Influence of agriculture on the groundwater chemical status in Slovenian alluvial plains
Geological Survey of Slovenia
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Main agricultural areas in Slovenia are situated on alluvial plains of the Sava, Drava and Mura rivers. These are also the most densely populated areas in the country. Because of this fact, ecological pressures on the alluvial plains groundwater quality are quite extensive. There are six main alluvial plains In Slovenia, and three of them have a bad chemical status: Savinjska dolina, Dravsko – Ptujsko polje and Prekmurje. The problem in the Dravsko – Ptujsko polje groundwater body is exceeded concentrations of atrazine and nitrates, whereas in Savinjska dolina and Prekmurje only nitrates are problematic.In the scope of EU Water Framework Directive implementation, the second Slovenian Water Management Plan is in preparation, including the measures for the improvement of groundwater bodies’ chemical status. The Water Management Plan covers the time period between years 2016 – 2021.During the first stage, the results of Slovenian national groundwater chemical monitoring and existing ecological pressures were carefully examined. It was established that the herbicide atrazine and its breakdown product desethyl-atrazine no longer present a serious problem. The concentration trend for both substances is directed downwards, because the substance was banned in the year 2002.A quite more serious problem is groundwater nitrate. It was realized that important part of the nitrogen present in the bad chemical status of groundwater bodies originates from agricultural activities. For the Dravsko polje aquifer, agricultural nitrogen presents 64 % of all the nitrogen produced. The proportion of cattle nitrogen is around 52 %, human 30 % and pig 13 %. On the basis of these findings, the proposed measures for groundwater chemical status improvement are directed in several ways. The first one is a more detailed estimation of groundwater pollution critical areas. All accessible groundwater monitoring points will be used for a better definition of the groundwater pollution plume.The second group of measures includes a more stringent control of the activities on the aquifer’s catchment areas. Special maps will be produced for the state agricultural inspection service, including maps of critical areas and maps of nitrogen eluation potential. The monitoring of nitrogen, phosphorus and potassium concentration in agricultural soil will also be established.The third group of measures includes activities for a better definition of future actions in the field of groundwater pollution prevention. In this scope a very important component are pilot animal farms, where technologies for reducing nitrate emissions from animal wastes to groundwater will be tested in real field conditions.Measures will also address the issue of groundwater pollution with pesticides. The concentrations of atrazine and desethyl-atrazine in groundwater have a pronounced decreasing trend in recent years. Unfortunately other pesticides replacing atrazine can be occasionally found in groundwater, e.g. metolachlor.