Organic carbon dynamics in soils of Mid-Atlantic barrier island landscapes

Abstract

Geomorphic processes associated with coastal wetlands often result in high carbon accumulation rates and relatively large carbon stocks. Barrier islands are an important component of coastal ecosystems and freshwater and brackish wetlands on these islands provide an important habitat for a number of animal and plant species. However, organic carbon dynamics in these landscapes have received relatively little attention. The objective of this study was to document the accumulation of organic carbon and understand the factors influencing soil carbon dynamics on barrier islands. Ten topographic transects were established on different landforms on Assateague Island National Seashore, MD, USA. Soil organic carbon stocks, aboveground carbon inputs, and decomposition rates were compared among landforms (representing differing degrees of landform stability and soil age) and drainage conditions. Soil organic carbon stocks (0–1.0 m) ranged from 0.49 to 18.8 kg C m−2, and increased in magnitude with soil age. Higher carbon stocks in the older soils were partly attributed to the increased time over which carbon had accumulated. Additionally, a shift from herbaceous dominated to forest dominated plant communities led to greater carbon inputs in older soils. Carbon stocks were also greater in the very poorly and poorly drained soils (relative to drier soils) where high levels of carbon inputs (plant biomass) exceed decomposition rates, which were slowed under anaerobic conditions. While rates of carbon accumulation (average 0.021 kg C m−2 yr−1) are somewhat low compared to other more productive systems, barrier island soils have the potential to store large amounts of organic carbon (relative to other soils) as organic-rich surface horizons are buried during overwash events.