Climate controls on terrestrial-to-aquatic biogeochemical fluxes in boreal forest watersheds

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Soil organic carbon represents Earth's largest actively cycling reservoir of carbon, underscoring our need to understand the drivers of its transformation and their sensitivity to climate change. Soil organic matter is also the largest reservoir of carbon, energy and nutrients in forest ecosystems, making the predictive understanding of its cycling with changing climate a priority for strategic management of our forest and aquatic resources. This research will determine the impacts of climate change on the buffering capacity of the upland boreal forest-to-headwater stream critical zone in regulating the delivery of soil dissolved organic matter (DOM) and nutrients to downstream aquatic ecosystems. This is particularly important given the predicted increases in temperature and precipitation for the boreal zone in the coming century. Infrastructure providing access to soil and groundwater flowpaths in boreal forest watersheds will be deployed across (1) an experimental site consisting of mature forest and harvested regenerating stands that exhibit large differences in hydrology, and (2) a climate transect of similar forest sites and associated headwater streams. The experimental sites will allow us to determine how increased hydrology impacts composition and export of DOM and nutrients delivered to the aquatic environment. The climate transect sites will allow us to assess how climate warming modifies these hydrological impacts. Manipulative experiments will provide a direct means to test the interaction of hydrology and temperature in regulating soil carbon losses. Our work combines geochemical, isotopic, and biological approaches to discern changes in the flux of DOM and nutrients with hydrology, warming and their interaction, and to elucidate the influence of biological and mineralogical mechanisms driving these changes. This research will benefit our supporting organizations, which include the forestry industry and both provincial and federal forest services, by providing a predictive understanding of climate change responses in boreal forests and their associated aquatic ecosystems. Results will inform forestry management practices aimed at reducing the potential negative interactive effects of climate change and harvesting.