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 cal culated from literature-derived exchange coefficients were greater tha n measured diffusive fluxes of CH4. In north Florida mixed hardwood sw amp experiments performed in the absence of ebullition, the calculated flux of CH4 was 3.6+/-2.6 (n = 22) times larger than the measured flu x. In an Everglades cypress dome, calculated CH4 fluxes were 3.1+/-2.5 (n = 3) times greater than measured;fluxes. New mass-transfer coeffic ients at zero windspeed were calculated for CH4 emission from the stag nant 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 va lues were significantly less than the calculated mass-transfer coeffic ient for CH4 (1.7 cm h(-1)) determined in another study. We hypothesiz e that insoluble organic surface films physically, chemically, or biol ogically 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 s tanding 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.