TY  - JOUR
A1  - Hartman, Jan F.
A1  - Gentz, Torben
A1  - Schiller, Amanda
A1  - Greule, Markus
A1  - Grossart, Hans-Peter
A1  - Ionescu, Danny
A1  - Keppler, Frank
A1  - Martinez-Cruz, Karla
A1  - Sepulveda-Jauregui, Armando
A1  - Isenbeck-Schroeter, Margot
T1  - A f ast and sensitive method for the continuous in situ determination of dissolved methane and its delta C-13-isotope ratio in surface waters
JF  - Limnology and Oceanography-methods
N2  - A fast and sensitive method for the continuous determination of methane (CH4) and its stable carbon isotopic values (delta C-13-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 delta C-13-CH4 with synthetic water standards. The detection limit of the M-CRDS for the simultaneous determination of CH4 and delta C-13-CH4 is 3.6 nmol L-1 CH4. A measurement precision of CH4 concentrations and delta C-13-CH4 in the range of 1.1%, respectively, 1.7 parts per thousand (1 sigma) and accuracy (1.3%, respectively, 0.8 parts per thousand [1 sigma]) was achieved for single measurements and averaging times of 10 min. The response time tau of 57 +/- 5 s allow determination of delta C-13-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 L-1) and lightest delta C-13-CH4 (-35.2 parts per thousand) 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 delta C-13-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.
Y1  - 2018
U6  - https://doi.org/10.1002/lom3.10244
SN  - 1541-5856
VL  - 16
IS  - 5
SP  - 273
EP  - 285
PB  - Wiley
CY  - Hoboken
ER  -