Carbon and Water Vapor Exchange in a Temperate Freshwater Marsh

The ability of wetlands to sequester carbon has given them a considerable amount of attention, especially in light of global climate change. To date, many wetland studies have focused on peatlands, however very few studies have been conducted on marshes. This study used the eddy covariance (EC) technique to measure net ecosystem carbon exchange (NEE) and energy exchange at a temperate freshwater cattail marsh near Ottawa, Canada. The objectives of the study were to use a 4-year dataset to determine the environmental controls on the variability of carbon and water vapor exchange. The annual cumulative NEE was on average -246 g C m-2 yr-1 ranging from -216 to -260 g C m-2 yr-1. Inter-annual differences in NEE were caused by variations in ecosystem respiration (ER) and gross ecosystem production (GEP). Additionally, the variability in accumulation between years was a result of the timing of spring and fall transitions in the carbon uptake and the length of the growing seasons, each of which were determined by prevailing weather conditions. Maximum daily average values of evapotranspiration (ET) reached 10.75, 9.07, 11.70 and 8.36 mm day-1 in 2005, 2006, 2007 and 2008 respectively. Bowen ratio values varied seasonally with values well below unity during the growing season (May to October) illustrating the dominance of latent heat. Examination of the decoupling coefficient (Ω) gives evidence that the marsh is a radiatively driven system. Overall, the marsh ecosystem was a large annual sink for CO2 as compared to other wetland ecosystems and that ET rates are highly dependent on radiative input.