ABSTRACT
ABSTRACT: Unconfined karstic aquifers in agricultural areas are vulnerable to human impacts. In karstic environment processes influencing water chemistry in both the vadose and phreatic zone can be observed. Mobile, slowly degraded, toxic nitrates present in such environments are the best indicators of groundwater anthropogenic contamination. Gaseous pollutants, polluted precipitation, agricultural chemicals and the rural economy are the main artificial sources of nitrates. The investigations took place in the karstic area of the Cracow Upland (in southern Poland) where a useable aquifer in the Upper Jurassic limestones occurs. This agricultural area is under strong human impact from the adjacent industrial-urban agglomerations of Cracow and Upper Silesia. At present the nitrate hydrochemical background of the vadose and phreatic zone is respectively 0.2-8.5 and 1.2-7.5 mg N-NO3/1, while its range is seven to eight times as great as the natural one (0-1 mg NNO3/1). Degradation of water quality is observed with an absence of the highest quality water (<1 mg N-N0311) within hydrochemical background, shift of hydrochemical background range (from 0.2-6.0 mg N-NO3/1 in the 60th), considerable share of supra-sanitary standards concentrations (>10 mg N-NO3/1) up to 110 N-NO3/1 within vadose zone and to 22 mg N-NO3/1 in phreatic zone (especially during thawing period and in autumn). Mean nitrate nitrogen concentrations in groundwater are: urban areas — 7.4 mg N-NO3/1, rural areas — 6.6 mg N-NO3/1, forests — 3.6 mg N-NO3/1. On the basis of groundwater flow modelling, as well as hydrochemical research, the estimated nitrogen load carried away from the usable Upper Jurassic aquifer (area of 652 km2) amounts from 0.97 to 2.58 kg N-NO3/24 h•km2.
