Changes to the hydrophysical properties of upland and riparian soils in a burned fen watershed in the Athabasca Oil Sands Region, northern Alberta, Canada.

Hydrogeologic setting strongly influences the hydrologic function of peatland systems. For base–rich fens in the Athabasca Oil Sands Region (AOSR) of the Western Boreal Plain, northern Alberta, local groundwater flow from gently sloping adjacent uplands has been shown to help sustain fen water tables and chemistry. Natural forest disturbance in the AOSR is dominated by wildfire, with peatlands susceptible to combustion and subsequent carbon release. However, few studies have aimed to characterize the degree of change to the hydrophysical properties of upland soils following wildfire. To address this, we measured differences in water repellency and hydrophysical properties of burned and unburned upland organic and mineral soils in a burned moderate–rich fen watershed (Poplar Fen), ~25 km north of Fort McMurray. Samples were taken in the fall of 2017, ~1.5 years after the watershed burned (May 2016). Study locations included burned and unburned jack pine–dominated upland and black spruce–dominated riparian areas. Results illustrated significantly lower water repellency and higher infiltration on burned locations of both land types. Furthermore, no significant differences were detected in organic soil moisture retention in uplands; however, burned organic soil samples had significantly lower water retention in riparian areas. We postulate the lower water retention in riparian areas was due to the greater organic layer thickness there, thus greater fuel load and potential for exceeding the temperature threshold of repellency destruction. Following retention, all soil cores exhibited high hysteresis, with differences in volumetric moisture content averaging 0.38 and 0.34 m3 m−3 at −10 cm pressure for upland and riparian locations, respectively. Our results are contrary to the increased hydrophobicity following burning that is commonly reported in boreal regions. The promoted infiltration, groundwater recharge and subsequent enhanced water supply to fens in the local groundwater system may help in accelerating the moss recovery process. • Burned areas exhibited significantly lower water repellency and higher infiltration. • Wildfire destroyed a greater proportion of hydrophobic substances than it produced. • Burned riparian soils had significantly lower water retention. • Higher ground heat fluxes and lower field soil moisture reduced surface evaporation. • Enhanced groundwater supply from uplands may accelerate the fen moss recovery process. [ABSTRACT FROM AUTHOR]