Simulating carbon dioxide exchange in boreal ecosystems flooded by reservoirs

A process-based reservoir model of Flooded Forest Denitrification Decomposition (FF-DNDC) was developed to simulate carbon dioxide (CO2) exchange from flooded boreal landscapes. The reservoir model is based on Forest-DNDC, a terrestrial biogeochemistry model which supports detailed soil carbon (C) processes including redox chemistry, with modification to represent the disturbed soil and vegetation C dynamics due to the presence of an overlying water column on the ecosystems. Soil decomposition rates and temperature and oxygen profiles were changed, and sedimentation to the soil surface was added. FF-DNDC was evaluated using CO2 exchange measurements from the newly created Eastmain-1 reservoir in northern Quebec, Canada. For the first four years of the reservoir (2006 to 2009), simulated daily CO2 emissions averaged 1.42 g C m−2 d−1 (ranging from 0.75 to 3.24 g C m−2 d−1) from the flooded forest and 0.74 g C m−2 d−1 (ranging from 0.51 to 1.09 g C m−2 d−1) from the flooded peatland. The simulated emissions were smaller than the thin-filmed boundary layer exchanges based on measured partial pressure of carbon dioxide (pCO2) but were larger than the exchanges measured using an eddy covariance system. However, the temporal patterns of simulated and measured exchanges were similar. We simulated potential CO2 emissions over 100 years, the expected operating lifetime of the reservoir, with assuming no change in climate. Simulated CO2 emissions decreased with time since flooding especially for the first four decades. The 100-year cumulative emissions from the flooded peatland were larger than those from the flooded forest. Sensitivity analysis indicated that vegetation and soil inputs and parameters controlling the quality and/or quantity of decomposable soil C in flooded ecosystems (e.g. woody vegetation biomass, soil organic carbon in organic and mineral layers, and carbon:nitrogen ratio in woody vegetation and soil) were important to the reservoir CO2 emission.