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Ou1928 648 J, ENVIRON, QUAL., VOL. 27, MAY-JUNE 1998 Monthly Loads. For flow-adjusted monthly dissolved- solids loads in the Gunnison River Basin, trend results for six of the site/analysis-period combinations indicated decreasing monthly loads, whereas trends in increasing monthly loads were detected for only 2 of the 12 site/ analysis-period combinations (Table 4 and Fig. 5). Annual Loads, Fewer significant trends in flow- adjusted annual dissolved-solids loads in the Gunnison River Basin were detected than for monthly loads for all three periods (Table 5 and Fig. 6). Of the 12 site/ analysis-period combinations, significant trends were re- ported for only three sites; two indicating decreasing loads of 0.61 and 0.50% and one indicating an increasing annual load of 1.38%. Each of the four sites in the Gunnison River Basin had at least one analysis period when no significant trends in flow-adjusted annual loads were detected. Loads at two sites had no significant trends detected for any of the three analysis periods. DISCUSSION Comparison to Previous Trend Studies In analyzing dissolved-solids trends in the down- stream part of the Colorado River Basin in Colorado, Butler (1996) primarily reported trends of decreasing flow-adjusted dissolved-solids concentrations and loads at the Colorado River near Cameo site, which is up- stream from salinity-control projects (Tables 3 through 5). For flow-adjusted periodic dissolved-solids concen- trations and monthly dissolved-solids loads, Butler (1996) reported significant downward trends for all three analysis periods. Twenty-nine percent of the flow- adjusted periodic concentration site/analysis-period combinations upstream from Cameo matched the down- ward trends reported by Butler (1996), and 64% of the site/analysis-period combinations for flow-adjusted monthly loads upstream from Cameo also had signifi- cant downward trends for the three periods. Seventy- one percent of the upstream sites, including all three on the main-stem Colorado River, had downward trends in flow-adjusted annual loads for 1986 to 1993, matching the downward trend in annual loads reported by Butler (1996) at the Cameo site for 1986 to 1993. Overall, the trend results indicating decreasing dissolved-solids concentrations and loads for the near Cameo site (But- ler, 1996) also are reported for sites upstream from Cameo. Previous studies have reported significant downward trends in flow-adjusted dissolved-solids concentrations and loads in the Colorado River Basin in Colorado, Wyoming, Utah, New Mexico, and Arizona (Kircher, 1984; Liebermann et aI., 198'9). Kircher (1984) reported a significant downward trend in flow-adjusted dissolved- solids loads at 20 of 26 sites in the Colorado River Basin. Table 5. Trends in flow-adjusted annual dissolved-solids loads, 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 dirertion Colorado River Basin Upstream from Cameo, CO 0.380 NS None Colorado River at Hot Sulphur Springs (2) 1970-1993 1980-1993 0.459 NS None 1986-1993 -297.00 -1.99 0.002 US Down Muddy Creek at Kremmling (3) 1986-1993 0.311 NS None Rock Creek at Crater (4) 1986-1993 -66.00 -3.83 0.014 S Down Eagle River at Gypsum (5) 1970-1993 -842.00 -0.53 0.058 MS Down 1980-1993 0.247 NS None 1986-1993 - 3 330.00 - 2.35 0.028 S Down Colorado River near Dotsero (6) 1970-1993 - 3 840.00 -0.92 <0.001 HS Down 1980-1993 - 2320.00 -0.59 0.027 S Down 1986-1993 - 3 000.00 -0.87 0.046 S Down Colorado River above Glenwood Springs (7) 1970-1993 0.524 NS None 1980-1993 0.775 NS None 1986-1993 -9350.00 -L77 0.022 S Down Roaring Fork River at mouth (8) 1970-1993 -799.00 -0.25 0.002 HS Down 1980-1993 0.402 NS None 1986-1993 0.842 NS None Colorado River near Cameo (9) 1970-1993 0.605 NS None 1980-1993 0.689 NS None 1986-1993 -41000.00 -2.95 <0.001 HS Down Gunnison River Basin Taylor River at Almont (10) 1970-1992 0.555 NS None 1980-1992 0.710 NS None 1986-1992 0.190 NS None East River at confluence with Taylor River (11) 1970-1991 0.404 NS None 1980-1991 0.379 NS None 1986-1991 0.227 NS None Uncompahgre River at Delta (U) 1970-1993 - 2 060.00 -0.61 <0.001 HS Down 1980-1993 0.430 NS None 1986-1993 4 210.00 1.38 0.003 HS Up Gunnison River at Grand Junction (13) 1970-1993 -6350.00 -0.50 0.027 S Down 1980-1993 0.676 NS None 1986-1993 0.413 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: US = highly significant, P :s 0.01; S = significant, P > 0.01 and :s 0.05; MS = marginaDy significant, P > 0.05 and :s 0.10; and NS = not significant, P > 0.10.