METHANE TRANSFER ACROSS THE WATER-AIR INTERFACE IN STAGNANT WOODED SWAMPS OF FLORIDA - EVALUATION OF MASS-TRANSFER COEFFICIENTS AND ISOTOPIC FRACTIONATION

Emission rates from the standing water of swamps to the atmosphere calculated from literature-derived exchange coefficients were greater than measured diffusive fluxes of CH4. In north Florida mixed hardwood swamp experiments performed in the absence of ebullition, the calculated flux of CH4 was 3.6+/-2.6 (n = 22) times larger than the measured flux. In an Everglades cypress dome, calculated CH4 fluxes were 3.1+/-2.5 (n = 3) times greater than measured;fluxes. New mass-transfer coefficients at zero windspeed were calculated for CH4 emission from the stagnant swamp water in the mixed hardwood swamps (0.75+/-0.54 cm h(-1), n = 22) and in the cypress dome (0.83+/-0.51 cm h(-1), n = 3). These values were significantly less than the calculated mass-transfer coefficient for CH4 (1.7 cm h(-1)) determined in another study. We hypothesize that insoluble organic surface films physically, chemically, or biologically inhibited CH, transfer from the flood-water to the atmosphere. Consistent with these findings we also observed greater retardation of (CH4)-C-13, efflux relative to 12CH(4), efflux in swamp experiments relative to those conducted in the laboratory. Methane emitted from standing water was depleted in C-13 by 0.8+/-0.3 parts per thousand (n = 16), 3.6+/-3.2 parts per thousand (n = 12), and 2.6+/-0.8 parts per thousand (n = 3) relative to the isotopic composition of dissolved CH4 in the laboratory, mixed hardwood swamps, and cypress dome.