Abstract
Inadequate knowledge of baseline conditions challenges ability for monitoring programs to detect pollution in rivers, especially where there are natural sources of contaminants. Here, we use paleolimnological data from a flood-prone lake (“SD2”, informal name) in the Slave River Delta (SRD, Canada), ∼500 km downstream of the Alberta oil sands development and the bitumen-rich McMurray Formation to identify baseline concentrations and proportions of “river-transported bitumen-associated indicator polycyclic aromatic compounds” (indicator PACs; Hall et al. 2012) and processes responsible for their deposition. Results show that indicator PACs are deposited in SD2 by Slave River floodwaters in concentrations that are 45 % lower than those in sediments of “PAD31compounds”, a lake upstream in the Athabasca Delta that receives Athabasca River floodwaters. Lower concentrations at SD2 are likely a consequence of sediment retention upstream as well as dilution by sediment influx from the Peace River. In addition, relations with organic matter content reveal that flood events dilute concentrations of indicator PACs in SD2 because the lake receives high-energy floods and the lake sediments are predominantly inorganic. This contrasts with PAD31 where floodwaters increase indicator PAC concentrations in the lake sediments, and concentrations are diluted during low flood influence intervals due to increased deposition of lacustrine organic matter. Results also show no significant differences in concentrations and proportions of indicator PACs between pre- (1967) and post- (1980s and 1990s) oil sands development high flood influence intervals (t = 1.188, P = 0.279, d.f. = 6.136), signifying that they are delivered to the SRD by natural processes. Although we cannot assess potential changes in indicator PACs during the past decade, baseline concentrations and proportions can be used to enhance ongoing monitoring efforts.
Highlights
The Alberta oil sands are the third largest proven crude oil reserve in the world, after Saudi Arabia and Venezuela (Alberta Energy 2014a)
Analysis of a sediment core from flood-dominated lake SD2, located at the apex of the Slave River Delta, revealed that river-transported bitumen-association indicator polycyclic aromatic compounds (PACs) were deposited in the SRD well before the onset of oil sands development in 1967, but in concentrations much lower than in a floodplain lake in the Athabasca Delta
Baseline knowledge of river contaminant concentrations and composition prior to perturbation is needed to detect pollution and to determine the processes of transport and deposition. We address this critical knowledge gap for river-transported bitumen-associated PAC deposition in the Slave River Delta in response to concerns regarding pollution from the development of the Alberta oil sands 500 km upstream
Summary
The Alberta oil sands are the third largest proven crude oil reserve in the world, after Saudi Arabia and Venezuela (Alberta Energy 2014a). Oil sands production will continue to be a significant component of Canada’s resource economy and energy security. As oil sands industrial activities have grown, so too have concerns and controversy regarding perceived associated negative effects on environmental and human health (Gosselin et al 2010). Among the concerns is the potential downstream transport of polycyclic aromatic compounds (PACs) that are contained in the bitumen reserves and potentially released into the environment during mining and processing of the oil sands (Kelly et al 2009, 2010; Gosselin et al 2010; Dowdeswell et al 2010). Because the Athabasca River and its tributaries flow through and erode strata containing bitumen (Fig. 1), it is necessary to quantify the contribution of naturally sourced contaminant loads to be able to detect pollution (Dowdeswell et al 2010)
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