Assessment of the ecological state of the water of Lake Malakhovo (Orenburg, Russia)

Background. Fresh surface water bodies are exposed to many anthropogenic and natural factors that can have a significant negative impact on the structure and functions of the entire ecosystem. Despite the fact that many efforts are being made to assess and manage the quality of surface waters, the problem of their pollution remains relevant to this day. The purpose of the study is a comprehensive environmental assessment of the state of Lake Malakhovo (Orenburg, Russia) based on organoleptic, generalized and hydrochemical indicators for 2022–2023. Materials and methods. The studies were carried out at three sites located both in the immediate vicinity and at the maximum distance from pollution sources using the following methods: photometric (determination of nitrite and nitrate nitrogen content), atomic absorption (establishment of iron mass concentration), titrimetric (determination of calcium, magnesium, sulfate ions and mass concentration of carbonates) and fluorimetric method (measurement of mass concentration of oil products). All studies were conducted in an accredited laboratory. Conclusions. According to the main organoleptic indicators, the water of the studied reservoir meets the quality criteria, with the exception of suspended substances, for which maximum excesses of up to 5.5 MPC (maximum permissible concentration) are observed in the autumn period, as a result of which the lake waters are classified as dirty (quality class V). For individual substances (iron and magnesium ions, sulfate ions, nitrites), excess of the maximum permissible concentration of fishery value was recorded. The ecological state of the waters in terms of nitrate and nitrite content in all sections deteriorates in the winter to quality class V. Exceeding the maximum permissible concentration of cultural and household value was not recorded. According to the results of calculating the hydrochemical pollution index, the water of the lake. Malakhovo (Orenburg) is classified mainly as moderately polluted, with the exception of the first section, located in close proximity to pollution sources, where the water in the autumn period is considered polluted.