187 Evaluating thresholds in stream macroinvertebrate community responses to stress

Tuesday, May 19, 2009
Ambassador Ballroom
David R. Smith , Leetown Science Center, U. S. Geological Survey, Kearneysville, WV
Nathaniel P. Hitt , Aquatic Ecology Branch, U.S. Geological Survey, Leetown Science Center, Kearneysville, WV
Craig D. Snyder , Leetown Science Center, U. S. Geological Survey, Kearneysville, WV
Stream macroinvertebrate communities exhibit known differences between high- and low-quality sites, but the form of this relationship remains poorly understood. Linear relations would suggest that communities change incrementally with increasing stress, but nonlinear relations would suggest that (1) environmental thresholds influence community structure and (2) metric performance may vary across site quality. We used data from the mid-Atlantic highlands region (USEPA EMAP data, n=871 observations) to compare linear and nonlinear quantile regression models of community responses to land use. Information theoretic criteria revealed differences among metrics in the relative importance of nonlinear models. Among the 14 metrics evaluated, the richness of tolerant taxa showed the strongest evidence for threshold responses to stress. In contrast, the proportional abundance of EPT taxa showed the least difference between linear and nonlinear models. Several metrics exhibited distinctions among linear and nonlinear models at different zones along the stressor gradient. For example, several metrics captured nonlinear responses to low-level degradation and therefore may be appropriate for use as ‘early-warning indicators' within relatively pristine sites.
See more of: Poster - Bioassessment
See more of: Contributed Sessions