The geochemistry of two hard water rivers,the Rhine and the Rhone: Part 3: The relations between calcium,bicarbonate, sulphate and pH

In the hard water rivers Rhine and Rhone the quotient Ca/HCO₃ is strongly related to the sulphate concentration and not to the pH. The relationship can be described (by least square analysis) for the Rhine: Ca/HCO₃) = 0.70 + 0.5 (SO₄), for the Rhone: (Ca/HCO₃) = 0.85 + 0.43 (SO₄). With a Teissier analysis (reduced major axis) a slope for both rivers of 0.58 has been found. These values equal the theoretically expected value of 0.5, when a solution of CaSO₄ is added to a saturated solution of CaCO₃. The source of the CaSO₄ (gypsum) is thought to be natural in the Rhone and anthropogenic in the Rhine. Acidification of both rivers is probably the result of decomposition of disposed organic matter.