Seismic Lines Are Associated With Enhanced Ground Layer Evapotranspiration in Peatlands

Evapotranspiration, the combined water loss through both evaporation from the ground surface and transpiration through the vegetation canopy, makes up a substantial portion of the water balance in peatlands in the western boreal region of Canada. Geologic exploration for petroleum resources has created a network of linear clearings, known as seismic lines, that have altered the local hydro-climatological conditions within the ecosystems that they cross, including peatlands. Accordingly, understanding the interaction between human activities and hydrological fluxes in peatlands is crucial for identifying the processes sensitive to these types of disturbances, especially in a region with a subhumid climate. This study aims to assess the effect of seismic lines on evapotranspiration from the understory at different sites in northern Alberta. Actual evapotranspiration (AET) was measured using weighing lysimeters and chamber techniques, and potential evapotranspiration (PET) was calculated based on the Penman and Priestley–Taylor equation. Understory AET on the seismic lines was 59% and 33% higher than in the adjacent ecosystem, based on lysimeter and chamber measurements, respectively. Furthermore, we also observed that the soil temperature, available photosynthetically active radiation (PAR) and plant community composition were the primary drivers of the AET measured using chambers, while wind speed and PAR controlled the AET measured by lysimeters. We estimated that ground layer PET on the line was 51% higher than off the line. These variations affected the Priestley–Taylor coefficient of evaporability (α) values so that the α value on the seismic line (0.73) was higher than off the line (0.61). Accounting for transpiration from trees, it was determined that the AET from seismic lines exceeds the AET from adjacent areas by 31%. Considering the ubiquitous nature and high spatial density of seismic lines in the boreal region, these changes to a dominant water loss mechanism will have a considerable impact on hydrological fluxes and result in an altered water budget, with potential implications at the watershed scale.