Arid Land Soils Research Articles

Effects of freezing and drying on the solubility of organics and metals in arid soils

Abstract Controlled laboratory studies were conducted to evaluate the effects of freezing‐thawing and wetting‐drying on concentrations of hazardous contaminants contained in municipal solid‐waste leachates and arid land soils. Leachates generated from 1,000‐L tanks loaded with typical municipal solid wastes and a 15‐year‐old City of Tucson (arid soil) landfill leachate were analyzed and compared. The leachates ranged in age from 0.25 to 15 years. Levels of pH, total dissolved solids (salts), organic carbon, Ca, Mg, Na, K, Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb, and Zn after dehydration treatments were compared to initial levels. The results indicate that both freezing and drying removed contaminants from solution. The extent of removal depends on pH as related to arid soils where dehydration dominates, on charge of the contaminants in its ionic state, and on age of the leachate. For the elements of interest in this study, an increase in pH would lessen contaminant solubility. For the older (3‐ to 15‐year‐old) leachates, pH increased from acidic to basic. With the exception of Na and K—elements that form univalent cations —contaminants contained in these older leachates were removed to a significant extent after one wetting‐drying cycle. For most leachates, pH levels increased significantly after treatment. However, pH increases were less than one unit for the most acid (pH < 5.4) leachates, although the increases were greater for leachates whose initial pH's were near 7.0 and for the older leachates (those greater than 3 years of age). A comparison of the sodium‐ and potassium‐adsorption ratios indicated that Ca and Mg disappeared more extensively from solution than Na and K. Overall, one wetting‐drying cycle was effective in lowering (p < 0.01) total and organic contaminant levels in the leachates. Although not as effective as wetting‐drying, freezing‐thawing also significantly reduced contaminant levels in the leachate solutions in cold arid land deserts. The largest reductions usually occurred after the first freeze‐thaw cycle. Further reductions occurred fairly uniformly with additional freeze‐thaw cycles as may be related to soil solutions of cold deserts.

Oil shale process water affects activity of vesicular-arbuscular fungi and rhizobium 4 years after application to soil

The effects of different concentrations of water from oil shale processing on the vesicular-arbuscular (VA) fungal and Rhizobium activity of an arid land soil were investigated 4 yr after contamination. Effects were assessed in field plots and by a greenhouse bioassay. Addition of process water had marked effects on the chemistry of the soil and increased concentrations of Ca, Mg, Na, NO 3 and NH 4 as well as raising the electrical conductivity. VA infection analysis of roots from field plots and the bioassay combined with counts of VA fungal spores indicate reduced mycorrhizal activity in treated soils. The individual species of VA fungi were found to be affected differently by the process water. Roots of the legume yellow sweetclover developed fewer nodules in soils treated with retort water. An acetylene reduction assay indicated that nitrogenase activity was reduced in nodules from soils treated with undiluted process water.

Research priorities and science policy objectives for the management of soils in arid lands

A review is made of the methods adopted for establishing priorities for research by some major grant-giving organisations concerned with agricultural research. The studies funded by these organisations im marginally on the particular problems of arid lands although the principles are much the same. For determining priorities for research on arid lands for which in general little background information exists it is necessary first to evaluate the resource. The review is illustrated by an account of the Autralian experience, in which the author was personally involved.

Cation Release from Sodium‐ and Calcium‐Saturated Clay‐Sized Soil Fractions

AbstractThe cation release of sodium‐ and calcium‐saturated clay fractions of two montmorillonitic and one vermiculitic aridland soils was compared with that of specimen Ca‐ and Na‐saturated montmorillonites. The clays were reacted with distilled water (0.25, 0.5, 1.0, and 2.5% wt/v) at 25°C. Hydrolysis rates of soil clays were roughly comparable to those of the specimen montmorillonites. Sodium hydrolysis exceeded calcium hydrolysis for soil clay fractions, whereas Na and Ca hydrolysis rates were about equal for the specimen montmorillonites, due to the dissolution of other silicates in the soil clays. Sodium kaolinite hydrolyzed so rapidly that it could not be prepared free of Cl without almost total loss of exchangeable Na. The suspensions were filtered after about 500 hours, and the solution compositions were used to determine ion activity products for the various montmorillonites and other silicate phases. Solutions were slightly supersaturated with respect to crystalline gibbsite. Most soil‐clay solutions were also supersaturated with respect to kaolinite, montmorillonite, K mica, and illite. Although the major cation chemistry of the Ca‐saturated soil clay suspensions was predominantly controlled by the surface hydrolysis reactions, the Na‐saturated suspensions were affected by dissolution of non‐smectite minerals. The weathering of less stable minerals also resulted in additional silica and aluminum release. This is consistent with feldspar undersaturation and montmorillonite supersaturation in the soil‐clay suspensions. The pure montmorillonites gave activity product values consistent with published montmorillonite stabilities.