Impacts of uncertainties in base-cation deposition on the assessment of critical loads for acid deposition

Less attention has been paid to changes in the concentration and the deposi tion amounts of base cations. This has brought about great uncertainty in t he determination of critical loads for acid deposition. The paper utilized a newly developed long-term soil acidification model (LTSAM), to simulate t he effects of atmospheric base cations on the critical load of red earth in Wenzhou, Zhejiang Province. Results showed that great changes in atmospher ic base-cation deposition decreased the critical load by 68%. This suggeste d that by only reducing S deposition without considering changes in the atm ospheric base-cation deposition, would substantially overestimate the criti cal load of soils. Therefore, more attention should be focused on changes i n base cations during reductions of SO2 emissions, and the long-term monito ring of base cation deposition needs to be strengthened, especially in Chin a.