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<br /> <br />11 <br /> <br /> <br />~ pesticides, fertilizers, organic debris, heavy metals, trace <br />N <br />~ minerals, farm oils and greases, bacteria (including <br />N <br />pathogenic organisms), nematodes and other forms of <br /> <br />pollution. Salinity, a major water pollutant, and its <br /> <br />effect on the aquatic environment, is addressed in this <br /> <br />report. <br /> <br />Salinity increases associated with return flows may be <br /> <br />brought about by both consumptive and non-consumptive uses <br /> <br />of applied water. The principal constituents comprising <br /> <br />return flow salinity are the water-soluble compounds of <br /> <br />calcium, magnesium, sodium and potassium. Minor amounts of <br /> <br />iron, aluminum, manganese and other cations may also be <br /> <br />involved. The dominant anions in the compounds are <br /> <br />carbonates, bicarbonates, sulfates, and chlorides. Any <br /> <br />combination of these cations, and anions form the salts or <br /> <br />"salinity" of irrigation return flows. <br /> <br />A basic process by which irrigation return flow <br /> <br />elevates the salinity of a hydrologic system with which it <br /> <br />is in contact is termed salt loading. This process <br /> <br />increases the total salt burden of the receiving waters by <br /> <br />adding salts. A second process is concentration, in which <br /> <br />the salinity of a water body or hydrologic system is <br /> <br />increased by evaporation. Evaporation merely reduces the <br /> <br />amount of water but does not reduce the total quantity of <br />