Weathering and the Environmental Proton Balance

The classical geochemical material balance (Goldschmidt, 1933) assumes that the H+ balance in our environment has been established globally by the interaction of primary (igneous) rocks with volatile substances  

In an oversimplified way one can say that acids of the volcanoes have reacted with the bases of the rocks the composition of the ocean (which is at the first endpoint (pH = 8) of the titration of a strong acid with a carbonate) and the atmosphere (which with its pco2 = 10 3 5 atm is nearly in equilibrium with the ocean) reflect the proton balance of reaction (5.25). Oxidation and reduction are accompanied by proton release and proton consumption, respectively. (In order to maintain charge balance, the production of e will eventually be balanced by the production of H+.) Furthermore, the dissolution of rocks and the precipitation of minerals are accompanied by H+-consumption and H+-release, respectively. Thus, as shown by Broecker (1971), the pe and pH of the surface of our global environment reflect the levels where the oxidation states and the H+ ion reservoirs of the weathering sources equal those of the sedimentary products. 

Weathering is a major H+ consuming process and pH-buffering mechanism, not only globally and regionally but it also plays a major role in local watersheds in soil processes, in nutrient uptake by plants and in epidiagenetic reactions in sediments. 

As Fig. 5.17 illustrates aggrading vegetation (forests and intensive crop production) produces acidity (see Eq. (viii) of the Appendix) since more cations are taken up by the plants (trees) H+ is released through the roots. The protons released react with 

Effect of plants (trees) upon H+-balance in soils 

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