Changes of nitrate concentrations in surface waters influenced by land use in the crystalline complex of the Czech Republic

Changes in nitrate pollution in surface waters brought by the construction of tile drainage systems and by conversion of cultivated land to grassland (followed by decrease in fertilizer use) in two districts were examined. The goal was to find out how nitrate concentrations have responded to changes in agricultural management. There were no major changes in land use in the Pelhrimov district after 1990, apart from decrease in mineral fertilizer use. In the Cesky Krumlov district, permanent grassland area increased by 55% (from 228.9 km2 to 353.3 km2) and by 241% (from 5.4 km2 to 13 km2) in the catchments investigated between 1990 and 2000 followed by reduction in use of fertilizers. In these two districts, 31 small catchments where long-term, or repeated, nitrate concentration monitoring was carried out between 1986 and 2005, were analyzed. Trend, regression and factor analyses were conducted on changes in nitrate concentrations, and to assess the impact of several factors on nitrate concentrations in water before and after conversion to grassland.Over the monitoring period 1986–2005, there was a significant decreasing linear trend in N–NO3- concentration in surface waters in all catchments in the Cesky Krumlov district. In the Pelhrimov district 3 of 23 catchments showed a significant decreasing trend in nitrate concentrations and 2 a significant increasing trend despite a decrease in mineral nitrogen consumption. The most important environmental factor affecting nitrate pollution was the proportion of ploughed land in the catchment. The greater the share of ploughed land in the catchment, the greater the nitrate contamination of surface water. The proportion of drained land in the catchment after grassing has no markedly influence on nitrate nitrogen concentration.