Assessment of the trophic level and self-cleaning ability of water polluted by nutrients in the Zarafshan River, Uzbekistan

The aim of this study was to assess the water quality of the Zarafshan River through a comprehensive evaluation of its trophic state, nutrient loads, self-cleaning ability, and the toxicity of nitrogen compounds for hydrobionts. This is the first study of its kind conducted on the Zarafshan River. The trophic state was determined by nutrient content, the self-cleaning ability was assessed using the nitrification index method, and the toxicity of nitrogen compounds was evaluated using the aggregation index. Eutrophication was observed at all studied river Gauging Stations (GS), primarily caused by high nitrate nitrogen concentrations. The self-cleaning ability of the water was classified as “high” in the lower reaches of the river and “medium” along its length. Major pollution sources were identified as agricultural influence from Siab collector (GS-3) and industrial wastewater from Navoiazot chemical factory (GS-8). It is recommended to intensify the monitoring of total phosphorus at GS-3 and mineral nitrogen at GS-8, alongside implementing measures to prevent anthropogenic pollution to mitigate nutrient contamination in the Zarafshan River.

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