Sensitivity, acidification and recovery of lakes in Nova Scotia, Canada

This thesis investigated the sensitivity, response, as well as confounding factors that affect the response of lakes in Nova Scotia to changes in sulphate (SO42-) deposition. This study showed that initial lake recovery (declines in SO42- water concentrations) reflected a combination of influences of SO42- deposition, sea salt deposition, as well as climate phenomena. The size of the exchangeable calcium pool was a good predictor of the surface water chemistry within homogenous landscape units, while catchment attributes, indicative of overall sites' buffering capacity, better predicted lake sensitivity at the provincial scale. The current chemical status, estimated using empirical relationships between water chemistry and catchment attributes, identified 13 % (and 6 % when potential influence of high organic acidity (DOC> 7 mg L-1) was excluded) of all lakes as having ANC < 20 mueq L-1, a chemical threshold previously indicated to ensure viable populations of acid-sensitive aquatic biota. The application of the dynamic hydro-geochemical MAGIC, using a statistical framework for systematic calibration and uncertainty propagation, revealed that under current emission legislation no improvement in surface water chemistry was predicted to occur by the end of the 21st century. Based on current sensitivity estimates, lakes with ANC < 20mueq L-1 and a proportion of lakes with ANC < 50 mueq L-1 (totalling over 13 % of all lakes in the province) are likely to remain acidified into the future (2006 - 2100). This research suggests that further emission reductions need to be considered for recovery to occur, particularly since changes in climate and soil base cation losses may further counteract any declines in SO42-deposition.;Key words: Nova Scotia, acidification, stock at risk, MAGIC, uncertainty, sulphate, Monte Carlo, calcium...