Estimation of Nutrient Load on the Kuibyshev Reservoir From the Catchment Area

The present level of external nutrient load and its separate parts on the Kuibyshev reservoir — the largest one on the Eurasian continent, was estimated. The mathematic model for calculating mean annual input of nitrogen and phosphorus from river drainage areas of non-homogeneous structure, and load on water bodies was developed. The main components of the load are the nonpoint nutrient emission by the underlying surface which is currently not affected by agricultural impact, the load generated by agricultural activity, discharges of pollutants from point sources into the hydrographic network of the catchment area and directly into the water-receiving reservoir, and the mass exchange with the atmosphere. The model includes calculating the retention of chemicals by catchments and by their hydrographic network. The model was calibrated against the data of State monitoring for the pilot areas: the catchment area of the Kazanka river (the left bank tributary) and the Sviyaga (the right bank tributary). The nutrient load generated by discharges from point sources of pollution was estimated using statistical reporting data. The values of atmospheric deposition of nitrogen and phosphorus on the surface of the study catchments were calculated using the data of field studies on the chemical composition of deposits. It is shown that implementation of the best available technologies into agricultural practice will not lead to any significant reduction in the nutrient load on the reservoir, because in recent years across most of the study area the rates of application of nutrients with organic and mineral fertilizers have been lower than the average removal of nitrogen and phosphorus with the harvested crops. An approximate estimation of nutrient load on the Kuibyshev reservoir was carried out for the left and the right bank sides of the catchment area. The background (natural) and diffuse (anthropogenic) components of the load are identified