Impact of sedimentation on wetland carbon sequestration in an agricultural watershed.
Landscape redistribution of soil C is common within agricultural ecosystems. Little is known about the effects of upland sediment deposition on C dynamics within riparian wetlands. To assess sedimentation impact, we obtained profile samples of wetland soil and used the combination of (137)Cs, (210)Pb, and (14)C chronological markers to determine rates of C sequestration and mineral deposition over the history of a wetland within a first-order catchment under agricultural management in the coastal plains of the United States. Substantial post settlement deposition in the wetland soil was evidenced in places by a 20- to 40-cm layer of mineral soil that buried the original histosol. Soil profiles contained a minimum in C content within the top 35 cm of the profile which originated from a rapid deposition from low C upland soils. Radiocarbon and radioisotope dating showed that increases in C above this minimum were the result of C sequestered in the past approximately 50 yr. Modeling the kinetics of modern C dynamics using the (137)Cs and (210)Pb markers within these surface profiles provides strong evidence for accelerated C sequestration associated with mineral sediment deposition in the ecosystem. These findings indicate that at the landscape scale, dilution of ecosystem C by import of low C upland sediment into wetlands stimulates C sequestration by pulling soil C content below some pedogenic equilibrium value for the ecosystem. They also indicate that over the history of the wetland, rates of C accretion may be linked to mineral soil deposition.
McCarty
Gregory
G
USDA-ARS Hydrology & Remote Sensing Lab. Building 007 BARC-West, Beltsville, MD 20705, USA. greg.mccarty@ars.usda.gov
Pachepsky
Yakov
Y
Ritchie
Jerry
J
D000383:Agriculture; D002244:Carbon / Q000032:analysis*; D002250:Carbon Radioisotopes / Q000032:analysis; D002588:Cesium Radioisotopes / Q000032:analysis; D019015:Geologic Sediments / Q000032:analysis*; D007856:Lead Radioisotopes / Q000032:analysis; D008956:Models, Chemical; D053833:Wetlands
D002250:Carbon Radioisotopes; D002588:Cesium Radioisotopes; D007856:Lead Radioisotopes; D002244:Carbon