EPA Research Partner Support Story: Development of Biological Condition Gradient models to advance assessment of non-wadeable rivers

Partner: New Mexico Environmental Department (NMED)
Challenge: Develop water quality assessment methods for highly altered systems, such as the middle Rio Grande
Resource: Integrated and organized existing physical, chemical, and biological data to develop and calibrate models for both fish and benthic macroinvertebrate communities based on the Biological Condition Gradient (BCG) approach and technical expertise
Project Period: 2018 – 2020

A lack of defined numerical thresholds limits the ability of the state of New Mexico to sustain, restore and protect non-wadeable rivers in the state, a major source of water for most of the state’s population. In addition, because these rivers have been greatly altered from their original conditions, “minimally disturbed” reference waters do not exist for determining threshold assessments.

"The Biological Condition Gradient models developed with EPA and an interdisciplinary team of experts are a leap forward for water quality protection of the middle Rio Grande. We look forward to continued collaboration with EPA in developing new methods to protect New Mexico’s water resources." – New Mexico Environment Department Water Protection Division Director Rebecca Roose

To address these challenges, EPA researchers, in collaboration with EPA Region 6 (South Central), NMED, Tetra Tech, and a panel of fish and macroinvertebrate experts from a number of organizations and universities, developed a suite of Biological Condition Gradient (BCG) models for fish and benthic macroinvertebrate communities of the middle Rio Grande, which is habitat for the threatened and endangered Rio Grande silvery minnow. The BCG provided the state with a tool to evaluate biological expectations over a range of stressor conditions within the middle Rio Grande.

EPA ORD, in collaboration with EPA Region 6, Tetra Tech and NMED, using data from EPA’s National Aquatic Resource Surveys, also found the BCG models to be potentially applicable to other sandy-bottomed rivers in the southwestern United States. With this development, other states in the intermountain region are interested in using the models for their sandy-bottomed strams.

NMED uses the BCG models to develop quantitative thresholds of biological condition to evaluate the level of impairment from stressors such as excess nutrients and sediments in the middle section of the Rio Grande. Similar thresholds may be developed for other non-wadeable, sandy-bottomed rivers within the state.