Evaluating physical habitat integrity in relation to the biological potential of streams

Physical habitat integrity, while a necessary condition for ecological integrity, is not well defined and rarely examined in relation to the biological potential of a stream. The relations of physical habitat to the biota need to be quantified so as to better establish reference conditions and to document those physical habitat alterations that actually impact the biota. I evaluated the relation of physical habitat to benthic invertebrate communities in Missouri, U.S.A., streams - at both reference quality and habitat-altered sites. Six common within-stream habitats were delineated from each of 45 streams of reference quality in three ecoregions. Distinctive assemblages of invertebrates were associated with each habitat type. A spatial hierarchy of the influence of habitat was evident. At the largest scale, physical attributes unique to ecoregions were more influential than local conditions in structuring invertebrate communities. Within an ecoregion, however, small-scale habitat conditions were more of an influence than stream location because communities collected from the same habitat type at different streams were more similar than those collected from different habitat types at the same stream. I used this information to develop reference habitat conditions for streams of each ecoregion. I then evaluated invertebrate communities from 20 streams with varying habitat conditions to model the variation and sensitivity of biological metrics in order to assess how the biota responded to habitat changes. Biological responses to habitat alterations were readily documented by taking into account both the presence or absence of particular habitats and the quality of each habitat type.