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Concentration of Nutrients in the Karašica River Surface Waters

Karašica River (tributary of the Danube) is a 81 km long river located in Hungary and Croatia, with catchment area of 910 km2. Originating in Hungary (east of Pecs), it flows towards the south. It crosses the Hungarian-Croatian border near the village of Luč (Municipality of Petlovac, Osijek-Baranja County) and continues its flow in an eastward direction, until it flows into the Danube River near Batina. Industrial pollution decreased notably throughout Croatia since 1991, so the aim of our study was to analyse Karašica River water quality to determine whether water quality has changed because of the pollution. For this purpose, concentration of nitrogen and phosphorus compounds in Karašica River surface waters was analysed. Samples were taken once a month in the period 2010–2015. During analysed period, concentration of total nitrogen ranged 1.434–5.683 mg/L, concentration of nitrites 0.007–0.126 mg/L, while concentration of nitrates ranged 0.114–5.42 mg/L. Concentration of orthophosphates ranged 0.018–0.299 mg/L, and concentration of total phosphorus ranged 0.05– 0.421 mg/L. The highest concentration of analysed nutrients was measured in the water samples collected at location Batina – total nitrogen (February of 2015), total phosphorus (October of 2014) and orthophosphates (May of 2015). The highest concentration of nitrites was measured in a water sample from location Branjin Vrh, in May of 2012. Analysed nutrients show a decrease in value during 2015, with lowest measured value of nitrites of 0.007 mg/L, nitrates 0.7 mg/L, total nitrogen 1.96 mg/L, orthophosphates 0.01 mg/L, and total phosphorus of 0.05 mg/L. According to current regulations in Croatia, based on chemical parameters surface water quality of Karašica River can be characterized as moderate. Further continuous monitoring of water quality is necessary in order to improve reliability of water quality categorization.

Karašica River, nitrates, nitrites, total nitrogen, orthophosphates, total phosphates

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