An organic geochemical record of inland migration in a coastal marsh, Chesapeake Bay, Maryland, USA

Abstract

Organic matter accumulation in marsh soils affects marsh survival under rapid sea level rise (SLR). This work describes the changing organic geochemistry of a salt marsh located in Blackwater National Wildlife Refuge on the eastern shore of Chesapeake Bay that is transgressing inland with SLR. Marsh soils and vegetation were sampled along an elevation gradient from the intertidal zone to the adjacent forest. Stable carbon isotope analysis of bulk organic matter suggests a broad transition towards C4-dominated marsh vegetation over time. Vegetative source of the organic matter shifts along a marsh-upland mixing line from herbaceous angiosperm-sourced lignin in the low marsh to a woody gymnosperm signature at the upper border of the marsh. Stable isotope and lignin chemistry results illustrate that landward encroachment of marsh grasses results in deposition of herbaceous tissues that exhibit relatively little decay. This presents a possible mechanism for organic matter stabilization as marshes migrate inland.