Krivenko O. The dynamics of inorganic nitrogen uptake by microplankton in the Black Sea

Subject: microplankton of the Black Sea. Aim: to evaluate the part of nitrate and ammonium in the formation of the Black Sea primary productivity. For the first time on the base of experimental data obtained during 1990 - 1993 period using 15N-method the main peculiarities of microplankton inorganic nitrogen uptake in the Black Sea were analyzed. The patterns of the forming of "new" and regenerated production and the factors determined their ratios were revealed. The provision of microplankton community with inorganic nitrogen compounds was estimated. It is shown nitrate and ammonium uptake rate vary from minimum values in winter to maximum one's in summer. The share of "new" production and integral nitrate content in the euphotic zone connected with hyperbolic dependency. In the deep-water area of the sea 0,52 molN/m2/year or 44 gС/m2/year "new" production are formed at the mean that amount 39% from the annual phytoplankton primary production. Average nitrate and ammonium concentration in the surfaceand the half-saturated constants for their uptake by microplankton are equal. Environmental content of inorganic nitrogen compounds limit their uptake rates and phytoplankton growth in the Black Sea from one at half to twice times. The degree of microplankton nitrogen provision decrease three to five times at the condition of nitrate and ammonium reserve depletion in the euphotic zone.