Effects of gamma irradiation treatment of oil sands process material on zooplankton accrual and early community development in field based mesocosms

Oil sands mining and extraction produce wastewater and tailings enriched in salts and naphthenic acid fraction compounds (NAFCs), which persist and are toxic to biota. I determined if gamma irradiation (GI) of oil sands process materials (OSPM), which breaks down NAFCs in fluid fine tailings (FFT) and water (OSPW), can stimulate development of biological communities and ecosystem processes by reducing NAFC concentrations and toxicity. In a 33-month field study. I tracked zooplankton community accrual and patterns of diel dissolved oxygen to determine the potential for carbon accumulation in a suite of 68-L outdoor mesocosms constructed from untreated and GI treated OSPM that were reinoculated with indigenous microbial communities and compared them to freshwater and hyposaline wetland reference mesocosms. GI reduced NAFC concentrations by 54 – 98% in OSPW and 0 – 62% in FFT. Zooplankton biomass, species richness and density were stimulated in GI treated OSPM mesocosms compared to the untreated OSPM mesocosms. After 1.5 years, zooplankton species richness and biomass in GI treated OSPM mesocosms were numerically equivalent to values in reference mesocosms, but density was still marginally impaired. Primary production in both untreated and GI treated mesocosms remained low compared to reference wetlands. The colonization of macrophytes was inhibited by untreated OSPM. Considerably fewer, and smaller emergent macrophyte stems developed in GI treated OSPM than in reference mesocosms. Submerged aquatic vegetation was sparse and only occurred in one GI treated OSPM replicate. Primary production and respiration rates of OSPM mesocosms were 20 – 30% of those observed in reference mesocosms. Lower biological activity of OSPM mesocosms was attributed to a lack of macrophyte colonization in tailings pond mesocosms, likely related to persistent turbidity and unsuitable sediment characteristics