USGS: Salinity levels improving in southwestern streams

According to the USGS salinity levels in many southwestern U.S. streams has dropped over the last couple of decades. From the article:

The U.S. Geological Survey (USGS) released a report today describing salinity levels in streams and ground water in parts of Arizona, California, Colorado, Nevada, New Mexico, Utah and Wyoming. The report concludes that although salinity varies widely throughout the region, levels have generally decreased in many streams during the past two decades. Elevated salinity levels, or concentrations of dissolved solids, can limit the suitability of water for many uses, including agricultural production and drinking water. Trends in dissolved-solids concentrations in streams were evaluated from 1974 through 2003. "The greatest change occurred during 1989 to 2003, when annual dissolved-solids concentrations decreased at more than half of the sites throughout the region," explained lead author and USGS hydrologist Dave Anning. "The reductions were widespread, as indicated by decreases at nearly all of the sites on the main stem of the Colorado and Green Rivers. We also noted increases at about one-third of the sites, while the remaining sites showed no trends."

Decreases in salinity are attributed, in part, to natural causes, such as geomorphic changes or climate variations. They also may be associated with human-related factors, such as changes in land and water use, reservoir management, trans-basin exports, and implementation of salinity-control projects. Salinity control projects include activities like using low water-use irrigation systems and re-directing saline water away from streams. USGS findings show that dissolved solids decreased from 1989 through 2003 at all sites downstream from salinity-control projects, and that the decreases were greater than decreases upstream from projects. For example, estimated annual loads of dissolved solids in the Gunnison River in the Upper Colorado River Basin decreased by about 162,000 tons per year downstream from the Lower Gunnison salinity-control unit, in contrast to a decrease of only 2,880 tons per year upstream from the unit. This net decrease is about 15 percent of the annual load in the lower Gunnison River. "This is good news," said Dr. Robert Hirsch, Associate Director for Water, "and shows successes from the region's investments in salinity control over the past several decades." Salinity-control projects have been implemented since the mid-1970s by the Bureau of Reclamation, U.S. Department of Agriculture, and the Bureau of Land Management to control salinity of water delivered to Mexico, per the 1974 Colorado River Basin Salinity Control Act...

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