SELENIUM BUDGETS FOR LAKE POWELL AND THE UPPER COLORADO RWER BASIN¹

Abstract

: A selenium budget for Lake Powell, Utah‐Arizona was determined based on selenium loads at the principal stream input sites to and the output site from the lake. Based on data collected during 1985‐1994, 83 percent of the selenium entering Lake Powell is accounted for at the output site. The rest of the selenium may be incorporated by lake sediment or used by the biota. Considerably more selenium per unit area is produced from the Colorado River Basin above the Colorado River‐Green River confluence than from the Green River Basin and the San Juan River Basin combined. The Gunnison River Basin and the Grand Valley in Colorado produce an estimated 31 and 30 percent of the selenium that reaches Lake Powell, respectively. Irrigation‐related activities are thought to be responsible for mobilizing 71 percent of the selenium that reaches Lake Powell. Selenium concentrations in water at Imperial Dam on the Colorado River upstream of the United States‐Mexico international border are similar to those at the output site of Lake Powell. Therefore, most selenium observed in downstream areas of the Colorado River therefore probably is derived mostly from the Colorado River Basin above Lake Powell.

Hypothesis of Historical Effects From Selenium on Endangered Fish in the Colorado River Basin

“…The Gunnison River basin and the Grand Valley are major contributors to selenium loading in the lower Colorado River basin (Engberg, 1999). An analysis of selenium loading in the Colorado River at the CO-UT state line indicated that about 13% of the load was from the Colorado River basin above irrigation influences, 44% was from the Gunnison River basin including the Uncompahgre Valley, and the remaining 43% from the Grand Valley (Butler et al, 1989).…”

“…The variation over time suggested to Anderson et al (1961) Anderson et al (1961) calculated that 73 to 178 kg/day of selenium were discharged from the Gunnison River to the Colorado River in 1936. By comparison, Engberg (1999) calculated that the Gunnison River passed 31 kg/day to the Colorado River in the period 1985 to 1994, which is less than half of historic loading. Between the time of the computations by Anderson et al (1960) and the computations of Engberg (1999), significant salinity control measures have been instituted by DOI and DOA in the Gunnison River basin.…”

“…The Gunnison River basin/Grand Valley ranked 4th for the highest median water concentration of selenium, 2nd for sediment, 7th for fish, and 1st for birds. Although the lower Colorado River Valley had low selenium in water, it was ranked 4th for sediments and 4th for fish (Engberg, 1998), due to selenium loading from the upper Colorado River basin (Engberg, 1999).…”

Developing integrated methods to address complex resource and environmental issues

“…The dominant anion in the load was sulfate, and the amount attributed to the Mancos is equivalent to 1,400,800 tonnes per year of gypsum dissolution. Nearly all the Se contamination in the UCRB is from natural weathering and irrigation of the Mancos (Clark, 1995;Engberg, 1999). Tuttle and Grauch (2009) estimated that 60 t a −1 of Se were derived from Mancos Shale landscapes in Colorado, representing nearly the entire 2005 Se load in the river near the Colorado-Utah border.…”

“…The Colorado River in the southwestern portion of the United States is considered one of the most stressed in the world because of increasing salinization and selenium (Se) contamination (Engberg, 1999;Serageldin, 2000). Nearly 36 million people and 4.…”