An evaluation of the equilibrium calculations within acidification models: The effect of uncertainty in measured chemical components

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Abstract
There is much concern over the effects of acidic deposition on soils and drainage waters. To better understand the processes regulating the acidification of surface waters, computer models have been developed which utilize equilibrium calculations to predict the concentration of chemical parameters such as pH, acid neutralizing capacity, dissolved inorganic carbon, Al and SO42−. A simple chemical equilibrium model (ALCHEMI) was used to evaluate the effect of uncertainty in the measurement of chemical constituents on thermodynamic calculations. For calculations where pH was not allowed to vary (fixed pH calculations), uncertainty in Al speciation was small (maximum of 7%) and largely due to imprecision in the measurement of total F and pH. When calculations were made from electroneutrality based on measured constituents (variable pH calculations), most of the uncertainty associated with the values of output parameters was due to imprecision in the determination of SO42−.