Coal bed natural gas (CBNG) development in the Powder River geologic basin (PRGB) may alter water quality, quantity, or aquatic habitats. CBNG product water is generally higher than surface waters in dissolved sodium and bicarbonate and sometimes exceeds toxicity levels for fathead minnows and daphnids. Montana and Wyoming water quality standards do not account for differential ion toxicity; toxicity data for most fishes of the PRGB are lacking, and there are minimal data available on composition of CBNG product water. One field study suggests that CBNG may limit fish distribution. Metals and trace elements in CBNG product water, wetlands, impoundments, sediments, and biological tissues may exceed chronic standards or other biologically relevant thresholds. Product-water dissolved oxygen, pH, and turbidity are comparable to surface waters, but spatiotemporal temperature variation may disrupt natural cues. Increased discharge from CBNG product-water discharge or groundwater depletion may alter the ecology of PRGB streams. Indirect effects may occur if development alters food webs, plant communities, or aquatic habitats. Road construction may increase sedimentation, and stream crossings may fragment fish populations. Impoundments may be a source of non-native fish species. The uncertainty concerning potential effects of CBNG development on fish in the PRGB highlights the need for further research and monitoring.
1. Extraction of coalbed natural gas (CBNG) often results in disposal of large quantities of CBNG product water, which may affect aquatic ecosystems. We evaluated the effects of CBNG development on fish assemblages in tributary streams of the Powder and Tongue rivers. We used treatment and control, impact versus reference sites comparisons, surveys of CBNG product-water streams and in situ fish survival approaches to determine if CBNG development affected fish assemblages. 2. Several of our results suggested that CBNG development did not affect fish assemblages. Species richness and index of biotic integrity (IBI) scores were similar in streams with and streams without CBNG development, and overall biotic integrity was not related to the number or density of CBNG wells. Fish occurred in one stream that was composed largely or entirely of CBNG product water. Sentinel fish survived in cages at treatment sites where no or few fish were captured, suggesting that factors such as lack of stream connectivity rather than water quality limited fish abundance at these sites. Fish species richness did not differ significantly from 1994 to 2006 in comparisons of CBNG-developed and undeveloped streams. Biotic integrity declined from 1994 to 2006; however, declines occurred at both impact and reference sites, possibly because of long-term drought. 3. Some evidence suggested that CBNG development negatively affected fish assemblages, or may do so over time. Specific conductivity was on average higher in treatment streams and was negatively related to biotic integrity. Four IBI species richness metrics were negatively correlated with the number or density of CBNG wells in the catchment above sampling sites. Bicarbonate, one of the primary ions in product water, was significantly higher in developed streams and may have limited abundance of longnose dace (Rhinichthys cataractae). Total dissolved solids, alkalinity, magnesium and sulphate were significantly higher in developed streams. 4. Biological monitoring conducted before the development of CBNG, and continuing through the life of development and reclamation, together with data on the quantity, quality and fate of CBNG product water will allow robust assessment of potential effects of future CBNG development worldwide.
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