Selenium, salt levels dropping in Colorado River
Levels of salt and selenium in the Colorado River have fallen in recent years, according to studies by the U.S. Geological Survey.
The amounts of salt and selenium seem to be dropping as a result of years of water freeing them from exposed soils, federal efforts to control them and, partially, increased development, said Ken Leib, the western Colorado studies section chief for the USGS.
Leib spoke Monday at a seminar by the Water Center at Mesa State College, “Natural Resources of the West: Water.”
The study showing the reductions of salt and salinity in the Gunnison and Colorado rivers is currently under review by the federal agency, but Leib said he hoped to have it released by early 2011.
The Colorado River passes through a salt dome near Glenwood Springs, and selenium and salt are released into the watershed by irrigation of mancos shale.
Measurements taken at a gauging station at the state line from 1986 to 2008 show the levels of salt and selenium in the Colorado dropping, Leib said.
Exposure to water over recent decades has leached salt and selenium, leaving less to be swept away by irrigation, Leib said.
It also appears that projects by the federal government aimed at salinity and selenium control are bearing fruit, he said.
It also appears that residential development might be playing a role in the reduced levels, Leib said.
Residential construction on previously irrigated fields has shown in a study conducted at Lewis Wash in Clifton that development can reduce levels of selenium and salt entering the river.
A similar study in Montrose, however, showed the opposite effect, leading researchers to note that residential development can have desirable and undesirable effects on water quality, Leib said.
“It’s a little confounding,” Leib said.
One possible beneficiary of reduced levels of selenium in the Colorado River is the endangered razorback sucker, which is particularly susceptible to harm from the element, Leib said.
Selenium, though necessary in trace amounts for life, has harmful effects in larger quantities.