A comparison of the biotic integrity of two sites in a northern Michigan river.

Abstract

Human modifications of the landscape can significantly impact aquatic ecosystems. Two sections of the Ocqueoc River (Presque Isle County, Michigan) differing in landscape context (forested vs. pasture land), were compared in their biotic integrity using indices to assess habitat and macro-invertebrate assemblages. It was hypothesized that the forested site would have a higher biotic integrity assessed than the pasture site. The indices revealed an overall higher biotic integrity at the forested site than at the pasture site. The Habitat Quality Evaluation Index (HQEI, M-DNR Procedure 51) assessed in the field ranked the forested site as having markedly higher quality characteristics, particularly for stream morphology and substrate composition. A guild analysis was used to compare the feeding roles represented by the aquatic macroinvertebrates which were collected and identified (generally to family level) from both sites. The guild composition at the forested site was more equally distributed and contained a greater percentage of sensitive guilds (e.g. predators) which implied that the forested site is less impacted than the pasture site. The descriptive rankings given to the two sites according to Hilsenhoff's (1988) pollution sensitivity index was ""excellent"" for the forested site and ""very good"" for the pasture site indicating that organic pollution may be present to a small degree at the pasture site while probably not at all at the forested. Species evenness computed with the Shannon index indicated a comparably better quality present at the forested site. Likewise, the multi-variable Benthic Index of Biotic Integrity (B-IBI) adapted from Kerans and Karr (1994) and Lammert (pers. comm.) showed higher quality at the forested site in terms of taxa richness, dominance, and abundance. The results strongly indicate that human activity can influence the biotic integrity of an aquatic ecosystem. Lower biotic integrity, as indicated by assessed habitat quality and macroinvertebrate composition, can result from land use changes due to agriculture (including vegetation loss, changed hydrology, and increased nutrient inputs). Although there is debate as to how this problem should be evaluated, enough evidence, including that collected by this study, indicates that there is a correlation between land use and aquatic biotic integrity.