In the spring of 2017, a study funded by Canada’s Oil Sands Innovation Alliance’s (COSIA) Demonstration Pit Lake (DPL) Joint Industry Project (JIP), was undertaken to investigate the effects of oil sands process water (OSPW) and densified fluid fine tails (dFFT) on aquatic ecosystems to support the development of end pit lake (EPL) technology. This study utilized mesocosms, simplified and replicated aquatic ecosystems, which had been designed and constructed by InnoTech Alberta in 2016. The mesocosms were exposed to OSPW and dFFT in late May of 2017, followed by four months of data and sample collection.
The presence of OSPW in the mesocosms was associated with increases in conductivity, turbidity, and various elements and compounds while concurrent decreases were observed in dissolved oxygen, water temperature at depth, and calcium. For the most part, the physicochemical effects of OSPW decreased over time. The presence of OSPW reduced the richness of the macroinvertebrate community while reducing the diversity (Shannon-Wiener) of the zooplankton community. Submerged vegetation was also negatively impacted by OSPW; C. demersum did not survive in mesocosms containing 50% or 100% OSPW by volume. Colonization of the bottom of the mesocosms with adventitious vegetation, while common in the control mesocosms, did not occur in mesocosms containing OSPW or dFFT. Conversely, the presence of OSPW and dFFT had a small stimulatory effect on the growth of emergent vegetation (T. latifolia and C. aquatilis). The acute toxicity of mesocosm water, which contained various dilutions of OSPW according to experimental group, was assessed using trout 96-hour LC50 and Microtox® assays. While both assays indicated fairly low levels of toxicity at the beginning of the study, trout mortality decreased over time while Microtox® toxicity remained unchanged
The effects of dFFT were similar to those attributed to OSPW, but often of lesser magnitude. Many of these effects were mediated by the slow efflux of solutes from the dFFT layer into the overlying water. In contrast, polycyclic aromatic hydrocarbons (PAHs) were strongly associated with the presence of dFFT but not OSPW despite both materials originating from the same DPL participant company. The surface-water concentration of these compounds decreased over time.