Contemporary forest harvesting impacts on water quality and treatability

Forested landscapes are critical source regions for the supply of drinking water globally. The increasing frequency and severity of climate shocks (e.g., wildfire, floods) in these regions can deteriorate source water quality. Forest harvesting has been proposed as an allied component of forest fuel management and pre-emptive mitigation of disturbance impacts on source water quality and treatability; however, forest harvesting can also deteriorate source quality and compromise treatability in the absence of sufficient operational response capacity. Critically, the impacts of forest harvesting on drinking water treatability have not been reported. Here, drinking water source quality and treatability impacts of three contemporary forest harvesting approaches (clear-cut with patch retention, strip-shelterwood cut, and partial cut) were evaluated in Alberta, Canada. Stream water turbidity, the concentration and character of dissolved organic matter, and disinfection by-product formation potential were evaluated over four years, in harvested and reference watersheds. No appreciable impacts of forest harvesting on water quality and treatability were observed. The results suggest that contemporary forest harvesting approaches may show promise as source water protection technologies for mitigating climate-exacerbated disturbance threats to drinking water treatability; however, further study is needed to establish causality and the contributions of other biotic and abiotic factors.