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. PART VI EVALUATION OF EXISTING SALINITY CONDITIONS I-" U'I f\:> .....:I A literature search and conversations with salinity erosion researchers reveal that practically no previous effort has been made to isolate January through April salt loads related to erosion and snowmelt runoff on lower elevation lands. BLM salinity/erosion studies in the Price River basin show that at least one drainage yielded significantly reduced salt loads ~ere experimental contour plowing and gully plugs were used for erosion control. The feasibility of erosion control as a mechanism to control salinity (including snowmelt runoff events) needs further investigation based on the BLM Price River studies. The extreme annual and seasonal variation in the runoff events could also result in wide fluctuations in salt loading. 9. Shifts in Ion constituents . Reductions in calcium and bicarbonate and increases in sodium and sulfate have been documented at Flaming Gorge Reservoir. Similar calcium bicarbonate reductions are hypothesized at Lake Powell. Precipi- tation of calcium carbonate from biological/chemical influences in the reservoirs has been hypothesized to limit salinity. Calcium reductions can result from precipitation, cation exchange (calcium exchanged for sodium), biological uptake, or chemical reaction between sodium bicarbon- ate and calcium sulfate. A number of mechanisms exist by which calcium and carbonate may he reduced. There is also evidence that in anoxic conditions, sulfates may be reduced to hydrogen sulfide gas and be released to the atmosphere. For the most part, once sod ium, chloride, and sulfate are in solution, they tend to remain. The overall significance of these mechanisms needs to be defined in terms of total salt reduction and economic benefits. Since calcium and bicarbonate are more readily treated by water softening methods than sodium, chlorides, or sulfate, the overall economic benefits of ion constituency shifts need careful future consideration. D. Conclusions Salinity concentrations at Lees Ferry and at Hoover, Parker, and Imperial Dams should remain, for at least the next few years, within the salinity standards. Unless an extended drought of several years or some unforeseen salt loading occurs, salinity should remain fairly stable, with small annual changes downstream from Hoover Dam in the next several years. Given good water conditions, salinity is likely to remain in the lower range of the predictions shown in Figures VII-l and VII-2. . The Colorado River Reservoir System is currently at a high storage level (Figure VI-3). If above-average runoff occurs in 1983, additional flood control releases may be required, and any increases in flow are expected to decrease salinity levels downstream due to dilution. 32