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Evaluation of Total Dissolved Solids and Specific Conductance Water Quality Targets with Paired Single-Species and Mesocosm Community Exposures
Nietch, C., Jim Lazorchak, B. Johnson, AND Joel Allen. Evaluation of Total Dissolved Solids and Specific Conductance Water Quality Targets with Paired Single-Species and Mesocosm Community Exposures. Presented at Society of Environmental Toxicology and Chemistry North America 35th Annual Meeting, Vancouver, BC, CANADA, November 09 - 13, 2014.
Present experimental data from laboratory and mesocosm exposures on the relative sensitivity of stream organsims and whole communities to excess total dissloved solids or specific conductance. The information is useful to the program, regional, and State office interested in establishing aquatic life criteria for these constituents.
Isolated single-species exposures were conducted in parallel with 42 d mesocosm dosing studies that measured in-situ and whole community responses to different recipes of excess total dissolved solids (TDS). The studies were conducted with cultured species and native taxa from moderately concentrated TDS waters. TDS and specific conductance (SpCond) of control mesocosms changed between recipes from ca. 75 and 200, mgL TDS, or 100 and 300 µS/cm SpCond. Excess TDS stocks were dosed to treatment mesocosms to increase concentrations as high as 2500 mgL TDS or 3500 µS/cm SpCond, with 2 to 4 intermediate doses to these extremes, depending on the recipe. Response measures included species survival and growth; macroinvertebrate drift, benthic abundance, and emergence; and periphytic algae biomass and taxonomy. Functional indicators, O2 metabolism and leaf litter decomposition were also measured. Ephemeroptera (mayfly) taxa proved the most sensitive to excess TDS among insects. The bivalve, C. fluminea exposed in the mesocosm appeared as sensitive as the native mayflies. Larval P. promelas were insensitive to excess TDS, but adult fish fecundity responded negatively. Algal periphyton was affected also, but were unlikely the driving factor for consumer responses. After combining all responses across recipes into a single sensitivity distribution based on the 25 percentile response, the lower 5th percentile of this distribution was lower than the minimum State-level water quality target for TDS of 500 mgL, but well above the proposed 300 µS/cm benchmark for SpCond proposed for central Appalachian headwaters. Data highlight the relative importance of the dominant ions comprising the excess TDS, suggesting strong rationale for qualifying new TDS/SpCond targets based on dominant anion.