The Dissolved Non-organic Phosphorous Content in the Water of the Kuybyshev Reservoir
The intra-year variability of dissolved non-organic phosphorous content under the Kuybyshev Reservoir anthropogenic euthrophication conditions has been investigated on the basis of many-year observations. The observations were conducted on the Volga River during the 2000-2015 period in the vicinity of the Zhiguly Dam. The Kutbyshev Reservoir is located upstream from the dam and the Saratov Reservoir is located downstream. It has been stated that the phosphorous content in water has a pronounced seasonal variation while the amplitude of within-year fluctuations of the phosphorous content depends on the intensity of algae mass growth process. In comparison with 1950s the amplitude of within-year fluctuations of the phosphorous concentration has increased significantly and currently it is 0.001-0.0149 mgR/dm<sup>3</sup>, this confirms the fact of the Kuybyshev Reservoir anthropogenic euthriphication process intensification. It has been found that the seasonal changes in the phosphorous and chlorophyll «a» concentrations are in anti-phase. As soon as the phosphorous concentration becomes less than 0.010 mgR/dm<sup>3</sup>, algae growth stops. Thus, phosphorous dissolve in water is a critical factor of the algae growth in the reservoir water. Decrease of the phosphorous concentration in the Volga water will enable to mitigate intensity and duration of the water blooming period in the Kuybyshev Reservoir but for this end it is necessary to restrain the non-organic phosphorous input to the reservoir from point and diffuse pollution sources.