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The origin of secondary phyllosilicates in serpentinitic soils of differing moisture regimes is incompletely understood. The objective of this study was to determine the genesis of weathering products in serpentinitic soils along a moisture regime gradient using conventional x-ray diffraction (XRD) methods and high-resolution transmission electron microscopy (HRTEM). The samples studied were obtained from an Aquic Argixeroll and a Cumulic Endoaquoll on the Trinity ophiolite, in the Klamath Mountains, California. The soils are from backslope and toeslope landscape positions associated with a 3.2-ha wetland on a stabilized landslide bench. Chlorite and serpentine are the major primary minerals in the soils. Chlorite is relatively stable and was found in the clay fraction of all horizons studied. Serpentine was observed in all horizons except the Aquic Argixeroll Cr2 horizon. The soil mineral assemblages indicate that chlorite transforms to vermiculite and both randomly and regularly interstratified chlorite/vermiculite by loss of the hydroxide-interlayer sheet. The vermiculite then alters to a high-charge smectite that was found only in the lower horizons of the backslope landscape position. Smectite is the predominant secondary mineral in all horizons. Serpentine transformation products could not be directly identified, but the prevalence of a low-charge smectite in the Cumulic Endoaquoll is interpreted as a precipitate from serpentine dissolution products. Thus, the abundant smectite in these serpentinitic soils is of two origins: (i) a high-charge phase derived from chlorite transformation that is found in the backslope landscape positions, and (ii) a low-charge phase neoformed by precipitation of elements released by serpentine weathering.

Although chlorites are an important source of Mg and micronutrients in soils, little is known about their weathering behavior in acidic environments. The effect of organic (acetic, oxalic, citric) and inorganic (hydrochloric, nitric, sulfuric) acids on the dissolution of ripidolite was studied at 25[degrees]C over an acid concentration range of 0.03 to 10 mM. The increasing ripidolite dissolution with increasing acid concentration can be described by the same empirical equation for all six acids used in this study. Because proton and ligand promoted dissolution mechanisms are additive, the influence of ligands can be calculated by subtracting the influence of protons from the total dissolution of ripidolite. We assume that the influence of [Cl.sup.-] in HCl systems can be neglected. Greater dissolution of ripidolite in the presence of the other acids at the same pH is attributed to the accompanying anion. At pH 3.5 and an anion concentration of [10.sup.-3.5] mol [L.sup.-1], the relative effectiveness of the acids used in this experiment in promoting dissolution was nitric (enhancement factor: 0.97) [congruent to] hydrochloric (1.00) [congruent to] acetic (1.01) < sulfuric (1.19) < citric (2.70) < oxalic acid (3.27). The dissolution of ripidolite was nonstoichiometric with a preferential release of Si relative to Al, Fe, and, in some cases, Mg at low proton and ligand concentrations for all six acids. At higher acid concentrations the dissolution becomes almost stoichiometric in the presence of inorganic acids, whereas in the presence of oxalic acid Al, Fe, and Mg were released preferentially relative to Si. In the presence of citric acid, Fe is released preferentially relative to Si. The alteration of chlorites in soils and the amount of released elements into the soil solution therefore depends on the composition of acidifying agents in soils.

Smectites are a major mineral group often found in the clay fraction of soils. Our objective was to evaluate the effect of pedologic environments on smectites in the arid Carrizo Plain, California. Six pedons (one Argixeroll, three Haploxeralfs, one Natrargid, and one Salorthid) were described and sampled along a geomorphic and salinity gradient transect. The transect soils have formed in alluvial parent materials derived from Miocene marine sandstones, siltstones, and shales. The fine clay fractions of transect soils were studied using x-ray diffraction, interlayer swelling with alkylammonium cations, and chemical analyses. Both beidellitic and montmorillonitic smectites occurred in the transect soils, suggesting multiple origins for these minerals. The chemical composition of the beidellites are similar to those of a tetrahedrally charged, dioctahedral mica. Since mica was identified in shale parent materials and in the fine silt and clay fractions of the soils, the beidellites are apparently a weathering product of mica. Minor variations in the chemical composition of mica precursors may account for observed differences in beidellite charge characteristics. The chemical composition of montmorillonites was variable, making a common origin for these minerals unlikely. Montmorillonites from saline pedons contained more Fe and Mg and less Al in the octahedral sheet than montmorillonites from nonsaline pedons. Montmorillonites in the nonsaline pedons are probably inherited from montmorillonites identified in parent materials, whereas montmorillonites in saline soils may be neoformed. Groundwater within the Salorthid was supersaturated with respect to both montmorillonite and beidellite.

Elevated concentrations of U are found in agricultural drainage waters from the San Joaquin Valley, CA, which are often disposed of in evaporation basins that are frequented by waterfowl. To determine the factors that affect aqueous U concentrations in the basins, sorption experiments with U(VI) were performed at various C[O.sub.2] partial pressures, dissolved Ca, Mg, and P concentrations, and carbonate alkalinities. Synthetic waters, comparable in inorganic constituents to irrigation and drainage waters, were prepared, spiked with 0.1 (soil) and 2 mg U(VI) [L.sup.-1] (synthetic goethite), and analyzed for U, P (when applicable), and major ions. Total chemical analyses were input into the computer program FITEQL to determine U(VI) speciation and generate U(VI) adsorption constants with the diffuse layer model (also referred to as the two-layer model). Maximum adsorption occurred in solutions with low carbonate alkalinities ([less than or equal to]3 mmol [L.sup.-1]), ionic strengths ([less than or equal to]0.03 M), Ca concentrations ([less than or equal to]4 mmol [L.sup.-1]), and P concentrations (

Vernal pools are seasonal wetlands that have unique plant and animal species. More than 10 vernal pools are found on the basalt-capped mesas of the Santa Rosa Plateau Ecological Preserve in southern Riverside County, California. In this study, one vernal pool catena was investigated to determine the relationships between soil morphology, soil chemical properties, and water movement. Soils on the summit and backslope are shallow and coarse-loamy, and are maintained as Entisols by extensive burrowing by rodents and their predators. Footslope soils are clayey Alfisols with strong prismatic structure. The basin and toesiope soils are Vertisols with strong angular blocky structure and slickensides. Iron oxides are concentrated in the upper slope soils, imparting 5YR hues and high chromas. Because Mn oxides are soluble at higher redox potential than Fe oxides, Mn has been preferentially dissolved, transported downslope with throughflow, and precipitated as oxides in the lower slope soils, which have 10YR hues and low chromas. Water infiltrates readily through the upper slope soils and moves downslope along the soil-basalt bedrock contact and within the vesicular basalt. In the basin, the Vertisols are wetted unevenly as water moves downward through soil cracks and upward from throughflow in the underlying vesicular basalt.

The result of the experiment conducted to find the solubilities of the precipitates during evapoconcentration of synthetic irrigation waters shows that the solubilities of the precipitated solids is proportional to the amount of silicon and magnesium present in the solid. The activities of calcium ion and carbonate ion, the mineralization of the organic matter and the presence of metastable forms of calcium carbonate are overestimated due to the oversaturation of calcite in soil solutions.

An experiment was conducted to assess the influence of NaCl and calcium magnesium acetate (CMA) on trace metal mobility in roadside soil and to examine the connectivity of trace metals absorbed from a soil treated with deicing salts to tiny organic molecules or to bigger colloidal particles. The soils which are influenced by NaCl road salt could provide trace metals through colloidal-assisted transport to groundwater. Collodial connected metals are not very significant under acute salinity, and this was indicated as there was only 18% variation between the concentration of metals in dialysis solutions of high-salt leachates.

Barren, shallow depressions known as slickspots are common features on sodic soil landscapes. Our objective was to determine the conditions and processes responsible for slickspot soil genesis in a closed basin grassland in the Central Coast Range province of California. The slickspots are irregularly shaped, 0.5 to 15 m long, and devoid of all vegetation throughout the year. The adjacent soils under grass have strong columnar structure below a thin ( 150 cm deep in the vegetated soil to within about 10 cm of the slickspot soil surface. Infiltration is severely impeded in the crusted slickspot soils, but not in the structured vegetated soils. Thus, leaching predominates over evapotranspiration in the vegetated soils (fine, montmorillonitic, thermic Typic Haploxeralfs), but is insignificant in the adjacent slickspot soils (fine, montmorillonitic, thermic Typic Natrargids). Water and dissolved salts leached through the vegetated soils move along a water potential gradient into the drier slickspot subsoils, then upward, following a gradient established by evaporation at the slickspot surface, resulting in salinization of the slickspot soils. Carbon-dated relict grass roots from the slickspot soils indicate that the slickspots have expanded at the expense of grassland within the last few tens to hundreds of years. Water and wind erosion at slickspot margins is increasing the size of these barren areas, which are too dry, compacted, and saline for vegetation to become reestablished.

The effectiveness of polymers, gypsum and their combination in improving the hydraulic conductivity of a saline sodic clay soil was investigated. The hydraulic conductivity of such a soil was significantly increased by polymer application when the soil had an exchangeable sodium percentage (ESP) less than 15. Polymer application at higher ESP levels had little or no effect. Combining gypsum and polymer application produced a significantly beneficial effect. The dominant mechanisms affecting the hydraulic conductivity of this soil were slaking and dispersion, rather than swelling.

Soils formed from serpentinite contain an abundance of Fe, Mn, Cr, Ni, and Mg, and low concentrations of the plant-essential nutrients Ca and K. The resulting vegetation is commonly xeromorphic and characteristically stunted. This study was conducted to (i) determine the spatial distributions of heavy metals and exchangeable cations ([M.sub.e]) in an ultramafic wetland and surrounding landslide terrain, and (ii) to interpret the distributions relative to environmental conditions and pedogenic processes on the component landscape positions. Distributions of dithionite-extractable metals ([M.sub.d]) and [M.sub.e] in surface soils (0-15 cm depth) were assessed by kriging and by landscape units, characteristic landscape position, soils, and vegetation. Abundance of [M.sub.e]s ranked in the following order: Mg [is greater than] Ca [much greater than ] K [is greater than] Mn [is greater than] Na [is greater than] Ni. The Ca/Mg ratios range from 0.13 to 3.77 (mean 0.43), with the highest ratios in a landscape unit with nonserpentine metamorphic colluvium over serpentinitic residuum. Exchangeable cations are concentrated within the wetland relative to surrounding terrain. Dithionite-extractable Fe, Mn, and Ni are concentrated in soils on the oxidizing, nonhydric lower landscape positions, near the hydrologic discharge point of the wetland. Chromium and Al are concentrated in the nonhydric upper landscape positions. Due to reducing conditions, the wetland contains low concentrations of Ma relative to the surrounding nonhydric terrain. Large vegetation differences between moisture class coupled with moderate vegetation differences between landscape units within the same moisture class, suggest that vegetation occurrence within the study area is controlled primarily by hydrology, and secondarily by elemental conditions.

Irrigation with blended drainage water can damage soil structure, impair infiltration, and increase runoff and erosion. This loss of permeability is often attributed to the slaking of aggregrates and clay dispersion, which leads to pore plugging. Soil swelling is usually considered an important factor only when exchangeable sodium percentages (ESP) exceed 15%. We hypothesized that swelling is more important than generally recognized in reducing soil hydraulic conductivity (HC), and swelling can occur at low ESP. In this study we attempted to identify the mechanisms reducing HC and the reversibility of the processes during gypsum and sulfuric acid application. Synthetic drainage waters with sodium adsorption ratios (SAR) of 1, 3, 5, and 8 and electrolyte concentrations (C) of 0, 2.5, 5, 10, 25, 50, and 100 [mmol.sub.c] [L.sup.-1], were leached through machine-packed soil columns to evaluate the effects of clay dispersion and swelling on HC. Following the initial leachings, the soils were amended with surface applied gypsum and [H.sub.2][SO.sub.4], and leached with deionized water. Clay concentration in the leachate was used as a measure of clay dispersion, and internal soil swelling was assumed to be proportional to changes in the water holding capacity at -22 kPa tension, Internal soil swelling at low electrolyte concentrations ([is less than] 12 [mmol.sub.c] [L.sub.-1]) reduced the number of large, free-draining pores and increased the water holding capacity of the soil at low tension. This loss in HC, which occurred at all SAR, was largely reversible with surface-applied gypsum. At SAR 5 and 8, there was irreversible plugging of soil pores by dispersed clay, as well as internal swelling. These findings suggest that even diluted drainage waters used for irrigation will have an adverse effect on soil structure, especially during rainfall.