M6 AM Suspended and Bedded Sediments and Nutrients: Exposure-response Relationships
Monday, 14 November 2005: 8:00 AM - 11:40 AM in 324-326

(PAU-1117-835428) Identifying biological thresholds of impact for sedimentation and nutrients in freshwater streams.

Paul, J¹, McDonald, M¹, ¹ NHEERL/ORD, USEPA, RTP, NC, USA

ABSTRACT- A conditional probability analysis (CPA) approach has been developed for identifying biological thresholds of impact for use in the development of geographic-specific water quality criteria for protection of aquatic life. This approach expresses the threshold as the likelihood of exceeding a given value of a pollution metric. Uncertainty and natural variability are inherently incorporated into the analysis. Application of this approach with survey data (probability-based sampling design) allows extrapolation of the results to the entire geographic area and eliminates possible bias in site selection. Data for freshwater streams from various states have been used for the analyses. Benthic community index values (EPT taxa richness) and fish IBIs were used to identify impacted stream conditions in the benthic and pelagic compartments. Indicators of sedimentation (percent fines in bed, mean particle size of bed, turbidity) and nutrients (total nitrogen, total phosphorus, chlorophyll a) were evaluated individually and in combination. Logistic regression analysis was used to determine odds ratios and relative risks. The results for multiple stressors (combination of indicators for sedimentation and nutrients) were not a simple linear combination of results for the individual indicators. Although final development of water quality standards requires a management decision, the development of scientifically-defensible approaches for establishing criteria based on significant deviations from expected biological condition across a wide range of geographic conditions should be a useful initial step in the process.

Key words: sedimentation, nutrients, wadable streams, multiple stressors