engleski

Comparison of nitrate-nitrogen leaching in diverse hydrological conditions

Groundwater represents an important water resource in Europe, providing two thirds of European population with drinking water. On the other hand, this resource is not infinitive and it is slowly renewing so now days water preservation represents one of the most important environmental issues. Diffuse pollution from agriculture, especially manure and fertilizer application, affects groundwater quality in a form of high nitrate concentrations. Hence, the quantity of nitrate in groundwater is strongly linked to the amount of applied nitrogen (in surplus) on agricultural land. Depending on various parameters, nitrate is washed out from soil either into surface water or leached down into groundwater. In order to determine and diminish negative effects of agricultural impact on groundwater quality, many European countries are adopting provisions in The Nitrate Directive. According to this directive, maximum allowed concentration of nitrate in drinking and groundwater is 50 mg/l. Also, it is obligatory to designate areas which show vulnerability to nitrate so adequate land and water management can be implemented in those zones. Five regions in Croatia are preliminary delineated as nitrate vulnerable zones. One of these regions is northern part of Varaždin County. Vulnerability of this county to nitrate pollution is caused by two reasons: 1) hydrogeological influence of the large rivers Drava and Mura - the whole area is dominated by alluvial soils with shallow active profile mainly on gravel base, 2) 59% of Varaždin County is agricultural land used for crop and vegetable production and livestock breeding. In April 2011 triplicate of zero-tension pan lysimeters was installed on agricultural plot (maize) in Varaždin County outside delineated nitrate vulnerable zones to monitor NO3-N fluctuation in correlation to precipitation amount. Each lysimeter is installed in open soil profile at a depth above less permeable horizons. Leachate is collected twice a month or after abundant rainfall and NO3-N concentrations were determined spectrophotometrically. Data were analyzed by analysis of variance (ANOVA). Total annual precipitation at meteorological station Varaždin has a 30-years average of 832 mm. In period 2011-2013 two years, 2011 and 2012, are hydrologically dry and 2013 is wet with total annual precipitation of 414, 589 and 1103 mm, respectively. Analysis on annual level excludes 2011 because the research does not cover the whole year. Research results show that 25% of total precipitation leached in 2012 and 13% in 2013. Results show that leachate amount in hydrologically significant precipitation period (11% in October 2011, 12% in October 2012, 12% in October 2013) corresponds to the leachate amount on annual level. ANOVA results confirm there is a statistically significant difference (F(2, 12)=5, 77, p=0.018) in NO3-N concentrations between hydrologically dry and wet years. In dry years NO3-N concentrations vary from 36 to 56 mg/l and in 2013 from 8 to 40 mg/l. A Tukey post-hoc test revealed that NO3-N concentrations were statistically significantly lower in wet conditions in 2013 (22 ± 15.2) comparing to dry conditions in 2011 (42.4 ± 7.7 mg/l, p = .027) and in 2012 (41.4 ± 7.3 mg/l, p = .035).

nitrate-nitrogen; leachate; hydrological conditions; lysimeter; maize

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