Box 8-2 Calcium Carbonate Mass Balance in Rivers

Ca2+ is the most common cation in rivers and lakes. It comes from dissolution of the mineral calcite by the action of C02 to produce 2 moles of HCO j for each mole of Ca2+  

Just between 1960 and 2000, C02 in the atmosphere increased by 17% (Box 20-1)—mostly from our burning of fossil fuel. This increase drives Reaction A to the right and threatens the existence of coral reefs,9 which are huge, living structures consisting laigely of CaCOj. Coral reefs are a unique habitat for many aquatic species. 

Concentrations of bicarbonate and calcium in many rivers conform to the mass balance for Reaction A [HC03 ] 2[Ca24 ]. [Data from w. stumm and J. J. Morgan, Aquatic Chemistry, 3rd ed. (New York Wiley-lnterscience. 1996). p. 189 and H. D. Holland. The Chemistry of the Atmosphere and Oceans (New York Wiley-lnterscience, 1978).] 

Now that we have considered the charge and mass balances, we are ready for the systematic treatment of equilibrium.10 Here is the general prescription  

Step 3 Write mass balance equations. There may be more than one. 

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