BIOGENIC POLLUTION INDEX OF THE PRIPYAT RIVER AS A TOOL FOR MONITORING SPATIAL-TEMPORAL CHANGES IN THE HYDRO ECOSYSTEM

Abstract

The article substantiates the suitability of the nutrient pollution index (NPI) as a tool for monitoring spatiotemporal changes in the hydroecosystem of the Pripyat River. The research aimed to assess the long-term dynamics of nutrient load and identify areas with increased contributions of nitrogen and phosphorus compounds, based on state monitoring data from the State Water Agency of Ukraine. Hydrochemical observations of 2005–2020 were used at sites 702, 616, 570, and 60 km from the mouth. The NPI was calculated from nitrate and phosphate concentrations normalized to the WHO maximum permissible levels (50 mg/dm³ for NO3‾ and 5 mg/dm³ for PO43‾) and classified according to the ecological state of surface waters using the nutrient pollution index. Analysis of the concentration distribution showed that the upper sections of 702 km and 616 km are characterized by a broader range and single nitrate peaks of up to 9–10 mg/dm3, while in the downstream sections (570 km and 60 km from the mouth) nitrate concentrations were more stable, and in the 60 km section increased variability was noted with maxima of up to 6–7 mg/dm3. The highest phosphate concentrations and the most significant variability were recorded in the 702 km section (up to 0.75–0.78 mg/dm3); 616 and 570 km are characterized by low median levels (0.05–0.08 mg/dm3) with episodic peaks of up to 0.5–0.7 mg/dm3. In comparison, in the 60 km section, maxima mostly did not exceed 0.3 mg/dm3. In most years, NPI values ​​were low and corresponded to the absence or weak biogenic pollution. On the scale of surface water pollution levels, the index rarely exceeded 1.4 (excellent status), and the transition to 1.5–1.6 was recorded only at the 616 km section in 2005. Heat maps showed a spike in NPI at the 702 km section (2011–2013) and increases at the 570 and 60 km sections in 2020, which may be useful for assessing eutrophication risks.