State Board approves regional biological regulatory approach
A biology-based approach for protecting the health of streams has been approved for implementation in the San Diego region – a landmark development that is based on more than a decade of research by SCCWRP and its partners to build the scientific foundation for regional, biology-based management of stream ecosystems.
The California State Water Resources Control Board approved the regulatory approach for protecting stream health in August, capping six years of in-depth stakeholder discussion and debate following the San Diego Regional Water Quality Control Board’s 2020 decision to adopt the approach. At the time of State Board approval, both regulatory and regulated stakeholders expressed support for implementing this approach across the San Diego region.
Throughout the six years, SCCWRP continued to advance scientific understanding of bioassessment’s role as a tool for protecting the health of diverse stream ecosystems – insights that have helped improve management confidence in the use of biology-based approaches in regulatory programs.
The San Diego Regional Board’s approach – codified as a water quality objective in a basin plan amendment – relies on the California Stream Condition Index (CSCI), a tool co-developed by SCCWRP more than a decade ago, to generate a single numerical score reflecting the overall health of a stream reach based on the composition of bottom-dwelling invertebrates observed there. Stream sites with CSCI scores that fall below 0.79 – which is a threshold derived from scores at minimally disturbed reference sites – are considered to be in biologically poor condition.
Unlike traditional chemistry- and toxicology-based approaches to regulating stream health, bioassessment-based approaches focus on evaluating the health of biological communities that are sensitive to changes in stream water quality and other environmental stresses.
Following San Diego Regional Board adoption of the regulatory approach in 2020, SCCWRP worked alongside both regulatory and regulated stakeholders to address multiple questions and concerns about applying a bioassessment-based approach to regulate watershed health. These issues included:
- Modified channels: Streams that flow through channels that have been modified via hardening, straightening and other changes tend to receive lower CSCI scores than streams in unmodified channels. As a result, stakeholders expressed concerns about applying a bioassessment-based approach to regulating modified channels, especially if improving bioassessment scores in these streams were to be dependent on removing or extensively modifying channel hardening features that provide flood control protections. SCCWRP found that while bioassessment scores in modified channels correlate with differences in water quality and degree of flow alteration, the correlation is much weaker than for streams in natural channels (SCCWRP Technical Report #1434, #1437). The finding sheds important light on the efficacy of pursuing improvements to water quality as a management strategy for boosting a modified stream’s CSCI scores. Ongoing SCCWRP research is working to develop more advanced stress-response modeling tools to further probe the issue. SCCWRP also has begun evaluating if potential physical habitation restoration projects in engineered channels – such as adding native riparian vegetation and other in-stream habitat, creating naturalistic side channels, and re-creating natural channel forms – can improve stream bioassessment scores without compromising flood-control functions. This research will help managers better understand if one or more of these management options is viable, and if so, what types of stream settings might be good candidates.
- Intermittent streams: The types of organisms that live in intermittently flowing streams can be substantially affected by natural stream drying, as some species lack adaptations to help them survive periods of dryness between flow events. As a result, stakeholders expressed concerns that a bioassessment-based approach to regulating intermittent streams could potentially misinterpret the absence of these species as signs of biological degradation. SCCWRP found that bioassessment scores in Southern California intermittent streams are comparable to perennial streams, and moreover, low scores in intermittent streams can confidently be interpreted as signs of degradation. At the same time, natural drying may lower bioassessment scores for intermittent streams in Northern California (SCCWRP Technical Report #1434, #1419). Ongoing SCCWRP research is working to establish a statewide approach for interpreting CSCI scores in intermittent streams
The San Diego Regional Board’s regulatory approach applies to both perennially and intermittently flowing streams. All natural and engineered channels with soft or natural stream beds are included, but streams that are deemed “fully hardened” as a result of being lined with concrete, rock and similar materials are excluded.
Bioassessment-based approaches to managing stream health are increasingly being incorporated into management programs statewide. For example, the most recent statewide Integrated Report used CSCI scores to identify impaired water bodies that are not supporting aquatic life beneficial uses; future reports are expected to use CSCI scores to identify healthy “Category 1” water bodies that support all uses. Much of the vetting for this approach that has occurred across Southern California is now being expanded statewide, with SCCWRP research helping the Water Boards to determine where and how to apply this approach.
As the bioassessment-based regulatory approach is implemented across the San Diego region, watershed managers across Southern California and beyond are increasingly expected to turn to the SCCWRP science that underlies this approach to help identify effective options for improving and protecting the biological health of streams statewide.
For more information, contact Dr. Raphael Mazor.
More news related to: Bioassessment, Indices of Biotic Integrity, Top News