Evaluation of Biogenic substances concentrations in Kulpė river

The objective of the article is to determine the variation in the concentration of biogenic substances in the Kulpė river. The theoretical part of this article reviews the division of Lithuanian surface waters into river basin districts and their ecological status. The damage caused to surface waters by the main groups of anthropogenic pollution, as well as preventive pollution reduction measures, is summarised, and the methodology of the study of the surface water is analysed. The samples of the Kulpė River were taken twice on 04/03/2023 and 04/25/2023 in order to determine the change in substances concentration. Sampling sites were selected based on the geographical location of the river, surrounding objects and river flow. During the study of river waters, the following indicators were determined: nitrates (NO3-N, mg/l N), ammonium nitrogen (NH4-N, mg/l N), total nitrogen (Nb, mg/l), phosphate phosphorus (PO4-P, mg/l P), total phosphorus (Pb, mg/l). According to the studied biogenic substances, the worst results were obtained in the northern part of the city of Šiauliai. The concentration level of the ammonium nitrogen reached a bad ecological status in the river sources and the central part of the city. Keywords: biogenic substances, anthropogenic pollution, surface water, Kulpė river.