Changes In Stream Water Quality Due To Logging Of The Boreal Forest In The Montmorency Forest, Quebec

摘要

Summer stream water quality was monitored before and following the logging of 50% of the boreal forest within three small watersheds (<50 ha) nested in the 'Ruisseau des Eaux-Volees' Experimental Watershed, Montmorency Forest (Quebec, Canada). Logging was conducted in winter, on snow cover according to recommended best management practices (BMPs) to minimize soil disturbance and protect advance growth. A 20-m forest buffer was maintained along perennial streams. In watershed 7.2, cut-blocks were located near the stream network and logging was partially allowed within the riparian buffer zone. In watersheds 7.5 and 7.7, logging occurred farther away from thestream network. Observations were also made for watershed 7.3 that collected the runoff from watersheds 7.2 and 7.5, and watershed 7.6, the uproad portion of watershed 7.7. The control watershed 0.2 was contiguous to the impacted watersheds and remained undisturbed. Following clearcutting, changes in summer daily maximum and minimum stream temperatures remained within ±1℃ while changes in diurnal variation did not decrease by more than 0.5 ℃. Concentrations of NO_3~- greatly increased by up to 6000% and concentrations of K~+ increased by up to 300% during the second summer after logging. Smaller increases were observed for Fe_(total) (up to 71%), specific conductance (up to 26%), and Mg~(2+) (up to 19%). Post-logging pH decreased slightly by no more than 7% while PO_4~(3-) concentration remained relatively constant. Suspended sediment concentrations appeared to increase during post-logging, but there was not enough pre-logging data to statistically confirm this result. Logging of moderate intensity and respecting established BMPs may account for the limited changes of water quality parameters and the low exceedances of the criteria for the protection of aquatic life. The proximity of the cutover to the stream network and logging within the riparian zone did not appear to affect water quality.