Modeling Impacts of Management on Carbon Sequestration and Trace Gas Emissions in Forested Wetland Ecosystems

A processbased model, Wetland-DNDC, was modified to enhance its capacity to predict the impacts of management practices on carbon sequestration in and trace gas emissions from forested wetland ecosystems. The modifications included parameterization of management practices fe.g., forest harvest, chopping, burning, water management, fertilization, and tree planting), inclusion of detailed anaerobic biogeochemical processes for wetland soils, and utilization of hydrological models for quantifying water table variations. A 150-year management scenario consisting of three stages of wetland forest, deforestationidrainage, and wetland restoration was simulated with the Wetland-DNDC for two wetlands in Minnesota and Florida, USA. The impacts of the management scenario on carbon ecosystem exchange, methane emission, and nitrous oxide emission were quantified and assessed. The results suggested that: (1) the same management scenario produced very different consequences on global warming due to the contrast climate conditions; and (2) methane and nitrous oxide fluxes played nonnegligible roles in mitigation in comparison with carbon sequestration. Forests are recognized for having considerable potential to sequester carbon (C) (Birdsey and Heath 2001). In the conterminous United States, wetlands comprise approximately 16% of the forested area, but they contain over 50% of the total soil C (Trettin and Jurgensen 2003). Unfortunately, analyses of C dynamics in forested landscapes typically presume upland soil conditions, thereby overlooking the potential and complexity associated with hydric soils. Accordingly, presuming aerated conditions across the forested landscape overlooks processes that are critical to the terrestrial C cycle, and completely discounts the complex interactions of management practices with C cycling in hydric soils. The forested wetland resource is not static. Both natural and managemen t-induced disturbance regimes are common and necessary. Until recently, disturbance regimes were considered to be detrimental to soil C in wetland forests. However, long-term field studies have now demonstrated that increased forest productivity on managed peatlands can result in soil C gains (Minkkinen and Laine 1998). Many forest management practices have been reported to enhance carbon mitigation. Recently, more comprehensive studies emphasized the importance of complete accounting for the entire carbon flows in and out of the system and the analysis of long-term patterns. Restoration of forested wetlands is now considered a means to enhance terrestrial C sequestration. Although there are no long-term field studies, short-term studies suggest high rates of sequestration (Trettin and Jurgensen 2003). A computer simulation model is an alternative tool addressing this type of questions. There are few opportunities to augment the accumulation of carbon in wetlands by improved management, although the theoretical foundations for the interactions involved in watershed are reasonably well established. Draining forested wetlands can enhance tree growth significantly, but the net ecosystem carbon changes are less clear-some studies report large net gains while others indicate large net losses of carbon to