Detection and Prediction of Toxic Aluminum Concentrations in High-Priority Salmon Rivers in Nova Scotia

Elevated concentrations of toxic cationic aluminum (Al_i) are symptomatic of terrestrial and freshwater acidification and are particularly toxic to salmonid fish species such as Atlantic salmon (Salmo salar). Speciated metal samples are rarely included in standard water monitoring protocols, and therefore the processes affecting Al_i dynamics in freshwater remain poorly understood. Previous analysis of Al_i concentrations in Nova Scotia (Canada) rivers found that the majority of study rivers had concentrations exceeding the threshold for aquatic health, but a wide-scale survey of Al_i in Nova Scotia has not taken place since 2006 (Dennis, I. F., & Clair, T. A., 2012, Canadian Journal of Fisheries and Aquatic Sciences, 69(7), 1174–1183). The observed levels of dissolved aluminum in Atlantic salmon (Salmo salar) rivers of Atlantic Canada have potential serious and harmful effects for aquatic populations. We present the findings of the first large-scale assessment of the Al_i status of Nova Scotia rivers in 17 years; we measured Al_i concentrations and other water chemistry parameters at 150 sites throughout the Southern Uplands region of Nova Scotia from 2015 to 2022. We found that Al_i concentrations exceeded toxic thresholds at least once during the study period at 80% of the study sites and that Al_i concentrations increased during the study period at all four large-sample study sites. Modeling of relationships between Al_i concentrations and other water chemistry parameters showed that the most important predictors of Al_i are concentrations of the dissolved fractions of Al, iron, titanium, and calcium, as well as dissolved organic carbon and fluoride. We developed a fully Bayesian linear mixed model to predict Al_i concentrations from a test data set within 15 μg/L. This model may be a valuable tool to predict Al_i concentrations in rivers and to prioritize areas where Al_i should be monitored. Environ Toxicol Chem 2024;43:2545–2556. © 2024 The Author(s). Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.