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<br />" J' <br /> <br />N <br />~ <br />l""" <br />cp. <br /> <br />f'". <br />Q <br />"- <br />i <br />," ~ <br />-1 J <br />i.' <br />,\f <br />J J <br />t + <br />",- 6 <br />, t .f <br />I f-z) <br />t d <br />'OJ; \. <br />-1.- <br /> <br />~~ <br />)\ J"" <br />r . " <br />~~:' <br />. r--- <br />""~ <br />-* <br /> <br />\ <br />----.j <br />). <br />~ <br /> <br />~ <br />~ <br /> <br />3 <br /> <br />During geologic time, salts moved from the earth's crust into the <br />water environment and were deposited in ancient lake and sea <br />beds. Through evaporation and precipitation they are once again <br />available to the forces of man and nature. Through the <br />weathering process these salts become part of the soil and water <br />environment. A large amount of salts are added to water during <br />the natural process of runoff as salts in the soil are dissolved. <br />In the Colorado River an estimated 47 percent of the 9 million <br />tons of salt carried in 10 million acre feet annually past Hoover <br />Dam are from natural sources (EPA,1971 & USBR,1990). <br /> <br />Salts added with the applied irrigation water will be leached <br />through the soil profile by the downward movement of water. A <br />salt balance favorable to crop production is maintained in the <br />root zone when the amount of salt leached is equal to the amount <br />added in the irrigation water. with a low leaching fraction <br />gypsum and lime may precipitate in the root zone, they are not <br />detrimental to plant growth. <br /> <br />Small amounts of salt may be leached by irrigation water from the <br />soil profile. The deep percolating waters may come in contact <br />with ancient lake and seabed deposits, picking up additional <br />salts on the way back to groundwater or surface flows. There is <br />also displacement and mixing of saline water in the underlying <br />aquifer by deep percolating irrigation water. <br /> <br />All drainage flows carry some minerals or salts. The amount of <br />salt picked up is dependent on the geo-hydro-chemical interaction <br />occurring at the specific site being irrigated. The hydosalinity <br />analysis provides a mass-balance accounting of both salt and <br />water for irrigation. <br /> <br />other sources of salt loading from human activity include seepage <br />from earthen canals that provide winter water for livestock, <br />stock pond seepage, fertilizer, road salt, municipal and <br />industrial return, gas and oil wells, septic systems, feed lots, <br />and accelerated soil erosion. <br /> <br />Watershed erosion results in salts from the soil going into <br />solution and entering the stream system. Surface soils derived <br />from ancient sea and lake beds contain about 2 or 3 percent salt. <br />In the process of soil erosion and transport of sediment, salts <br />go into solution. In some areas land treatment and grazing <br />management can improve watershed condition and reduce salt <br />loading (Irons,1965; Hedlund,1975 & Rasely,1988). <br /> <br />Common units which relate to salinity which will help to visually <br />understand the salt and water budget follow: <br /> <br />Salinity is frequently expressed as Electrical Conductivity (EC), <br />Total Dissolved Solids (TDS), or as a gravimetric measure in mgjl <br />(milligrams per liter). The EC of saline soil and of waters are <br />also reported in decisiemens per meter (dSjm which is equivalent <br />