Identification of dominant natural sources of polycyclic aromatic hydrocarbons in river sediments in Alberta

Sediment collected from the rivers of southern Alberta, Canada, presents patterns of polycyclic aromatic hydrocarbons (PAHs) that demonstrate a varied origin within the Rocky Mountains. An influx of PAHs from sub-bituminous coal sources from erosional processes as the river exit the mountains dominates the pattern of PAHs in the river sediment across the prairies to the Alberta-Saskatchewan border (a distance of 750 km for the Red Deer River and 925 km for the Bow River) continues much further downstream. The concentrations of PAHs are similar to the well-studied Athabasca River in the Alberta Oil Sands Region. Although these results relate to rivers flowing east from the Rocky Mountains in Canada, it is likely that coal-sourced PAHs will contribute to any river where erosion of coal formations is possible within the watershed. A distinctive natural pattern of strongly pyrogenic PAHs from nearby thermal hot springs was also discovered near Banff. Natural pyrogenic PAH sources, aside from wildfires, are uncommon and generally related to hydrothermal vents and igneous intrusions into source rocks. This is the first time the authors are aware of sediment from a thermal spring presenting such PAH patterns.