Hydrocarbon transport in the Mackenzie River, Canada

Abstract

This study examines the sources and transport of hydrocarbons to the lower Mackenzie River in response to concern over the environmental impact of human activities, particularly those related to hydrocarbon development, within the Mackenzie River basin. We carried out two time-of-travel studies by boat, commencing at the confluence of the Liard and Mackenzie Rivers and extending 1250km downstream to a major distributary channel in the Mackenzie delta near Inuvik. The first study, carried out in 1985, characterized summer flow conditions, and the second study reflected snowmelt inputs during spring breakup in 1986. Samples of suspended sediment and water were obtained at a total of eight sites and analyzed for n-alkanes and PAHs. n-Alkanes were present in suspended sediments at all sites in both sampling periods. Based on their distributions and isomer patterns, alkanes in the river appear to originate from three main sources: Great Slave Lake is a source of algal alkanes; a source of undegraded petroleum-related alkanes, possibly from erosion of bituminous shale bedrock; and a source of high molecular weight alkanes, possibly related to combustion. PAHs also enter the river from several sources. Under low flow conditions, low levels of PAHs from petroleum-related sources, possibly seeps, were detected, while under high flow conditions, PAH patterns were dominated by atmospherically-deposited combustion-related PAHs that had been carried into the river by snowmelt.