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<br />W <br />....:l <br />00 <br />00 <br /> <br />. <br /> <br />Sources of Salinity. The salinity problem has its root in a number <br /> <br />. <br /> <br />of causative factors. The naturalland and water system, with its expansive <br /> <br />and diffuse nature, contributes over half of the total salt load in the river. <br /> <br />Natural factors in the Colorado system which can cause salt loading and <br /> <br />. <br /> <br />concentrating effects include: the arid nature of the climate; the geology <br /> <br />of the basin with its vast areas of erodable, salt yielding shales; the great <br /> <br />. <br /> <br />tracts of range aad forest lands which consume wa'ter and then concentrate <br /> <br />the residual salt in less water as it moves by subsurface flow to the river. <br /> <br />A significant quantity of the total salt level at Imperial Dam is contributed <br /> <br />. <br /> <br />by the Upper Basin. However, this region also contributes a similar <br /> <br />proportion of the total water supply within the basin. <br /> <br />Man's activities, particularly in agriculture, contribute salts and <br /> <br />. <br /> <br />then concentrate them through consumptive uses such as evapotranspiration <br /> <br />losses from irrigated agriculture and reservoir surfaces and through <br /> <br />. <br /> <br />municipal and industrial uses. Thus, many factors contribute to salinity <br /> <br />increases within the water of the basin as it mOves downstream. <br /> <br />Saline Water Use. In terms of man's use of water, the kinds of <br /> <br />. <br /> <br />dissolved salts, in addition to the total salinity level, are important. High <br /> <br />levels of the sodium ion do not increase hardness interfering with industrial <br /> <br />and domestic supplies; but for agriculture it has undesirable effects on <br /> <br />. <br /> <br />plant growth and soil structure. Crops must be substituted or yield losses <br /> <br />sustained. The calcium ion is usually considered beneficial in irrigation <br /> <br />. <br /> <br />water but causes the water condition known as "hardness".for <br /> <br />4 <br /> <br />. <br />