5 Use of Radioisotopes to Study Biogeochemical
Cycling of Elements in Aquatic Environments
5.1 Introduction
The metabolic and filtering activity of hydrobionts is the main factor in the
cycling of elements and their deposition in the bottom sediments of water
basins (Kuznetsov 1970; Krumbein 1978). Among the most important of them
are C, N, P, S, Ca, Mn, Fe, and Co. All of them have long-living radioisotopes
except nitrogen, which also has the radioisotope C 3 N), which is very shortliving. Its half-life is only lOmin. Nevertheless, it was also used for N2 fixation
and nitrification experiments. For routine work in the field it evidently cannot
be used; for this purpose the stable isotope of nitrogen 15N is applied. Concerning the use of 14C, only the problems of its application in studying the
turnover of methane is considered in this chapter. The cycling of phosphorus
and sulfur is among the most vital problems of hydro biology and biogeochemistry. The dynamics of phosphorus significantly controls the productivity
and the environmental parameters of aquatic ecosystems. The use of radiotracers is now the main way of quantification of phosphorus metabolism and
of studying its mechanisms. For this, we have two l3-emitting radioisotopes of
phosphorus, 32p and 33p' The sulfur turnover controls the redox conditions and
oxygen regime in the water bodies and regulates the dynamics and deposition
of numerous metals in water basins. Therefore it is very fortunate to have such
a perfect tool for its study such as its radioisotope 35S, which has a long life
and a soft beta radiation. Basic knowledge about sulfur cycling was acquired
precisely because of its wide use. The deposition of Ca as CaC03 by aquatic
organisms, which use the lime for the construction of their skeletons and shells,
is among the most widespread biogeochemical processes on our planet. For its
quantification we have a convenient radioisotope, 45Ca, which is also the 13emitter. Cobalt is one of the most important micro nutrients, being the persecutor of vitamin B12• It participates in the formation of Fe-Mn nodules on the
oceanic floor. To study its turnover, the radioisotope 57CO is used, which is a
long-living y-emitter. Fe and Mn also are important components of active cell
constituents - enzymes and pigments and participants of oxidation-reduction
processes in water basins. Their dynamics is studied with the use of long-living
radioisotopes 55Fe and s4Mn. The former emits X-rays and Auger electrons, and
the latter is the y-emitter.
In practice, radioisotopes are usually used for solving three major problems of the biogeochemical dynamics of elements and their compounds: (1)
measuring in situ rates of turnover processes and the turnover time, (2) eval-
Cycling of Elements in Aquatic Environments
5.1 Introduction
The metabolic and filtering activity of hydrobionts is the main factor in the
cycling of elements and their deposition in the bottom sediments of water
basins (Kuznetsov 1970; Krumbein 1978). Among the most important of them
are C, N, P, S, Ca, Mn, Fe, and Co. All of them have long-living radioisotopes
except nitrogen, which also has the radioisotope C 3 N), which is very shortliving. Its half-life is only lOmin. Nevertheless, it was also used for N2 fixation
and nitrification experiments. For routine work in the field it evidently cannot
be used; for this purpose the stable isotope of nitrogen 15N is applied. Concerning the use of 14C, only the problems of its application in studying the
turnover of methane is considered in this chapter. The cycling of phosphorus
and sulfur is among the most vital problems of hydro biology and biogeochemistry. The dynamics of phosphorus significantly controls the productivity
and the environmental parameters of aquatic ecosystems. The use of radiotracers is now the main way of quantification of phosphorus metabolism and
of studying its mechanisms. For this, we have two l3-emitting radioisotopes of
phosphorus, 32p and 33p' The sulfur turnover controls the redox conditions and
oxygen regime in the water bodies and regulates the dynamics and deposition
of numerous metals in water basins. Therefore it is very fortunate to have such
a perfect tool for its study such as its radioisotope 35S, which has a long life
and a soft beta radiation. Basic knowledge about sulfur cycling was acquired
precisely because of its wide use. The deposition of Ca as CaC03 by aquatic
organisms, which use the lime for the construction of their skeletons and shells,
is among the most widespread biogeochemical processes on our planet. For its
quantification we have a convenient radioisotope, 45Ca, which is also the 13emitter. Cobalt is one of the most important micro nutrients, being the persecutor of vitamin B12• It participates in the formation of Fe-Mn nodules on the
oceanic floor. To study its turnover, the radioisotope 57CO is used, which is a
long-living y-emitter. Fe and Mn also are important components of active cell
constituents - enzymes and pigments and participants of oxidation-reduction
processes in water basins. Their dynamics is studied with the use of long-living
radioisotopes 55Fe and s4Mn. The former emits X-rays and Auger electrons, and
the latter is the y-emitter.
In practice, radioisotopes are usually used for solving three major problems of the biogeochemical dynamics of elements and their compounds: (1)
measuring in situ rates of turnover processes and the turnover time, (2) eval-