A fundamental unit of replication in stream bioassessment research: the μ-basin

R.C. Bailey. Department of Biology, The University of Western Ontario, London, Ontario, Canada N6A 5B7

One of the most deceptively simple, yet intrinsically complex, parts of stream bioassessment research is defining a site. Some define the length of a site arbitrarily by multiplying the stream width by a factor of 10 or 20. Others use a geomorphological definition of a stream reach, and the reach is the site. I propose that for bioassessment research in a given area, μ-basins between 100 and 250ha are defined. Within these μ-basins, both outflow site and drainage basin characteristics can be quantified, and variation among μ-basins described and modeled. The properties of sites in larger basins (including cumulative effects of stressors) can then be predicted by up scaling models built with μ-basins. I will illustrate the determination and description of μ-basins with the Upper Thames River basin in southwestern Ontario.