Environmental Engineering Reference
In-Depth Information
temperature was 200
◦
C and the detector was at 225
◦
C. The column, 6' x 1/8”
stainless steel packed with Poropak Q (80/ 100 mesh), was maintained at 40
◦
C.
The carrier gas was N
2
flowing at 25 mL min
−
1
, and the retention time for
CH
4
was about 0.7 min. Peak areas were quantified with an HP 3396 Series II
electronic integrator. A known amount of standard gas (Scotty, Supelco) was
injected in quadruplicate and served for quantification. Analytical precision
was
5%.
For CH
4
analysis aboard
R/V Professor Vodyanitskiy
, a modification of the
vacuum degassing method described by Lammers and Suess [27] was used [38].
1600 ml of water were injected into pre-evacuated 2200 ml glass bottles lead-
ing to quantitative degassing. The gas phase was subsequently recompressed
to atmospheric pressure and the CH
4
concentration of the extracted gas was
determined by gas chromatography. A Shimadzu GC14A gas chromatograph
equipped with a flame ionization detector was used in connection with a Shi-
madzu CR6A Integrator. Nitrogen was used as carrier gas, and separation was
performed using a 4 m 1/8' SS column packed with Porapack Q (50/80 mesh)
run isothermally at 50
◦
C.
The carbon isotopic composition of dissolved methane (δ
±
13
C
CH
4
) was de-
termined by a method described earlier [41]. Precision of the method was
±
1
‰.
2.3 CH
4
Oxidation Rates
Water for measuring microbial methane oxidation was filled in triplicates in
20 ml crimp-seal bottles and capped gas-tight. From each triplicate, one sample
was killed with 50 µl concentrated formaldehyde solution which functioned
as a blank. Aliquots of 50 µl tritiated methane (
3
H-CH
4
) were added to the
bottles and incubated in the dark at ambient temperatures imitating natural
conditions. Immediately after the incubation an aliquot of the water was mixed
with scintillation cocktail (Ultima Gold, Packard) and measured to determine
the actual amount of tracer added to the sample. After the samples stood
uncovered overnight they were bubbled for 20 min with nitrogen to eliminate
all unreacted tritiated methane. An aliquot of the bubbled water was mixed with
the scintillation cocktail and measured again. Measurements were performed
by means of a scintillation counter (1600CA Tri-Carb, Packard). Turnover rates
(k value, d
−
1
) were calculated from the ratio of tracer remaining in the water to
total tracer added.
2.4 Lipid Analysis
Particulate organic matter for lipid analyses was collected from specific water
depths by filtration of large volumes (up to 1,000 l) of water through 142 mm
diameter glass fiber filters (GFF; nominal pore size 0.7µm, precombusted at
