Incorporating the Biological Condition Gradient concept into the National Aquatic Resource Surveys: How Do We (or Can We) Get There from Here?

A continuing challenge to interpreting bioassessments of streams and rivers across the US is that benchmarks are often based on “reference” sites that represent the lowest levels of human disturbance available in a state or region. These lowest levels, and the biological condition associated with them, vary substantially across the landscape. This variability constrains our ability to make comparisons of biological condition at larger scales. The Biological Condition Gradient (BCG) provides a conceptual framework that purports to provide a common scale of condition that can improve our ability to make comparisons at larger scales and help put least-disturbed conditions in different regions into context. To date, the BCG concept has been developed for individual states or relatively small regions. The EPA’s National Rivers and Streams Assessment (NRSA) is a national-scale assessment of stream and rivers that acquires biological, stressor, and landscape-level data from a large number of sites using consistent field and laboratory methods, and allows inferences to be made from the set of sampled sites to a much larger target population. Given the fact that both the BCG concept and NRSA have matured over the past 10-20 years, we wonder if the time has come to try to incorporate the BCG concept into NRSA, with the anticipated outcome being national estimates of condition based on the BCG. In this presentation, we will attempt to compare and contrast the BCG approach with the assessment approach used for the NRSA (which is based on the more time-tested use of multimetric indices), describe areas where we think data from NRSA are appropriate for use in BCG development, and identify remaining questions and impediments to applying the BCG concept in NRSA. Our objective is to start constructive dialog and thinking about what the process would look like to make it happen.

Impact/Purpose

A continuing challenge to interpreting bioassessments of streams and rivers across the US is that benchmarks for biological assemblage indicators are often based on “reference” sites that represent least disturbed (best available) condition in a state or region. Least disturbed condition varies substantially across the landscape, constraining our ability to make comparisons at larger scales. This presentation is intended to facilitate constructive thinking and dialog regarding the feasibility of incorporating the Biological Condition Gradient (BCG) concept into the assessments produced from the National Rivers and Streams Assessment (NRSA), one of the EPA’s National Aquatic Resource Surveys. The BCG concept represents an approach that potentially places least disturbed conditions into a common context. The NRSA acquires data at multiple scales from a large number of sites across the nation to assess biological and stressor conditions, and is designed to allow inference from the set of sampled sites to a much larger target population. We will attempt to compare and contrast the approaches used for the BCG and for the NRSA to identify areas where we think the two approaches are compatible and areas where questions remain. The anticipated outcome of incorporating the BCG concept into the NRSA would be national-scale estimates of condition based on the BCG. These results are more directly applicable to EPA Office of Water, EPA Regions, and States to address the reporting objectives of the Clean Water Act, developing numeric biocriteria, and provide information to assist decisions related to status and change in the amount of the resource that is meeting or not meeting designated uses.

Citation

Peck, Dave, Steve Paulsen, AND A. Herlihy. Incorporating the Biological Condition Gradient concept into the National Aquatic Resource Surveys: How Do We (or Can We) Get There from Here? Annual Meeting of the Pacific Northwest Chapter of the Society for Freshwater Science, NA (Virtual meeting), None, November 18 - 19, 2020.