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Community-Level Effects of Excess Total Dissolved Solids Doses Using Model Streams
Citation:
Nietch, C., Jim Lazorchak, B. Johnson, B. Ramakrishnan, P. Weaver, D. Macke, K. Daniels, S. DeCelles, D. Brown, AND C. Impellitteri. Community-Level Effects of Excess Total Dissolved Solids Doses Using Model Streams. Presented at Society of Environmental Toxicology and Chemistry, Nashville, TN, November 17 - 21, 2013.
Impact/Purpose:
Presentation to update environmental chemistry and toxicology community on observed effects of excess TDS formulations on a whole stream benthos. This work informs the setting of effluent guidelines and aquatic life criteria for total dissolved solids.
Description:
Model stream chronic dosing studies (42 days) were conducted with four different total dissolved solids (TDS) recipes. The recipes differed in their relative dominance of major ions. One was made from sodium and calcium chloride salts only. Another was similar to the first, but also included minor additions of salts of strontium, barium, magnesium, potassium, and bromide. A third was dominated by sulfate and bicarbonate while attempting not to skew sodium to calcium ratios beyond what is found in real systems. The last was comprised of sodium bicarbonate. The TDS composition and dosing gradients were derived from field data for streams where high potential for excess TDS impact exists. The recipes were dosed to a continuously renewed natural river water feed that represented a moderately hard water quality. All tests followed a dose response design and paired single-species exposures in both bench- scale whole effluent testing (WET) and ex-situ formats with whole community responses. In the model streams, measurements of periphytic biomass, chlorophyll content, and algal speciation were made. Macroinvertebrate counts, biomass, emergence and drift were assessed. Nutrient cycling, metabolism, and litter decomposition indicators were also tracked during each TDS dosing period. When the ions in excess came from the addition of sodium and calcium chloride only, the results indicated change in the stream periphyton occurring at TDS around 700 mg/L (EC20), macrobenthic structure was significantly altered after 1000 mg/L, and insect development (growth and emergence) was affected at TDS as low as 300 mg/L. These TDS sensitivity thresholds appeared to increase (i.e., communities are less sensitive) when the recipe included the minor cations of strontium, barium, magnesium, and potassium in relevant proportions. Communities appeared more sensitive to the TDS recipe dominated by sulfate and bicarbonate anions. The results provide community-level context for existing State-level TDS criteria for aquatic life, which generally ranges between 500 and 1500 mg/L pending designated use and natural background conditions, and is often qualified by chloride and sulfate content. The observed whole community responses suggest reconsideration of TDS aquatic life criteria may be warranted in some effluent dominated systems.
