Nitrates in springs and rivers of East Ukraine: Distribution, contamination and fluxes

•Hydrogeological settings, seasonal flow and anthropogenic inputs influence nutrients dynamic.•Level of nitrate contamination in springs was higher than the limit recommended by WHO.•Nitrate fluxes revealed disturbance of nitrogen balance in aquatic systems by groundwaters. Spatial and temporal variation of nitrate concentrations has been studied in 4 rivers and 21 springs of the transboundary (Russia/Ukraine) Seversky Donets watershed in eastern regions of Ukraine – Kharkiv, Donetsk and Lugansk oblasts. Samples have been taken from 13 sites on the Lopan, Udy, Oskol and Seversky Donets rivers together with springs on left and right river banks between August 2013 and May 2014 and analysed on major ions and nitrates. Water temperature, pH, electrical conductivity, redox potential have been measured on site. The results showed high spatial and temporal variability of nitrate concentration in both surface and groundwater. The hydrogeological settings, seasonal trends and human impact were major factors influencing nitrates mobility and accumulation in contaminated springs, which contributed to surface water pollution. Mean nitrate concentrations were 26.7mgL−1 (C.V.=92%) in springs and 6.9mgL−1 (C.V.=114%) in rivers. The nitrate fluxes from springs to rivers were estimated at ca. 3 t km−2 annually. About 1/5 of spring water samples were characterized with higher nitrate concentrations than limits recommended by WHO and National Drinking Water Standards (Ukraine). Springs have been classified according to nitrate concentration and enrichment as high, moderate and low contaminated.