Современный режим биогенных веществ в Можайском водохранилище

The paper deals with the seasonal dynamics of nutrients in the Mozhaysk reservoir in 2018/2019. The factors of seasonal variability of the vertical distribution of nitrogen, phosphorus and mineral silicon compounds are considered basing of monthly measurements. The regime of nutrients in the Mozhaysk reservoir and the ratio of their various forms is largely determined by the formation and duration of the density stratification of water. During hypoxia phosphorus and ammonium are recovered from the bottom sediments. By the end of summer nitrates and dissolved mineral phosphorus are almost completely consumed by algae in the epilimnion. During the growing season organic phosphorus occur mainly in suspended form within the phytoplankton cells. Mineral silicon is actively consumed in May during the development of diatoms, while in the hypolimnion its concentration is stable throughout the period of stratification. Longitudinal heterogeneity in the nutrient content is caused by both the mixing conditions, and the varying genesis of water mass in a particular area of the reservoir. It is shown that over the past 30 years the internal nutrient load in the reservoir has increased as a result of increasing duration of density stratification and, as a consequence, the period of anoxia. At the same time, the input of nitrogen and phosphorus compounds to the reservoir with rivers has decreased as a result of land-use change.