ABSTRACT
Surface mining in the Athabasca Oil Sands Region (AOSR) of western Canada disrupts natural landscapes and permanentlyalters their hydrological functions. Wetlands cover ~55% of the region, primarily fen peatlands, and although provincial regu-lations require companies to restore disturbed ecosystems to a functional state, fens remain difficult to construct due to theircomplex hydrology and dependence on water exchange with surrounding uplands. Evapotranspiration (ET), a key component ofthe water balance, is particularly important in the sub-humid AOSR, where increasing reclamation activity demands accuratequantification of vertical water loss, as it influences ecohydrological feedbacks and long-term wetland sustainability. This studyevaluates ET and energy dynamics in a constructed fen, built atop ~80 m deposit of composite tailings and capped with 10 m oftailings sand, using eddy covariance (EC) measurements and vegetation surveys conducted across five non-consecutive years be-tween 2015 and 2023. Mean ET from April 1 to October 31 was 250 ± 49.9 mm, aligning with values from natural and constructedboreal peatlands. On average, ET was 15% higher in warmer and drier years. While intra-annual ET variability was mainly in-fluenced by vapour pressure deficit and net radiation, a long-term decline in ET coincided with Typha latifolia expansion, whosecanopy reduced water loss by sheltering the open water. Flux partitioning revealed that transpiration exceeded evaporation byup to 70%, highlighting the role of Typha in reducing energy input and limiting turbulent mixing over the ponded water surface.Despite declining ET, latent heat flux remained the dominant component of the energy balance, suggesting functional similarityto natural fens. With rainfall exceeding ET in 80% of the years, the study site did not experience any prolonged drought periods.These findings enhance understanding of surface-atmosphere interactions and inform wetland reclamation strategies, particu-larly the role of vegetation change.