Nitrogen Transformations in Stream Sediments: 15 N Studies

Laboratory studies were carried out on sediment samples taken from a perennial stream draining an agronomic watershed. Columns of sediment were placed in acrylic plastic tubes, overlain with isotopically labeled nitrate, and incubated at 15°C. An optical emission spectrometer was used to determine the excess 1 5 N in each of the NO 3 , NH 4 , and organic nitrogen fractions at various times. It was concluded that the previously observed loss of nitrate from aerated water overlying stream sediment was indeed the result of denitrification. It was also established that nitrification and denitrification were proceeding simultaneously and that less than 2 percent of the added labeled nitrogen was immobilized.