CARBON CYCLING IN MESOHALINE CHESAPEAKE BAY SEDIMENTS .1. POC DEPOSITION RATES AND MINERALIZATION PATHWAYS

Organic carbon cycling in sediments at two locations in the mesohaline Chesapeake Bay was analyzed using available data on sediment sulfate reduction, sediment oxygen consumption, and particulate organic carbon (POC) deposition and burial. Estimates of POC deposition based on the sum of integrated sediment metabolism and POC burial compared well wi th direct estimates derived from chlorophll-a collection rates in mid- water column sediment traps. The range of POC deposition estimates (15 -31 mol C m(-2) yr(-1)) accounted for a large fraction (36-74%) of ave rage annual net primary production in the mesohaline Bay. The differen ce between rates of POC deposition and permanent burial indicated that 70-85% of deposited carbon is mineralized on the time scale of a year . Carbon mineralization through sulfate reduction accounted for 30-35% of average net primary production, and was likely responsible for 60- 80% of total sediment carbon metabolism Oxidation of reduced sulfur ac counted for a large but quantitatively uncertain portion of SOC in mid -Bay sediments. Our results highlight the quantitative significance of organic carbon sedimentation and attendant anaerobic sediment metabol ism in the carbon cycle of a shallow, highly productive estuary.