Probable Impacts of Various Range Improvement Practices on Diffuse Salt Production

Abstract

During 1976 a study of soil profile salt concentrations and probable salt loading by surface runoff was made on 73 range improvement sites in Utah, Colorado, New Mexico, and Arizona. The range improvement practices studied included gully plugs, contour furrowing, pitting, pinyon-juniper chaining, and various sagebrush-control treatments. Results of these studies indicated that the impact of gully plugs and contour furrows on potential diffuse salt production is somewhat variable and may in fact indicate that these treatments have only a minor potential impact, probably because the overland flow route is not a major source of diffuse salt movement, at least on lands sampled in this study. On pinyon-juniper sites and the various sagebrush treatments, the lack of difference in salt concentrations between treated and untreated sites was the only consistent trend. In general the measured salt concentrations in surface soils of either pinyonjuniper or sagebrush sites present a problem of little concern as related to salt production within the major river basins. Salinity in the Colorado River is of major national concern, for not only has it resulted in losses to the regional economy, but also high salinity levels have aggravated relations with the Republic of Mexico. Even in its virgin state, the salt load of the Colorado River in its lower reaches was about 600-700 ppm. However, man’s development of water resources has affected both the quantity and quality of water supplies. Salinity levels in the lower reaches of the river now average 850 ppm with a predicted concentration of 1,300 ppm by the year 2000. The sources and causes of dissolved solids within the Colorado River are of importance; for if they can be identified, strategies may be developed for effective management and control. In addition, this information would allow estimates to be made of downstream costs associated with upstream salt production, thus facilitating the development of economic trade-offs on a basin-wide level. Recent estimates suggest that the largest single man-caused source of salinity is irrigation return flow, amounting to about a third of the total salt load. Natural sources such as salt wells and springs, plus concentration by evaporation, account for another third. The remaining salt load is attributed to diffuse sources Authors are graduate research assistant and associate professor, rangeland hydrology, Watershed Science Unit, College of Natural Resources, Utah State University, Logan,