An assessment of the acidification and recovery of headwater catchments in Nova Scotia, Canada using soil-chemical models

The response of 20 acid-sensitive headwater catchments in 5 regions of Nova Scotia to reduced acidic deposition, and the need for further sulphur (S) was investigated using steady-state and dynamic soil-chemical models. The need for nitrogen (N) reductions using steady-state models was also considered, although only in a minor role. There were significant decreases in concentrations of sulphate (SO42-) in surface waters, suggesting that SO2 emissions reductions have had a positive effect in the region. Based on the Steady State Water Chemistry (SSWC) model and the First-order Acidity Balance (FAB) model, the critical load of strong acid is exceeded at 9 and 13 of the 20 study lakes, respectively. The SSWC model predicts that S deposition must be reduced by 37.3 mmolc m-2 a-1 to prevent critical loads from being exceeded at 95% of the lakes. The FAB model indicates that reductions of 32.7 mmolc m-2 a-1 (N) and 42.1 mmolc m-2 a-1 (S) are necessary to protect 95% of the lakes.; Mineral weathering rates at five representative catchments estimated using a variety of soil profile-based methods (Zr Depletion, Clay Content, and the PROFILE model) were low and the critical load for forest soils is currently exceeded (23 to 61 mmolc m-2 a -1) at all 5 sites. (Abstract shortened by UMI.)...