Energy and carbon fluxes from an oil sands pit lake

• Published in: The Science of the total environment Vol. 752; p. 141966
• Main Authors: Clark, M. Graham, Drewitt, Gordon B., Carey, Sean K.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 15.01.2021
• Subjects: Carbon emissions; Eddy covariance; Evaporation; Mine closure; Oil sands; Pit lake; Mine closure; Oil sands; Eddy covariance; Evaporation; Carbon emissions; Pit lake
• ISSN: 0048-9697; 1879-1026
• DOI: 10.1016/j.scitotenv.2020.141966

Currently, post-mining landscape plans in the Athabasca Oil Sand Region include large watersheds terminating in pit lakes. In 2012, Base Mine Lake (BML), was constructed with the aim of demonstrating technologies associated with lake reclamation in the region. This paper examines the first 6.5 years of lake-atmosphere energy and carbon exchange. Energetically, BML behaved similar to other northern lakes, storing large quantities of heat in the spring and releasing it in the fall as sensible and latent heat fluxes. At various times a hydrocarbon sheen formed on the lake, which may have suppressed evaporation. However, simple linear relationships failed to statistically quantify the impacts and more comprehensive modelling of the variability may be required. At daily scales, variability in evaporation was well explained by the product of vapour pressure deficit and wind speed as well as the available energy (R2 = 0.74), while sensible heat was explained by the product of wind speed and the difference in air and surface temperature as well as available energy (R2 = 0.85). Spring CH4 fluxes were high, particularly around ice melt, with a maximum flux of 3.3 g m−2 day−1. Otherwise fluxes were low, except during irregular periods. The peak flux of these periods occurred following ~58 h of continuously falling pressure, relating cyclone activity to these large periods of methane emissions. Annually, CO2 and CH4 fluxes were initially high, with median fluxes of 231 mg CO2 m−2 h−1 and 23 mg CH4 m−2 h−1 in 2014. However, the median fluxes reduced quickly and over the least three years of the study (2017 through 2019) the median fluxes declined to 36 mg CO2 m−2 h−1 and 10 mg CH4 m−2 h−1. Overall, BML behaves similar to other boreal lake ecosystems with above average carbon fluxes compared to other constructed reservoirs. Relative pressure preceeding peak CH4 emissions (top). Grey shading indicates the 32 to 68th percentiles (±1 SD), black line is median. Middle panel shows the 2017 CH4 fluxes (grey), with 24 hour gap filled mean (black), to illustrate the peaks (pink arrows) identified by the detection algorithm. Horizontal dotted line is the 90th percentile of CH4 fluxes used to set the minimum threshold for the peak detection. The bottom panel is the air pressure over the same period. The 2017 timeseries was selected for this example because it had the most complete CH4 flux and pressure records. [Display omitted] •Reclamation activities produced a lake energetically similar to other boreal lakes.•Methane emissions are related to cyclone activity.•Methane emissions are largest in the spring, around changing ice conditions.•Initially carbon emissions are high.•After three years' carbon emissions are comparable to other reservoirs.