Study of Sulfate Reduction
243
metabolic actIvIty is hydrogen sulfide, which directly reacts with dissolved
oxygen (see above, Sect. 5.2.1). H 2S is the cytochrome poison, which reacts
with its iron. The appearance of free H 2S in the environment fundamentally
changes the composition of biota inhibiting the native flora and fauna
and favors tolerant plants, such as Viva and cyanobacteria, or animals, such as
polychaetes or tendipedides. The migration of hydrogen sulfide from bottom
sediments - their main domain of activity - up to the water column entails
hypolimnetic anoxia and supports the quasi permanent existence of anoxic
H 2S-zones, thus resulting in the fundamental transformations of aquatic
ecosystems which undermine their productivity and self-purification
capacity.
The most important feature of sulfate reduction from the standpoint of
aquatic ecology is its immediate enhancement under the influence of anthropogenic eutrophication. Natural aquatic ecosystems, including eutrophic ones,
adapt to an established ratio between oxic and anoxic processes, having the
basic stock of toxic sulfides neutralized as Fe-sulfides. Then any external manmade inflow of organic matter, especially of foreign matter, first of all enhances
the sulfate reduction in the bottom sediments. The excess of free hydrogen
sulfide poisons the bottom fauna, causing mass mortality. When rising up to
the water column from the sediment, it causes anoxia, thus also influencing
the composition and abundance of zooplankton and reSUlting in mortality of
benthovorous fish. Often the appearance of H 2S in the water column harms
the phytoplankton, especially in shallow marine environments (Sorokin et al.
1996b). This impact causes the change of its composition to favor the domination of cyanobacteria, which are not only tolerant of H 2S but often have a
special affinity to its presence. The domination of cyanobacteria in pelagic
biotopes usually ends with their massive "blooms", which are often caused by
potentially toxic species, with catastrophic sequences for the environment. This
is a typical scenario for anthropogenic impact on coastal marine ecosystems,
in which microbial sulfate reduction plays the primary role. The investigation
and monitoring of this process should be among the chief priorities during
ecological studies of aquatic environments and their monitoring.
The study of microbial sulfate reduction includes the evaluation of the following parameters:
1. Measuring the stock of labeled sulfides in bottom sediments;
2. monitoring the appearance of free H 2S in water columns during the periods
of hypolimnetic or near bottom anoxia;
3. estimating the rate of H 2S production in upper (O-20cm) layers of bottom
sediments and in anoxic strata of the water column; and
4. studying the location of active populations of sulfate-reducing bacteria in
water bodies.
The stock of labile soluble acid or acid volatile sulfides (AVS) in bottom
sediments is analyzed by distillation of H 2S gas, which is evolved during acid
decomposition of AVS, with the flow of nitrogen and its trapping with alka-
243
metabolic actIvIty is hydrogen sulfide, which directly reacts with dissolved
oxygen (see above, Sect. 5.2.1). H 2S is the cytochrome poison, which reacts
with its iron. The appearance of free H 2S in the environment fundamentally
changes the composition of biota inhibiting the native flora and fauna
and favors tolerant plants, such as Viva and cyanobacteria, or animals, such as
polychaetes or tendipedides. The migration of hydrogen sulfide from bottom
sediments - their main domain of activity - up to the water column entails
hypolimnetic anoxia and supports the quasi permanent existence of anoxic
H 2S-zones, thus resulting in the fundamental transformations of aquatic
ecosystems which undermine their productivity and self-purification
capacity.
The most important feature of sulfate reduction from the standpoint of
aquatic ecology is its immediate enhancement under the influence of anthropogenic eutrophication. Natural aquatic ecosystems, including eutrophic ones,
adapt to an established ratio between oxic and anoxic processes, having the
basic stock of toxic sulfides neutralized as Fe-sulfides. Then any external manmade inflow of organic matter, especially of foreign matter, first of all enhances
the sulfate reduction in the bottom sediments. The excess of free hydrogen
sulfide poisons the bottom fauna, causing mass mortality. When rising up to
the water column from the sediment, it causes anoxia, thus also influencing
the composition and abundance of zooplankton and reSUlting in mortality of
benthovorous fish. Often the appearance of H 2S in the water column harms
the phytoplankton, especially in shallow marine environments (Sorokin et al.
1996b). This impact causes the change of its composition to favor the domination of cyanobacteria, which are not only tolerant of H 2S but often have a
special affinity to its presence. The domination of cyanobacteria in pelagic
biotopes usually ends with their massive "blooms", which are often caused by
potentially toxic species, with catastrophic sequences for the environment. This
is a typical scenario for anthropogenic impact on coastal marine ecosystems,
in which microbial sulfate reduction plays the primary role. The investigation
and monitoring of this process should be among the chief priorities during
ecological studies of aquatic environments and their monitoring.
The study of microbial sulfate reduction includes the evaluation of the following parameters:
1. Measuring the stock of labeled sulfides in bottom sediments;
2. monitoring the appearance of free H 2S in water columns during the periods
of hypolimnetic or near bottom anoxia;
3. estimating the rate of H 2S production in upper (O-20cm) layers of bottom
sediments and in anoxic strata of the water column; and
4. studying the location of active populations of sulfate-reducing bacteria in
water bodies.
The stock of labile soluble acid or acid volatile sulfides (AVS) in bottom
sediments is analyzed by distillation of H 2S gas, which is evolved during acid
decomposition of AVS, with the flow of nitrogen and its trapping with alka-