Modeling of soil CO2 efflux during water table fluctuation based on in situ measured data from a sedge-grass marsh

Abstract

Soils of wetland ecosystems serve as a huge storage of organic carbon. Its decomposition and consequent release of CO2 into the atmosphere is highly affected by soil hydrology, and this release of CO2 may severely increase during future climate change. The aim of this study was to describe the immediate response of soil CO2 efflux to temperature and changes in water level. Soil CO2 efflux from a marsh, temperature and the water table were continuously measured in situ during a gradual decrease of the water table and its consequent rapid increase after heavy rain. CO2 efflux fluctuated as it followed diurnal changes in temperature. However, it showed an increasing trend as the water table decreased. After the rain, the water table rose above the soil surface and soil CO2 efflux dropped fast to nearly zero. A simple model based on soil temperature and water table level was created to estimate soil CO2 efflux. There was far better agreement between this model and measured data than with the widely used model based only on temperature. The results showed the importance of including the soil water conditions in models for estimating soil CO2 efflux at sites with a high water table level.