Abstract
Agriculture is one of the several major sources of nitrate pollution, and therefore the EU Nitrate Directive, designed to decrease pollution, has been implemented. Point sources like septic systems and broken sewage systems also contribute to water pollution. Pollution of groundwater by nitrate from 19 shallow wells was studied in a typical agricultural region, middle Podravina, in northwest Croatia. The concentration of nitrate ranged from <0.1 to 367 mg/l in water from wells, and 29.8 % of 253 total samples were above maximum acceptable value of 50 mg/l (MAV). Among regions R1–R6, there was no statistically significant difference in nitrate concentrations (F = 1.98; p = 0.15) during the years 2002–2007. Average concentrations of nitrate in all 19 wells for all the analyzed years were between recommended limit value of 25 mg/l (RLV) and MAV except in 2002 (concentration was under RLV). The results of the repeated measures ANOVA showed statistically significant differences between the wells at the point source distance (proximity) of <10 m, compared to the wells at the point source distance of >20 m (F = 10.6; p < 0.001). Average annual concentrations of nitrate during the years studied are not statistically different, but interaction between proximity and years is statistically significant (F = 2.07; p = 0.04). Results of k-means clustering confirmed division into four clusters according to the pollution. Principal component analysis showed that there is only one significant factor, proximity, which explains 91.6 % of the total variability of nitrate. Differences in water quality were found as a result of different environmental factors. These results will contribute to the implementation of the Nitrate Directive in Croatia and the EU.
Highlights
The most important and abundant source of drinking water in the European Union (EU) is groundwater constituting over 80 % of the supply (Council Directive 2000)
Concentration of nitrate (N = 114) in the research area of middle Podravina ranged from \0.1 to 367 mg/l in groundwater from shallow wells, and 29.8 % of the samples were above the maximum acceptable value (MAV)
Log-transformed to provide a more symmetric distribution, show that the average concentration of nitrate in all 19 wells for all the analyzed years was between recommended limit value of mg/l (RLV) and MAV except in 2002 when the concentration was under the RLV
Summary
The most important and abundant source of drinking water in the European Union (EU) is groundwater constituting over 80 % of the supply (Council Directive 2000). Pollution of groundwater is caused by different pollutants, among which nitrate plays the most important role. Nitrate pollution from agriculture is an issue of major concern for the UN (Addiscott et al 1991), and a series of environmental policies have been implemented in the EU to decrease nitrogen (N) emissions from agriculture. The Nitrate Directive is one of the main policies to reduce nitrate leaching from agriculture primarily through good agricultural practise and the application of organic and mineral fertilizers according to regulations (Velthof et al 2014). Nitrate concentration in natural waters has been increasing during the last few decades, coinciding with the
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