Carbon Storage in the Soils of a Mesotidal Gulf of Maine Estuary

Abstract

Estuaries have the highest primary productivity of all ecosystems, yet the soils in estuarine environments have been largely overlooked in C sequestration studies. This research quantified organic C stored in the top 1 m of soils from the Taunton Bay estuary in Hancock County, Maine. Taunton Bay is centrally located within Maine's Island–Bay Coastal Complex, a physiographic region that encompasses 47% of the state's coastline. Riverine inputs of sediments and sediment‐associated organic matter to this and most Maine estuaries are quite low. These estuary soils form by incremental additions of reworked glaciofluvial marine sediments and estuarine organic matter to the soil surface. The organics are protected from decomposition by anaerobic conditions. As sea level rises, the estuary area increases by inundating and submerging the soils at its edges. The average concentration of soil organic C in the top 1 m of these estuary soils is 2.4% and the average soil bulk density is 0.67 g cm−3 The organic C content is 136 Mg C ha−1, which is greater than the C content in the top 1 m of Maine's upland soils. These results suggest that systematically quantifying and dating the C in estuarine soils will provide valuable data for use in regional and global C budgets and climate models.