PS 37-16 - Ecological value of low-salinity produced water from coal bed methane extraction and exploration in low-order streams of the arid west

Abstract: Small, low-order, low-volume streams are key ecological features of landscapes throughout the arid western United States. In ecoregions where larger rivers with substantial perennial flow are few and far between, the vascular plants, algae, benthic macroinvertebrates and in some cases, fish, form the basis for maintaining an aquatic ecosystem and riparian corridor, as well as the terrestrial and aerial organisms the stream supports. Ongoing drought and increasingly rapid spring snowpack melt can drive formerly perennial surface-flow streams to intermittency and even an ephemeral state, while increasing the duration of dry periods in historically ephemeral systems. The purpose of this ongoing, multi-year study is to assess the comparative health of benthic macroinvertebrate (BMI) communities in small streams that are either ephemeral, without continuous flow, or perennial due to discharge of low-salinity, NaHCO₃-dominated, coal bed methane (CBM) water in the Raton Basin of southern Colorado. Sample collection was both semi-quantitative using 500 µm D-nets, and opportunistic (for large invertebrates such as crayfish); samples were preserved and identified to the lowest practical taxon. Multi-year data have demonstrated the presence of robust BMI communities; a variety of taxa were identified including Diptera, Coleoptera, Ephemeroptera, Trichoptera, and others listed as sensitive by the Colorado Department of Public Health and Environment. Although produced water supplying the streams may periodically show whole effluent toxicity (WET) with Ceriodaphnia dubia, those occurrences are not indicative of the overall BMI community health. Information collected to date suggest that ongoing release of CBM produced water is critical in maintaining the aquatic communities in these streams, and in-stream biomonitoring may be the best course of action to ensure the health of the communities, per the directives of the Clean Water Act.