The Oregon Department of Environmental Quality and California’s North Coast Regional Water Quality Control Board have both included the Klamath River on their Clean Water Act section 303(d) lists of impaired waters. Identified impairments include excursions of criteria for nutrients, temperature, and organic enrichment/low DO for segments of the river in California. Oregon lists several portions of the Klamath River and its tributaries for excursions of criteria for DO, chlorophyll a, temperature, pH, and ammonia.
The California Nutrient Numeric Endpoint (NNE) approach is being used to set initial nutrient endpoints for water bodies requiring nutrient TMDLs. California is taking a risk-based approach in which targets are developed for response variables (or secondary indicators) such as algal density. Those response targets can then be converted to site-specific nutrient targets through the use of modeling tools.
This case study focuses on the periphyton target and development of nutrient numeric endpoints associated with that target, specifically TN. Nutrient loading in the Klamath River produces high levels of periphytic algae. To date, targets have not been established for that endpoint. Periphyton affects the balance of DO and pH in the river and excess growth can directly impair designated uses, and is, therefore, important to consider as a response endpoint. Targets for DO and pH are defined in basin plans, and the relationship between those endpoints, planktonic algal growth, and nutrients is addressed in an existing calibrated model.
The California NNE approach recommends setting response targets for benthic algal biomass in streams based on maximum density as mg/m2 chlorophyll a. A specific concern for the Klamath River is that the risk of Cladophora prevalence increases with increasing maximum benthic chlorophyll a. The California NNE method was applied to the analysis of periphyton in the Lower Klamath River and appears to provide a reasonable fit to observed maximum periphyton density (as chlorophyll a) (Tetra Tech 2006a).
Reference:
Tetra Tech (Tetra Tech, Inc.). 2006a. Nutrient Numeric Endpoints for TMDL Development: Klamath River Case Study – California NNE Case Study. Prepared for Region 9 U.S. Environmental Protection Agency and the California State Water Resources Control Board. Accessed October 2016. http://www.waterboards.ca.gov/plans_policies/docs/nutrients/klmth_rvr.pdf EXIT.