High-resolution mapping to assess risk of groundwater pollution by nitrates from agricultural activities in Wielkopolska Province, Poland

The purpose of this research was to determine the groundwater intrinsic vulnerability to pollution of shallow groundwater in Wielkopolska Province, Poland and to assess the risk of pollution by nitrates. Wielkopolska is known as an area where the problem of water pollution by nitrates has existed for a long time due to intensive agriculture. DRASTIC method and its optimized version as well as four other risk evaluation methods were selected to assess the risk pollution with nitrates. The results of either method did not correlate with nitrate concentrations recorded in the total of 1679 groundwater monitoring points. Therefore a new method of groundwater pollution risk assessment (NV-L) was proposed. The new method is based on optimized results of the DRASTIC system and the L parameter which considers not only land use types, but also the amount of nitrogen loading leached from soil as a result of fertilizer consumption, and from wet deposition. The final results of NV-L method showed that the largest part of the study area is covered by a very low class of pollution risk (30.6%). The high and very high classes occupy 11.6% of the area, mostly in the areas designated until 2012 as the Nitrate Vulnerable Zones. Validation of the results of all methods showed that the other methods than NV-L cannot be used as a basis for reliable assessment of the risk of groundwater pollution by nitrates, as they do not take into account the nitrogen load leached from the soil profile.