Spatiotemporal Variations of Total and Dissolved Trace Elements and Their Distributions Amongst Major Colloidal Forms Along and Across the Lower Athabasca River

With a wide variety of natural and potential anthropogenic inputs, the Athabasca River (AR) has been the focus of recent attention. In addition to natural inputs of trace elements (TEs) from tributaries, industrial activities such as mining and upgrading of bitumen have been viewed as additional, potentially important anthropogenic sources, but evidence is limited. To quantify the spatiotemporal variations of TE concentrations and their forms, water samples were gathered along a 125-km stretch of the river from upstream to downstream of the industrial region, and at three points across the river, along five transects perpendicular to the flow. The samples were collected in the autumn of 2017 and the spring of 2018, using novel, metal-free sampling methods. The concentrations of total (i.e. acid-extractable), and dissolved (i.e., < 0.45 μm) TEs were measured to compare with water quality guidelines, and their size-based distribution amongst major colloidal forms was determined to better assess their biological significance. The results quantify spatiotemporal variation in total and dissolved concentrations of TEs along and across the AR. In both seasons the majority of TEs occurred in the particulate fraction. None of the TEs were significantly enriched in the particulate fraction, relative to crustal abundance. The average concentrations of TEs were below the CCME surface water quality guidelines. The PCA analysis identifies tributary contributions of total and dissolved TEs to the AR.