English
 
Help Privacy Policy Disclaimer
  Advanced SearchBrowse

Item

ITEM ACTIONSEXPORT

Released

Journal Article

Effect of gas bubbles on the diffusive flux of methane in anoxic paddy soil

MPS-Authors

Rothfuss,  F
Department of Biogeochemistry, Alumni, Max Planck Institute for Terrestrial Microbiology, Max Planck Society;

/persons/resource/persons254197

Conrad,  R       
Department of Biogeochemistry, Alumni, Max Planck Institute for Terrestrial Microbiology, Max Planck Society;

External Resource
Fulltext (restricted access)
There are currently no full texts shared for your IP range.
Fulltext (public)
There are no public fulltexts stored in PuRe
Supplementary Material (public)
There is no public supplementary material available
Citation

Rothfuss, F., & Conrad, R. (1998). Effect of gas bubbles on the diffusive flux of methane in anoxic paddy soil. Limnology and Oceanography, 43(7), 1511-1518. doi:10.4319/lo.1998.43.7.1511.


Cite as: https://hdl.handle.net/21.11116/0000-000F-CB81-A
Abstract
The emission of CH(4) from paddy soil is driven by CH(4) concentration
gradients in the submerged soil. CH(4) concentration gradients between
anoxic methanogenic and oxic methanotrophic soil layers were measured in
paddy soil microcosms by using gas diffusion probes with a spatial
resolution of 1 mm. The CH(4) emission rate was measured by placing a
microcosm into a chamber containing an atmosphere of either synthetic
air (80% N(2), 20% O(2)) or N(2). The CH(4) flux was 1.6 +/- 5.4 nmol
cm(-2) d(-1) under synthetic air and 288 +/- 10 nmol cm(-2) d(-1) under
N(2). The difference between the oxic and the anoxic CH(4) fluxes was
due to CH,oxidation. The vertical CH(4) concentration gradients
indicated CH(4) oxidation at 2-3 mm depth. Below this depth CH(4)
concentrations increased steadily to about 10 mm depth, below which
accumulation of gas bubbles was observed. The diffusive flux calculated
by Fick's first law from the Linear part of the gradient was 166 +/- 14
nmol cm(-2) d(-1). Obviously, the flux calculated from molecular
diffusion was smaller than the flux that was actually measured under
N(2). An important condition for the use of Fick's law is that the slope
of the gradient used for the calculation is taken in the direction where
the slope is steepest. This direction is not necessarily identical with
the vertical direction if CH(4) concentrations also change in horizontal
direction. Measurement of horizontal and vertical CH(4) profiles
demonstrated that the gradients had a three-dimensional structure. The
reason for this structure was that the isopleths of identical CH(4)
concentrations followed the uneven surface of the gas bubble layer as
the main direct source for the CH(4) diffusion gradients. We conclude
that gas bubbles do not only directly cause a CH(4) flux by ebullition
but also indirectly affect the diffusional flux of CH(4) in soil or
sediment. When the diffusive CH(4) flux was calculated from the
concentration gradient at 6-8 mm depth, it was larger (224 +/- 70 nmol
cm(-2) d(-1)) than from that at 3-5 mm depth (125 +/- 86 nmol cm(-2)
d(-1)). Thus, a transport process in addition to molecular diffusion
seemed to be active in the upper soil layers, possibly bioirrigation.