Phenomenal changes in the forms of nitrogen: results from a coastal zone of south west India

Abstract

A unique phenomenon along the south west cost of India triggers an active fisheries season with the advent of “mudbanks”. These regions, better described as “zones of biorhythm”, involve different forms of nitrogen which act as nutrients during the propagation of mudbanks. High concentrations of urea and ammonia were observed prior to the formation of mudbanks, signifying the availability of different forms of nitrogen for later assimilation from a reservoir pool. In common with many features of upwelling areas, the variability of nitrite concentration under different phases of the biorhythm is brought about by the processes involved in the nitrification-denitrification process. The marked increase in the concentration of organic nitrogen as compared to a non-mudbank area is indicative of the presence of organically webbed forms of nitrogen. This organic form acted as a “reserved nutrient” (or inducer) for near-future utilisation subsequent to the assimilation of inorganic nitrogen forms. The study emphasises the role of sediments in nitrate uptake and its regeneration which is related to forms of nitrate in the overlying water media.