Soil disturbance as a driver of increased stream salinity in a semiarid watershed undergoing energy development Carleton R. Bern a,⇑ , Melanie L. Clark b , Travis S. Schmidt c , JoAnn M. Holloway a , Robert R. McDougal a a Crustal Geophysics and Geochemistry Science Center, U.S. Geological Survey, Denver Federal Center, Denver, CO 80225, USA b Wyoming-Montana Water Science Center, U.S. Geological Survey, Cheyenne, WY 82007, USA c Colorado Water Science Center, U.S. Geological Survey, Fort Collins, CO 80526, USA article info Article history: Received 25 June 2014 Received in revised form 27 January 2015 Accepted 6 February 2015 Available online 23 February 2015 This manuscript was handled by Laurent Charlet, Editor-in-Chief, with the assistance of Barbara Mahler, Associate Editor Keywords: Coalbed methane Discharge Hydrograph Oil and gas development Marine shale Total dissolved solids summary Salinization is a global threat to the quality of streams and rivers, but it can have many causes. Oil and gas development were investigated as one of several potential causes of changes in the salinity of Muddy Creek, which drains 2470 km 2 of mostly public land in Wyoming, U.S.A. Stream discharge and salinity vary with seasonal snowmelt and define a primary salinity–discharge relationship. Salinity, measured by specific conductance, increased substantially in 2009 and was 53–71% higher at low discharge and 33–34% higher at high discharge for the years 2009–2012 compared to 2005–2008. Short-term processes (e.g., flushing of efflorescent salts) cause within-year deviations from the primary relation but do not obscure the overall increase in salinity. Dissolved elements associated with increased salinity include cal- cium, magnesium, and sulfate, a composition that points to native soil salts derived from marine shales as a likely source. Potential causes of the salinity increase were evaluated for consistency by using measured patterns in stream chemistry, slope of the salinity–discharge relationship, and inter-annual timing of the salinity increase. Potential causes that were inconsistent with one or more of those criteria included effects from precipitation, evapotranspiration, reservoirs, grazing, irrigation return flow, groundwater discharge, discharge of energy co-produced waters, and stream habitat restoration. In contrast, surface disturbance of naturally salt-rich soil by oil and gas development activities, such as pipeline, road, and well pad construction, is a reasonable candidate for explaining the salinity increase. As development con- tinues to expand in semiarid lands worldwide, the potential for soil disturbance to increase stream sali- nity should be considered, particularly where soils host substantial quantities of native salts. Published by Elsevier B.V. 1. Introduction Salinity, the sum of dissolved salts or solutes in water, is a glob- al challenge to water-quality management and a wide variety of human activities can increase the salinity of streams and rivers (Cañedo-Argüelles et al., 2013). Excessive salinity can make water unsuitable for domestic use (DeZuane, 1997) and negatively impact irrigated agriculture (Ayers and Westcot, 1985) and wildlife (Chapman et al., 2000; Hart et al., 1991). Water and energy devel- opment have always been intertwined as energy development can impact water quality and availability (Entrekin et al., 2011; Olmstead et al., 2013) and vice versa (Nicot and Scanlon, 2012). Such interactions are part of the water-energy nexus that will increasingly influence how both of those resources are used world- wide (Healy et al., in press; Schnoor, 2011; Voinov and Cardwell, 2009). In the western United States, new energy development technologies are spurring the development of unconventional oil and gas resources including shale gas, oil recovered by hydraulic fracturing and coalbed methane (CBM) (Breyer, 2012; Kerr, 2010). In western Wyoming, the Wyoming Landscapes Conservation Initiative (WLCI) has been organized to ensure wild- life and habitat viability in southwest Wyoming as the region undergoes significant energy development (http://www.wlci.gov/). One component of that work has been monitoring of streams for water quality changes. In this paper, an upward shift in salinity for a given discharge rate is documented for Muddy Creek, a semiarid watershed in the development area. The goal of the study is to determine the cause of that increase in salinity to the extent possible with available data. Globally, surface water quality faces a variety of threats, but for a given watershed it is rare to have sufficient data to link changes to causes. Establishing cause and effect can be difficult in large and com- plex natural systems. Stream water composition, particularly from http://dx.doi.org/10.1016/j.jhydrol.2015.02.020 0022-1694/Published by Elsevier B.V. ⇑ Corresponding author. Tel.: +1 303 236 1024; fax: +1 303 236 3200. E-mail address: cbern@usgs.gov (C.R. Bern). Journal of Hydrology 524 (2015) 123–136 Contents lists available at ScienceDirect Journal of Hydrology journal homepage: www.elsevier.com/locate/jhydrol