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Abstract: The goal of our research was to conduct a systematic study of ground water nitrate pollution in the Niraj (Nyárád) River Basin, to evaluate this contamination, and it’s causes. Samples of water were obtained from individual water sources (wells) from villages and from surface water sources. In the individual water sources the concentration of nitrate has increased significantly over time, exceeding in many cases the maximum contaminant level, indicating a potential health risk to nearby residents. The relationship between the potential pollution sources and groundwater nitrate pollution was analyzed in function of the agricultural practices, the nature of the pollution sources (punctual and diffuse pollution sources), the geographical conditions, hydrological conditions, and rainfall regime. During our research we linked the diffuse and punctual pollution sources with the spatial distribution of nitrate pollution of groundwater. According to our research the main cause of pollution of the groundwater with nitrate is the type of agricultural practices employed, especially small scale farming with animals and bad management of the manure/waste and the untreated household’s wastewater. In the Niraj catchment area, in 43% of the sampled wells, the nitrate pollution exceeds 50 mg/l. The results differ in different parts of the catchment area, in the upper part (over 350 m a.s.l.) the proportion of the sampled wells (where the concentration of the nitrate is higher than 50 mg/l) is 26%, and in the lower part (under 350 m a.s.l.) the percentage of the sampled wells where the concentration of the nitrate is higher than 50 mg/l is 64%. These differences are probably caused by the soil properties and topography. According to our results, on the terraces and downstream the localities, there exists a concentration of nitrate pollution. The nitrate pollution of the groundwater depends also on the rainfall regime.

Keyword: nitrate pollution; nitrate leaching; Nitrate Directive, Niraj (Nyárád) River cachement area, pollution sources, water sampling.