Wednesday, June 6, 2007 - 4:15 PM
315

Does space matter? Addressing the importance of spatial variation on the development of a stressor gradient

Adam G. Yates and Robert C. Bailey. Department of Biology, University of Western Ontario, 1151 Richmond St. N., London, ON N6A 5B7, Canada

Establishing the degree to which a stream is exposed to potential stressors is an important step towards relating changes in the biological community to human activities on the landscape.  Currently, this is usually determined by summing stressors for a site’s entire catchment area, as either total counts (e.g. number of hog farms) or in percentage of land use (e.g. % cropland).  It is reasonable, however, to expect that the contribution of a given stressor could vary depending upon its location within the watershed.  As a result, two basins with the same total number or area of stressors could have very different biological communities.  This study measured the effect of spatial configuration on estimates of a site’s exposure to stressors by considering how far a stressor is from the stream.  To accomplish this we compared the placement of 494 rural, headwater basins along a stressor gradient by two methods: 1. summed stressors over the entire basin, and 2. summed stressors in four distinct spatial zones based upon distance from the stream.  Results demonstrated strong correspondence between the two stressor gradients, leading us to conclude that spatial configuration of stressors has little effect on estimates of a stream’s exposure to human activity.                  

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