Nitrogen cycle in marine sediments

Nitrogen is considered to be a limiting nutrient for marine primary production, and the cycling of nitrogen is, therefore, an important factor in the regulation of primary production. Part of the mineralization of algal nitrogen occurs in the sediment, and two methods have been used to investigate this process: 1) measurement of the amount of algal nitrogen that falls to the sediment surface, and 2) measurement of the amount of mineralized nitrogen that leaves the sediment to the water column. As a supplement to the second method, the actual rates of nitrogen mineralization may be assessed by measuring the net and total rates of ammonium production, the latter using a 15N-ammonium dilution technique. In addition, by measuring rates of nitrification, denitrification, nitrogen fixation and ammonium binding, the availability of ammonium and nitrate for diffusion from the sediment may be determined and compared with the measured sediment-water fluxes. All these processes are influenced to some extent by the benthic fauna.