ABSTRACT
Nitrogen is one of the most limiting nutrients regulating the productivity in terrestrial, wetland, and aquatic ecosystems. These ecosystems contain a complex mixture of nitrogen compounds existing in both organic and inorganic forms. The relative proportion of each form depends on the sources of nitrogen entering these systems, and the relative rates and turnover times of these compounds. Organic forms are present in dissolved and particulate forms, whereas inorganic nitrogen (ammonium N, nitrite N, and nitrate N) is present in dissolved forms. Particulate forms are removed through settling and burial, whereas the removal of dissolved forms is regulated by various biogeochemical reactions functioning in soil and overlying water column. The relative rates of these processes are affected by physicochemical and biological characteristics of the soil and water column and the organic substrates present. Although the basic nitrogen transformations in terrestrial, wetland, and aquatic ecosystems are the same, relative rates and storages are different in each of these ecosystems.
