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<br />N <br />00 <br />~ <br />. CJ1 <br /> <br />in the Basin as presented by EPA in its report, "The Mineral Quality <br /> <br /> <br />Problem in the Colorado River Basin ," with revisions from later <br /> <br />studies by the USER. Addi~ional studies may indicate the need for <br />further revisions. <br /> <br />The loss of water to phreatophyte and other riparian vegetation <br /> <br /> <br />and to evaporation from the river water surface and backwater areas <br /> <br />is sizeable, particularly in the.river reach below Hoover Dam. <br /> <br />Salinity Resultin~ From Man's Actions <br /> <br /> <br />River salinity has increased through salt loading and salt <br /> <br /> <br />concentrating as a result of man's beneficial use of the Basin's <br /> <br />waters. <br /> <br />Irrigation is the major consumer of water in the Basin and is <br /> <br /> <br />responsible for the largest of the increases in salinity caused by <br /> <br /> <br />man's activities. Irrigation contributes to both salt loading and <br /> <br /> <br />salt concentration. Water is removed through evaporation and <br /> <br /> <br />consumption by the plants, but practically all of the dissolved <br /> <br />salt is returned to tte river, concentrating the salts in a smaller <br /> <br /> <br />volume of water. In reany areas, return flows also leach salts from <br /> <br /> <br />the soil and underlying geologic formations which adds to the river's <br /> <br /> <br />salt load. <br /> <br />Reservoir evaporation also contributes to increasing the salt <br /> <br />concentration because evaporation removes water and the salt load <br />is concentrated in a s~aller volume of water. Out-of-basin exports <br />and in-basin uses which do not return salt to the system also affect <br />the salinity concentration. <br /> <br />-15- <br /> <br />. <br />