Abstract
This article presents data on the distribution of various forms of mineral nitrogen and phosphorus in water sources of Southeastern Kazakhstan for the period from 2014 to 2023. It was found that the content and ratio of mineral nitrogen forms varied. Among nitrogen compounds, nitrates predominated, accounting for 82–86% of the total nitrogen. However, no exceedances of the maximum permissible concentrations (MPC) for water bodies of fishery importance were detected. Ammonium and nitrite nitrogen accounted for 12–17% and 0.8–2.1% of the total nitrogen, respectively. Nevertheless, exceedances of their MPC by 1.2 to 3.0 times were observed in almost all seasons. Dissolved mineral phosphorus (phosphate ions) was detected in water at all surveyed locations in low concentrations (0.005–0.0400 mg/dm³) due to the low solubility of its compounds and intensive uptake by aquatic organisms. The most polluted areas were the tributaries of the Tasotkel Reservoir: the Shu River (near the village of Kainar) and the Toktash River. A decrease in the concentration of nitrogen and phosphorus compounds was observed from the upper to the lower reaches of the Shu River. Self-purification of the Shu River’s water masses was noted for all compounds: phosphorus (57.8%), nitrite nitrogen (49.0%), ammonium nitrogen (35.9%), and nitrate nitrogen (15.6%). Over the study period, based on average annual concentrations of nitrogen and phosphorus compounds, the water quality of all observed sites corresponded to class 1–3, with occasional seasonal drops to class 5.