A biogeochemical model of acidification: MAGIC is alive and well

For 40 years, Model of Acidification of Groundwater In Catchments (MAGIC) has been used to simulate the acidification of soils and waters due to acid deposition. The original model (MAGIC v8) has now been updated and re‐implemented in the C++ Mobius platform and is available as open source. MAGIC‐Forest includes new modules describing hydrology, forest growth, and soil carbon. The Mobius platform facilitates automatic optimization of calibrated parameters and multipoint calibrations using Monte‐Carlo routines. The usefulness of MAGIC is demonstrated here by application to the 50‐year data series for deposition and runoff at Birkenes, a small, calibrated catchment in southern Norway. Acid deposition has declined dramatically at Birkenes since the peak in the 1970s. Sulfate is 90% lower. Stream water has recovered strongly. Decreased concentrations of sulfate have led to increased acid‐neutralizing capacity, pH, and reduced concentrations of toxic aluminum. These changes are well‐simulated by MAGIC. The sulfate control on organic carbon solubility added as part of MAGIC‐Forest improves the simulations. The MAGIC‐Forest modeling tool is now available for applications to scenarios of land‐use and climate change.