Groundwater Carbon Exports Exceed Sediment Carbon Burial in a Salt Marsh

• Published in: Estuaries and coasts 2022-09, Vol.45 (6), p.1545-1561
• Main Authors: Correa, Rogger E., Xiao, Kai, Conrad, Stephen R., Wadnerkar, Praktan D., Wilson, Alicia M., Sanders, Christian J., Santos, Isaac R.
• Format: Article
• Language: English
• Subjects: Blue carbon; Carbon capture and storage; Carbon cycle; Carbon dioxide; Carbon dioxide emissions; Carbon sequestration; Carbon sources; Coastal carbon; Coastal Sciences; Coastal wetland; discharge sgd; Dissolved inorganic carbon; Dissolved organic carbon; Earth and Environmental Science; Ecology; Emissions; Environment; Environmental Management; Environmental Sciences & Ecology; estuarine research reserve; Exports; Fluxes; Freshwater & Marine Ecology; gas-exchange; Groundwater; Inlets (waterways); inorganic carbon; Lead isotopes; Marine & Freshwater Biology; Mass balance; north inlet estuary; nutrient inputs; Oceanografi, hydrologi, vattenresurser; Oceanography, Hydrology, Water Resources; organic-carbon; porewater exchange; Radioactive tracers; Radon; Salt marshes; Saltmarshes; Sediment; Sediments; Soil erosion; south-carolina; Submarine groundwater discharge; Surface water; time-series; Water and Health
• ISSN: 1559-2723; 1559-2731
• DOI: 10.1007/s12237-021-01021-1

Salt marshes can sequester large amounts of carbon in sediments, but the relation between carbon storage and exportation remains poorly understood. Groundwater exchange can flush sediment carbon to surface waters and potentially reduce storage. In this study, we estimated groundwater fluxes and associated carbon fluxes using a radon ( 222 Rn) mass balance and sediment carbon burial rates using lead ( 210 Pb) in a pristine salt marsh (North Inlet, SC, USA). We used δ 13 C to trace carbon origins. We found that groundwater releases large amounts of carbon to the open ocean. These groundwater fluxes have the potential to export 7.2 ± 5.5 g m −2 of dissolved inorganic carbon (DIC), 0.2 ± 0.2 g m −2 of dissolved organic carbon (DOC) and 0.7 ± 0.5 g m −2 of carbon dioxide (CO 2 ) per day. The fluxes exceed the average surface water CO 2 emissions (0.6 ± 0.2 g m −2 day −1 ) and the average sediment carbon burial rates (0.17 ± 0.09 g m −2 day −1 ). The δ 13 C results suggest that groundwater carbon originated from salt marsh soils, while the sediment carbon source is derived from salt marsh vegetation. We propose that the impact of salt marshes in carbon cycling depends not only on their capacity to bury carbon in sediments, but also on their high potential to export carbon to the ocean via groundwater pathways.