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

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).

Ecosystem consequences of potential range expansions ofOrconectes virilisandOrconectes rusticuscrayfish in Canada — a review

Canadian water bodies are presently experiencing fluctuations in orconectid crayfish ranges largely as a result of human activities. The range of Orconectes virilis , Canada’s most widespread crayfish, is expanding westward into previously uninhabited water bodies of Alberta. This species is also set to re-colonize watersheds in the eastern extent of its range as post-acidification recovery of aquatic ecosystems continues. In addition, the non-native Orconectes rusticus has invaded Central Canada. This species has the potential to rapidly invade boreal water bodies and out-compete native congeners, including O. virilis. Both these crayfish species are known to affect benthic ecosystems and their invasions may have adverse consequences for Canadian water bodies if left unchecked. Here we review the current documented distribution of O. virilis and O. rusticus in Canada, and identify the potential impacts that their invasion may have on boreal aquatic ecosystems. Finally, we consider options that resource managers might consider to contend with these invasions.