My dissertation research addresses the following questions: (1) what are the current carbon accumulation rates in pristine fens, (2) does the Grand Ditch water diversion have a negative effect on carbon storage of fens, (3) how much must the water table be lowered in fens before significant changes in gas efflux occurs, and (4) if CENTURY ecosystem model can be used to simulate long-term carbon accumulation fens.  Carbon cycling in fens was found to be directly controlled by site hydrological regime.  The five fens studied accumulated carbon in years when water table remained at or above the soil surface for most of the summer.  However, both pristine and hydrologically modified fens lost carbon when the water table dropped beneath the soil surface for more than three weeks during the summer.  The water table only had to drop beneath the soil surface threshold to elicit a large gaseous carbon response.  Carbon dioxide, methane and total gaseous carbon efflux respond significantly to temperature and water table depth when the water table is above the soil surface.  However, with the water table beneath the soil surface CO2 and total carbon efflux nearly doubled, while CH4 efflux decreased more slowly.  In addition, temperature was not a significantly factor on efflux rates when the water table was below the soil surface. Lowering the water table to greater depths beneath the soil surface had little additional effect on CO2, CH4, and total gaseous carbon efflux.  CENTURY was able to simulate carbon cycling in peatlands by altering three anaerobic variables.  However, CENTURY was unable to properly simulate hydrological conditions in a third peatland, after calibrating it for two, because of limitations in how anaerobic conditions are created.  Once independently calibrated, the usefulness of using an ecosystem model for peatlands became apparent by allowing predictions to be made of peat composition and consequence when exposed to drying conditions.  CENTURY predicted that most of the fen peat stored came from root material, which was easily decomposed when exposed to drying conditions.