Jonathan Maynard, Anthony O'Geen, and Randy Dahlgren. University of California-Davis, One Shields Ave, Davis, CA 95616
In the U.S., an estimated one third of all eroded material is deposited in small sediment sinks such as wetlands. Constructed and restored wetlands are being used in California to treat agricultural runoff, and may serve as important carbon sinks. This study examines the spatial and temporal dynamics of carbon and sediment accumulation to evaluate the potential for carbon sequestration in an eight-year-old seasonally saturated constructed wetland. Net sedimentation and net above-ground biomass were measured in 2004 and 2005. Sediment cores were collected to the antecedent (time zero) soil layer, which ranged between 2 and 50 cm below the surface. All samples were analyzed for total carbon. The spatial variability of carbon and sediment accumulation was modeled with geostatistics. Average sediment accumulation rate, nearly doubled from 2004 to 2005, with rates of 5.8 kg m-2 y-1 (range: 0-80 kg m-2 y-1) in 2004 and 11.9 kg m-2 y-1 (range: 0-93 kg m-2 y-1) in 2005. Average carbon accumulation rate did not change between years, with rates of 0.290 kg m-2 y-1 in 2004 and 0.294 kg m-2 y-1 in 2005, indicating a change in carbon source between years. Average carbon content in the top 2.5 cm of the wetland surface was 24 g kg-1 and decreased to 10 g kg-1 in sediment directly overlaying the antecedent layer. Average total carbon content of soils in the contributing watershed is 8 g kg-1. This indicates an enrichment of carbon in the surface layer due to the addition of endogenous carbon sources. Average carbon content in sediment directly above the antecedent layer was similar to topsoil in surrounding agricultural land, indicating no net loss of carbon from transported sediment. Wetlands can play a significant role in carbon storage through processes such as in-situ enrichment and protection of carbon deposited by erosion.
