Predicted Releases of Greenhouse Gases from Land-use Change of a Proposed Hydroelectric Reservoir in Canada Using a Carbon Mass-balance Model

English Abstract:

Understanding the potential contributions of large projects to greenhouse gases (GHGs) in the atmosphere is increasingly important in the current social context of heightened awareness about climate change. Regulatory agencies are requiring greater attention to activities and projects that have long-term changes to land-use that could result in substantial releases of GHGs to the atmosphere. Here we present a site-specific carbon cycle in the form of a landscape carbon mass-balance model. This model is used to predict the net GHG emissions as part of an environmental assessment for a proposed hydroelectric reservoir located in northeast British Columbia. We based the model inputs on local biophysical and geophysical properties of the site, and modeled several hypothetical Project scenarios. The model was based on the exchange (flows) of carbon between the primary carbon stores (stocks). These stocks included atmosphere (CO₂ and CH₄), surface water, soil, sediment, terrestrial plants, wetlands, and large ruminants. A baseline model was first constructed to model existing conditions and calibrated to a long-term net-zero carbon mass-balance. The baseline model was then adjusted for post-flooding landscape parameters and results were compared to the baseline model to determine the Project’s net GHG emission. Overall, the model predicted a net GHG emission of the Project in the order of 43,400 to 58,200 t CO₂e/yr for the assumed 100 yr Project lifespan as a result of the land use change. Based on the Project’s anticipated 5,100 GWh energy output, this translated to between 8.5 and 11.4 CO₂e/kWh from land-use change (9.7 and 13.3 g CO₂e/kWh, including construction-related emissions), which is at the lower end of the reported range of life-cycle assessments (8 to 60 g CO₂e/kWh) for boreal hydroelectric reservoirs. These results were not surprising given the Project is a tertiary reservoir drawing hydraulic capacity from a large upstream reservoir and due to its northern latitude location where the river is narrow and the resulting hydroelectric reservoir is relatively deep.