Effects of aspen harvesting on groundwater recharge and water table dynamics in a subhumid climate

Numerical experiments were developed using different water table depths and soil textures to investigate the impact of aspen harvesting on hydrological processes on the Western Boreal Plain. The effect of harvesting on soil moisture dynamics, fluxes at the water table, and water table fluctuation were compared for different harvesting scenarios simulated under wet and dry climatic cycles. Strong interaction between shallow water tables (i.e., 2 m) and atmospheric variability is observed for all soil textures and is reduced as the vadose zone thickens, particularly after a dry cycle, as a series of positive net atmospheric fluxes are needed to reduce soil moisture storage in order for recharge to occur. Because of harvesting, the water table fluxes can increase by 50 mm month(-1), while on a yearly basis, this increase can reach 200 mm yr(-1), with rainfall events taking between 1 and 5 years to become recharge (i.e., time lag). Also, the water table is expected to rise between 1 and 3.5 m, with rainfall-water table rise time lags of 1-3 years; however, the peak manifestation of harvesting on water table elevation can take up to 7 years after harvesting. The effects of aspen harvesting are more pronounced during wet cycles, and the development of forestry activities in the Boreal Plain should consider not only preceding precipitation but also the preceding precipitation-reference evapotranspiration ratio, water table depth, and soil texture. The interaction of these factors needs to be considered in order to develop sustainable forestry plans and avoid waterlogging conditions.