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<br />Reprinted from the JOIln/al of EI/vironmental Quality
<br />Volume 27, no, 3, May-June 1998, Copyright () 1998, ASA, CSSA, SSSA
<br />677 South Segue Rd" Madison, WI 53711 USA
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<br />Salinity Trends in Surface Waters of the Upper Colorado River Basin, Colorado
<br />
<br />ABSTRACT
<br />
<br />Nancy J. Bauch* and Norman E. Spahr
<br />
<br />Dissolved-solids data collected in the Upper Colorado River Basin
<br />upstream from Cameo, Colorado, and in the Gunnison River Basin
<br />were analyzed for trends in Bow-adjusted dissolved-solids concentra-
<br />tions and loads for water years 1970 to 1993, 1980 to 1993, and 1986
<br />to 1993. Trend results for Bow-adjusted periodic dissolved-solids con-
<br />centrations for the Colorado River Basin upstream from Cameo, CO,
<br />generally were downward or no trend was indicated. Trends in Bow-
<br />adjusted monthly and annual dissolved-solids loads primarily were
<br />downward or absent. These trend results partly agree with the down-
<br />ward trends reported by a previous investigation for the Colorado
<br />River near Cameo site. In the Gunnison River Basin, trends in Bow-
<br />adjusted dissolved-solids concentrations and loads were not detected
<br />for more than one-half of the site/analysis-period combinations. Of
<br />the trends that were present, most indicated decreases in concentra-
<br />tions and loads rather than increases. In both the Colorado River
<br />Basin upstream from Cameo, CO, and the Gunnison River Basin,
<br />trends in Bow-adjusted dissolved-solids concentrations and Bow-
<br />adjusted monthly and annual dissolved-solids loads may be affected
<br />by a variety of factors. These include channel evolution and hydrologic
<br />variation, water quality and Bow rate of groundwater discharges and
<br />springs, sample size and period of record of dissolved-solids data, and
<br />changes in land use in the basin.
<br />
<br />THE Colorado River supplies municipal and indus-
<br />trial water for more than 18 million people in seven
<br />western states and is the source of irrigation water for
<br />more than 1.7 million acres of land (U.S. Department
<br />of the Interior, 1995). As water is used and reused,
<br />salinity, also referred to as the concentration of dis-
<br />solved mineral salts or dissolved solids in water, in-
<br />creases in the Colorado River in a downstream direction
<br />(Law and Hornsby, 1982). Salinity can affect municipal
<br />and industrial water users by clogging plumbing fixtures
<br />and increasing water-softening costs and can cause
<br />lower crop yields and damage to agricultural fields.
<br />These effects are especially prevalent in the lower Colo-
<br />rado River Basin (Law and Hornsby, 1982). To address
<br />the salinity problems, Congress passed the Colorado
<br />River Basin Salinity Control Act of 1974 (Public Law
<br />93-320). This Act authorized the construction of four
<br />salinity-control projects in the basin and the planning
<br />of 12 additional projects. Two of the salinity-control
<br />projects, the Grand Valley Unit and the Lower Gunni-
<br />son Basin Unit (Fig. 1), are located in western Colorado
<br />and were implemented in 1979 and 1988, respectively.
<br />Butler (1996) investigated salinity trends to determine
<br />if these salinity-control projects in western Colorado
<br />have had an effect on dissolved-solids concentrations
<br />
<br />U,S, Geological Survey, Water Resources Division, Colorado District,
<br />MS 415, Box 25046, Denver Federal Center, Lakewood, CO 80225,
<br />Received 15 May 1997, *Corresponding author (njbauch@usgs,gov),
<br />
<br />Published in J, Environ, Qual. 27:640-655 (1998),
<br />
<br />and loads in the Colorado River. The study area in-
<br />cluded the downstream parts of the Upper Colorado
<br />River Basin in Colorado from Cameo, CO, to the Colo-
<br />rado-Utah stateline and the lower Gunnison River Ba-
<br />sin, areas where the two salinity-control projects are
<br />located (Fig. 1). To supplement the dissolved-solids
<br />trends information in Butler (1996), dissolved-solids
<br />data and trends in the middle and headwater areas of
<br />the Colorado River Basin upstream from Cameo, CO,
<br />and in the upper Gunnison River Basin in Colorado are
<br />analyzed (Fig. 1).
<br />The purpose of this article is to investigate trends in
<br />dissolved-solids concentrations and loads in the Colo-
<br />rado River Basin upstream from Cameo, CO, and in
<br />the Gunnison River Basin. Specifically, the objectives
<br />are to:
<br />
<br />1. Determine periodic cpncentrations and monthly
<br />and annual loads of dissolved solids at sites in the Colo-
<br />rado River Basin upstream from Cameo, CO, and in
<br />the Gunnison River Basin.
<br />2. Determine trends in dissolved-solids concentra-
<br />tions and loads at these sites.
<br />3. Determine if the downward trends in dissolved
<br />solids observed near Cameo by Butler (1996) also are
<br />observed at the upstream sites.
<br />4. Identify reasons for dissolved-solids trends.
<br />
<br />Numerous reports pertaining to water resources, sa-
<br />linity, salinity control, and dissolved-solids concentra-
<br />tions, loads, and trends in the Upper Colorado River
<br />Basin are available. A comprehensive study of the water
<br />resources of the Upper Colorado River Basin was com-
<br />piled by lorns et al. (1965). Warner et al. (1985) investi-
<br />gated the relation between groundwater and salinity in
<br />the Basin, and Norris (1987) evaluated surface-water
<br />quality in the North Fork of the Gunnison River Basin.
<br />The Bureau of Reclamation (1983, 1984, 1986) con-
<br />ducted salinity studies in the Grand Valley area of the
<br />Colorado River Basin and in the Uncompahgre River
<br />Valley within the Gunnison River Basin. Investigations
<br />of the saline springs in the Glenwood Springs-Dotsero
<br />area have been reported by the URS Corporation (1981)
<br />and by Eisenhauer (1983). The mineral quality of the
<br />Colorado River Basin was studied by the U.S. Environ-
<br />mental Protection Agency (1971) and by Blackman et
<br />al. (1973), while Law and Hornsby (1982) detailed the
<br />salinity problem in the Basin. Since 1963, the Bureau of
<br />Reclamation has published a biennial report on salinity,
<br />
<br />Abbreviations: USGS, U,S, Geological Survey; NWIS, National Water
<br />Information System; BOR, Bureau of Reclamation; CDPHE, Colo-
<br />rado Department of Public Health and Environment; CDS, calculated
<br />dissolved solids; USEPA, V,S, Environmental Protection Agency;
<br />STORET, STOrage and RETrieval system; SUM, Sum of Constit-
<br />uents; ROE, Residue on Evaporation at 180 degrees Celsius.
<br />
<br />640
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