A dynamic, process-based model of surface water acidification, MAGIC, has been applied to over a thousand sites across the UK. The model is calibrated to surface water samples collected during a survey for the Critical Loads programme, and utilises the best available and consistent estimates of soil physical and chemical properties, rainfall and runoff volumes, and deposition chemistry. A total of 698 sites were successfully calibrated. At these sites, freshwater chemistry was reconstructed from 1857 to the present day (1997), and forecast to 2047 based on future decreases in sulphur (S) deposition in response to the Second S Protocol. The decline and recovery in surface water ANC were modelled at a national scale, a clear spatial distribution in water quality is apparent from these maps.
Model outputs capture distinct regional patterns of acidification and recovery. The most acidic present day conditions are found in acid-sensivitive regions of Northern England (the Pennines, Lake District and North York Moors). Although a significant proportion of sites in these areas failed to calibrate, those that did are predicted to have experienced severe historic decreases in Acid Neutralising Capacity (ANC) in response to high levels of acidic deposition. The model also indicates significant acidification in the moderate deposition areas of Wales and Galloway, whereas in the low-deposition region of Northern Scotland , acidification has been minor despite areas of acid-sensitive geology.
