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Stream mesocosm response sensitivities to simulated ion stress in produced waters from resource extraction activities
Citation:
Nietch, C., Jim Lazorchak, B. Johnson, AND P. Weaver. Stream mesocosm response sensitivities to simulated ion stress in produced waters from resource extraction activities. Presented at SETAC North America Focused Topic Meeting: Environmental Quality Implications of Unconventional Natural Gas Development, Denton, TX, March 17 - 19, 2016.
Impact/Purpose:
To increase the ecological relevance of laboratory exposures intent on determining species sensitivity to ion stress several stream mesocosm dosing studies were conducted that pair single-species and community-level responses in-situ and allow for direct comparison among different ionic mixtures of excess specific conductivity. This work is a synthesis of the results placed within the context of setting water quality targets for ion stress.
Description:
To increase the ecological relevance of laboratory exposures intent on determining species sensitivity to ion stress from resource extraction activities we have conducted several stream mesocosm dosing studies that pair single-species and community-level responses in-situ and allow for direct comparison among different ionic mixtures of excess specific conductivity. Two ion recipes were dosed in parallel to reflect the major ion distribution found in both produced waters from Eastern deep well brines and in leachates from spoils of coal mining operations. Three additional mesocosm tests dosed 1 or 2 major salts each to compare responses of produced and leachate ion mixtures to effects observed for a dominating cation-anion pairing. All stock salt solutions were mixed with a natural river water background and continuously dosed to a naturally and continuously colonized stream benthos over a 42 day period. Dose-response models were fit to numerous single-species and community-level (e.g., ephemeroptera emergence, total insect drift, periphytic diatom density) endpoints. Significant 25% inhibition concentration (IC25) effects were estimated, and these were ranked to produce a mesocosm response sensitivity distribution for each recipe. From these distributions hazard concentration (HC) was used to compare the relative sensitivity among recipes. HC10, or the 10th-centile of the IC25 response distribution for specific conductance was significantly higher (i.e., lower sensitivity) for the recipe mimicking the major ion distribution in Eastern deep well brines compared to the one meant to reflect coal spoil leachate. Comparatively, a sodium/calcium chloride recipe produced higher sensitivity than the deep well brine ion mixture, while sodium bicarbonate and magnesium sulfate recipes showed greater sensitivity (i.e., lower HC10s) than both the sodium/calcium chloride and the surface coal leachate recipes. Collectively, results suggest that stream biotic communities are more sensitive to conductivity stress from resource extraction activities that produce waste waters rich in sulfate and bicarbonate compared to those dominated by chloride. An in-stream water quality target of at most 1000 S/cm would be needed to be protective of stream communities exposed to ionic stress from produced waters of deep well brines, and one less than 500 S/cm would be necessary for waters receiving excess ions from sulfate and bicarbonate or sodium/calcium chloride salts only.
