The radionuclides in environ-ecological systems are important for numbers of reasons. These include the potential radiological impact on biota and human health, and their use as tracers for environmental processes. Therefore, man can make use of radionuclides to know the ecosystem. Important aspects include: (1) radionuclide criteria in the environments and the ecosystem: equilibrium relationship between the radioactive ratio and the ecosystem, or the important significance of environmental radionuclides in the ecosystems; and (2) radionuclide behavior in the environments and the ecosystem: the transfer relationships of radionuclides between different components of the ecosystem. In order to understand the impacts of bio-geochemical processes in different ecosystems, it is essential to investigate the variety of radionuclide activity, and the interactions with the environment of all stages. The VII International Congress of Ecology was organised by the International Association for Ecology (INTECOL) in conjunction with the Italian Ecological Society (SITE). It was held in Florence, Italy on 19~25 July,1998. With support from the Program Committee, we established a Symposium on Radionuclides in Ecological Systems (RNES) organised as below. On this symposium, the discussion focuses on the geochemical behaviours of 210Pb,137Cs and7Be, as three fallout radionuclides with different originating.This presentation is concerned with recent progress on the dating lake sediments by 210Pb and137Cs, and the bio-geochemical behaviors of the 210Pb,137Cs and 7Be in the terrestrial and aquatic ecosystems. With the fallout radionuclides such as 210Pb,137Cs and7Be are of increasing importance to a wide range of environmental and ecological programs, in order to know their role in the evolution of ecosystems by acting as propellers of genetic variation, it is essential to establishing a global database for environmental
radionuclides.