Figure 3.

Using of the production of ¹³C-DIC as a measure of CCE by riverbed methanotrophs during short-term incubations. (a) Production of ¹³C-DIC from the oxidation of ¹³C-CH₄ over ~60 h to the point of CH₄ limitation. Mean±s.e., n=5 (b) as (a) but with the ¹³C-DIC as a function of the amount of ¹³C-CH₄ oxidised during the first 15 h, that is, the period when the linearity of DIC production was strongest (r²=0.93, P<0.001) and each datum is the result of a single incubation. Here as the intercept is not different to 0, the slope (0.48) is equivalent to the ratio of DIC to CH₄ and 1–0.48 is a measure of carbon fixation efficiency, that is, 0.52 × 100=52% fixed. Note this estimate of 52% was indistinguishable from the estimate based on the recovery of organic carbon during the previous repeat batch incubations of 52%.