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SOURCES AND ESTIMATED LOAD OF BIOAVAILABLE NITROGEN ATTRIBUTED TO CHRONIC NITROGEN EXPOSURE AND CHANGED ECOSYSTEM STRUCTURE AND FUNCTION
Citation:
Jorgensen*, E E., S M. Holub*, P. M. Mayer*, M E. Gonsoulin*, R. G. Silva, A. E. West**, S. J. Tunnell, J. E. Clark, J. L. Parsons, D. M. Engle, AND E. C. Hellgren. SOURCES AND ESTIMATED LOAD OF BIOAVAILABLE NITROGEN ATTRIBUTED TO CHRONIC NITROGEN EXPOSURE AND CHANGED ECOSYSTEM STRUCTURE AND FUNCTION. Presented at First Interagency Conf. on Research in Watersheds, Benson, AZ, October 28 - 30, 2003.
Impact/Purpose:
To inform the public.
Description:
Bioavailable nitrogen is a limiting nutrient throughout the Eastern United States. Research demonstrates that exposure to large doses of nitrogen leads to deleterious environmental impacts. However, effects of chronic exposure to lower doses of nitrogen are under-appreciated. Since 1998, we've been conducting an integrated multi-disciplinary study investigating ecosystem feedback associated with chronic exposure to low doses of nitrogen. In this nitrogen-limited ecosystem, the ability of the soil system to adapt to new nitrogen inputs was compromised after 1 year of exposure when concentration of nitrate in the soil increased 4x. Changes to the plant, macro-invertebrate, herbivore, and microbial communities each reduced ecosystem nitrogen use efficiency thereby producing a self-reinforcing positive feedback loop leading to greater concentrations of soil nitrate. Ecosystems similarly exposed to excess or new sources of nitrogen may be capable of leaching 25-75% of new nitrogen annually, including essentially additions during seasons of dormancy, even where winter is temperate in south-central Oklahoma These experiments demonstrate that even the relatively small amount of nitrogen deposited in precipitation has the capability to change multiple aspects of ecosystem structure and function. Wherein outputs of nitrogen to the atmosphere can reasonably be expected to increase, it is prudent to identify and develop management options now to both restore ecosystems that are already compromised and to buffer affects to ecosystems that are at risk from new nitrogen inputs.