Evolution of a saline wetland in western boreal Canada: a study based on diatoms, pollen, and non-pollen palynomorphs

Abstract:

Wetland ecosystems, which comprise over 50% of northern Alberta’s land base, are under increasing pressures as a result of intensive development related to oil sands extraction. According to provincial guidelines, mined area must be reclaimed to an “equivalent capacity” and should contain ~33% wetlands by area. Paleoecological studies have proven useful for the development of restoration strategies through establishment of pre-disturbance baselines and assessing the possibility of returning ecosystems to pre-disturbance state. The task of wetland reclamation is challenged by salinization in the post mined environment, thus understanding the evolution of natural saline wetlands will aid in the development of improved reclamation strategies. The study was carried out in a natural saline wetland situated ~10 km southeast of Fort McMurray, Alberta. Paleoecological changes were investigated using diatoms, pollen and non-pollen palynomorphs in sediment cores taken from a pond in the central part of the wetland. Variations in physicochemical properties and microfossils assemblages in the core demonstrate dynamic changes associated with saline wetland initiation and its trajectory. The transition from clay sediments, characterized by low concentration of microfossils, to gyttja indicates that lake drainage preceded establishment of the wetland. Upcore shifts in microfossil assemblages reflect cycling between periods of very high salinity (recorded by a dominance of marine-brackish and brackish diatoms) followed by period of decreased salinity (indicted by a rise in fresh-brackish species) with gradual increases in salinity thereafter. Identification of the processes driving variation in salinity over time may be useful in the post-mined reclamation setting. Assessment of temporal changes in ecosystem functioning associated with differences in level of dissolved salts may lead to different reclamation approaches capable of dealing with the higher salinity conditions.