**7. Summary**

North Lithuanian karst region, as the mostly Lithuanian territory, is used for agricultural practise. The leaching of nutrients from agricultural fields is one of surface and groundwa‐ ter pollution sources. Polluted drinking groundwater is dangerous for people's health. The salt‐saturated water becomes more aggressive and intensifies karst process of the rocks lying below, which definitely causes a risk to people's property or event life.

Most chemical matter contained in the soil is water‐soluble; therefore, hydrological regime changes in the ecosystem are closely related to changes in nutritive leaching. By means of drain, much nitrate nitrogen and other elements contaminating the stream (drainage receivers') water are leached out. The stream water mineralization was determined by soil texture, type of land use and fertilizers applied in the areas drained. Higher amount of nitrogen and phosphorus are leached out in winter and spring periods and at the onset of run‐off after a dry period (due to the leaching of nitrogen that was not used during the dry period).

The bigger rivers have more intensive agitation processes in the flow and receive run‐off from greater areas, while quality of small streams is under immediate impact of local factors and distinguished impact of particular factors in the catchments. The concentration of nitrate nitrogen is up to 2.1 times smaller in the rivers than it is in the stream.

Chemical composition of groundwater is mostly depended on the type of soil and location of a well in respect of sinkholes and meteorological conditions. In the dry period, peat‐filled sinkhole water is at higher level and less polluted with nitrate nitrogen, chlorine and sulphate compounds.
