Weathering, 296 alkalinity calculation

Nickel (8) calculated the thickness of the proposed "residual layer" on albite from the mass of dissolved alkalis and alkaline earths released during laboratory weathering and the measured surface area, and determined that the thickness ranges from 0.8 to 8.0 nm in the pH range of natural surface waters. Although he interpreted his results differently, they anticipate later findings on the pH dependence of residual layer compositions (see below). 

Calculating the bicarbonate concentrations with (3), it is possible to plot the measured average pH values of Table 2 against the calculated loglHCOs ]. The result is shown in Fig. 5a. For pH >5.5 a linear relationship, very close to that reported in the literature, can be observed (pH = loglHCOa ] + 11.2). However, for acid lakes the calculated bicarbonate concentrations seem to be too low. It is reported that at pH<6 the release of metals from soils or sediments as a consequence of weathering processes becomes more and more important. Consequently aluminium hydroxides can influence alkalinity. In [18] the equation for calculating alkalinity was modified as follows ... 

This method may be used for soils, and for groundwater and surface runoff water from catchments. It identifies the mean, long-term sources of acidity and alkalinity in the system and then determines the maximum acid input that will bring about a balance that is biologically safe. Weathering rates, biomass acidity input, acid inputs from nitrogen transformations and alkalinity outflux are estimted. Models like MACAL referred to above can be used or more simple mass balance calculation performed. 

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