Biodiversity and Climate Change

Abstract Nitrogen (N) saturation arises when atmospheric inputs of N exceed bio-logical N demand, resulting in loss of NO3- in streams, accompanied by the loss of nutrients (Ca and Mg) that are essential to forest health. Previous studies have shown that some watersheds the Fernow Experimental Forest (FEF), West Virginia, USA, are among the more N-saturated sites in North America. Research from the Gilliam laboratory at Marshall University (West Virginia, USA) began focusing specifically on N biogeochemistry in 1993 with establishment of plots at FEF to carry out long-term in situ (“buried bag”) incubations in three watersheds: two control (WS4, WS7) and one treatment (WS3). This was done in conjunction with the Fernow Watershed Acidification Study, established by the USDA Forest Service in 1989 to treat an entire watershed (WS3) with aerial applications of 35 kg N ha –1 year –1. The initial period (1993–1995) exhibited increases in rates for all watersheds, but especially in treated WS3. This period has been followed by declines in net nitrification, which is consistent with current declines in stream NO3 – and has been especially pronounced in WS3 since 1998. Also during this time, sampling of the herbaceous layer (vascu-lar plants ≤ 1 m in height) has revealed pronounced changes in response to N treat-ments on WS3, especially in the increase of the shade-intolerant Rubus spp. Future work will investigate the effects of freezing on soil N dynamics. Preliminary results indicate that freezing exacerbates the symptoms of N saturation already seen in soils at FEF, further increasing already high rates of net nitrification