The contribution of the Raut, Bac, and Botna tributaries to the variability of nitrogen forms in the Dniester river in spring 2025

The study examines the influence of the Raut, Bac, and Botna tributaries on the nitrogen regime in the Dniester River, within the context of increasing anthropogenic pressures. Water samples were collected upstream, at confluence points, and downstream. Mineral nitrogen forms were measured using spectrophotometric methods, and organic nitrogen by the Kjeldahl method. The results indicate a pronounced dominance of mineral nitrogen in the tributaries (88- 96%), far exceeding levels upstream in the Dniester (48-51%). The Bac River has the most severe impact, contributing ammonium over 335 times higher than in upstream Dniester and exceeding 15 mgN/L at the confluence, resulting in a 6.8-fold increase in ammonium downstream, as well as a significant rise in nitrites (0.032 mgN/L) and total nitrogen (1.023 mgN/L) downstream. The Raut River delivers the highest quantities of nitrates (3.23 mgN/L), while the Botna River, despite having high concentrations, is attenuated by dilution with the Dniester River water. Overall, the findings reveal an elevated risk of eutrophication, driven by the Nmin/Norg imbalance and the river"s ecological vulnerability due to its specific hydrological regime and limited buffering capacity.