Small forested watersheds in the Catskills can vary up to 17-fold in the concentration of nitrate in streamwater (Lovett et al. 2000). This is important because nitrate is a significant acidifying agent in the streams, and can cause harmful algal bloom when it is delivered to downstream estuaries and coastal waters. We are investigating the cause of nitrate variation through comparative studies in Catskill watersheds. Most of the variance in watershed nitrate export can be explained by the carbon to nitrogen ratio (C:N) of the watershed soils, and this ratio appears to be mainly controlled by the tree species composition of the watershed (Lovett et al. 2002).
Sugar maples, in particular, seem to create soils with a low C:N ratio, which leads to high rates of nitrate release to stream water, while soils under red oak and eastern hemlock have higher C:N ratios and lower nitrate release (Lovett et al 2004, Lovett and Mitchell 2004, Christenson et al. 2009). Other factors may also inhibit nitrate production under oak soils, such as abiotic retention of nitrogen (Fitzhugh et al. 2003a and 2003b). Increasing accumulation of nitrogen in the soils from continued atmospheric deposition may result in decreased ability of oak forest soils to retain nitrogen (Templer et al. 2005).