Methane stable isotopic distributions as indicators of gas transport mechanisms in emergent aquatic plants

Methane stable isotope distribution patterns vary markedly between plants utilizing convective throughflow ventilation relative to those which primarily employ molecular diffusion. In diffusive plants, methane sampled from lacunal air was C-13-enriched by 10.6 +/- 3.7 parts per thousand relative to sedimentary CH4. In plants possessing the convective flow system, differences between plant lacunal methane collected in daylight and sediment methane were not apparent, and averaged -0.9 +/- 2.1 parts per thousand. At night, as convection gave way to molecular diffusion, the isotopic distributions in Typha domingensis Pers. and Typha latifolia L., convective-flow plants, became similar to distributions observed in diffusive plants, with plant lacunal methane becoming C-13-enriched. Diurnal variations in the isotopic signature of methane emitted from Typha were also observed; methane is emitted in daylight was C-enriched by 4 - 7 parts per thousand relative to night emissions. The results indicate that methane isotopic distributions are useful indicators of plant gas transport mechanisms. Diurnal variation in isotopic distribution patterns confirm observations that plants with convective throughflow ventilation switch to molecular diffusion in the absence of sunlight.