Using Single-Species and Whole Community Stream Mesocosm Exposures for Identifying Major Ion Effects in Doses Mimicking Resource Extraction Wastewaters

Abstract

Wastewaters and leachates from various inland resource extraction activities contain high ionic concentrations and differ in ionic composition, which complicates the understanding and effective management of their relative risks to stream ecosystems. To this end, we conducted a stream mesocosm dose-response experiment using two dosing recipes prepared from industrial salts. One recipe was designed to generally reflect the major ion composition of deep well brines (DWB) produced from gas wells (primarily Na⁺, Ca²⁺, and Cl^-) and the other, the major ion composition of mountaintop mining (MTM) leachates from coal extraction operations (using salts dissociating to Ca²⁺, Mg²⁺, Na⁺, SO₄^2- and HCO₃^-)-both sources being extensive in the Central Appalachians of the USA. The recipes were dosed at environmentally relevant nominal concentrations of total dissolved solids (TDS) spanning 100 to 2000 mg/L for 43 d under continuous flow-through conditions. The colonizing native algal periphyton and benthic invertebrates comprising the mesocosm ecology were assessed with response sensitivity distributions (RSDs) and hazard concentrations (HCs) at the taxa, community (as assemblages), and system (as primary and secondary production) levels. Single-species toxicity tests were run with the same recipes. Dosing the MTM recipe resulted in a significant loss of secondary production and invertebrate taxa assemblages that diverged from the control at all concentrations tested. Comparatively, intermediate doses of the DWB recipe had little consequence or increased secondary production (for emergence only) and had assemblages less different from the control. Only the highest dose of the DWB recipe had a negative impact on certain ecologies. The MTM recipe appeared more toxic, but overall, for both types of resource extraction wastewaters, the mesocosm responses suggested significant changes in stream ecology would not be expected for specific conductivity below 300 µS/cm, a published aquatic life benchmark suggested for the region.

Keywords: Marcellus shale; algal periphyton; ionic strength; mesocosms; mountain top mining; periphyton; salinity; specific conductivity; stream invertebrates; total dissolved solids; water quality.

Figure 1.

ESF mesocosms set-up for excess TDS dosing study. Each mesocosm represents one half of the channel unit depicted here. Two mesocosms shared a head and tail tank. Recipes are delivered from dosing tank. Unglazed terra cotta tiles depicted in orange. Gravel baskets depicted in textured grey. Abbreviations defined in text.

Figure 2.

Single-Species toxicity tests using cultured individuals exposed to both DWB and MTM recipes and a moderately hard water (MHRW) control. Each test was run twice: pre (left panel) and during dosing (right panel): (a,b) are for C. dubia; (c,d) are H. azteca; (e,f) are P. promelas; and (g,h) are for N. triangulifer. Data are means per dose ± 1 sd, with n = 3 per dose. Colored bars represent significant difference from control (p < 0.05) per Dunnett’s test.

Figure 3.

Single-Species ex situ / in situ test results for the DWB and MTM dosing recipes. Ex situ tests (left panel) and in situ tests (right panel): (a,b) for P. promelas; from Cincinnati and Duluth cultures, respectively (see text); (c) N. triangulifer; (d) C. fluminea; and (e) L. fasciola. Data are means per dose tested ± 1 sd, with n = 4 and 2 per dose for ex situ and in situ, respectively. Colored bars represent significant difference from control (p < 0.05) per Dunnett’s test.

Figure 4.

Taxa-level response sensitivity distributions for DWB (a) and MTM (b) recipes. Data are EC₅₀ SpCond. ETD is elapsed day during dosing period. Individual responses are color-coded by ETD. Horizontal lines are 95% CLs for EC₅₀ from LL2.4 DRM fit. ETD = 856 denotes a cumulative measure, summed over all events between days 8 and 56. ETD = 1529 and 4356 denote measures averaged among 15 and 29 or 43 and 56 sampling dates, respectively (periphyton measures only).

Figure 5.

Dosing recipe EC₅₀ RSD comparisons grouped by levels of ecological organization. The shaded area about each curve represents the 95th prediction probability for the best RSD fitting function. Left panel of graphs (a–c) are based on EC₅₀ SpCond. Right Panel graphs (d–f) are based on ionic strength.

Figure 6.

HC_5s by dosing recipe and level of ecological organization from RSDs based on specific conductivity (a) and ionic strength (b). Error bars are 95% confidence interval for the estimate from the RSD fitting function.

Figure 7.

PRCs for community-level measures: periphyton biovolume densities and gravel invertebrate counts relative abundances for DWB (a,c) and MTM (b,d) recipes, respectively. PRCs are based on Euclidean distance. Stars designate that the results of the permutation test indicated at least one significant difference in community assemblage across doses for the corresponding dosing day. Taxa and their relative loadings (in parentheses) on secondary y-axis (see Supplementary Materials for interpretation). Inconsequential taxa removed from listing for (c,d) for legibility. Table S12 includes complete PRC taxa loading lists. PRC results for each dose are normalized to the control, horizontal line at zero.

Figure 8.

System-level measures: Total invertebrates counted from sampled gravel baskets (a), drift net deployments (b), and captured emergence (c) by recipe and dose. Percentages at top of graphs are Bray–Curtis similarities between specific dose and control based on Taxa1 assemblages. Dosing period average bulk periphyton responses, including total dry weight (d), ash free dry mass (e), and chlorophyll (f). Bars with blue are significantly different from control dose (p < 0.05) per Dunnett’s test. Data are means of two replicate mesocosms ± 1 sd.