ABSTRACT
Nitrogen is an essential macroelement for all living organisms in the biosphere. As a major component of proteins and nucleic acids, nitrogen is one of the most limiting nutrients regulating the productivity in terrestrial, wetland, and aquatic ecosystems. 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. The ionic form is present under acidic soil conditions, whereas the un-ionized, gaseous form is present under alkaline conditions. Ammonia is also absorbed on a soil cation exchange complex or fixed in the crystal lattice of clay minerals. Nitrate is readily soluble in water and highly mobile in soils. Nitrification of ammonia N in soil is a source of nitrate.
