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1 ?????I1,1? ? ?l7tihN? C/Lt W"",! ?(binSWA?S?^?6?t1 ?a Wetlands, Irrigation and Salinity Control: Lower Gunnison River Basin, Colorado 1 AV6 Eldie W. Mustard2 and Claudia D. Rectod C.?® V- Abstract. -A total of 8,773 ha of wetlands was inven- toried on a 72,800-ha area as part of an environmental assessment for a salinity control project in the Lower Gunnison River Basin, Colorado. Wetlands were evaluated for wildlife habitat value and use. Implementing measures to reduce salt loading to the Colorado River will cause wetland losses. Mitigation suggestions are given. INTRODUCTION The Colorado River Salinity Control Act (P.L. 93-320) was enacted by Congress in 1974 in response to downstream water users' con- cern over the increasing salinity in the Colorado River. This concern was voiced by Mexico and Lower Colorado River Basin states that depend on waters of the Colorado River for irrigation, industrial, domestic and recreation uses. Salinity, therefore, is both a national and an international prob- lem. Salt loading to the Colorado River comes from two primary sources: natural or geolo- gic and man-caused salt loading from irrigation water conveyance systems and irrigated farming. Essentially, salts from saline soils are dissolved as water flows over the land surface or percolates through the soil profile and saline aquifers, eventually reaching the ground water and the Colorado River. The Act instructed the Departments of Interior and Agriculture and the Environmen- tal Protection Agency to carry out its objec- tive: salinity control. It also identified specific areas, including the Lower Gunnison River Basin, where salt loading from water 1Paper presented at the Mitigation Symposium, Fort Collins, Colorado, July I6-20 1979. State Biologist, Soil Conservation Service, Denver, Colorado. 3Formerly Biologist (temporary), Soil Conservation Service; now employed by National Park Service, Colorado National Monument, Fruita, Colorado. 310 conveyance systems and on-farm irrigation was to be studied and ways to reduce it deter- mined. The Bureau of Reclamation (BOR) and Soil Conservation Service (SCS) were desig- nated by their respective departments to make these studies. Briefly, the magnitude of salinity in the Colorado River is as follows. Measure- ments4 at Imperial Dam in Arizona indicate that the Colorado River transports 6.3 million t of salt per year (BOR and SCS 1977). These salts come from many areas, including the Lower Gunnison River Basin which contributes over 1.0 million t per year. Studies in the Lower Gunnison River Basin have shown that on-farm irrigation contributes 240,000 t per year, with the remainder attributed to natural sources, major irrigation water conveyance systems, industrial and municipal sources. Various ways to reduce salt loading con- tributed by irrigation include: lining or piping major canals and laterals, closing existing open drains, lining on-farm irriga- tion and tailwater ditches and improving the efficiency of irrigation water use on crop- lands. These practices, by decreasing the amount of water that seeps from conveyance systems or is applied to irrigated croplands, 4Metric conversions are as follows: 1 metric ton (t) = 1.1 ton 1 hectare (ha) = 2.5 acre 1 kilometer (km) = 0.6 mile I meter (m) = 3.3 feet 1 centimeter (cm) 0.4 inches 0.03 meter3/sec (m3/s) - 1 cubic foot/second (cfs) Celsius temp. (°C) = 5/9 (F -32) Fahrenheit temp. (°F) = 9/5 C + 32