Abstract
Abstract. Acid deposition released large amounts of aluminium into streams and lakes during the last century in northern Europe and eastern North America. Elevated aluminium concentrations caused major environmental concern due to aluminium's toxicity to terrestrial and aquatic organisms and led to the extirpation of wild Atlantic salmon populations. Air pollution reduction legislation that began in the 1990s in North America and Europe successfully reduced acid deposition, and the aluminium problem was widely considered solved. However, accumulating evidence indicates that freshwater systems still show delays in recovery from acidification, with poorly understood implications for aluminium concentrations. Here, we investigate spatial and temporal patterns of labile cationic forms of aluminium (Ali) from 2015 to 2018 in 10 catchments in Nova Scotia, Canada; this region was one of the hardest hit by acid deposition, although it was not considered to have an aluminium problem due to its high dissolved organic carbon (DOC) concentrations that were expected to reduce Ali concentrations. Surprisingly, our results show the widespread and frequent occurrences of Ali concentrations that exceed toxic thresholds in all sampled rivers despite high DOC concentrations. Generalized linear mixed model results reveal that DOC, instead of being inversely related to Ali, is the strongest predictor (positive) of Ali concentrations, suggesting that the recruitment properties of DOC in soils outweigh its protective properties in streams. Lastly, we find that, contrary to the common conceptualization that high Ali levels are associated with storm flow, high Ali concentrations are found during base flow. Our results demonstrate that elevated Ali concentrations in Nova Scotia continue to pose a threat to aquatic organisms, such as the biologically, economically, and culturally significant Atlantic salmon (Salmo salar).
Highlights
Increased rates of acid deposition, predominantly deriving from upwind fossil fuel burning, resulted in the acidification of soils, rivers, and lakes during the last century (e.g., Kerekes et al, 1986), depleting base cations and increasing toxic aluminium concentrations in soils and drainage water
Increased aluminium concentrations caused the extirpation of native Atlantic salmon (Salmo salar) populations in many rivers (Rosseland et al, 1990), for example in Scandinavia (Henriksen et al, 1984; Hesthagen and Hansen, 1991), the eastern USA (Monette and McCormick, 2008; Parrish et al, 1998), and Nova Scotia, Canada (Watt, 1987)
Mean Ali concentrations across all sites range from 13 to 60 μg L−1 (Table 1), with the highest mean concentrations occurring in the eastern part of the study area (Fig. 1a) where one site had 100 % of samples in exceedance (Fig. 1b)
Summary
Increased rates of acid deposition, predominantly deriving from upwind fossil fuel burning, resulted in the acidification of soils, rivers, and lakes during the last century (e.g., Kerekes et al, 1986), depleting base cations and increasing toxic aluminium concentrations in soils and drainage water. Sterling et al.: Ionic aluminium concentrations exceed thresholds et al, 2001; Monteith et al, 2014; Skjelkvåle et al, 2005; Stoddard et al, 1999; Warby et al, 2005), including reduced concentrations of aluminium (Al) in the USA (Baldigo and Lawrence, 2000; Buchanan et al, 2017; Burns et al, 2006) and Europe (Beneš et al, 2017; Davies et al, 2005; Monteith et al, 2014). Recent evidence highlights delayed recovery from acidification in other regions (Houle et al, 2006; Warby et al, 2009; Watmough et al, 2016), including Nova Scotia (Clair et al, 2011), raising questions about the possibility of elevated aluminium concentrations in freshwater systems
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
