Using Sodium Carbonate to Seal Leaky Stock Ponds in Eastern Montana

Abstract

Mixing sodium carbonate into the top 100 to 150 mm of soil in three farm ponds constructed in calcareous soil in eastern Montana effectively reduced seepage losses for about 3 years following treatment. Seepage rates the first year after treatment were decreased to 20 to 40% of the pretreatment rate, but they were 60 to 100% of the pretreatment rate 4 years after treatment. Efficient livestock utilization of rangeland forage resources requires that stock water be distributed over the grazing area and available in sufficient quantity to last the entire grazing season. In arid and semiarid grazing regions, where natural lakes, ponds, and streams do not provide season-long water supplies, it has become a standard practice to construct artificial water impoundments like dugouts and small dams. The capacity of each constructed pond is usually less than 6,000 m3 and ponds are distributed to provide easy access to water throughout the pasture system. Most water in stock ponds is lost by evaporation and seepage with only a very small fraction actually used by livestock. Various methods have been used to reduce losses by controlling both evaporation and seepage. For reducing evaporation, floating monomolecular films of long-chain, fatty alcohols (Roberts 1958; Roberts 1959; U.S. Bureau of Reclamation 1958), floating barriers of plastic spheres and blocks, and floating films of low melting-point wax (Cooley and Myers 1973; Cooley 1975) have been tested. Floating covers of foamed rubber and low melting point wax have successfully reduced evaporation by as much as 90% on small tanks (1 lm diameter, or smaller), but they have not been used on lakes or ponds. On larger lakes or ponds, monomolecular layers successfully reduce evaporation by only about 20%-primarily because wind action breaks the film and exposes free water to the evaporative processes. Seepage has been reduced with varying degrees of success by installing physical barriers like concrete and asphalt on reservoir soil surfaces (Dedrick 1975); flexible membranes, like sheet plastic and sheet rubber, buried beneath reservoir soil surfaces (Dedrick 1975; Laing 1975); or clay material, like bentonite, placed and compacted on reservoir soil surfaces (Dedrick 1975; Jamison and Thornton 1963; Laing 1975). Disadvantages of these seepage control measures are either the cost of materials and labor for initial installation and maintenance or the mechanical damage caused by weather, frost, and wild and domestic livestock. Author is research hydraulic engineer, U.S. Dep. Agr., Science and Education Administration, Agricultural Research, Northern Plains Soil and Water Research Center, P.O. Box 1109, Sidney, Montana 59270. This research is a contribution from the U.S. Dep. Agr. Science and Education Administration, Agr. Res., in cooperation with the Montana Agr. Exp. Sta. Journal Series No. 691. Manuscript received February 1, 1979. Several researchers (Dedrick 1975; Jamison and Thornton 1963; Laing 1975; Reginato et al. 1968; Reginato et al. 1973) have tried to decrease seepage with soil chemical treatments using various sodium compounds including sodium chloride, sodium carbonate, and sodium polyphosphates. Sodium in these compounds replaces the calcium and magnesium cations on the exchange complex causing the soil aggregates to disperse and the clay colloids to swell, thus sealing soil pores through which water seeps (Nakayama 1966). Sodium carbonate was an effective sealant in Arizona studies, because this salt provided not only sodium cations necessary for soil dispersion but also carbonate anions, which combined with calcium and magnesium and precipitated as insoluble salts (Nakayama 1966; Reginato et al. 1973). Seepage in these study ponds was drastically reduced after initial sodium carbonate treatment, but it gradually increased to an undesirable rate in about 3 years as calcium and magnesium in runoff water replaced sodium applied in the treatment. At this time, seepage was reduced to the immediate post-treatment rate by broadcasting a mixture of sodium carbonate and sodium chloride on the water surface. Seepage rates in stock ponds in eastern Montana range from less than 7 mm/day to more than 30 mm/day. The ponds where seepage exceeds 15 mm/ day generally become dry in late summer or early fall before livestock can efficiently utilize available rangeland forage. A low-cost method of sealing leaky stock would extend the available water supply into the fall and provide an economical opportunity for better forage use. A mail survey of all farm owners and operators in Sheridan County, Montana, provided an estimate of 800 to 900 stock ponds within the county. Nearly two-thirds of the ponds were classified as having poor and fair seepage rates, an indication of the number of ponds in this county alone that might benefit from an effective, low-cost sealing method.