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<br />. <br /> <br />o <br />o <br />..... <br />~l <br /> <br />ASSf:SSING STRATEGIES FOR CONmll. (J' FARM-llERIYED <br />SALINIrr IN TIiE LPPER COlORADO RIVER B^SIN <br /> <br />Over twelve m11110n residential water users and the crops en o\ler one <br /> <br />mlllion irrigated acres 11" the southlli8stern U.S. and Mexico are. to varying <br /> <br />degrees. aaversely affected by salinit)' (ofssohed mineral salts) in Colerado <br /> <br />River water. <br /> <br />Salinity levels whfch exceed roughly 500 mllligrams per liter <br /> <br />(~/1) can reduce agricultural prOducthfty and shorten the useful life and <br /> <br />increase operating costs of pipes and water-using equ1plTLent in householdS and <br />industries. The U.S. Environmental Agenc)' (1971) attributes about 55~ of the <br /> <br />concentration of dissolved salts measured in the lower reaches of the river to <br /> <br />natural sources, which inclUde salt springs and surface runoff from the <br /> <br />sedimentary geolo~1c formations and 5011s common throughout the basin. An <br /> <br />estimated 37S of the measured salt concentration is assignee to diffuse <br /> <br />irrigation return flows, primarl1y from Upper Basin sources 1n ColoradO, Utah <br /> <br />and Wyom1ng. Industrial and mun1c1pal contr1buttons are negligible, 50 ~ost of <br /> <br />the balance artses from the concentrating effects of reservoir evaporation. <br /> <br />Irrigation of crops in:pl1es eventual concentration of sa11n1ty in 5011 <br />moisture, because the small amount of salts invariably dissolved 1n the .ater <br /> <br />rema1n after a portion of the water 15 evaporated from grow1ng plants. In <br /> <br />order to preserve product1vity, irrigators must leach salts from their s011s by <br /> <br />excess 1 rrigat ion (Young ane Horner). <br /> <br />The resulting sal1ne waters often <br /> <br />accumulate 1n grouncweter cepos1ts and crain 1nto ne1ghbortng streams. $a11ne <br /> <br />return flo'lfS from 1rr1gated lands in the Upper Coloraco Sasin are unusual 1n <br />that most of the salt loading der1ves from the d1ssolv1ng of solu:le salts w1th <br /> <br />1 <br />