PARENT SESSION
TP1 - Arid Ecosystems: Unique Considerations
Chair: Gensemer, Bob1, 1 ENSR Corporation, Fort Collins, CO
Co-chair: Meyerhoff, Richard2, 2
2:10 PM to 5:30 PM - Tuesday, 19 November 2002
Room Ballroom G-I
(416) Application of Ambient Water Quality Criteria to Ephemeral and Effluent-dependent Waters.
Gensemer, Robert*,1, Dethloff, Gail1, Gerath, Mark2, Curley, Ed3, Sierra, Karen3, 1 ENSR International, Fort Collins, CO2 ENSR International, Westford, MA3 Pima County Wastewater Management, Tucson
ABSTRACT- While Ambient Water Quality Criteria (AWQC) are intended to be protective of aquatic life and their uses nation-wide, they may not always be appropriate for the unique species assemblages and characteristics of ephemeral and effluent-dominated watercourses in the arid western U.S. Therefore, as part of the Arid West Water Quality Research Project, we evaluated four existing and/or proposed AWQC (copper, selenium, diazinon, and ammonia) for their relevance to these unique aquatic ecosystems. Our results suggest that existing AWQC magnitude, frequency, and duration (i.e., averaging period) values for these four criteria seem to be generally appropriate for use in effluent-dominated systems in the arid west. However, the unique nature of these systems may call into question the straightforward application of AWQC. Important factors in this regard could include whether effluent flows sufficiently stabilize the natural variability in stream water flows in arid lands, and whether flow-related changes in water quality characteristics might significantly influence pollutant bioavailability. In contrast to effluent-dependent systems, changes in AWQC for naturally ephemeral streams might be even more necessary to set appropriate water quality standards. Such changes could begin with applying EPAs site-specific modification procedures (e.g., recalculation, water-effects ratio, resident species) to all waters classified as ephemeral (i.e., via use of an appropriate designated use category). In addition, the default averaging period and/or frequency of allowed excursions may also require modification owing to the unique hydrologic and biotic characteristics of these ephemeral ecosystems. Additional study of arid west ephemeral and effluent-dependent systems is warranted to verify these conclusions.
Key words: ambient water quality criteria, ephemeral waters, effluent-dependent waters, arid west