An Iterative Procedure for Identifying High-Quality Reference Sites From a Set of Less-Than-Pristine Catchments.

Selection of reference sites for bioassessment purposes usually relies on determining the amount of landscape alteration that has occurred within catchments upstream of candidate sites. By definition, biota in streams draining unaltered catchments are in reference condition. However, few catchments exist that have not been altered in some way. Furthermore, such pristine catchments are usually found in unique settings, and we cannot use data from their streams to infer what reference conditions should be like elsewhere. How much can we relax the landscape criteria used to initially screen reference sites and be confident that biological integrity is still similar across sites? Once a set of high-quality reference sites is selected based on stringent landscape criteria, bioassessments will reveal what other sites in the region are equivalent to reference. These sites can be used to increase the sample size of reference sites and to some extent the range of environmental conditions represented by the reference sites. By applying this iterative procedure, we have more than doubled the number of reference sites in several regions.