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Health and Environmental Effects Research

WED Scientists Attend Gordon Research Conference on Catchment Science

John Stoddard and Gretchen Oelsner, NHEERL Western Ecology Division (WED) researchers, were invited participants at the July 2009 Gordon Research Conference on Catchment Science: Interactions of Hydrology, Biology, and Geochemistry, held in Andover, NH. The theme of the conference was "Thresholds, Tipping Points, and Nonlinearity: Integrated Catchment Science for the 21st Century." Dr. Stoddard led a discussion on catchment-scale responses to acidification and recovery from acidification. Dr. Oelsner presented a paper entitled "Changes in Nitrogen Retention in Catskill Long-Term Monitoring Catchments." Scientists attending this conference shared their cutting-edge research, especially evidence for and against nonlinear behavior that affects the ability to understand and predict responses to environmental change at the catchment scale. It is known that many physical and biological systems are inherently nonlinear, but nonlinear behavior in catchments has not been addressed adequately. Catchment scientists only recently have begun to consider the evidence for catchment nonlinearity by examining physical, ecological, and biogeochemical processes that could produce, for example, specific "thresholds" or "tipping points" in response to individual disturbances or perturbations. A more complete understanding of these processes is needed to better assess the likely responses of catchments to climate change, various types of disturbances, and different land management practices.

Dr. Stoddard's and Dr. Oelsner's participation was based on their research from the Environmental Monitoring and Assessment Program's TIME/LTM monitoring information that has been collected since 1990. The LTM program makes frequent measurements over many years of the chemistry of a set of acid-sensitive lakes and streams, allowing scientists to evaluate trends in acidity in these sensitive areas. The TIME program, by contrast, monitors a statistically chosen sample of lakes and streams once a year and enables scientists to determine what proportion of the lakes and streams in a region is affected. Together, the two methods provide a clear picture both of trends in acidity over time and, also, of its extent over the landscape at any given moment. Scientists and policymakers need both types of information to solve the problem of acid rain.

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