Tree Species Management and Nitrate Contamination of Groundwater: A Central European Perspective

Abstract

Nitrate concentrations in seepage water from pristine forests usually are very low, regardless of species composition. In most parts of Europe, anthropogenic nitrogen deposition has led to increased nitrate leaching from forests, and the rates of nitrate leaching in seepage water may be influenced by the dominant tree species. Spruce forests have a higher leaf area than beech forests, and also maintain high leaf area throughout the year. This leads to higher rates of N deposition from the atmosphere and to higher interception losses (resulting in a less deep seepage) compared to beech stands. For these reasons, spruce-dominated forests tend to have more than double the concentrations of nitrate in seepage water compared with broadleaved forests. These species effects depend in part on the age of the forests and on the fate of nitrate in deeper soil layers. In Bavaria, the Southernmost State of Germany active plantation management shifted the balance from the original broadleaved forests towards spruce dominated forests in the 18^th and 19^th century. Planting of forests in the late 20^th Century shifted to an emphasis on broadleaved species, and this shift contributes to reductions in nitrate concentrations of seepage water in areas with high N deposition. For sensitive areas like ground water protection zones mixed-species forests with higher proportions of broadleaved species are recommended in order to reduce the risk of excessive nitrate leaching.