Where does the carbon go? Long-term effects of forest management on the carbon budget of a temperate-forest water-supply watershed.

While forest management commonly seeks to increase carbon (C) capture and sequestration, in some settings, a high density of C storage may be detrimental to other land uses and ecosystem services. We study a forested, drinking-water-supply watershed to determine the effects of forest management on C storage with the implicit understanding that greater storage of C will lead to increased quantity of carbon exported hydrologically into a source-water reservoir. Using a custom implementation of CBM-CFS3, a Canadian model to simulate C transformations and movement in forested systems, and a custom forest disturbance and management model, we simulate various management scenarios and their C outcomes. The largest forest C pool, mineral soils, is very slow to change and manipulating DOC export through this pool would likely not be feasible within human management timescales. Other pools, in which C has lower residence time and from which C is more readily mobilized, are a more promising area for future research into hydrologic DOC export under varying management regimes. Our findings indicate that management activities can serve to reduce forest C storage, but further research is required to connect these outcomes to hydrologic export.