Groundwater discharges in the western Canadian oil sands region impact river water quality. Mapping groundwater discharges to rivers in the oil sands region is important to target water quality monitoring efforts and to ensure injected wastewater and steam remain sequestered rather than eventually resurfacing. Saline springs composed of Pleistocene‐aged glacial meltwater exist in the region, but their spatial distribution has not been mapped comprehensively. Here we show that formation waters discharge into 3 major rivers as they flow through the Athabasca Oil Sands Region adjacent to many active oil sands projects. These discharges increase river chloride concentrations from river headwaters to downstream reaches by factors of ~23 in the Christina River, ~4 in the Clearwater River, and ~5 in the Athabasca River. Our survey provides further evidence for the substantial impact of formation water discharges on river water quality, even though they comprise less than ~2% of total streamflow. Geochemical evidence supporting formation water discharges as the leading control on river salinity include increases in river chloride concentrations, Na/(Na + Ca) ratios, Cl/(Cl + SO4) ratios and decreases in 87Sr/86Sr ratios; each mixing trend is consistent with saline groundwater discharges sourced from Cretaceous or Devonian aquifers. These regional subsurface‐to‐surface connections signify that injected wastewater or steam may potentially resurface in the future, emphasizing the critical importance of mapping groundwater flow paths to understand present‐day streamflow quality and to predict the potential for injected fluids to resurface.
Temperature variations in surface and bottom water at 10 monitoring stations in Lake Illawarra were determined over the period 28 January 1972 to 31 May 1974. Except for the bay near Tallawarra Power Station, no permanent vertical temperature gradients were found. A statistically significant correlation was found between water temperature and distance from the power station, but no such relationship could be established for tidal heat flow either alone or acting together with the thermal discharge from the power station. Mean water temperature for Lake Illawarra fluctuated in the range 11.6-25.6� C, compared with 15.7-24.0�C for the sea adjacent to Wollongong Harbour. Seasonal maxima and minima in lake water temperature occur 3 weeks earlier than those of the sea.
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