Environmental Engineering Reference
In-Depth Information
3.5 Lipid Biomarkers for Methane Oxidizers in the Water
Column
Lipids indicative for methane oxidizing bacteria and/or archaea were in-
vestigated at the two upper slope sites (7617, 7623), and at the central site
(7605). Two glycerol-ethers namely archaeol and sn-2-hydroxyarchaeol, in-
dicative of methanogenic or methanotrophic archaea, depending on the isotope
signature [14, 23], were detected in the water column. Both compounds were
only present in the anaerobic zone of the Black Sea and totally absent in the
aerobic water layer. Concentrations in the anaerobic layer could be determined
only for archaeol. They were found directly below the chemocline at 100 m
in low abundances of 0.3 to 1.5 ng/l (Fig. 4). sn-2-Hydroxyarchaeol could be
detected only as a trace compound in the samples at 130 m from the central
station (7605) and from 170 m at the SW station (7623) where it occurred with
∼
0.1 ng/l. These concentrations are very low compared to those that are found
in sediments off Oregon where up to 8 µg/g sediment of both compounds have
been measured [4]. Due to the low abundance it was not possible to measure
isotope signatures, hence it cannot be concluded whether the biomarkers are of
methanogenic or methanotrophic origin.
3.6 Methane Oxidation Rates
Methane oxidation rates using tritium labeled methane were measured at
the two shallow stations 038 (seep) and 055 (reference) and at the deep slope
stations 064 (reference) and 072 (seep). There was on average a 30 times higher
oxidation rate at the seep site (0.02 to 1.6 nM d
−
1
) compared to the shallow
reference site (0.001 to 0.05 nM d
−
1
). In contrast, at the deep sites no significant
difference was observed between reference and seep sites with the anoxic water
column values of 0.03 to 3.1 nM d
−
1
.
3.7 Fluorescence in Situ Hybridization of Methanotrophic
Microorganisms
To identify the methanotrophic community that is responsible for anaerobic
methane oxidation in the anoxic Black Sea water column, filtered samples from
the lower slope stations 064 (reference) and 072 (seep) were investigated by
FISH (a method using specific fluorescently labeled gene probes which allows
the detection of microorganisms under the microscope). Using 16S rRNA-
targeted oligonucleotide probes specific to both groups, it was possible to detect
ANME-1 and ANME 2 group cells, usually found in sediments, in the water
column of the Black Sea. Cell counts of filters from the water column above
the methane seep site revealed ANME-1 and ANME-2 cells in concentrations
of up to 4 % of all DAPI stained cells (Table 1, [8]). Interestingly, cells counts
