Acidification capacity model: formulation and application

A theoretical computation approach and a classification method of two-reference-states for the acidification capacity of natural waters are developed after its definition, determination procedure and classification methods are demonstrated. In the theoretical computation of acidification capacity, the alkalinity, pH, chemical oxygen demand and Al(III) components of waters are chosen as the original parameters. The contribution of carbonate, dissolved organic matter, and soluble aluminum to the acidification capacity is, respectively, emphasized. On the basis of theory of aquatic chemistry and the aquatic status of Southwest Area of China, the calibration value of methyl orange alkalinity to TIP alkalinity is calculated as 49 μM. The CaCO3 water system which balances with CO2 in the atmosphere, and the water system which holds the critical pH and balances with CO2 in the atmosphere are considered as the reference state of the waters difficult to acidification and the critical state of acidified water. The annual amount of acid deposition including precipitation and dry deposition is used as the reference criterion to classify the waters easy and difficult to acidification. As a case study, this model is applied to the southwest area of China, and some compatible results have been obtained. This model makes it possible to estimate the acidification trend of natural waters in a large scale of area.