<br />001934
<br />
<br />654
<br />
<br />J, ENVIRON, QUAL., VOL. 27, MAY-JUNE 1998
<br />
<br />SUMMARY
<br />
<br />Dissolved-solids data and trends in the middle and
<br />headwater areas of the Colorado River Basin upstream
<br />from Cameo, Colorado, and in the Gunnison River Ba-
<br />sin in Colorado were studied and analyzed for 1970 to
<br />1993, 1980 to 1993, and 1986 to 1993. Upstream from
<br />Cameo, CO, trends in flow-adjusted periodic dissolved-
<br />solids concentrations varied. All sites with concentration
<br />data for 1970 to 1993 had significant downward trends
<br />in concentration, whereas trends generally did not occur
<br />for 1980 to 1993 and 1986 to 1993. Significant downward
<br />trends in monthly loads at sites upstream from Cameo
<br />were indicated for the majority of the site/analysis-
<br />period combinations. For flow-adjusted annual dis-
<br />solved-solids loads, trend results were downward or not
<br />present for sites upstream from Cameo for all three
<br />analysis periods. These trend results partly agree with
<br />the downward trends in flow-adjusted periodic dis-
<br />solved-solids concentrations and monthly and annual
<br />loads reported by Butler (1996) for the Colorado River
<br />near Cameo site.
<br />In the Gunnison River Basin, trends for flow-adjusted
<br />periodic dissolved-solids concentrations indicated that
<br />most results were not statistically significant. Of the 12
<br />possible site/analysis-period combinations, there were
<br />two sites with downward trends in concentration and
<br />two sites with upward trends. The trend results for
<br />monthly dissolved-solids loads varied, with more de-
<br />creasing loads over the three analysis periods than in-
<br />creasing loads. For annual dissolved-solids loads in the
<br />Gunnison River Basin, there were two trend results
<br />indicating decreasing loads, one result indicating an in-
<br />creasing load, and the remaining nine site/analysis-
<br />period combinations indicating no trends.
<br />Trend results for dissolved-solids concentrations and
<br />loads depend on many different factors. As noted by
<br />the site Roaring Fork River at the mouth, fluctuation
<br />in annual dissolved-solids loads remains after loads were
<br />adjusted for streamflow, a result that also is present at
<br />the other sites in the basin for periodic concentrations
<br />and monthly loads. Significant downward trends in dis-
<br />solved-solids concentrations and loads at the Colorado
<br />River near Cameo site may be affected by channel evo-
<br />lution and hydrologic variation in the surface-water trib-
<br />utaries between the Cameo site and Glenwood Springs
<br />and also by groundwater springs and seeps around Glen-
<br />wood Springs and between the two sites. Trend results
<br />differ depending on sample size and period of analysis
<br />and may be affected by changing land-use practices. In
<br />the Gunnison River Basin, although the Uncompahgre
<br />River at Delta site is downstream from salinity-control
<br />projects, trend results indicated increasing dissolved-
<br />solids concentrations and loads at the Delta site for 1986
<br />to 1993. Because salinity-control projects did not begin
<br />until 1988 and were ongoing past 1993, a longer period of
<br />record is needed for the investigation of salinity trends at
<br />the Delta site. Additional studies on the water quality
<br />and discharge of springs, dissolved-solids data, and land
<br />use are needed to determine their effects on dissolved-
<br />solids concentrations, loads, and trends in the Upper
<br />Colorado River Basin in Colorado.
<br />
<br />ACKNOWLEDGMENTS
<br />
<br />The authors would like to thank David L. Butler and David
<br />K. Mueller, U.S. Geological Survey, for their technical assis-
<br />tance during the preparation and analysis of salinity data.
<br />We would also like to express our appreciation for reviews
<br />provided by David K. Butler, Terry Shertz, and Mary Kidd,
<br />U.S. Geological Survey, that improved the manuscript.
<br />
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