Influence of subsurface drainage systems on nitrate pollution of water supply aquifer (Tursko well-field, Poland)

This study presents the behavior of nitrate in the recharge zone of Tursko well-field (south Wielkopolska, Poland). The presence of a contaminant plume derived from land drainage systems was documented. The contamination is reflected mainly by the high concentration of nitrate (>80 mg/l). It was documented that the contaminant plume migrates in the aquifer along a flow path from the contamination source to the well-field. The factor that retards nitrate migration is bacterial denitrification. As a result of the denitrification, the nitrate concentration decreases systematically along flow lines, but the concentration of other parameters—products of denitrification (sulfate and total hardness)—increases. The occurrence of denitrification was confirmed by measuring the gaseous excess of N 2 (the product of denitrification) and by using the isotopes of 15 N and 18 O dissolved in nitrate. These methods also enable the intensity of denitrification to be assessed.