The California State Water Resources Control Board (SWRCB) is developing nutrient water quality objectives for the state’s surface waters. Among the approaches the SWRCB staff is considering is the process-based approach known as the Nutrient Numeric Endpoint (NNE) framework.
The NNE framework is intended to serve as numeric guidance to translate narrative water quality objectives (WQOs). It consists of two tenets: (1) assessment and recommended numeric (regulatory) endpoints based on the ecological response of an aquatic water body to eutrophication (e.g., algal abundance, DO) to assess water body condition and (2) scoping-level models that link the response indicator endpoints to nutrient inputs and other site-specific factors and management controls.
This study found statistically significant relationships and thresholds of adverse effects of benthic chlorophyll a, ash-free dry mass (AFDM), and TN and TP concentrations on indicators of benthic macroinvertebrate (BMI) and algal community structure—employed in this study as indicators of aquatic life (Fetscher et al. 2014).
Fetscher et al. (2014) investigated the relationships between eutrophication stressors (e.g., nutrient and primary producer abundance indicators) and BMI and algal community structure as measures of aquatic life indicators (ALI). BMI and algal community structure were selected because (1) they are the assemblages of choice for bioassessment in California statewide and regional programs, (2) BMI and/or diatom community composition have been used as the basis for developing WQOs in other states and countries, and (3) a large and geographically broad set of ambient survey data is available for both assemblages, using standardized field and laboratory protocols. Other potential indicators of ALI attainment such as DO or pH could be used for setting biomass/nutrient WQOs, but data on diel ranges and fluctuations are not available statewide.
California’s perennial, wadeable streams—as assessed during the bioassessment index period of late spring through mid-summer—exhibited a skew toward the low end of the primary producer abundance gradient. Nearly 66 percent of perennial wadeable stream kilometers had estimated benthic chlorophyll a and 59 percent had estimated TN and TP values below the 75th percentile of each variable at reference sites statewide (Horvitz and Thompson 1952). Among the regions, a gradient in algal abundance and nutrient concentrations was observed from high in urban and agricultural areas (e.g., South Coast, Central Valley) to low in less densely developed areas of the state (e.g., North Coast and Sierra regions) (Fetscher et al. 2014).
The majority of the state’s wadeable streams sampled are below the 75th percentile of minimally disturbed reference sites. Statistically detectable thresholds were found for benthic chlorophyll a, AFDM, and nutrients; benthic chlorophyll a thresholds were below current NNE endpoints protective of beneficial uses recommended in the Tetra Tech study (2006b). Validation exercise indicates that there is considerable room for improvement in benthic biomass spreadsheet tool (BBST); inclusion of landscape and site-scale factors provide avenue for model refinement (Fetscher et al. 2014).
References:
Fetscher, E., M. Sutula, A. Sengupta, and N.E. Detenbeck. 2014. Linking Nutrients to Alterations in Aquatic Life in California Wadeable Streams. EPA/600/R-14/043. U.S. Environmental Protection Agency, Washington, DC. Accessed October 2016.
https://cfpub.epa.gov/si/si_public_record_report.cfm?dirEntryId=274010&simpleSearch=1&searchAll=LINKING+NUTRIENTS+TO+ALTERATIONS.
Horvitz, D.G. and D.J. Thompson. 1952. A generalization of sampling without replacement from a finite universe. Journal of the American Statistical Association 47:663–685.
Tetra Tech (Tetra Tech, Inc.). 2006b. Technical Approach to Develop Nutrient Numeric Endpoints for California. Prepared for U.S. Environmental Protection Agency Region 9 and California State Water Resource Control Board. Accessed October 2016.
http://www.waterboards.ca.gov/water_issues/programs/nutrient_objectives/development/docs/techapproach_freshwater2006.pdf EXIT.