Environmental Engineering Reference
In-Depth Information
Figure 1.
Phylogenetic position of the strain BS-1, isolated from the Black Sea chemocline,
within other brown colored green sulfur bacteria. The partial sequence obtained from the sedi-
ment at 109 cm below sea floor (
Env. sequence A
) is identical to that from the chemocline.
Bar
represents 0.1 fixed nucleotide exchanges.
Typically, accumulations of phototrophic sulfur bacteria have been observed
between 2 and 20 m, rarely up to 30 m depth [74]. In such environments, values
for the light transmission to populations of phototrophic sulfur bacteria range
from 0.015 to 10% [57, 74]. Due to the lower position of the chemocline, the
in situ
light intensities in the Black Sea were expected to be significantly lower
and consequently represent the limiting factor for the growth of the green sulfur
bacteria [60, 61].
A first estimate for the light transmission to the top of the population of
green sulfur bacteria at 78 m depth was based on Secchi disk measurements
and arrived at a value of 0.2% of surface light intensity [5]. Another estimate,
similarly derived from Secchi depth readings amounted to 0.0006% of total in-
cident solar radiation, corresponding to 0.012µmol Quanta m
−
2
s
−
1
[12]. Based
on a more detailed calculation which took into consideration the chlorophyll-
specific attenuation coefficient [52], the light transmission reported by Repeta
et al. [60] and data from irradiance measurements at Odessa [54], the under-
water irradiance available for photosynthesis in the Black Sea chemocline was
estimated to be 0.003 µmol Quanta m
−
2
s
−
1
(max. in June 0.01 µmol Quanta
m
−
2
s
−
1
). This corresponds to 0.0005 % (0.002 %) of the surface irradiance
(600 µmol Quanta m
−
2
s
−
1
in winter) [54].
