Watkins, Matthew

Many communities in Canada rely on water sourced from boreal forest headwaters for their drinking water. The Boreal Shield Ecozone is highly susceptible to climate change which threatens to exacerbate the effects of natural and human-driven disturbances such as wildfire, insect infestation and harvesting on water quality. Therefore, examining source water quality in headwater catchments within the Boreal Shield Ecozone is crucial to elucidating the potential implications of these disturbances to water treatment processes in the context of a changing climate. A synoptic water sampling investigation was conducted to evaluate how dissolved organic carbon (DOC) quantity and quality and disinfection by-product formation-potential (DBP-FP) quantity varied across space and time in the Algoma region of central Ontario. Over a five-month timeframe (June 2021 - October 2021), 168 streamflow estimates and 176 water samples were collected across 30 catchments (catchment areas from 0.2 - 106.8 km2) which varied in their forest disturbance histories. DOC concentration ([DOC]) ranged from 2.4 - 38.2 mg L-1 and tended to be higher in harvest-dominated sites, while no discernible differences in SUVA254 were observed between catchment types. DOC export estimates ranged from 1.0 - 63.2 g C m-2 over a 141-day period (June 5th - Oct. 23nd, 2021). Fluorescence indices for quantifying DOC composition suggested that all catchments were dominated by humified and terrestrially sourced carbon. DBP-FP values were positively correlated to UV-254 (r = 0.76 - 0.78) and [DOC] (r = 0.85 - 0.88), such that DBP-FP spatiotemporal patterns were strongly coupled to DOC dynamics. Multiple linear regression analysis identified that open water was negatively related to [DOC] and SUVA254 and explained the most variability in their spatiotemporal patterns. In addition, catchment area, which was negatively related to [DOC] and SUVA254, and legacy insect infestation and harvesting disturbance helped improve model explanatory power. Other predictor variables, such as slope, wetland cover, coniferous forest cover and recent forest disturbance (i.e., 5-year harvesting and 5-year insect infestation), showed relatively poor explanatory power. Variability in DOC export estimates may be explained by harvesting disturbance (adjusted r2 = 0.68 - 0.82). The results of this study emphasise that complex processes across the terrestrial-aquatic continuum, which are influenced by several factors, such as runoff, forest disturbance and landscape heterogeneity, govern the spatiotemporal patterns in water quality across boreal headwaters within the Algoma region.