In situ Measurements of Nutrient and Oxygen Fluxes in a Coastal Marine Benthic Community

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Abstract
Benthic nutrient and oxygen fluxes were measured during summer in the nearshore zone of the Georgia Bight, USA. NH4+, NO2- NO3- and PO43- were released by the sediments to the overlying water, while dissolved organic nitrogen was taken up by sediments. Oxygen uptake was equivalent to 1.1 g cm-2 d-1 [d = day]. Based on other data available for this area the benthos accounted for the remineralization of approximately 55% of net primary production and 25% of total community (benthic and pelagic) metabolism. To balance a simple C budget for the nearshore region during summer an outside source of organic matter, most likely originating in adjacent estuaries, is required. The benthos supplied 16% of the N and 53% of the P required by phytoplankton. Pore water nutrient concentrations suggested substantial denitrification (estimated at 4.9 mg N m-2 d-1 by mass balance) in sediments which may have caused the low N:P benthic release ratios observed. The results support the hypothesis that benthic processes in shallow marine areas control the availability of N and P for water column production.