Synthesizing reference conditions for highly degraded areas through best professional judgment

Abstract

Reference sites, comparable in physical and chemical characteristics to test sites with the exception of the effect of interest, provide a set of species to contrast against test site data and assign a condition to test sites in the Reference Condition Approach. However, what if disturbance is ubiquitous and comparable reference sites are absent? Here, we use the Detroit River as a case study where development and industrialization has rendered reference sites absent. In this paper, a novel application of best professional judgment was developed to generate a set of species characteristic of reference conditions. The synthesized assemblage functions as substitute to a sampled reference site and can be applied analogously towards determining condition and assessing recovery. Members of the Huron–Erie Corridor Steering Committee, comprised of agency partners that manage the corridor, were surveyed to produce a hypothetical data matrix of the fishes present in the river in the absence of anthropogenic disturbance. The synthesized assemblages were assessed using an Index of Biotic Integrity and subsequently integrated into a Principal Coordinates Analysis with test site fish assemblage data. Recovery and response to remediation was determined by the position of the test sites within confidence ellipses. The results indicated signs of recovery in upstream sites of the Detroit River, but no recovery at downstream sites. The application of the best professional judgment approach towards reference conditions provides a novel and versatile method to interpret species assemblage change and allows practitioners the ability to select specific assemblages coincident with restoration objectives.