and agricultural lands.