Surface-waters: chemistry constituents

The activities of Mg++ and Ca++ obtained from the model of sea water proposed by Garrels and Thompson have recently been confirmed by use of specific Ca++ and Mg++ ion electrodes, and for Mg++ by solubility techniques and ultrasonic absorption studies of synthetic and natural sea water. The importance of ion activities to the chemistry of sea water is amply demonstrated by consideration of CaC03 (calcite) in sea water. The total molality of Ca++ in surface sea water is about 10 and that of COf is 3.7 x 1C-4 therefore the ion product is 3.7 x 10 . This value is nearly 600 times greater than the equilibrium ion activity product of CaCO of 4.6 x 10-g at 25°C and one atmosphere total pressure. However, the activities of the free 10ns Ca++ and COj = in surface sea water are about 2.3 x 10-3 and 7.4 x 10-S, respectively thus the ion activity product is 17 x 10 which is only 3,7 rimes greater than the equilibrium ion activity product of calcite. Thus, by considering activities of sea water constituents rather than concentrations, we are better able to evaluate chemical equilibria in sea water an obvious restatement of simple chemical theory but an often neglected concept in sea water chemistry. 

The complexity of water chemistry and the diversity of its constituents results in a system of water quahty criteria that is based on the relationship between pollutant concentrations and environmental and human health effects. The compilation of the Environmental Protection Agency currently covers 157 priority pollutants (EPA, 1999). It lists estimations of maximum and continuous concentrations of pollutants in surface water according to the latest scientific information. Accordingly, the analytical-chemical requirements of water analyses and the correct assessments of their results are enormous (cf Kolle, 2001). 

The Chemistry of Soil Constituents, D.J. Greenland, M.H.B. Hayes, Eds., Wiley (1978) (Includes double layers, electrosorption, water near surfaces) The Chemistry of Soil Processes, D.J. Greenland. M.H.B. Hayes, Wiley (1981) (Includes transport, precipitation, adsorption). 

Farmer VC (1978) Water on partial surfaces In Greenland DJ and Hayes MHB (eds) The chemistry of soil constituents. Wiley, New York, pp 405 49 Farmer VC, Russel JD (1967) Infrared absorption spectrometry in clay studies. Clays Clay Miner. 15 121-142. 

Before we consider controls on the chemistry of surface and groundwaters in some detail, we will examine the general composition of such waters. Listed in Table 8,8 are the median concentrations of major, minor, and trace constituents in surface- and groundwaters (Turekian 1977), where major, minor, and trace concentrations are above 1 mg/L, between 1 mg/L and 1 yug/L, and less than 1 /U,g/L, respectively. 

As previously mentioned, hydrogen (as a elemental component of water) is the only heteroatom we consider in this review. The adorption and subsequent chemical behaviour of moecules on surfaces is certainly one of the most active areas of both experimental and computational surface science studies. For such a small and seemingly simple adorbate, the many types of possible interactions of water on oxide surfaces lead to richly complex chemistry. Water may be physisorbed intact, chemisorbed molecularly or dissociatively. In the last case, surface hydroxyls are formed, with the oxygen constituent of the hydroxyl originating either from the dissociated water molecule or the surface oxygen atoms. The H atom in the hydroxyls may be considered to be acidic (added to or abstracted from oxide anions as tf) or basic (as part of OIT added to or removed from metal cations). For all adsorbed species, molecular or dissociated, water or hydroxyl, there is the capability of strong hydrogen bond formation between other H, OH or O surface species. 

From the standpoint of regional tropospheric chemistry—which involves near-surface abundances of ozone, wet and dry deposition of acidic species, and transport and lifetimes of trace atmospheric constituents—the climate variables of interest include the variability of distributions of temperature, precipitation, clouds, and boundary-layer meteorology. In the global sense, these variables are controlled by surface and atmospheric temperature and water content. The distributions of temperature and water vapor are in turn controlled by solar and longwave radiation transfer involving the surface and the atmosphere. 

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