Temporal and spatial trends in precipitation chemistry in the Georgia Basin, British Columbia

Abstract

During the 1960s and 1970s, scientific evidence on the impacts of atmospheric acid deposition led to international negotiations to control emissions of compounds (primarily sulphur (S) and nitrogen (N) oxides) that undergo long-range transport. More recently, there has been growing interest in acid rain research in western Canada, e.g., the Georgia Basin, British Columbia, where S and N emissions are expected to increase during the next two decades. In the current study, long-term trends (1990-2007) in precipitation chemistry were evaluated at four stations (Saturna, British Columbia; Egbert, Ontario; Chapais Quebec; and Kejimkujik, Nova Scotia) using the Mann-Kendall statistical test. Precipitation chemistry at Saturna suggests that the Georgia Basin is less influenced by anthropogenic (S and N) emissions compared with monitoring stations in eastern Canada; nonetheless, long-term (1990-2007) trends in precipitation chemistry at Saturna [pH (significant increase) sulphate (significant decrease) and nitrate (decrease)] mirrored those at sites in eastern Canada suggesting all stations (across Canada) have responded similarly to large-scale emissions reductions under the Canada-United States Air Quality Agreement. The chemistry of precipitation and snow in the current study was well characterised by location and elevation, providing a way to estimate long-term mean annual base cation and chloride precipitation chemistry (ions showing no trend) at unmonitored sites for contiguous regions in the Georgia Basin.