Abstract
In anoxic conditions the oxidation of organic matter occurs in different stoichimetric reactions. Therefore modelling of oxic/anoxic transformation requires parameterization of the cycles of several elements simultaneously, in contrast to models dealing only with nutrient cycles under oxic conditions, where it is possible to use the Redfield ratios. An O-N-S-Mn model is considered to describe the biogeochemical sources. Rates of biochemical processes mediated by bacteria are described by first-order equations using semiempirical functions of O2 concentration.
The processes of turbulent diffusion, sedimentation, and biogeochemical transformation of compounds were parameterized in the frames of one-dimensional and two-dimensional coupled models. The model was calibrated using data observed for the vertical distribution of compounds in the upper layers of the Black Sea. The calculated spatial distributions of nitrogen compounds (total organic nitrogen, ammonium, nitrate, nitrite), inorganic reduced sulfur compounds (hydrogen sulfide, elemental sulfur, thiosulfate, sulfate), dissolved and particulate manganese, as well as dissolved oxygen agree reasonably well with the observations.
Model estimations confirm that the existence of anoxic conditions is controlled primarily by the peculiarities of organic matter decay (a consequence of oxidant consumption) in conjunction with restricted aeration. According to the model simulations, the most sensitive hydrochemical parameters from point of view of vertical advection anomalies are particulate manganese, organic matter and elemental sulphur. The results of work undertaken so far suggests that future development of the model should concentrate on the improvement of parameterization of peculiarities of sedimentation connected with manganese cycle, organic matter balance, and the use of hydrophysical model results for the description of advection and diffusion.
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Yakushev, E.V. (1999). An Approach to Modelling Anoxic Conditions in the Black Sea. In: Beşiktepe, S.T., Ünlüata, Ü., Bologa, A.S. (eds) Environmental Degradation of the Black Sea: Challenges and Remedies. NATO Science Series, vol 56. Springer, Dordrecht. https://doi.org/10.1007/978-94-011-4568-8_7
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DOI: https://doi.org/10.1007/978-94-011-4568-8_7
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