Weathering and soil

No corrosion occurs in a completely dry environment. In soil, water is needed for ionisation of the oxidised state at the metal surface. Water is also needed for ionisation of soil electrolytes, thus completing the circuit for flow of a current maintaining corrosive activity. Apart from its participation in the fundamental corrosion process, water markedly influences most of the other factors relating to corrosion in soils. Its role in weathering and soil genesis has already been mentioned. 

Soil is a key component of the rock cycle because weathering and soil formation processes transform rock into more readily erodible material. Rates of soil formation may even limit the overall erosion rate of a landscape. Erosion processes are also a key linkage in the rock cycle... 

Field studies have shown that the first 5-6 mm of rain falling on a heated desert surface evaporate almost immediately, whilst single storms with more than 20 mm rain lose a major part of it by lateral runoff. Hence, it is estimated that from the already low rainfall in the arid zone an important part is lost for weathering and soil formation. The importance of this runoff... 

Nordstrom, D.K. 2004. Modeling low-temperature geochemical processes. In Drever, J.l. (ed.) Surface and Ground Water, Weathering, and Soils 5, Holland, H.D. Turekian, K.K. (ed.) Treatise on Geochemistry, Elsevier, 37-72. 

Products of weathering and soil colloids, e.g., aluminum silicates, kaolinite, gibbsite, Si02... 

Fig. 13.7 Generalized aerobic and anaerobic biodegradation pathways for n-alkanes. Reprinted from Abrajano TA, Yan B, O Malley V (2005) High molecular weight petrogenic and pyrogenic hydrocarbons in aquatic environments In Drever JI (ed) Surface and ground water, weathering and soils vol 5 Treatise on Geochemistry pp 475-509. Copyright 2005 with permission of Elsevier...

In addition to chemical and mineralogical alterations, weathering and soil formation also induce physical changes in the rock. A more or less dense, non-porous, massive rock turns into a porous material containing air and water and thereby becomes suit-... 

McCracken, K. L. 1998. Dynamics of dissolved organic carbon during weathering and soil formation. Ph.D. Dissertation, University of New Hampshire, Durham. 

Merrill G. P. (1906) A Treatise on Rocks, Rock Weathering and Soils. McMiUian, NY. 

Geochemical processes associated with weathering and soil formation are dominated by alteration of feldspars (and volcanic glass), feldspars accounting for 70% of the upper crust, if the relatively inert quartz is discounted (Taylor and McLennan, 1985). Advancing weathering leads to a shift towards an aluminum rich composition that can be approximated by the chemical index of alteration (CIA) of Nesbitt and Young (1984)... 

In certain environments, localized anomalously low concentrations of soil O2 have been used by exploration geologists to indicate the presence of a large body of chemically reduced metal sulfides in the subsurface. Oxidation of sulfide minerals during weathering and soil formation draws down soil gas po below regional average. Oxidation of sulfide minerals generates solid and aqueous-phase oxidation products (i.e., sulfate... 

Suiface and (iround Water, Weathering, and Soils James I. Drever, University of Wyoming... 

Many plants can vary considerably as to their quantities of active chemical constituents. This variability may depend on the time of year of harvest age of the plant method of pollination and/or conditions of watering, wind, weather, and soil. These variables can lead to considerable differences in the finished product after manufacturing. 

By varying the conditions of synthesis much can be learned about the experimental parameters which govern iron oxide formation during weathering and soil formation (pedogenesis) (Schwertmann, 1985 1988a Fitzpatrick, 1988 Schwertmann and Taylor, 1989). 

Based on the mineralogy controlling weathering and soil development, sensitivity of ecosystem to acid deposition is assessed with a comprehensive consideration on the effect of temperature, soil texture, land use and precipitation. The results show that the most sensitive area to acid deposition in China is Podzolic soil zone in the Northeast, then followed by Latosol, Dark Brown Forest soil and Black soil zones. The less sensitive area is Ferralsol and Yellow-Brown Earth zone in the Southeast, and the least sensitive areas are mainly referred to as Xerosol zone in the Northwest,... 

In the pedosphere, the FA and the low molecular weight HA, which are water-soluble, are of particular interest. The interaction of these humic substances is important both in the processes of weathering and soil formation. According to Schnitzer (1971) FA constitutes between 25 and 75%... 

The retention or removal of ions, molecules, and compounds in the weathering and soil environment depends on the nature, strength, and abundance of the proton donors. The biota directly or indirectly affects the production of the proton donors. 

Silicon reactions are central to rock weathering and soil development. Silicon is the soil component lost in greatest amount from rock minerals during weathering, and the transformations of silica into secondary minerals are the major reactions of soil development. The sand fraction of soils is usually >90% quartz (SiC>2), the most prevalent form of Si in soils. Highly weathered soils may contain as little as 20% Si (Table 2.1a). A1 and Fe ore deposits are essentially highly weathered soils from which most of the Si has been lost. 

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