THE EFFECT OF CARBON-DIOXIDE EQUILIBRIUM ON PH IN DILUTE LAKES

Difficulties in measuring in situ pH in dilute acidified lakes have often resulted in an assumption of atmospheric carbon dioxide equilibrium to compute this pH. Unfortunately, the sensitivity of pH to carbon dioxide content of dilute waters is high. The results of our experimental study show the carbon dioxide equilibrium is seldom attained in a dilute lake. As a result, invoking an atmospheric equilibrium assumption can lead to pH estimation errors of greater than one (1) pH unit at pH = 6. A more accurate method to estimate in situ pH is presented. The method uses measured acid neutralizing capacity and total inorganic carbon. Contribution of humic substances to acid neutralizing capacity is taken into account.