Nitrogen cycling on five headwater forested catchments in Mid-Appalachians of Pennsylvania

Nitrogen cycling has been studied since 1988 on five headwater forested catchments in the Mid-Appalachian region of northeast United States to determine impacts of atmospheric deposition. Nitrogen dissolved in streams was dominated by NO₃-N but dissolved organic nitrogen was a significant component of stream export. Watershed input-output budgets showed nitrogen retention varied from 63-96% of estimated atmospheric deposition inputs. Retention and losses of nitrogen occurred primarily in the uplands on Baldwin Creek basin, with lesser losses occurring in riparian lowland regions around seeps and the main stream corridor. With the exception of one basin that experienced forest decline and salvage logging, no significant trends in stream NO₃-N concentrations have been detected over the past 15 years due to the Clean Air Act.