Publication Date:
2021-06-09
Description:
A fast and sensitive method for the continuous determination of methane (CH4) and its stable carbon isotopic
values (d13C-CH4) in surface waters was developed by applying a vacuum to a gas/liquid exchange
membrane and measuring the extracted gases by a portable cavity ring-down spectroscopy analyser
(M-CRDS). The M-CRDS was calibrated and characterized for CH4 concentration and d13C-CH4 with synthetic
water standards. The detection limit of the M-CRDS for the simultaneous determination of CH4 and d13CCH4
is 3.6 nmol L21 CH4. A measurement precision of CH4 concentrations and d13C-CH4 in the range of
1.1%, respectively, 1.7& (1r) and accuracy (1.3%, respectively, 0.8& [1r]) was achieved for single measurements
and averaging times of 10 min. The response time s of 5765 s allow determination of d13C-CH4 values
more than twice as fast than other methods. The demonstrated M-CRDS method was applied and tested
for Lake Stechlin (Germany) and compared with the headspace-gas chromatography and fast membrane CH4
concentration methods. Maximum CH4 concentrations (577 nmol L21) and lightest d13C-CH4 (235.2&) were
found around the thermocline in depth profile measurements. The M-CRDS-method was in good agreement
with other methods. Temporal variations in CH4 concentration and d13C-CH4 obtained in 24 h measurements
indicate either local methane production/oxidation or physical variations in the thermocline. Therefore,
these results illustrate the need of fast and sensitive analyses to achieve a better understanding of
different mechanisms and pathways of CH4 formation in aquatic environments.
Repository Name:
EPIC Alfred Wegener Institut
Type:
Article
,
isiRev
Format:
application/pdf
