Modelling Surface Water Acidification Using One and Two Soil Layers and Simple Flow Routing

Summary

The Model of Acidification of Groundwater In Catchments (MAGIC) was applied to two sites in Scotland to assess the influence of model structure on hindcast and forecast water quality variables. Three model structures were implemented for each site; a single soil layer model, a two soil layer model and a two layer model with simple flow routing. The structures were calibrated using a fuzzy optimization procedure that provided estimates of calibration uncertainty for all variables. All three structures at both sites were capable of reproducing observed surface water chemistry. The different model structures, however, produced significant differences in the simulation of soil and soil water variables. These differences were related to the difficulty of estimating base cation weathering and soil base cation exchange in the aggregated or distributed structures. The differences in simulation results among the model structures were small, however, compared to measurement errors. We conclude that, given currently available data, a one-layer model structure is sufficient for long term simulation of acid deposition effects on the sites studied.