Considerations when Using the Reference Condition Approach for Bioassessment of Freshwater Ecosystems

Abstract

The use of the reference condition approach (RCA) in environmental assessments is becoming more prevalent. Although the RCA was not explicitly described in Green's (1979) book on statistical methods for environmental biologists, we expanded his decision key for selecting an appropriate environmental study design to include this approach. The RCA compares the biological community at a potentially impacted ‘test’ site to communities found in minimally impacted ‘reference’ sites. However, to implement the RCA there are a number of assumptions and decisions that must be made. We compare several common multimetric and multivariate bioassessment methods to illustrate that four key decisions inherent in the RCA framework (i.e., criteria used for reference site selection, for grouping similar reference sites, for comparing test and reference sites, and for evaluating the cause of impacts) can markedly affect test site appraisals. Specific guidelines should be developed to select appropriate reference sites. Based on analyses of real and simulated data, we recommend a minimum of 20, but preferably 30 to 50 reference sites per group, and verification of groupings with more than one classification method. New approaches (e.g., test site analysis) incorporating the strengths of both multimetric and multivariate methods can be used to compare test and reference sites. Additional ecological information, models relating degree of impact to a stressor or habitat gradient, and variance partitioning can also be used to isolate the probable cause of impairment, and are particularly valuable when appropriate reference sites are unavailable.

Cautions on using the Before-After-Control-Impact design in environmental effects monitoring programs

“…If the impact occurred before any monitoring began, the Impact site can be compared to a nearby (or upstream) Control site, but this design is suboptimal because it assumes the Control and Impact sites were similar prior to the impact. If the timing and location of the impact are unknown, the Reference Condition Approach has been suggested as a method for quantifying impairment of an affected site, but specific and rigorous guidelines must be met for this approach to be considered sound (Bowman and Somers 2005). If the impact has not yet occurred, but the timing and location are known, the Before-After-Control-Impact (BACI) design was suggested as optimal (Green 1979).…”

Science-based Framework for Environmental Benefits Assessment

“…The use of reference approaches in environmental assessments is becoming more prevalent (Bowman and Somers 2005). Reference approaches generally involve comparing characteristics of a 'project' site to those found in a minimally impacted 'reference' site or to a suite of reference sites representing some range of conditions.…”

A tiered method for discriminant function analysis models for the Reference Condition Approach: model performance and assessment

“…The resultant RCA databases include BMI abundance data, water chemistry and site-, chan-nel-, and watershed-level habitat data for hundreds of reference and test sites. The habitat variables are used at the sitematching step of RCA assessment (Bowman and Somers 2005). In the Benthic Assessment of Sediment (BEAST) approach, clustering based on BMI followed by Discriminant Functions Analysis (DFA) is used as the site-matching strategy (Reynoldson et al 1995(Reynoldson et al , 1997.…”

“…The BEAST approach assumes discrete groupings of reference sites, but in reality, BMI communities may span a continuum. As a result, test sites may be classified into the incorrect cluster of reference sites (Bowman and Somers 2005). A similar clustering method is used for Australian River Assessment System (AUSRIVAS; Simpson and Norris 2000).…”