Factors controlling streamwater nitrate concentrations in a forested headwater catchment, Krusne Hory Mountains, Czech Republic

The Krusne Hory Mountains have been heavily impacted by high atmospheric pollutant deposition. Long-term routine sampling (1978-96), longitudinal streamwater sampling (1992-94), and intensive streamwater sampling during rainstorms and snowmelt (1996) in a 210 ha forested catchment were used to evaluate streamwater nitrate concentration variations and controlling processes. Streamwater NO( )3 concentrations at Jezeri varied from 40 to 280 mu eq l(-1) during 1978-96. They were affected by long-term decreases in atmospheric N deposition and landscape manipulations, including forest dieback and removal, liming and reforestation. Forest removal reduced dry deposition, but forest removal and liming increased nitrification. Streamwater NO3 concentrations decreased on average from 220 to 80 mu eq l(-1) since 1980 due to forest regrowth. Streamwater NO3 concentrations vary seasonally due to biological uptake of N and hydrological changes, e.g. high runoff during snowmelt. The highest NO3 concentrations (300 mu eq l(-1) occur during spring snowmelt at the highest elevations. Nitrification of the forest floor results in the mobilization of excess HO3. Lowest NO3 concentrations (40 mu eq l(-1)) occur at the lowest elevations in a mature beech forest during the growing season. They are attributed to removal by vegetation. These low concentrations, however, are still much higher than for N-Limited forest systems and indicate N saturation.