Improving the TMDL process using watershed risk assessment principles.

Area of Science:

• Environmental Science
• Ecotoxicology
• Water Resource Management

Background:

• Ecological Risk Assessment (ERA) identifies causal links between stressors and ecosystem impacts.
• Watershed-scale ERAs share similarities with Total Maximum Daily Load (TMDL) development, focusing on stressors, sources, and water quality standards.
• Current TMDL approaches often prioritize specific stressors over ecological endpoints, potentially failing to protect designated uses.

Purpose of the Study:

• To explore the application of Watershed Ecological Risk Assessment (WERA) principles to enhance TMDL development.
• To improve the scientific rigor and effectiveness of TMDLs in achieving environmental goals and designated uses.
• To identify specific WERA principles beneficial for TMDL formulation and implementation.

Main Methods:

• Conceptual model development for problem identification in TMDLs.
• Transparent selection of Numeric Targets based on assessment endpoints derived from designated uses.
• Analysis of co-occurring stressors and explicit uncertainty analysis within the TMDL linkage step.

Main Results:

• WERA principles offer a structured approach to problem formulation and target setting in TMDLs.
• WERA integration is particularly valuable for TMDLs lacking numeric standards (e.g., nutrient, sediment TMDLs).
• Applying WERA can ensure that TMDL targets protect broader designated uses, not just numeric water quality criteria.

Conclusions:

• Incorporating WERA principles into TMDL development can significantly improve scientific rigor and ecological relevance.
• WERA-informed TMDLs are more likely to achieve desired environmental outcomes and protect ecosystem health.
• Stakeholder engagement throughout the WERA-TMDL process is crucial for successful implementation.