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

Abstract

Benthic nutrient and oxygen fluxes were measured during summer in the nearshore zone of the Georgia Bight, USA. Ammonium, nitrite, nitrate and phosphate 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-* d-'. 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 carbon 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 Nm-2 d by mass balance) in sediments which may have caused the low N : P benthic release ratios we observed. The results support the hypothesis that benthic processes in shallow marine areas control the availability of N and P for water column production.