МІГРАЦІЯ БІОГЕННИХ ЕЛЕМЕНТІВ З ДОННИХ ВІДКЛАДІВ ЯК ДОДАТКОВЕ ВНУТРІШНЄ НАВАНТАЖЕННЯ ПОЖИВНИМИ РЕЧОВИНАМИ НА ВОДОЙМИ УРБАНІЗОВАНОЇ ТЕРИТОРІЇ

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There were investigated the seasonal and spatial dynamics of the content of nutrients in the lakes of the Opechen’ system. It has been established that the content of nutrients in reservoirs of the urbanized territory, in addition to the external load, depends significantly on their migration from the bottom sediments under oxygen deficiency and reduction conditions. The concentration of dissolved oxygen and the value of the redox potential were within 0–16.2 mg/dm3 and -129÷295 mV. Dissolved oxygen deficiency (0–5.4 mg/dm3 and 0–44% saturation) and transitional redox or reduction conditions (-129÷69 mV) in the water of the bottom horizon were observed throughout the year. The increase in the concentration of dissolved oxygen (12.1–16.2 mg/dm3 and 107–175% saturation) occurred only in the surface water horizon during the spring-autumn period. The concentration of ammonium nitrogen, nitrite and nitrate ions varied within 0–13.17, 0.006–0.186 and 0.016–0.142 mg N/dm3. The content of inorganic phosphorus and dissolved silicon reached 0.010–3.121 mg P/dm3 and 0.03–6.4 mg/dm3. The concentration of ammonium nitrogen, inorganic nitrogen, inorganic phosphorus and dissolved silicon near the bottom was always higher than in the water of the surface horizon. This is due to the formation of oxygen deficiency, transitional redox or reduction conditions, which increase the migration of nutrients from bottom sediments. The N:P ratio decreased from winter to autumn on average in the range of 7,2–2,6, which indicates an increase in the concentration of phosphorus in the water relative to nitrogen and the formation of favorable conditions for the development of blue-green algae. Favorable conditions for the supply of inorganic nitrogen and phosphorus from the bottom sediments are formed when the concentration of dissolved oxygen is ≤4 mg/dm3 and the value of the redox potential is ≤100 mV. It was established that the concentration of oxygen and the value of the redox potential affect the content of inorganic nitrogen and phosphorus, but the relationship between the studied indicators is nonlinear. The oxygen regime and the value of the redox potential don’t affect the content of dissolved silicon, and its concentration depends on the seasonal features of the development of diatoms.