Deoxygenation and remineralization above the sediment-water interface; an in situ experimental study

Abstract

An in situ chamber of volume 3881 and bottom area 0·64 m 2 was used to determine the flux of oxygen and inorganic nutrients across an estuarine sediment-water interface over a 65-day period. Over the first 7 days, oxygen uptake was 378 mg m −2 day −1 and the rates of ammonium and phosphate release were 2·22 and 0·34 mg at. m −2 day −1, respectively. The water became anoxic in 14 days. The rates of flux in a similar chamber containing only detritus recently settled from the water column were 371 mg m −2 day −1 (oxygen), 1·66 mg at. m −2 day −1 (ammonium) and 0 12 mg at. m −2 day −1 (phosphate), demonstrating that detritus contributes substantially to exchange across the sediment-water interface. The evolution of the two chambers was similar over the latter part of the experimental period. A third chamber containing only water exhibited very minor changes. The role of detritus in nutrient recycling at the sediment-water interface is discussed in relation to the productivity of shallow water bodies such as the estuary in which the experiment was conducted, which itself undergoes periodic deoxygenation during prolonged stratification. The measured flux of nitrogen across the interface was found to represent approximately 31% of the mean daily phytoplankton requirement.