Effects of Forest Management on Nitrate Concentrations in Seepage Water of Forests in Southern Bavaria,Germany

We performed seepage water studies in three forested study areas in Southern Bavaria, Germany in order to identify forest management effects on nitrate concentrations. In total 95 stands representing different age classes (up to 100 years), tree species (mainly spruce and beech) and regeneration methods (from clearcut to single tree selection) were included. In the period between 1998 and 2000, water samples were taken from below the rooting zone with tension lysimeters and nitrate concentration was determined. Average nitrate concentrations were calculated for each stratum (stand age, tree species, regeneration method). These data were combined with forest inventory data in order to predict regional nitrate leaching. Nitrate concentrations were generally higher in mature spruce stands than in mature beech stands. In spruce stands, we observed a clear age-related pattern, with negligible nitrate concentrations in stands younger than 40 years and higher concentrations in older stands. In beech stands nitrate concentrations were low and independent of age. In clearcut areas nitrate concentrations were significantly higher than in areas treated with small-scale regeneration methods. Forest management effects were highest in the study area with the highest N-input and lowest in the study area with the lowest N-input and highest N-retention capacity. In general changes of forest management have mainly long-term effects. The reduction of nitrogen deposition remains a crucial factor in avoiding increased nitrate leaching into forest groundwater resources.