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

Abstract

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.