Soil-Moisture Chemistry

In high-rainfall climates the chemistry of soil water may resemble that of the local precipitation. Such conditions exist where evapotranspiration (ET) losses are minimal because of low temperatures and/or high humidity, or where the soils are quartz-sand-rich and deficient in weatherable minerals. 

Note Except for pH. concentrations are in mg/L. Values in parentheses are estimates. The Na/(Na+Ca) ratio is in terms of species weights. Woodstock granite soil water also contains A1 = 0.1 mg/L, and Te = 0.00 mg/L. Sierra Nevada granite soil water has Al — 0.00 mg/L and Fe - 0.12 mg/L. Kauai soil water has Al — 0.00 mg/L and Fe = 0.18 mg/L. All soil waters are from the A horizon except the Woodstock granite soil, which is from the deep C horizon. 

Source Modified from R. M. Garrels and F. T. Mackenzie. Evolution of sedimentary rocks. Copyright 1971. Used by permission. 

General Controls on Natural Water Chemistry Chap. 8 

A detailed look at the evolution of soil-moisture chemistry was reported by Sears (1976). In his study Sears assumed the average composition of precipitation shown in Table 8.7. Table 8.7 also lists analyses of the soil moisture he collected from suction lysimeters at 1- and 3-m depths in respective B- and C-horizon soils formed by the weathering of underlying sandy dolomite. The 1-m sample is chiefly a Na -NOj water, with the nitrate probably from fertilizer. The TDS is about 70 mg/L at 1 m and has increased to 500 mg/L at the 3-m depth. In order to explain changes occurring between the 1- and 3-m depth, it is useful to select a solute we can assume to be practically un-reactive in the soil. The best common species for this purpose is probably Cl, with which we can then compare other species concentrations. Relative increases from 1- to 3-m depth are shown in the third column. Increases compared to chloride are given in the fourth column. 

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Table 8.6 contrasts soil moisture chemistry in a variety of soils and climates. All of the tabulated locations, except for the Sierra Nevada soil, are near the ocean, so that one would expect their precipitation to be dominated by Na and Cl. If ET alone controls infiltrating soil-water chemistry, this same dominance by Na and Cl should persist in the soil water. Such is the case for moisture from the Kauaian soil, which is also in an area of very high rainfall, consistent with its low TDS content of about 30 mg/L. 

Soils—Heavy metal content. 2. Havy metals—Environmental aspects. 3. Soil moisture. 4. Soil chemistry. I. Kingery, William L. II. Title. 

The composition of soil moisture is inlluenced by processes and inputs listed below. Explain how each of these can contribute to soil-water chemistry ... 

Shown in Fig. 9.9 are water-composition ranges for some humid-climate streams (in New Jersey), a dilute, freshwater lake (Lake Huron) and lake-bottom muds from the Great Lakes (Sutherland 1970), and deep-soil moisture from Pennsylvania (Sears 1976 Sears and Langmuir 1982). Lake Huron and the Delaware River are dilute, humid-climate waters. They both plot near the kaolinite-gibbsite boundary. Their composition can be described as water dominated. In other words, their chemistries are controlled chiefly by dilution with fresh rainfall and runoff, not by reactions with geological materials. In a study of acid rain (water-dominated) control of soil moisture and ground-water chemistry of a sandy aquifer in Denmark, Hansen and Postma (1995) found that pore waters were close to equilibrium with gibbsite and supersaturated with kaolinite (Fig. 9.9). Precipitation pH = 4.34 at the site, and log([K+]/lH+]) = -0.95. 

Sears, S. O., and D. Langmuir. 1982. Sorption and clay-mineral equilibria controls on moisture chemistry in a C-horizon soil. J. Hydrol. 56 287-308. 

EM rates in the subsurface depend on electric current, soil pore fluid, grain size, ionic mobility, and contamination level. The direction and quantity of contaminant movement are influenced by soil type, pore fluid chemistry, contamination level, and electric current (Yeung, 1994). EK remediation can be used for both saturated and unsaturated soils, but for better efficiency, the soil moisture content should be high enough to allow EM. Nonionic species would be transported along with the electroosmotically induced fluid flow. The efficiency of extraction relies on several factors such as species type, solubility, electrical charge, and concentration relative to other species (Mitchell, 1993). 

System reliability is of the utmost importance to water suppliers and their customers. However, corrosion problems can vary greatly within a single system because many variables affect corrosion, for example, pipe material, pipe age, pipe wall thickness, water additives, corrosion inhibitor treatment, soil chemistry, soil moisture content and/or local groundwater level, and stray currents [2]. Table 8.2 summarizes some of the physical, environmental, and operational factors that can affect the deterioration rate of water distribution systems and lead to their failrue [4]. 

In most cases, this ideal cannot be met and will not yield the desired understanding of the chemistry of interest. This can sometimes be overcome by simple mediation of soil, such as bringing the soil sample to some standard moisture state before making certain measurements such as pH or salt concentration. 

They then summarize the work of several research teams and individuals working to experimentally determine values for Kd [1, pp. 28-30]. These efforts were made in a number of different soils, with different moisture levels, different organic content, and different soil chemistry. Published results for these conditions naturally differ widely however, it appears that values of 0.5 < Kd < 4.0... 

The sample portion used for moisture determination was split into a half-pint jar. A pint jar was used to contain the portion of soil reserved for chemical analysis and was immediately sealed. The pint jars were stored on dry ice and shipped within 3 days to the CDFA Chemistry Laboratory in Sacramento, California for analysis. The third portion of the sample was used to determine texture, organic matter content, pH, electrical conductivity and moisture. This portion was collected in a plastic bag and stored in a refrigerated chamber at 3° C. 

The chemical composition of rice husk ask is similar to that of many common organic fibers and it contains of cellulose 40-50%, lignin 25-30%, ash 15-20% and moisture 8-15%. Typical analyses of rice husk ask is shown in Table 8.2. The content of each of them depends on rice variety, soil chemistry, climatic conditions, and even the geographic localization of the culture. 

On this subject, see R. F. Miller and K. W. Ratzlaff, Chemistry of Soil Profiles Indicates Recurring Pattern and Modes of Moisture Migration , Proc. Amer. Soc. Soil Science, 1965. J. Pouquet, Water Movements in Soil Surface Layers , Bull. Assoc. Geogr. Fr., 1965. 

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