Rate of weathering

These reactions, however, are complex and generally proceed through a series of reaction steps. The rate of weathering of siUcates may vary considerably, depending on the arrangement of the siUcon tetrahedra in the mineral and on the nature of the cations. 

Ugolini, F.C. (1986). Processes and rates of weathering in cold and polar desert environments. In "Rates of Chemical Weathering of Rocks and Minerals" (S. M. Colman and D. P. Dethier, eds), pp. 193-235. Academic Press, New York. 

Modeling of the transport of the long-lived nuclides, especially U, require knowledge of the input at the water table as a boundary condition for aquifer profiles. There are few studies of the characteristics of radionuclides in vadose zone waters or at the water table. Significant inputs are likely to occur to the aquifer due to elevated rates of weathering in soils, and this is likely to be dependent upon climatic parameters and has varied with time. Soils may also be a source of colloids and so provide an important control on colloidal transport near recharge regions. 

Frostad, S., Klein, B., Lawrence, R.W. 2002. Evaluation of laboratory kinetic test methods for measuring rates of weathering. Mine Water and the Environment, 21, 183-192. 

Lown, D. J. 1986. Controls on the rate of weathering and clay mineral genesis in airfall tephras a review and New Zealand case study. In Coleman, S. M. Dethier, D. P. (eds) Rates of Chemical Weathering of Rocks and Minerals. Academic Press, New York, 265-330. 

Lake level could also influence silica levels. For example, the decline in lake level resulted in a large loss of surface area and decreased the amount of contact between lake water and sandy littoral areas that contain weath-erable silicate minerals. Rates of weathering are usually enhanced by acidification and would help to explain the interbasin differences observed at pH 4.7. However, weathering rates of LRL sediment are unknown (see Sediment Processes section). In addition, although the differences between the basins were significant, they were small (0.01-0.03 mg of Si02 per liter) and may be accounted for by small differences in hydrological factors. 

Little is understood of the mechanism involved in the improvement of a wood surface after treating with chromium-containing chemicals and the subsequent durability of applied finishes (5). The data in Table II show that the reduction of the rate of weathering (as measured by loss of springwood) is directly related to chromium concentration. 

Leaching, the passage of water through the soil profile, is a process that occurs in soils in areas of moderate to high rainfall, and which results in the loss of exchangeable cations (such as Ca, Mg, K, and Na - see Section 5.5). Unless the rate of weathering of soil minerals is sufficiently rapid to replace these losses, the exchange sites will become occupied by H" and which are acidic cations. 

Wessels, D. C. J. Schoeman, P. (1988). Mechanism and rate of weathering of Clarens sandstone by an endolithic lichen. South African Journal of Science, 84, 274-7. 

Here the density of the solid is p and a is another geometric constant. Geometric surface areas have often been used to estimate rates of weathering in held systems (White and Peterson, 1990). In addition, when volumetric rates of dissolution are estimated from rates of interface advance by Equation (10), these rates are implicitly normalized by geometric surface area (e.g., Brantley et al, 1993 Brantley and Chen, 1995). 

Benedetti M. F., Menard O., Noack Y., Caralho A., and Nahon D. (1994) Water-rock interactions in tropical catchments field rates of weathering and biomass impact. Chem. Geol. 118, 203 -220. 

Paces T. (1986) Rates of weathering and erosin derived from mass balance in small drainage basins. In Rates of Chemical Weathering of Rocks and Minerals (eds. S. Coleman and Dethier). Academic Press, Orlando, pp. 531-550. 

However, even in such areas tree roots can penetrate great distances (25-30 ft (lft = 0.3048 m)) below the surface (Nepstad et al., 1994) and reach bedrock (see also Figure 2). If there is a change in the plant cover due to drought, flood, disease, storms, or forest fires, so that the depth of root penetration changes, rate of weathering in low relief areas can change. Also, there... 

Bormann et al. (1998) attempted to determine whether rates of weathering of primary minerals were being underestimated due to failure to include weathering products accumulating in the biomass and in soil. They compared two sandbox ecosystems (large monitored lysimeters) at Hubbard Brook, NH, one with red pine and the other relatively nonvegetated (containing sporadic lichens and mosses). 

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