SEASONAL AND LONG-TERM CHANGES IN THE CONCENTRATIONS OF BIOGENIC SUBSTANCES IN THE KAMA CASCADE RESERVOIRS

Abstract

The paper provides an analysis of seasonal and long-term changes in the concentrations of biogenicsubstances in the Kamskoe, Votkinskoe, and Nizhnekamskoe reservoirs. The analysis was conducted based on data of theKama Basin Water Authority for 2005–2022 and of the Automated Information System for State Monitoring of WaterBodies (AIS SMWB). The obtained results were verified with the Yearbooks of the Surface Waters Quality in the RussianFederation for 2010–2022. The analysis has shown that the concentrations differ slightly; the data provided in the yearbooks do not allow analyzing seasonal concentrations.It has been found that river runoff (including wastewater) brings the majority of biogenic substances into theKamskoe Reservoir (51%). The influx of total nitrogen and phosphates from all sources is greatest in the NizhnekamskoeReservoir – 61% and 84% respectively.The highest concentrations of ammonium ion are observed in the spring – the period of the reservoir filling, andthe lowest concentrations – during the summer-autumn stabilization of the water level. High concentrations of nitratesand nitrites in the Kamskoe and Nizhnekamskoe reservoirs are characteristic of the periods of the winter drawdown andspring filling. In the Votkinskoe Reservoir, nitrates and nitrites have the highest concentrations in different seasons. Thereare more nitrates during the winter drawdown and more nitrites during the summer-autumn stabilization. The lowestconcentrations of phosphates in all reservoirs of the Kama cascade are observed during the spring filling and summerautumn stabilization of water levels. Iron concentrations during the spring filling are higher than during the summerautumn stabilization. The exception is the Kamskoe Reservoir, where the highest concentrations of iron are noted duringthe winter drawdown.As to the MPC for fishing purposes (MPCf), there are no excesses for average concentrations of biogenic substances in different seasons, with the exception of total iron. However, there are some local exceedances. The high naturalconcentration of iron leads to a 1.8–4.7 times excess of MPCf by seasons in the Kamskoe Reservoir, with these excessesdecreasing further along the cascade. The long-term period of observations has revealed a tendency toward a decrease inthe concentrations of nitrites and phosphate ions, while total iron shows the tendency for increasing concentrations.