SENSITIVITY ANALYSIS OF A SIMULATION-MODEL OF METHANE FLUX FROM THE FLORIDA EVERGLADES

To determine parameters having the greatest influence on methane flux, I developed a 7-compartment, 4-layer model of methane production in t he Florida Everglades. The four layers consist of a bottom sediment la yer, a top, active sediment layer, an algal-mat layer, and an overlyin g water layer. The compartments are acetate (a major end product of an aerobic decomposition), sulfate-reducing and methane-producing bacteri a (major competitors for acetate), sulfate, methane, methane-oxidizing bacteria, and oxygen. Acetate production, depth of the active sedimen t layer, diffusion rate of oxygen into the sediment, and methane oxida tion rate had the greatest influence on methane flux. A two-way sensit ivity analysis showed that a change in one of these parameters could e nhance or diminish the influence of another. Acetate production was th e most sensitive parameter; as it increased, the rate of methane flux increased. Increased oxygen diffusion or methane oxidation diminished the effect of acetate production. Increased depth of the active sedime nt layer enhanced the effect of acetate production. As depth increased , the amount of acetate produced per area increased, increasing methan e production and methane flux. At depths greater than 0.22 m, methane flux asymptotically tapered off. The increased depth increased the dis tance over which methane must diffuse. This constrained the amount of methane flux from the system. At shallow depths, increased oxygen diff usion and methane oxidation produced significant changes in methane fl ux. With increasing depth, the influence of these parameters became in significant. This was attributed to the smaller contribution of oxygen diffusion to the larger volume of sediment, which constrained oxygen concentration and thus methane oxidation.