Changes in freshwater acidification trends in Canada's Atlantic Provinces: 1983-1997

Sixty-three lakes were sampled semi-annually for acid precipitation - related variables in Canada's Atlantic Provinces, Nova Scotia and Newfoundland from 1983 to 1997. A further 31 sites were sampled beginning in 1989 in Nova Scotia. We analyzed the water chemistry data for trends in pH, acid neutralization capacity, sulfate and base cations using the whole data set for the original 63 sites and the most recent eight years' data for all sites. We also analyzed acid deposition at two CAPMoN precipitation chemistry sites located at the two extremes of the sampling region for trends. We found that hydrogen deposition decreased by 20% in Newfoundland and 30% in Nova Scotia, and sulfate decreased by 36 and 34%, respectively. Sulfate and base cations in lake waters showed decreases as expected, though lake acidity and acid neutralization capacity did not show improvements. The conflicting trends in chemical variables suggest that though anthropogenically-induced weathering is diminishing in this region, conditions have not returned to `natural' background conditions.