TY - JOUR

T1 - Potential carbon fixation via methane oxidation in well-oxygenated river bed gravels

AU - Trimmer, Mark

AU - Maanoja, Susanna T

AU - Hildrew, Alan G

AU - Pretty, James L

AU - Grey, Jonathan

PY - 2010/3

Y1 - 2010/3

N2 - Due to a combination of local methanogenesis and high background concentrations in the groundwater, water in the River Lambourn is 51 times supersaturated with methane (162 nmol CH4 L−1). Pore-water concentrations of methane in the gravels of the riverbed were much lower throughout the year (71 nmol CH4 L−1), suggesting significant methane oxidation. To investigate the potential for methane oxidation as a novel chemosynthetic source of carbon to the food web, we made simultaneous measurements, in laboratory chambers, of primary production, respiration, and methane oxidation associated with the gravels. Biomass-specific net primary production was up to 2.7 µmol O2 mg−1 chlorophyll (Chl) h−1 and was similarly high for respiration (2.7 µmmol O2 mg−1 Chl h−1). We also found active methane (CH4) oxidation with the rate increasing in proportion to concentration. At the maximum rate of 0.18 µmol CH4 mg−1 Chl h−1 and a growth efficiency of 0.8, net carbon fixation via methane oxidation was equivalent to 6% of the carbon fixed via net photosynthetic primary production. However, production via methane oxidation could be proportionately much greater under the shade of the profuse instream or riparian vegetation, deep in the gravels, and especially during winter, when light is limiting (< 25 µmol quanta m−2 s−1).

AB - Due to a combination of local methanogenesis and high background concentrations in the groundwater, water in the River Lambourn is 51 times supersaturated with methane (162 nmol CH4 L−1). Pore-water concentrations of methane in the gravels of the riverbed were much lower throughout the year (71 nmol CH4 L−1), suggesting significant methane oxidation. To investigate the potential for methane oxidation as a novel chemosynthetic source of carbon to the food web, we made simultaneous measurements, in laboratory chambers, of primary production, respiration, and methane oxidation associated with the gravels. Biomass-specific net primary production was up to 2.7 µmol O2 mg−1 chlorophyll (Chl) h−1 and was similarly high for respiration (2.7 µmmol O2 mg−1 Chl h−1). We also found active methane (CH4) oxidation with the rate increasing in proportion to concentration. At the maximum rate of 0.18 µmol CH4 mg−1 Chl h−1 and a growth efficiency of 0.8, net carbon fixation via methane oxidation was equivalent to 6% of the carbon fixed via net photosynthetic primary production. However, production via methane oxidation could be proportionately much greater under the shade of the profuse instream or riparian vegetation, deep in the gravels, and especially during winter, when light is limiting (< 25 µmol quanta m−2 s−1).

U2 - 10.4319/lo.2010.55.2.0560

DO - 10.4319/lo.2010.55.2.0560

M3 - Journal article

VL - 55

SP - 560

EP - 568

JO - Limnology and Oceanography

JF - Limnology and Oceanography

SN - 0024-3590

IS - 2

ER -