230
Use of Radioisotopes to Study Biogeochemical Cycling of Elements
are taken into two 250-ml BOD bottles. Before being charged with I4C_
carbonate working solution, 0.5 ml 0.5% solution of N-serve in ethanol,
(5mgl- 1 final concentration), is injected into one of them (experimental) and
0.5 ml of only ethanol into the second (control). The control with ethanol is
needed because N-serve is insoluble in water. The subsequent procedure is as
JescribeJ above fur measuring Jark CO2 uptake. After the exposure time
(12-15 h) ends, the samples in the bottles are fixed and prefiltered. Two parallel filtrations are made from each sample to obtain the means. The probable
rate of nitrification (An) is calculated as follows: An = (Ae - Ae) 10f.lgNI-I
day-\ where Ae and Ae are dark CO2 assimilation (f.lgCI-I day-I), correspondingly in the control with only ethanol and in the experimental bottle with Nserve. To measure nitrification in nitrifying bacterial populations of the bottom
sediment, the same technique is used. The experiments are carried out in
50-cm 3 serum bottles filled with 30ml of water +5 cm 3 of fresh sediment sample
taken from the upper layer of the core; 0.1 ml of the sample is added into one
sample, and 0.1 ml of only ethanol is added into another; 0.1 ml of the same
N-serve ethanol solution is added correspondingly into one sample and 0.1 ml
of only ethanol solution to another. The subsequent procedure is as described
above for measuring the dark I4C02 uptake in bottom sediments (see Sect.
4.4.2.2.).
5.5 Studying Sulfur Cycling with the Aid of 35S
5.5.1 Introduction
The cycling of sulfur and its compounds is among the most important factors
which control biogeochemical dynamics of aquatic ecosystems and, consequently, the quality of the environment. Sulfur as a chemical element has outstanding features, which are determined by the exclusively large scale of its
valence, which ranges from 2+ down to 6-. Therefore, sulfur and its compounds
may carry out functions of both electron donors and acceptors. They serve in
aquatic ecosystems as the basic energy link between the aerobic and anaerobic domains separated by the redox zone. Reduced sulfur compounds like
S2-, S20 /-, and elemental sulfur are readily oxidized aerobically with dissolved
oxygen, and with the combined oxygen of nitrates with the participation of
specific bacterial populations as well as during purely chemical oxidation. In
the bottom sediments and in anoxic layers of the water columns, oxidized
sulfur compounds and elemental sulfur accomplish the function of basic electron acceptors, being reduced to sulfides by specific sulfate-reducing bacteria.
The dynamics of sulfur compounds is among the main factors regulating redox
conditions, such as the oxygen regime and nitrogen cycling in water basins.
Sulfides and free H 2S, which are produced during anaerobic sulfate reduction,
are toxic for some aquatic organisms (animals, algae), but welcomed by others
Use of Radioisotopes to Study Biogeochemical Cycling of Elements
are taken into two 250-ml BOD bottles. Before being charged with I4C_
carbonate working solution, 0.5 ml 0.5% solution of N-serve in ethanol,
(5mgl- 1 final concentration), is injected into one of them (experimental) and
0.5 ml of only ethanol into the second (control). The control with ethanol is
needed because N-serve is insoluble in water. The subsequent procedure is as
JescribeJ above fur measuring Jark CO2 uptake. After the exposure time
(12-15 h) ends, the samples in the bottles are fixed and prefiltered. Two parallel filtrations are made from each sample to obtain the means. The probable
rate of nitrification (An) is calculated as follows: An = (Ae - Ae) 10f.lgNI-I
day-\ where Ae and Ae are dark CO2 assimilation (f.lgCI-I day-I), correspondingly in the control with only ethanol and in the experimental bottle with Nserve. To measure nitrification in nitrifying bacterial populations of the bottom
sediment, the same technique is used. The experiments are carried out in
50-cm 3 serum bottles filled with 30ml of water +5 cm 3 of fresh sediment sample
taken from the upper layer of the core; 0.1 ml of the sample is added into one
sample, and 0.1 ml of only ethanol is added into another; 0.1 ml of the same
N-serve ethanol solution is added correspondingly into one sample and 0.1 ml
of only ethanol solution to another. The subsequent procedure is as described
above for measuring the dark I4C02 uptake in bottom sediments (see Sect.
4.4.2.2.).
5.5 Studying Sulfur Cycling with the Aid of 35S
5.5.1 Introduction
The cycling of sulfur and its compounds is among the most important factors
which control biogeochemical dynamics of aquatic ecosystems and, consequently, the quality of the environment. Sulfur as a chemical element has outstanding features, which are determined by the exclusively large scale of its
valence, which ranges from 2+ down to 6-. Therefore, sulfur and its compounds
may carry out functions of both electron donors and acceptors. They serve in
aquatic ecosystems as the basic energy link between the aerobic and anaerobic domains separated by the redox zone. Reduced sulfur compounds like
S2-, S20 /-, and elemental sulfur are readily oxidized aerobically with dissolved
oxygen, and with the combined oxygen of nitrates with the participation of
specific bacterial populations as well as during purely chemical oxidation. In
the bottom sediments and in anoxic layers of the water columns, oxidized
sulfur compounds and elemental sulfur accomplish the function of basic electron acceptors, being reduced to sulfides by specific sulfate-reducing bacteria.
The dynamics of sulfur compounds is among the main factors regulating redox
conditions, such as the oxygen regime and nitrogen cycling in water basins.
Sulfides and free H 2S, which are produced during anaerobic sulfate reduction,
are toxic for some aquatic organisms (animals, algae), but welcomed by others