Monday, November 13, 2006 - 11:10 AM

Carbon Storage in the Estuarine Soils: The Missing Sink?.

Laurie Osher, Univ of Maine, 5722 Deering Hall, Orono, ME 04469-5722

Estuaries have the highest rates of conversion of atmospheric CO2 into biomass of any ecosystem in the world. Although the shallow subtidal and unvegetated intertidal component of an estuary often compose 40 to 90% of the estuarine area, only C of coastal marsh ecosystems have been quantified and included as potential sinks in global carbon cycle models. This was, in part, because the spatial distributions of estuarine components had not been identified in local, regional or global scale maps. The situation is also an artifact of our history: Until recently, soil scientists did not consider these submerged sediments as soils, and thus did not apply the tools of soil science to measure chemical and physical properties. In Maine, we've observed that 2.4% C is the average concentration of soil organic C in the top meter of submerged soils in a typical Maine estuary. The high surface soil n-values (>0.7) and low mean bulk densities (< 1.0 g cm-3) of these soils contribute to the organic C storage in the top 1m being similar to those reported for Maine’s upland forest soils (136 Mg C ha-1). However, the mean residence time of C at a meter depth in upland forest soils is thousands of years, but the C in the top meter of most estuarine soils has been deposited in the last few hundred years. In addition, more C is buried annually as sea level continues to rise. These results suggest that including the estimated annual flux of C from the atmosphere to non-marsh estuarine soils will account for much of the C missing from the annual global carbon budget.