Spatiotemporal Patterns of Surface Runoff Formation in Small Rivers of Nizhny Novgorod

This study addresses the pervasive issue of watercourse pollution, with particular emphasis on diffuse pollution due to its wide spatial distribution, limited research attention, multitude of pollutant sources, and significant impact on water quality. The research focuses on diffuse pollution of urban rivers, which face heightened anthropogenic pressures; it examines the pollution of watercourses in Nizhny Novgorod over a period of 30 years, enabling a comprehensive understanding of the impact of urban watercourses on the environment and the assessment of pollutant loads into the Volga and Oka rivers. A database of the qualitative composition of small rivers was created during the study, allowing for spatial and temporal analysis and revealing trends and patterns in the distribution of pollutant concentrations in the rivers. It was found that in almost all small rivers of the city, the permissible concentrations (MPC) for all considered substances—iron, copper, nickel, lead, cadmium, trivalent chromium, zinc, aluminum, manganese, ammonium nitrogen, nitrate and nitrite nitrogen, mineral phosphorus, and petroleum products—were significantly exceeded. The main sources of pollution are transport, certain machinery manufacturing, shipbuilding, and automobile manufacturing enterprises, as well as the Sormovo CHP plant. Based on the obtained data, pollutant loads and discharges from urban areas into receiving water bodies were calculated. It was found that the main pollutants are biogenic elements (ammonium and nitrate nitrogen), and the most polluted of the three considered rivers (Levin, Rakhma, and Parasha) in terms of mineralization is the Rakhma River.