Uncertainty in a regional-scale assessment of cadmium accumulation in the Netherlands

Atmospheric deposition and agricultural activities may cause the cadmium (C d) content in the rural environment in the Netherlands to exceed legal envi ronmental standards. A simple process-oriented model, SOACAS, in combinatio n with a Geographical Information System was used to assess the magnitude o f the Cd accumulation on a regional scale. The objective of this study was to quantify the uncertainty in the Cd accumulation due to data uncertainty, Another objective was to study whether maps of simulated and observed Cd c ontents were statistically different when the uncertainty in both maps was considered. From a Monte Carlo analysis we derived that the model behaved v irtually linear within the range of model inputs considered, and concluded that first-order uncertainty analysis (FOUA) was appropriate for mapping pr ediction uncertainties. The maps crested by FOUA indicated that the contrib ution of individual model parameters to the total uncertainty was soil depe ndent, and that the pedotransfer function for Cd sorption gave the largest contribution to the total uncertainty. In an earlier analysis we found that in 25% of the total area SOACAS underestimated the average levels of curre nt Cd contents by >50%. The model predictions and the observations were sta tistically different at a much smaller area (10% of the total area), showin g that ignoring uncertainty may result in misleading interpretations when t he model is compared with field measurements.