Use of Radioisotopes to Study Biogeochemical Cycling of Elements in Aquatic Environments

Abstract

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 (¹³N), which is very short-living. Its half-life is only 10 min. 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 hydrobiology and biogeo-chemistry. The dynamics of phosphorus significantly controls the productivity and the environmental parameters of aquatic ecosystems. The use of radio- tracers is now the main way of quantification of phosphorus metabolism and of studying its mechanisms. For this, we have two ß-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.