Modelling of anoxic conditions formation as an example of the Black Sea

Abstract

A model describing nitrogen and sulfur cycles in suboxic and anoxic conditions is considered. The modeled vertical distributions of nitrogen compounds (total organic nitrogen, ammonium, nitrate, nitrite) and inorganic reduced sulfur compounds (hydrogen sulfide, elemental sulfur, thiosulfate, sulfate) as well as dissolved oxygen are adequately corresponded to the observed situation.

The model takes into account the processes of turbulent diffusion, sedimentation and biogeochemical transformation of compounds.

On the base of the model it was demonstrated, that the anoxic and suboxic conditions form because of organic matter mineralization in condition of restricted oxygen influx. The vertical distribution of rates of sulfur and nitrogen cycles processes were calculated within the frames of the model.

According to model the total amount of gaseous nitrogen formation connected with denitrification equals 1 Tg N/yr for all the Black Sea. Numerical experiments with the model show the the process of anoxic conditions formation conected with dam construction and increaing of flux of organic matter.