Characterization of selenium in the lower Gunnison River basin, Colorado, 1988-2000

Salinity and selenium yield maps derived from geostatistical modeling in the lower Gunnison River Basin, western Colorado, 1992–2013

“…Mast and others (2014) used laboratory leaching experiments and geochemical modeling to investigate selenium speciation and mobilization, concluding that selenium is released mainly through dissolution of soluble salts and gypsum found in soil and bedrock. Monitoring is ongoing in the lower Gunnison River Basin and other parts of western Colorado to improve understanding of salinity and selenium loading, source areas, and trends (Butler and Leib, 2002;Leib, 2008;Thomas and others, 2008;Mayo and Leib, 2012;Stevens and others, 2018;Henneberg, 2020). The installation of a 30-well monitoring network on the east side of the Uncompahgre River in the lower Gunnison River Basin has facilitated additional studies to characterize groundwater quality and groundwater-surface water interactions in the area (Mills and others, 2016;Thomas and others, 2019;Mast, 2021).…”

Characterization of groundwater quality and discharge with emphasis on selenium in an irrigated agricultural drainage near Delta, Colorado, 2017–19

“…Sunflower Drain is one of the largest tributary sources of selenium to the Gunnison River upstream from the Uncompahgre River (Butler and Leib, 2002) and is currently part of a water-quality monitoring network supported by the SMP (Reclamation, 2011). Continued monitoring is important for tracking current conditions as well as long-term trends in selenium concentrations and loads.…”

“…Most studies to date have focused separately on either selenium occurrence in surface water or groundwater. Comprehensive surface-water studies of selenium loading in the LGRB were conducted by Butler and Leib (2002) and more recently by Stevens and others (2018). The most extensive groundwater study was conducted by Thomas and others (2019), who characterize the hydrology and water quality of shallow groundwater using a 30-well network on the east side of the Uncompahgre River.…”

Source contributions to suspended sediment and particulate selenium export from the Loutsenhizer Arroyo and Sunflower Drain watersheds in Colorado

“…Selenium has long been recognized as a water-quality constituent of concern in the lower Gunnison River Basin because of its effects on aquatic ecosystems (Butler and Leib, 2002). In 2013, the Bureau of Reclamation established the Selenium Management Program for the lower Gunnison River Basin in response to a Programmatic Biological Opinion issued by the U.S.…”

“…All landscapes underlain by Mancos Shale have the potential to be sources of particulate selenium to rivers, but where mobilization of dissolved selenium is great, mobilization of particulate selenium may also be high. Loutsenhizer Arroyo (Montrose County, Colorado) and the agricultural drainage feature locally known as Sunflower Drain (Delta County, Colorado, near the municipality of Delta) have been recognized and studied as watersheds that contribute substantially to dissolved selenium loads in the lower Gunnison River Basin (Butler and Leib, 2002;Mast and others, 2014;Mast, 2021). Both watersheds have mixed land uses that include rangeland, recreational areas, and agricultural lands that require substantial imports of water for irrigation, which generates substantial return flows (Thomas and others, 2019).…”