Evaluation of estimation methods and base data uncertainties for critical loads of acid deposition in Japan

Abstract

Simplified steady state mass balance model for critical load (CL) estimation was applied to a test area in Japan to evaluate applicability of the model. Three different criteria for acidification limits (1: [Al3+]<0.2 eq. m−3, 2: Al/BC<1.0 mol mol−1, 3:Al depletion criterion) were used. Mean values and spatial distribution patterns of CL values calculated by these criteria were extremely different from each other. The first criterion produced much higher CL than the second criterion in the Japanese condition with high annual precipitation. Improvements including definition of the criterion were considered necessary. As quantitative data of the base cation weathering rate (BCw) was lacking, the rate was specified based on surface geology and the soil type of each site. To evaluate uncertainty of BCw used for CL calculation, ion content and particle-size distribution were measured for the soils collected from the test area, and BCw was estimated with PROFILE model based on these measurements. It appeared that BCw estimates by surface geology were adequate as a mean value, but they had uncertainty of about 50% of the average values due to variability of ion contents within the same surface geology group.