Selenium Mobilization from Shales

Science Center Objects

Selenium (Se) and salinity (total dissolved solids) are water-quality concerns in much of the arid western US where agricultural and urban irrigation overlie Cretaceous-age shale.  Leaching of Se and salinity from shale can degrade water quality and negatively affect aquatic biota in receiving water bodies. In the upper Colorado River Basin, programs since 1985 have worked to reduce Se and salinity loads to the Colorado River through implementation of best management practices; however, there is still a lack of understanding of how periodic recharge (wetting and drying) control mobilization of Se and salinity from shale. Monitoring results also indicate statistical relations between dissolved nitrate and Se concentrations, suggesting that nitrate may play an important role in Se mobilization. 

This study has evaluated physical and chemical processes controlling Se and salinity mobilization from shales in the upper Colorado River Basin.  Specific research questions addressed by this study include:

  • How do recharge and water-table fluctuations (wetting and drying) affect the mobilization of Se and salinity from shales?
  • How does the presence of  dissolved nitrate in groundwater affect Se mobilization from shales?  
Study site locations, major drainages, and areas underlain by Mancos Shale in the lower Uncompahgre River Basin

 Loutzenhizer Arroyo, a tributary of the Uncompahgre River, has some of the greatest Se concentrations in the river basin 

(Public domain.)