Environmental Engineering Reference
In-Depth Information
Figure 2.
Relation between productivity and available light intensities (determined directly
above the bacterial layer) in different anoxygenic photosynthetic communities.
1
Black Sea [45];
2
Big Soda Lake [10];
3
Mary [6, 57];
4
Knaack Lake [58];
5
Mahoney Lake [50];
6
Mirror
Lake [6, 57];
7
Rose Lake [6, 57],
8
Lake Cis o [22];
9
Lake Vilar [22];
11
Paul [6, 57];
12
Peter
[6, 57].
are confined to the upper layers of the H
2
S-containing zone [80]. Since their
population densities are rather low (maximum of 2 cells per ml], it appears
unlikely that they cause significant losses of the bacterial population by grazing.
Similarly, losses by sedimentation appear to be very low, since no biomarkers
of green sulfur bacteria could be detected in sediment traps incubated below
the chemocline of the Black Sea (see Section 6 below).
Besides CO
2
-fixation, green sulfur bacteria could theoretically be significant
for sulfide oxidation in the Black Sea chemocline. Jørgensen et al. [33] observed
a peak maximum of H
2
S oxidation in a depth of 85 m at the top of the sulfide
zone. It was accompanied by a similarly sharp maximum of dark CO
2
fixation
and of total bacterial numbers. Sulfide oxidation experiments with H
2
35
S with
samples from that depth showed maximum rates of up to 1.4 mmol m
−
2
h
−
1
[33] which confirmed previous data [67]. Chemical oxidation of sulfide by
oxidized metals such as iron and manganese could only account for
<
0.1% of
the measured H
2
S oxidation rates as calculated from the iron fluxes into the
chemocline.
