Effect of environmental factors on production and bioavailability of dissolved organic carbon from substrates available in a constructed and reference fens in the Athabasca oil sands development region

Abstract

Fen peatlands cover a large proportion of the landscape in boreal Alberta and thus these ecosystems are likely to be constructed as part of mine closure following oil sands mining. Peatlands are large sources of dissolved organic carbon (DOC); however, little is known about DOC dynamics in constructed peatlands. We investigated DOC production and its bioavailability from substrates collected from a constructed fen and natural fens (reference ecosystems) in the Athabasca oil sands region near Fort McMurray, Alberta. Dominant vegetation and other substrates used in fen construction, like peat, petroleum coke, tailings sand and upland soil, were collected for the study. The effect of substrate type, salinity and temperature on DOC production and bioavailability were analyzed in a laboratory incubation study. Sedges and trees produced the largest amount of DOC, followed by peat and moss in all the fens, whereas the substrates from the constructed fen such as petroleum coke, tailings sand and upland soil produced very little DOC per unit dry mass. In addition, temperature and salinity were also significant explanatory variables for both initial (30 day) and final (60 day) net DOC production rates. It was also observed that greater production of DOC resulted in lower pH and higher electrical conductivity (EC) in incubation jar water. In addition, the quality of DOC depended upon the type of substrate. Specific ultraviolet absorbance at 254nm wavelength (SUVA254) indicated that sedges produced DOC having less aromatic humic substances than peat, tailings sand, upland soil and petroleum coke. Substrate, salinity and temperature at which DOC was produced, and interactions among these factors were all found to significantly explain variation in DOC bioavailability. Aromatic content of DOC produced, based on SUVA254, had an effect on its bioavailability. As various substrates produced different amounts and quality of DOC, and since construction material like petroleum coke and tailings sand produce very little DOC, it is likely that establishment of the vegetation community and its composition will play an important role in DOC dynamics at the constructed fen in the future.