The formation of atmospheric nitrogen gas by denitrifying bacteria may represent a significant nutrient sink in natural ecosystems. The rate of denitrification has often been difficult to measure in situ, however, and new methodologies should stimulate research on distribution of activity in space and time. The load of fertilizer nitrogen in modem agriculture has led to increasing nutrient reservoirs in recipient subsoils, aquifers, inland waters and coastal seas. By its conversion of nitrate to atmospheric nitrogen, bacterial denitrification is the only biological process to potentially...