Characterizing sediment sources and natural hydrocarbon inputs in the lower Athabasca River, Canada

Abstract

The Athabasca River drains an area of 160 000 km2 in northern Alberta, Canada, with much of the lower basin underlain by oil-sand deposits. The oil sands occur primarily in the McMurray Formation of the Cretaceous Period, with outcrops evident along the banks of the Athabasca River, as well as the lower portions of several tributaries. Since the oil sands represent a natural diffuse source of hydrocarbons to the aquatic environment, understanding the nature and extent of sediment-bound hydrocarbon contaminants in the context of the sediment regime of the Athabasca River is important. Described are fluvial geomorphic characteristics of the lower Athabasca River, which provide a basis for assessing sediment-bound hydrocarbon contaminants. Suspended sediment derived from main stem and tributary sources between Fort McMurray and Embarras account for 1.2 Mt, or 18%, of the mean annual load of the Athabasca River. Of this load, approximately 53% of the sediment input originated from tributaries, the remainder from main-stem sources. The majority of sediment contributed along the main stem occurs in the vicinity of Embarras, well downstream of oil-sand sources. Natural oil-sand sediment contributions are likely much less than 3% of the annual load downstream of Fort McMurray. Key words: sediment, fluvial geomorphology, oil sands, hydrocarbons, polycyclic aromatic hydrocarbon (PAH), contaminants, environmental monitoring, Athabasca River.

Oil sands development contributes polycyclic aromatic compounds to the Athabasca River and its tributaries

“…1). The Athabasca River is exposed to the McMF 50 km upstream of Fort McMurray and is present within its banks to Eymundson Creek (38).…”

Assessment of seven Canadian rivers in relation to stages in oil sands industrial development, 1972–2010

“…3). Previous reports indicated that differences in water quality along tributaries of the Athabasca River were due to the influence of incisement of the rich bitumen beds in the McMurray Formation (e.g., Conly et al 2002Conly et al , 2007Headley et al 2001Headley et al , 2005Alberta Government 2010). However, prior studies were substantially shorter in duration and spatial extent than the 38 year study described here.…”

“…Bitumen, a form of heavy crude oil, contains particulate organic material, hydrocarbons, associated metals, and sulfur compounds (WHO 2004). Earlier assessments (2001)(2002)(2003)(2004)(2005)(2006)(2007) attributed the presence of contaminants and heavy metals in the Athabasca River and its tributaries to natural erosion of the geological strata that contain bitumen (e.g., Conly et al 2002Conly et al , 2007Hedley et al 2001Hedley et al , 2005. The Alberta Government (2010) concluded, "there has been no increase in concentrations of contaminants as oil sands development has progressed."…”

The Characterization and Distribution of Inorganic Chemicals in Tributary Waters of the Lower Athabasca River, Oilsands Region, Canada

“…1), oil-sand material can be found within 75 m of the surface and portions of the oil and deposits are exposed, especially along the banks of the Athabasca River, as well as the lower portions of several tributaries, where rivers have incised into the McMurray Formation. [6] The erosion of the exposed oil sands deposits has distributed hydrocarbons throughout the region's river system and these hydrocarbons arising from natural processes may be referred to as naturally derived hydrocarbons. [7] Heavy metals and major ions co-occur with elevated levels of naturally occurring petroleum hydrocarbons and complex mixtures of naphthenic acids.…”