Tree Harvest and Stream Discharge as Controls on the Mobilization of Aluminum in the White Mountain National Forest, New Hampshire USA

Over the past half-century, impaired stream water quality due to acid deposition has been a chronic issue in the northeastern United States. Acid deposition is associated with mobilization of inorganic monomeric aluminum, which has the potential to harm aquatic life and tree roots. Along with acid deposition, some types of timber harvest have been shown to cause aluminum to leach from the soils; however our understanding of how discharge affects mobilization of different aluminum species is poorly understood. This paired watershed study compares monomeric inorganic aluminum in stream and soil waters in four recently harvested and four reference (little or no harvest in last ten years) watersheds in the White Mountain National Forest in northern New Hampshire, USA with respect to stream flow. The current data suggest an inequality in the proportion of aluminum in the streams that is in the inorganic monomeric form in the harvested and control watersheds at different flows. We see a negative relationship between percent inorganic aluminum and discharge in the reference watersheds; however, we see a positive relationship between percent inorganic aluminum and discharge in the harvested watersheds. This suggests that in order to understand how aluminum, especially the most toxic form of aluminum, is mobilized in watersheds, we need to better understand the mechanisms involved at different flows. Such information is basic to improving forest management practices to preserve stream water quality.