Moss cellulose 18O applied to reconstruct past changes in water balance of a boreal wetland complex, northeastern Alberta

A water and vegetation sampling program including peat coring was carried out within the McClelland Wetland, a boreal peatland complex situated within the rapidly developing oil sands mining region of northeastern Alberta, Canada. This study investigated both the current and past hydrology of the site to improve understanding of the spatiotemporal evolution of water sources, pathways, and vegetation succession prior to impending oil sands development in the western half of the watershed. The study used vegetation surveys and isotopic tracers (O-18, H-2) for contemporary characterization of water sources and evaporation gradients, whereas flark orientation was used to identify general flow directions. Use of O-18 preserved in a-cellulose within moss macrofossils and wood, combined with evidence from vegetation successions in several cores, provided detailed information on historical changes in the peatland as far back as 11,300 cal. years BP. Reliability of O-18 archives from moss cellulose to reconstruct O-18 in source water was confirmed in a sub-survey conducted at 227 sites where water and moss were both sampled and analyzed to quantify isotopic fractionation in dominant moss species. Overall, the study established existence of long-term groundwater source areas around the margins of the peatland, as well as contemporary permafrost thaw zones within the peatland itself. Both contemporary (spatial) and historical (temporal) O-18 gradients reflect precipitation-derived origins for shallow groundwater sources with strong evaporative enrichment along the direction of flow. Historical reconstruction suggests persistence of open wet areas at the site amid several episodes of regional climatic and associated hydrologic changes.

Automated summary

A water and vegetation sampling program was conducted at McClelland Wetland in northeastern Alberta, Canada to study the current and past hydrology, revealing long-term groundwater source areas and contemporary permafrost thaw zones. Isotopic tracers, vegetation surveys, and flark orientation were used to characterize water sources, pathways, and evaporation, providing insights into historical peatland changes and spatial-temporal evolution.