ASSESSING THE LEVEL OF CHEMICAL WATER POLLUTION IN THE ANGRAPA RIVER BASIN, KALININGRAD REGION

Abstract

The Angrapa River basin in the Kaliningrad Region is a transboundary water body that is potentially subject to significant anthropogenic stress. Despite the ecological significance of the area, including the Vishtynetsky National Park, there have been no systematic studies of the chemical pollution in the watercourses. The purpose of this work is to provide a comprehensive assessment of the water pollution levels in the basin, identifying spatial patterns and key influencing factors. In 2023–2024, four rivers of the basin (Angrapa, Pissa, Krasnaya, and Russkaya) were monitored, with 63 water samples collected in different hydrological seasons. Based on laboratory analysis of the samples, water pollution indices (WPI) and specific combinatorial indices (SCI) were calculated, which were then extended to the corresponding sections of the watercourses. According to the specific combinatorial water pollution index (SCWPI), the water quality of the Angrapa River basin is classified as 3b very polluted, and as 4a dirty when taking into account the critical pollution indicators (CPI). The study has found that the most polluted is the Russkaya River – 4.82 (4a dirty) with an average number of CPI = 4, with 70 % of the catchment area occupied by agricultural land. The least pollution has been found in the Krasnaya River – 2.88 (3a polluted) with an average number of CPI = 1, the area of which is characterized by high forest cover (60 %). The level of water pollution increases from the source to the mouth of the river: areas with a high percentage of forest cover have cleaner water compared to areas dominated by agricultural land and urban areas. According to the WPI, water quality is at its worst in autumn (average WPI is 5.53 – V class, dirty), while it improves in winter (1.74 – III class, moderately polluted). Major MPC exceedances were registered for iron (97 % of the samples), petroleum products (70 % of the samples), chemical oxygen consumption (71 % of the samples), biochemical oxygen consumption (60 % of the samples), dissolved oxygen (48 % of the samples), phosphates (35 % of the samples), nitrites (22 % of the samples), and ammonium (19 % of the samples). The main factors affecting water quality include agricultural activities, urbanization, high iron content in groundwater, seasonal water availability, and natural cycles of aquatic and riparian vegetation.