Nitrogen cycling and controls on denitrification in mesohaline sediments of Chesapeake Bay

Nitrogen is a key nutrient in the eutrophication of coastal and estuarine systems. In shallow water systems, sediment recycling can be an important source of nutrients for phytoplankton growth. The balance between nitrogen recycling and denitrification regulates the importance of sediments as a nitrogen source. To assess controls on denitrification, we conducted intensive seasonal measurements of sediment water exchange and denitrification using sediment core incubations. Peak rates of denitrification were observed in fall and spring (>100 mumol N2-N m-2 h-1) followed by a decrease to 10 mumol N m-2 h-1 in summer. Although denitrification rates were stimulated by labile organic carbon additions from the water column, the overall efficiency of the process sharply declined as temperature increased and bottom water O2 declined. Macrofauna activity was shown to enhance sediment transport of O2 by >5 fold, increase organic matter decomposition and maintain a high rate of denitrification efficiency.