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ECOLOGICAL EFFECTS OF NITROGEN DEPOSITION IN THE WESTERN UNITED STATES
Citation:
Impact/Purpose:
State-of-the-science assessment intended for use by academic science community, policy analysts in NGOs and all levels government organizations, and the interested public.
Description:
Article synthesizes existing studies (biological, ecological, biogeochemical) on the effects of nitrogen deposition to aquatic and terrestrial ecosystems in the western United States. In the western U.S, vast acreages of land are exposed to low levels of atmospheric deposition, with interspersed hotspots of elevated N deposition downwind of large, expanding metropolitan centers or large agricultural operations. Biological response studies in western North America demonstrate that some aquatic and terrestrial plant and microbial communities are significantly altered by N deposition. Greater plant productivity is counterbalanced by biotic community changes and deleterious effects on sensitive organisms (lichens and phytoplankton) that respond to low inputs of N (3_8 kg N ha_1 yr_1). Streamwater nitrate concentrations are elevated in high_elevation catchments in Colorado and are unusually high in southern California and in some chaparral catchments in the southwestern Sierra Nevada. Chronic N deposition in the West is implicated in increased fire frequency in some areas and habitat alteration for threatened species. In between hotspots, N deposition is too low to cause noticeable effects, or has not been studied.