Turnover of 15NH4 + Tracer in Sediments

The main purpose in experimenting with the addition of ¹⁵NH₄⁺ to sediment is to obtain information on the dynamics of the NH₄⁺ pool in sediments. Most investigations of the nitrogen cycle in sediments are concerned with the determination of the extent to which the sediment is a source of mineralized nitrogen to the overlying water. When this is the purpose, net rates of change in the NH₄⁺ pool are the measurements of most interest. If the situation demands a more complete understanding of the processes which result in these net changes, then ¹⁵NH₄⁺ methods are very helpful. In anaerobic incubations, if there is an independent estimate of the rate of NH₄⁺ incorporation into microbial biomass, it is possible to calculate the probable C:N ratio of the PON, which is undergoing hydrolysis and degradation. A major problem arises after the addition of ¹⁵NH₄⁺ to sediment.