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<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 /> <br />REFERENCES <br /> <br />Apodaca, L.A, N,E, Driver, V.e. Stephens, and N,E. Spahr. 1996, <br />Environmental setting and implications on water quality, Upper <br />Colorado River Basin. Water Resour. Invest. 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