Catchment-scale modelling of carbon fluxes in the Great Lakes basin

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The purpose of this proposal is to develop a catchment-scale carbon model for the Great Lakes basin that can be used to predict dissolved organic carbon (DOC) fluxes from the Canadian portion of the terrestrial environment into the Great Lakes.  This is important because the breakdown of DOC can lead to the production of significant quantities of greenhouse gases.  We will focus on several large watersheds that will be selected to represent dominant land use categories; those draining into Lakes Erie and/or Ontario will be predominately agricultural while those draining into Huron and/or Superior will be primarily forested.  Our intent is to extrapolate our results to other parts of the Great Lakes basin so that we can estimate total carbon flux. We plan to employ two very different modelling approaches in this study.  Firstly, we will use a simple approach based on empirical relationships relating land use and dissolved organic carbon (DOC) flux from catchments, and relating water chemistry and partitioning of carbon between permanent storage in lake sediments and degradation to produce greenhouse gases.  The latter pathway contributes to Canada's greenhouse gas emissions.  This approach will allow us to estimate the organic carbon flux into the Great Lakes from the Canadian side.  However, this is a steady-state model, and it cannot be used to make direct predictions about the impacts of changes in external factors, e.g. climate, on DOC flux.  The second approach will utilize process-based dynamic modelling.  We will start with two existing models, one a nutrient model (INCA) that has been widely used in the study of nitrogen, and the other (MAGIC) a catchment-scale biogeochemistry model that has been widely used in the study of soil and water acidification.  Each of these models can be adapted to include a carbon.  The former model is driven by land use and hydrologic data, while the latter utilizes hydrologic data, soil and water chemistry and information about anthropogenic stressors, particularly acid deposition.  Each can and has been linked to climate change through both alterations to hydrology and through climate-related effects on processes such as mineralization rates.