Effect of Elevated Co sub(2) on Carbon Pools and Fluxes in a Brackish Marsh

The effects of long-term exposure to elevated atmospheric CO sub(2) (ambient + 340 ppmv) on carbon cycling were investigated for two plant communities in a Chesapeake Bay brackish marsh, one dominated by the C sub(3) sedge Schoenoplectus americanus and the other by the C sub(4) grass Spartina patens. Elevated CO sub(2) resulted in a significant increase in porewater concentrations of DIC at 30 cm depth (p < 0.1). The CO sub(2) treatment also yielded increases in DOC (15 to 27%) and dissolved CH sub(4) (12-18%) in the C sub(3) marsh (means for several depths over the period of June 1998 and June 1999), but not at a significant level. Elevated CO sub(2) increased mean ecosystem emissions of CO sub(2) (34-393 g C m super(-2) yr super(-1)) and CH sub(4) (0.21-0.40 g C m super(-2) yr super(-1)) in the C sub(3) community, but the effects were only significant on certain dates. For example, CO sub(2) enrichment increased C export to the atmosphere in the C sub(3) community during one of two winter seasons measured (p = 0.09). In the C sub(4) community, gross photosynthesis responded relatively weakly to elevated CO sub(2) (18% increase, p > 0.1), and the concomitant effects on dissolved carbon concentrations, respiration, and CH sub(4) emissions were small or absent. We concluded that elevated CO sub(2) has the potential to increase dissolved inorganic carbon export to estuaries.