Ionic aluminium concentrations exceed thresholds for aquatic health in Nova Scotian rivers

Abstract

Abstract. Cationic aluminium species are toxic to terrestrial and aquatic life. Despite decades of acid emission reductions, accumulating evidence shows that freshwater acidification recovery is delayed in locations such as Nova Scotia, Canada. Further, spatial and temporal patterns of labile cationic forms of aluminium (Ali) remain poorly understood. Here we increase our understanding of Ali spatial and temporal patterns by measuring Ali concentrations in ten streams in acid-sensitive areas of Nova Scotia over a four-year time period. We observe widespread and frequent occurrences of Ali concentrations that exceed toxic thresholds (> 15 μg L−1). Ali patterns appear to be driven by known Ali drivers – pH, dissolved organic carbon, dissolved aluminium, and calcium – but the dominant driver and temporal patterns vary by catchment. Our results demonstrate that elevated Ali remains a threat to aquatic ecosystems. For example, our observed Ali concentrations are potentially harmful to the biologically, economically, and culturally significant Atlantic salmon (Salmo salar).