Atmospheric Inputs and Ecological Function

Kathleen C. Weathers
Institute of Ecosystem Studies

Ecological Thresholds Meeting
November 4-5, 2002


Ultimately, our interest in ecological thresholds is likely to be focused on evaluating changes in ecosystem function. In many cases, however, atmospheric fluxes of pollutants and nutrients are the critical drivers of those changes. The idea is not new; since the 1990s approximately two-dozen European Community (EC) countries have been using the so-called "critical loads" approach-essentially identifying and setting the thresholds for ecological response to pollutant deposition-to guide policy for emissions reductions. The EC community's efforts at broad-scale monitoring in which they link emissions to deposition to thresholds of ecosystem response, and their new focus on interactions among elements, may provide insight and context for the consideration of thresholds in ecological systems here in the US. Although we know something about ecosystem response to disturbances such as eutrophication and acidification within specific systems, total atmospheric deposition is poorly described in the US at many spatial scales and for many types of landcover and landuse. Furthermore, it can vary by 300% over small (10s of meters) and large (1000s of kms) spatial scales as a result of multiple atmospheric thresholds and the interactions between and among atmospheric processes, landscape structure, and depositional inputs. Understanding the different drivers of atmospheric deposition from spatial scales that range from tens of meters to kilometers may help in identifying geographically explicit regions where terrestrial and aquatic threshold responses may occur.