Environmental Engineering Reference
In-Depth Information
energy limited. Physiological adaptations to such habitats include slow
growth and resting or static stages. Some lakes (e.g., Lake Tahoe and
Crater Lake) and many groundwater habitats are extreme oligotrophic en-
vironments.
DEEP SUBSURFACE HABITATS
Scientists viewed deep subsurface groundwaters as essentially sterile
habitats until recently. Such a view is incorrect because bacteria, fungi, and
protozoa can be cultivated from subsurface samples (Fig. 15.9), and bac-
teria have been found as deep as 400-500 m (Balkwill and Boone, 1997).
A study in Finland documented bacteria at a depth of 940 m (Haveman
and Pedersen, 1999). These deep microbial communities include a moder-
ately diverse group of bacteria capable of many common nutrient trans-
formations (e.g., denitrifiers, sulfate reducers, and nitrogen fixers) and a
somewhat diverse assemblage of heterotrophic microorganisms (Sinclair
and Ghiorse, 1989). Depth limits of organisms may be set by temperature
tolerances because geothermal heating increases temperatures with depth
(Ghiorse, 1997).
The following are obvious questions that arise upon finding such or-
ganisms: How long have they been there and what are they living on? The
answer to the first question is surprising. Many of these sediments were de-
posited millions of years ago and pore water ages of 1200 years have been
measured where active microbes have been isolated (Kieft
et al.,
1998). The
microbial communities inhabiting at least some groundwaters are likely de-
rived from the microbes present when the sediments were deposited (Amy,
1997). Apparently, some communities in deep groundwaters have been iso-
Bacteria
(# viable cells per g dry wt)
Eukarya
(counts per g dry wt)
10
0
10
2
10
4
10
6
10
8
10
0
10
1
10
2
10
3
10
4
0
0
Protozoa
Fungi
20
20
40
40
60
60
80
80
100
100
120
120
140
140
160
160
180
180
200
200
A
B
FIGURE 15.9
Distribution of bacteria (A) and protozoa and fungi (B) in deep subsurface
sediments at Savannah River (© 1989 from
Geomicrobiol. J.
Fig. 2, p. 22, and Fig. 3, p. 23,
by J.L. Sinclair and W.C. Ghiorse. Reproduced by permission of Taylor and Francis Inc.).
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