High-elevation lakes are sensitive to acidification from atmospheric deposition owing to their generally small catchment areas, thin soils and low bedrock weathering rates. The Georgia Basin, southwest British Columbia, Canada, receives atmospheric inputs from emissions originating in Vancouver, Victoria, and from marine traffic in the Strait of Georgia. There is growing concern on the influence of this air pollution on high-elevation systems in the region. Water chemistry and catchment characteristics were used to assess the sensitivity of 72 lakes in the Georgia Basin to acidic deposition. Twenty percent of the study lakes had pH levels less than 6, and acid neutralising capacity (ANC) concentrations below 20 μeq L–1, which are key thresholds for biological sustainability. Base cation and trace metal concentrations were low, typical of the dilute nature of high-elevation lakes (median conductivity = 7.0 μS cm–1). Nonetheless, concentrations of trace metals (such as lead) decreased with distance from major cities. The primary factors influencing the pH and ANC of surface waters were investigated using multiple linear regression; both ANC and pH were related to longitude and the proportion of the catchment dominated by ice and glaciers. Increasing sulphur deposition resulted in decreasing pH. The median critical load of acidity (sulphur) for the study lakes was approximately 70 meq m–2 y–1; 18% of the lakes received sulphur deposition (range: 6-81 meq m–2 y–1 for the period 2005-2006) in excess of their critical load

Global climate models predict increased temperature and precipitation in the Georgia Basin, British Colmbia; however, little is known about the impacts on high-elevation regions. In the current study, fifty-four high-elevation lakes (754–2005 m a.s.l.) were studied to investigate the potential influence of climate change on surface water acid-sensitivity. Redundancy analysis indicated that the concentration of nitrate, dissolved organic carbon, and associated metals was significantly influenced by climate parameters. Furthermore, these components differed significantly between biogeoclimatic zones. Modelled soil base cation weathering for a subset of the study lakes(n=11)was predicted to increase by 9% per 1°C increase in temperature. Changes in temperature and precipitation may potentially decrease the pH of surface waters owing to changes in anthropogenic deposition and organic acid production. In contrast, increased soil base cation weathering may increase the critical load (of acidity) of high-elevation lakes. Ultimately, the determining factor will be whether enhanced base cation weathering is sufficient to buffer changes in natural and anthropogenic acidity. Mountain and high-elevation regions are considered early warning systems to climate change; as such, future monitoring is imperative to assess the potential ramifications of climate change on the hydrochemistry and acid-sensitivity of these surface waters.