The effect of sediment flushing by density displacement of interstitial water on pelagic primary production and microbial activity

Nutrient and oxygen levels and ratios, primary production and data on bacterial activity recorded during an enclosure experiment carried out in July/August 1974 in Kiel Bight are presented and discussed. Considerable amounts of nutrients were released from the sediments due to density displacement of interstitial water and this was found to have a direct effect on phytoplankton production. Ammonia levels outside the enclosure were low and, in contrast to other nutrients and oxygen which were highly correlated with each other, ammonia showed no correlation with any other parameter. Presumably, ammonia released from the sediments escaped detection due to rapid uptake by phytoplankton. Reactive nitrogen, specifically ammonia thus seemed to be the limiting factor for primary production during the experiment. Sediment flushing also led to increased bacterial numbers and activity in the water column, however, this effect could only be measured inside the enclosure. These aspects of sediment/water interaction and their effect on the dynamics of shallow coastal ecosystems are discussed