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<br />n ,\ t ,'")
<br />~ii t:..
<br />
<br />minor amounts of potassium, silica, fluoride, carbon-
<br />ate, and nitrate. For most natural waters, alkalinity is a
<br />measure of dissolved carbon dioxide in water and, in
<br />the study area, almost all the alkalinity in the Colorado
<br />and Gunnison Rivers is from bicarbonate ions. A sta-
<br />tistical summary of major-ion and alkalinity concentra-
<br />tions for samples collected during water years 1970-93
<br />at the three gaging stations for the Grand Valley Unit is
<br />in table 7. A large proportion of the gain in dissolved
<br />solids in the Colorado River from irrigation in the
<br />Grand Valley is from calcium, magnesium, sodium,
<br />and sulfate. That conclusion was determined using
<br />approximate mass-balance calculations on major-
<br />ion loads for the three gaging stations and using
<br />~hf':mical clMa for irri2'atinn-drainaQe samoles from
<br />- .
<br />the Grand Valley and Uncompahgre Project (Butler
<br />and others, ] 994). The mean chloride concentration
<br />for station 09163500 (table 7) can be derived directly
<br />from chloride loads for stations 09095500 and
<br />09152500 and inclusion of some consumptive water
<br />loss in the Grand Valley. The differences in mean
<br />alkalinity concentrations among the three stations
<br />are small (table 7). Alkalinity concentrations probably
<br />
<br />300.000
<br />
<br />(/)
<br />z
<br />l2
<br />~
<br />ci 200,000
<br />..
<br />o
<br />-'
<br />(/)
<br />'"
<br />~
<br />o 100,000
<br />(/)
<br />'"
<br />w
<br />:;
<br />o
<br />(/) 0
<br />(/)
<br />o
<br />-'
<br />..
<br />::>
<br />z
<br />~ -100,000
<br />'"
<br />w
<br />l-
<br />(/)
<br />::>
<br />C3 -200,000
<br />..
<br />~
<br />o
<br />-'
<br />"-
<br />
<br />,
<br />"
<br />"
<br />"
<br />"
<br />"
<br />"
<br />"
<br />"
<br />"
<br />,
<br />,
<br />"
<br />"
<br />"
<br />......."\......
<br />
<br />....
<br />....
<br />
<br />,
<br />,
<br />"
<br />
<br />.300.000
<br />1968 1970
<br />
<br />~
<br />1972 1974
<br />
<br />1978
<br />
<br />1976
<br />
<br />are controlled by chemical equilibria of carbonate
<br />minerals. Therefore, monotonic trend tests using the
<br />seasonal Kendall test were done on calcium, magne-
<br />sium, sodium, and sulfate concentrations because
<br />these major ions would most be affected by irrigation
<br />practices and potentially by salinity-control projects.
<br />Trend tests were done for three time periods: 1970-93,
<br />J 980-93, and 1986-93.
<br />Only 5 of 36 trend tests on unadjusted major-ion
<br />concentrations were significant or highly significant
<br />(table 8). The only highly significant trends in major-
<br />ion concentrations were for magnesium concentrations
<br />at station 09095500 for water years 1986-93 and
<br />for sodium concentrations at station 09152500 for
<br />1970-93. The trends in maior-ion concentrations for
<br />1986-93 were either zero or increasing, except for the
<br />magnesium concentrations for station 09095500,
<br />which seems to be anomalous. The upward trends for
<br />concentrations during] 986-93 were not unexpected
<br />because the beginning of the period generally had low
<br />concentrations at the end of the high-flow years, which
<br />then were followed by several dry years when conccn-
<br />trations of major ions were expected to increase.
<br />
<br />STATION 09095500
<br />STATION 09152500
<br />STATION 09163500
<br />
<br />-----
<br />,/ "
<br />'. ........ .;;r.t':......... .......... ",'" '.. .........
<br />'// ,
<br />'--_/ ,
<br />"
<br />,
<br />,
<br />"
<br />,
<br />,
<br />,
<br />,
<br />"
<br />,
<br />,
<br />
<br />".
<br />
<br />....
<br />
<br />1980
<br />
<br />1966
<br />
<br />1988
<br />
<br />1990
<br />
<br />1992 1994
<br />
<br />1984
<br />
<br />1982
<br />
<br />WATER YEAR
<br />
<br />Figure 8. LOWESS smooth Curves of f1ow.adjusted annual dissolved.solids loads for stations 09095500
<br />Colorado River near Cameo, 09152500 Gunnison River near Grand Junction, and station 09163500 Colorado
<br />River near the Colorado.Utah State line, water years 1970-93.
<br />
<br />22 Trend Analysis of Selocted Water-Quality Dolo Assoclatad With Salinity-Control Prolects In tho Grsnd Volley.
<br />In the Lower Gunnison River Basin, and at Meeker Dome, Western Colorado
<br />
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