FLUXES OF DISSOLVED ORGANIC-CARBON FROM CHESAPEAKE BAY SEDIMENTS

Benthic fluxes of dissolved organic carbon (DOC) were measured over an annual cycle at two contrasting sites in Chesapeake Bay. At an organi c-rich, sulfidic site in the mesohaline portion of the Bay (site M) DO C fluxes from the sediments ranged from 1.4 to 2.9 mmol/m2/d. Measured benthic DOC fluxes at site M corresponded to approximately 3-13% of t he depth-integrated benthic C remineralization rates (SIGMAOCR), and a greed well with calculated diffusive DOC fluxes based on porewater DOC profiles. This agreement suggests that DOC fluxes from site M sedimen ts were likely controlled by molecular diffusion. The second site that was studied is a heavily bioturbated site in the southern Bay (site S ). The activity of macrobenthos did not appear to enhance DOC fluxes f rom these sediments, since measured benthic DOC fluxes (<0.5 mmol/m2/d ) were lower than those at site M. The ratios of benthic DOC fluxes to SIGMAOCR values at site S were also slightly smaller than those obser ved at site M. Benthic DOC fluxes from Chesapeake Bay sediments do not appear to significantly affect the transport of DOC through this estu ary, although uncertainties in the reactivity of DOC in estuaries make s this conclusion somewhat tentative at this time. However, when these results are used to make a lower limit estimate of the globally integ rated benthic DOC flux from marine sediments, a value similar to that previously calculated by BURDIGE et al. (1992) is obtained. This obser vation further supports suggestions in this paper about the importance of benthic DOC fluxes in the oceanic C cycle.