Evaluation of different approaches for modeling effects of acid rain on soils in China

Acid deposition is an environmental problem of increasing concern in China. Acidic soils are common in the southern part of the country and soil acidi fication caused by acid deposition is expected to occur. Here we test and a pply two different approaches for modeling effects of acid deposition and c ompare results with observed data from sites throughout southern China. The dynamic model MAGIC indicates that, during the last few decades, soil acid ification rates have increased considerably due to acid deposition. This ac idification will continue if sulfur deposition is not reduced, and if reduc ed more rapidly than base cation deposition. With the Steady State Mass Bal ance model (SSMB), and assuming that a molar ratio of Ca2+/Al3+ < I in soil water is harmful to vegetation, we estimate a slight probability for excee dance of the critical load for present deposition rates. Results from both modeling approaches show a strong dependence with deposition of base cation s as well as sulfur. Hence, according to the models, changes in emission co ntrol of alkaline particulate matter prior to sulfur dioxide will be detrim ental to the environment. Model calculations are, however, uncertain, parti cularly because available data on base cation deposition fluxes are scarce, and that model formulation of aluminum chemistry does not fully reproduce observations. An effort should be made to improve our present knowledge reg arding deposition fluxes. Improvements to the model are suggested. Our work indicates that the critical loads presented in the regional acid depositio n assessment model RAINS-Asia are too stringent. We find weaknesses in the SSMB approach, developed for northern European conditions, when applying it to Chinese conditions. We suggest an improved effort to revise the risk pa rameters for use in critical load estimates in China. (C) 2000 Elsevier Sci ence B.V. All rights reserved.