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

• Water cycle variations characterized for prominent boreal peatland complex. • Verified efficacy of isotope method for spatio-temporal hydrologic reconstruction. • Modern water sources and flowpaths inferred by vegetation and isotopes ( 18 O, 2 H). • Historical conditions reconstructed from vegetation and 18 O succession in peat. • Quantitative transfer of 18 O from water to peat moss verified for dominant species. 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 ( 18 O, 2 H) for contemporary characterization of water sources and evaporation gradients, whereas flark orientation was used to identify general flow directions. Use of 18 O preserved in α-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 18 O archives from moss cellulose to reconstruct 18 O 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) 18 O 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.