Monday, June 4, 2007 - 4:30 PM
216

Distinguishing natural from anthropogenic regulation of algae in aquatic ecosystems

R. Jan Stevenson, Zoology/Center for Water Sciences, Michigan State University, 203 Natural Science Building, East Lansing, MI 48824

Assessments of human effects on ecological systems can be improved greatly by accounting for natural variability in conditions.  In this study, assessments of human effects on diatom species composition was distinguished from natural variation in 119 streams throughout the lower peninsula of Michigan using three statistical approaches to determine sensitivity of assessments to statistical approach.  Diatom species composition was characterized with a trophic diatom index.  Relationships of the trophic diatom index to 37 watershed variables characterizing climatic and hydrologic conditions, soil textures, and land use were evaluated with three statistical approaches.  One approach was traditional forward stepwise regression and the second was forward stepwise regression of residuals from preceding models.  The third approach was classification and regression tree.  All statistical approaches indicated the importance of riparian land use and one variable or another related to hydrologic conductivity, e.g. percent coarse soils or a Darcy groundwater indicator.  Deviations in the trophic diatom index from natural were then determined using the three models to assess ecological conditions with very similar results among streams.  Similarity in the results of these analyses indicated the importance of scientific interpretation as well as political and social factors in application of results by environmental managers.      

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