THE RELATIONSHIP BETWEEN LAND COVER AND STREAM CONDITION: A COMPARISON OF INVERTEBRATE AND LANDSCAPE METRICS.

M.G.S. Wood and J.D. Allan. School of Natural Resources & Environment, University of Michigan, Ann Arbor MI 48109-1115

The expectation that macroinvertebrate assemblages respond to landscape or habitat degradation in a dose-response relation underlies many bioassessment investigations. Focusing on the sub-catchments of the Huron and Raisin watersheds in southeastern Michigan, we examined the response of multiple invertebrate metrics, in relation to both catchment and buffer-scale measures of land use and landscape pattern. Some 47 sites were sampled during 1999 and 2000 using 250 um D-nets, and we identified 500+ invertebrates per site to genus in most instances. The percent of natural (forest + wetland) land-cover in both the sub-catchment and buffer was highly and positively correlated with EPT and clinger taxa, and negatively correlated with percent dominant taxa. Pattern (fragmentation) metrics calculated at the sub-catchment scale such as overall patch density, wetland patch density and an interspersion index also were effective predictors of some invertebrate indices. In general, invertebrate metrics incorporating information about Trichoptera, Plecoptera and clinger taxa showed the strongest correlations with land cover metrics. However, the roughly similar predictive relations between invertebrate metrics and various land cover measures (% cover vs. pattern metrics, and catchment vs buffer metrics) present challenges in interpretation of the potential causal connections between land use and biotic response.