General Chemistry of Surface- and Groundwaters

An important conclusion one can draw from the Sears study and other, similar studies is that in areas with well-developed soils, the chemistry of underlying shallow groundwaters is often chiefly determined by processes taking place in the soil and less by processes operating in the saturated zone below. In this case, groundwaters from the underlying dolomite are similar to the water from the soil 3 m deep. Similarly, the chemical composition of effluent streams (streams fed chiefly by ground-water) is also quickly determined by interactions with adjacent soils (see Section 7.8). 

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. 

It is important to note that water analyses rarely include the concentrations of dissolved gases or carbonic acid (H2CO3). To be complete, the tabulated average concentrations in Table 8.10 should list the carbonic acid concentration, which, for typical surface- and groundwaters at near-neutral pH s, equals several to tens of milligrams per liter. The following concentrations of carbonic acid are present at 25°C, depending on the CO2 pressure 

Dissolved oxygen and nitrogen concentrations in air-equilibrated surface water at 25°C are also significant and equal about 8 and 14 mg/L, respectively, which makes both species major constituents. 

General Controls on Natural Water Chemistry Chap. B 

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