U. Bosse et al., INHIBITION OF METHANE OXIDATION BY AMMONIUM IN THE SURFACE-LAYER OF ALITTORAL SEDIMENT, FEMS microbiology, ecology, 13(2), 1993, pp. 123-134
The diffusive flux of CH4 from the sediment into the water was measure
d in intact sediment cores taken from the littoral of Lake Constance.
CH4 fluxes were measured under oxic and anoxic conditions. Emissions u
nder anoxic conditions were used to estimate the potential diffusive f
lux. The results showed that about 79% of the CH4 diffusing upwards wa
s oxidized at the sediment surface. Kinetic measurements of CH4 oxidat
ion in diluted surface sediment gave V-max = 1.2 mu mol CH4 ml(sed)(-1
)h(-1). This was high enough to explain the oxidation rates calculated
from the flux measurements. NH4+ was added to the water overlaying th
e sediment cores to measure its influence on CH4 oxidation. This treat
ment resulted in increased concentrations of pore water NH4+ which wer
e measured with a NH4+ microelectrode. Pore water NH4+ concentrations
of < 4 mM had no effect on CH4 oxidation while concentrations between
4 and 10 mM NH4+ reduced the CH4 oxidation rates by about 30%. Measure
ment of CH4 oxidation rates in diluted surface sediment gave similar r
esults. At CH4 concentrations of 21 mu M, the CH4 oxidation rate decre
ased at NH4+ concentrations greater than or equal to 4 mM, and was com
pletely inhibited at NH4+ concentrations > 20 mM. Measurements of pote
ntial NH4+ oxidation rates were below the detection limit of 0.5 nmol
NO2- produced ml(sed)(-1)h(-1). Thus, the NH4+ oxidizing activity was
about 3 magnitudes lower than the CH4 oxidizing activity, and it is un
likely that NH4+ oxidizers are important for CH4 oxidation in this lit
toral sediment.