Environmental Engineering Reference
In-Depth Information
TABLE 15.1
Upper Salinity Tolerances of Members of
Selected Groups of Organisms
a
Upper salinity
Organism
range (%)
Fish
11
Nematodes
12.5
Ostracods
13
Gastropods
15.9
Rotifers
16
Isopods
16
Copepods
17.6
Diatoms
20.5
Chironomids
28.5
Ephydra cinerea
30
Anostracans (
Artemia salina,
brine shrimp)
33
Cyanobacteria
35
Ciliate protozoa
35
Green algae
(Dunaliella)
35
Anostrocans
(Parartemia salina)
35.3
Phototrophic bacteria
40
Extreme halophilic bacteria
Saturated
a
Data from Javor (1989).
salt and dust storms that have negative impacts on human health. The in-
crease in salinity and numerous introductions of animals have caused sharp
decreases in biodiversity (Williams, 1993). Other saline lakes, notably
Mono Lake in California, are subject to similar pressures. Such lakes are
unique and should be conserved.
HOT SPRINGS
Hot springs associated with geothermal activity have piqued the inter-
est of many scientists. Visitors to thermal areas such as Yellowstone Na-
tional Park are generally not aware that many of the beautiful colors they
see in the pools and streams formed by the hot springs are actually living
microorganisms. These colors on the benthos are actually highly organized
microbial mats (Castenholz, 1984). Many
thermophilic
(heat-loving) or-
ganisms not only tolerate but also actually require the presence of elevated
temperatures to grow successfully. Habitats above about 55°C are mainly
inhabited by Bacteria and Archaea. These habitats have lower biotic di-
versity and thus form an attractive system for ecological research.
The chemistry of hot springs is variable; they can range from water that
is highly acidic (as low as pH 0.2) to very basic (pH 11). The distribution
of pH values is generally bimodal, with acidic springs dominated by sul-
fates, basic springs dominated by carbonates or silicates, and few neutral
springs (Brock, 1978). Different organisms dominate at these pH extremes.
Anoxic waters high in sulfide generally feed acidic springs, which form
sulfuric acid on exposure to the atmosphere and have high concentrations
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