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001926 646 J, ENVIRON, QUAL., VOL. 27, MAY-JUNE 1998 Table 3. Trends in now-adjusted dissolved-solids concentrations, Upper Colorado River Basin in Colorado, water years 1970 to 1993, 1980 to 1993, 1986 to 1993. Number after site name refers to site number in Fig. 1. Data for Colorado River near Cameo and Gunnison River at Grand Junction from Butler (1996). Trend Site Period Slope Percent P value SL direction Colorado River Basin upstream from Cameo, CO Colorado River at Hot Sulphur Springs (2) 1970-1993 -0.30 -0.36 <0.001 HS Down 1980-1993 0.682 NS None 1986-1993 0.352 NS None Muddy Creek at Kremmling (3) 1986-1993 0.336 NS None Rock Creek at Crater (4) 1986-1993 0.131 NS None Eagle River at Gypsum (5) 1970-1993 -2.11 -0.44 0.028 S Down 1980-1993 0.946 NS None 1986-1993 0.689 NS None Colorado River near Dotsero (6) 1970-1993 -1.15 -0.51 0.016 S Down 1980-1993 0.110 NS None 1986-1993 1.000 NS None Colorado River above Glenwood Springs (7) 1970-1993 -L47 -0.45 <0.001 US Down 1980-1993 0.498 NS None 1986-1993 0.217 NS None Roaring Fork River at mouth (8) 1970-1993 -L74 -4.88 <0.001 HS Down 1980-1993 0.879 NS None 1986-1993 4.21 1.22 0.032 S Up Colorado River near Cameo (9) 1970-1993 -2.23 -0.44 0.001 HS Down 1980-1993 -3.20 -0.66 0.051 MS Down 1986-1993 -14.30 -2.82 <0.001 HS Down Gunnison River Basin Taylor River at Almont (10) 1970-1992 0.107 NS None 1980-1992 '0.164 NS None 1986-1992 0.651 NS None East River at conDuence with Taylor River (11) 1970-1991 0.882 NS None 1980-1991 0.533 NS None 1986-1991 1.95 1.16 0.071 MS Up Uncompahgre River at Delta (12) 1970-1993 -9.13 -0.66 <0.001 US Down 1980-1993 0.584 NS None 1986-1993 13.90 1.07 0.008 US Up Gunnison River at Grand .Junction (13) 1970-1993 -4.86 -0.73 <0.001 US Down 1980-1993 0.804 NS None 1986-1993 0.274 NS None Periods are in water years; slopes are in milligrams per liter per year; percent is the slope expressed as percent change per year; P value is the significance level of the test; SL is significance level; levels are: HS = highly significant, P ,,; 0.01; S = significant, P > 0.01 and ,,; 0.05; MS = marginally significant, P > 0.05 and ,,; 0.10; and NS = not significant, P > 0.10. a confidence level of 90%. The significance level of the trend result gives the probability of rejecting the null hypothesis of no trend. As the significance level of the test increases, the probability of rejecting the null hy- pothesis (no trend) increases, and the probability in- creases that there is in fact a trend in the data. For highly significant results, in 99% of the cases, the trend test will correctly indicate a trend when there is actually a trend present. For significant and marginally signifi- cant results, the rates are 95 and 90%, respectively. Trends were not calculated for the Alva B. Adams Tunnel at East Portal because the flow represents water diverted out of Grand Lake rather than streamflow. The tunnel is important, though, to measurements of downstream salinity in the Colorado River Basin. Al- though about 9000 tons of dissolved solids are removed annually from the basin through the Adams Tunnel (Table 2), the primary effect of the tunnel is the removal of high quality water out of the basin, leaving less water available downstream for dilution of dissolved solids. Colorado River Basin Concentrations. In the Colorado River Basin up- stream from Cameo, CO, trend results for flow-adjusted periodic dissolved-solids concentrations are listed in Ta- ble 3. For the Colorado River near Cameo site (site 9), Butler (1996) reported significant downward trends in periodic dissolved-solids concentrations for all three analysis periods. In comparison, trends in concentration for sites upstream from Cameo varied (Fig. 4). Periodic concentration data for 1970 to 1993 for the five upstream sites, including the three sites on the main-stem Colo- rado River, had significant downward trends, whereas concentrations at these same five sites had no trends for 1980 to 1993. All results upstream from Cameo for 1986 to 1993, again including the three main-stem sites, indicated no trends except for the Roaring Fork River at the mouth (site 8), which showed an upward trend (Table 3; Fig. 4). Monthly Loads. As with periodic dissolved-solids concentrations, trends in flow-adjusted monthly dis- solved-solids loads for the Colorado River near Cameo (site 9) indicated significant decreasing monthly loads for all three analysis periods, as reported by Butler (1996) (Table 4). Sites upstream from Cameo had varied trend results (Table 4 and Fig. 5). Four upstream sites, including two on the main-stem Colorado River, had significant downward trends in monthly dissolved-solids loads for 1970 to 1993, whereas no significant trend in