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Multiple anthropogenic activities are driving the salinization of freshwater environments threatening water resources worldwide. Accordingly, this research will first examine the spatial and temporal variability of major ions (i.e. Ca2+, Mg2+, Na+, K+, SO42−, CO32−, and HCO3−) upstream and downstream of the northernmost major city in North America (Edmonton, Canada). Second, this research will estimate the relative contributions of the major sources of chloride (Cl), the main constituent of road deicers, to the sub-basin around Edmonton. Monthly water quality data was for three sites on the North Saskatchewan River (NSR): Rocky Mountain House (RMH - downstream of the Rocky Mountain headwaters), Devon Bridge (upstream of Edmonton) and Pakan Bridge (downstream of Edmonton). Change ratios investigate the downstream alterations of major ions at Pakan and Devon, relative to RMH. Seasonal Kendall tests examine temporal trends (1987–2017). A mass-balance approach then quantifies the major sources of Cl in the sub-basin of the NSR between Devon and Pakan. Progressing from the Rocky Mountain headwaters (at RMH) to downstream of Edmonton (at Pakan), Cl− increased by >5.5 times, Na+ by 4.8 times and K by 2.7 times. No significant temporal trends for Cl−, Na+ and K+ were evident at Devon (upstream of Edmonton), whereas all three significantly increased at Pakan (downstream of Edmonton). Deicers (54%), agriculture (20%), along with waste water treatment plant and industrial effluent (15%) were the largest Cl sources in the NSR Devon-Pakan sub-basin. In total, 77 Gg yr−1 of Cl (or 6 t km2 yr−1) is added to the Devon-Pakan sub-basin, of which, 43 Gg yr−1 is retained. Understanding and managing the major drivers of freshwater salinization will be of increasing importance in the 21st century owing to the potential salinization of freshwater resources in the context of a changing climate.

The accurate determination of water quality criteria exceedance frequencies, distribution statistics (e.g., mean, median and percentile concentrations) and temporal trends in constituent concentrations is critical to effective water resources management. Here we examine the effect of sampling regime on the accuracy of trace metal concentration, water quality criteria exceedance, and trend statistics at three sites in a turbid and highly dynamic river (mean ± 1 standard deviation total suspended solids [TSS] concentration = 56 ± 148 mg L−1, 278 ± 777 mg L−1 and 521 ± 909 mg L−1). Daily TSS data from the Red Deer River (RDR) in Alberta, Canada were used to generate a 10-year baseline data set of total Pb, Hg, Cu and Cd concentrations based on linear regression relationships. The baseline data was then sub-sampled to create fixed frequency (3-day, 7-day, 14-day, 30-day, 60-day and 90-day) and flow augmented (30-day + Q ≥ 90th percentile) regimes. Precision increased with increased sampling frequency for all statistics over both annual and decadal time scales. However, annual statistical estimates exhibited consistently poorer precision than estimates summarized over 10 years. For estimates of annual mean and 90th percentile concentrations, precision decreased as the variation in daily constituent concentrations in the baseline data set for each year increased. Estimates of median concentrations were generally more precise than the mean or 90th percentile, while estimates of criteria exceedance had particularly poor precision and exhibited systemic bias when the frequency of exceedance in the baseline data was low (i.e.

International audience; The source dynamics of total and dissolved material in riverine systems are being affected by anthropogenic activities resulting in the degradation of waterways worldwide. Identifying the main sources of total and dissolved material is thus central to the management of increasingly scarce water resources. Here, we utilize data generated from water quality monitoring programs to investigate the sources of total and dissolved material in a large, semi-arid basin in western Canada. Our research focuses on the confluence of two major tributaries in the South Saskatchewan River Basin (SSRB) in the Province of Alberta: the Bow River (25,611 km$^2$) and the Oldman River (28,270 km$^2$). A tributary tracing technique coupled with a Deconvolutional-MixSIAR (D-MIXSIAR) modelling approach is used to estimate the potential source contributions of total and dissolved material from major tributary sites to target node sites on the main stem of the Bow River and Oldman River in addition to target nodes downstream of their confluence. In total, 812 samples were taken from 29 sites across the SSRB. A novel approach to selecting fingerprints for modelling is presented based on the analyses of additional quality control samples (146 duplicate and 172 blank samples). Overall, the Rocky Mountain headwater catchments were found to dominate the supply of material modelled using total recoverable (68%) and dissolved (76%) metals. There were seasonal fluctuations in source dynamics evident where the Bow River dominated the supply of total (69%) and dissolved (57%) material during the ice-covered season (November-March), and the Oldman River dominated the supply of total (73%) and dissolved (59%) material during the open water season (April-October). On the one hand, these seasonal dynamics are potentially the result of the extensive regulation of flow, particularly along the Bow River. On the other hand, the intensification of agriculture in the prairie/plain catchments may also facilitate the excess supply of total relative to dissolved material. For example, the Little Bow River, with ~70% agricultural land cover, contributed ~14 times more total material than anticipated based on discharge and 1.6 times more than anticipated based on unit area during the open water season. Overall, this research has improved our understanding of the source dynamics of total and dissolved material in the SSRB, providing the foundation for focussed studies targeting the main sources of total and dissolved material in this large, semi-arid basin in western Canada. In addition, our research highlights the potential of using existent data generated from water quality monitoring programs along with quality control best practices to help improve our understanding of the source dynamics of total and dissolved material in waterways around the world.

Wildfires can have severe and lasting impacts on the water quality of aquatic ecosystems. However, our understanding of these impacts is founded primarily from studies of small watersheds with well-connected runoff regimes. Despite the predominance of large, low-relief rivers across the fire-prone Boreal forest, it is unclear to what extent and duration wildfire-related material (e.g., ash) can be observed within these systems that typically buffer upstream disturbance signals. Following the devastating 2016 Fort McMurray wildfire in western Canada, we initiated a multi-faceted water quality monitoring program that suggested brief (hours to days) wildfire signatures could be detected in several large river systems, particularly following rainfall events greater than 10 mm. Continuous monitoring of flow and water quality showed distinct, precipitation-associated signatures of ash transport in rivers draining expansive (800–100,000 km2) and partially-burned (