A COMPARATIVE-EVALUATION OF DIFFERENT APPROACHES FOR ASSESSING SOIL ACIDIFICATION IMPACTS

Long-term impacts of acidic depositions on soils can be predicted with coupled applications of acid deposition models and approaches to assess soil acidification. Soil acidification assessment can be achieved by using the following approaches: (i) Mechanistic modelling (ii) Experimental acid buffering capacity (ABC) method (iii) Qualitative evaluations The mechanistic modelling approach adopted in this study utilises predicted acid deposition rates and soil properties as well as dominant soil mechanisms including utilisation, immobilization, nitrification, dissociation, association, carbonate weathering, silicate weathering, aluminium hydroxide disintegration, and cation exchange. The experimental ABC method, on the other hand, was based on titration curves obtained by adding different dilutions of H2SO4 to known quantities of soil samples. The sensitivities of the soil samples to acidification were also evaluated using a qualitative approach based on the pH and cation exchange capacity (CEC). A comparative evaluation of these approaches was made using the results of an environmental impact assessment (EIA) study conducted for a proposed coal-fired thermal power plant to be sited at Aliaga near Izmir, Turkey. In this context, the regional soils were first evaluated qualitatively. Then, the results of mechanistic and experimental approaches were compared in terms of the time required to reach certain critical pH levels. For the case of less sensitive calcareous soils, the mechanistic modelling approach yielded more conservative predictions. In the case of highly sensitive non-calcareous soils, however, the experimental ABC approach resulted in more conservative predictions