Journal of Environmental Radioactivity 47 (2000) 101}114 Mathematical model of Cs dynamics in the deciduous forest S.V. Mamikhin*, A.L. Klyashtorin Soil Science Faculty, Moscow State University, Vorob'evy Gory, Moscow 119899, Russia Received 1 May 1998; received in revised form 15 January 1999; accepted 16 February 1999 Abstract A mathematical model of Cs behaviour in the forest ecosystem is presented. The behav- iour of this radionuclide is assumed to obey the same regularities as the behaviour of its stable chemical analogue, potassium. Radionuclide dynamics are considered in parallel with the dynamics of the phytomass. Radionuclides contained in the vegetation are pooled into two basic compartments: external and internal contamination, with separate analysis of each. The model was veri"ed using the data obtained in the 30-km zone of the Chernobyl NPP in 1986}1994. The algorithm described was found to be the most e$cient in terms of Cs behaviour in the forest environments.  1999 Elsevier Science Ltd. All rights reserved. 1. Introduction Mathematical modelling is an e!ective method to study and forecast the conse- quences of radioactive contamination of the biosphere due to nuclear weapons testing and accidents at nuclear installations. The studies of the consequences of the Cher- nobyl NPP accident have promoted the intensive development of mathematical modelling of radionuclide behaviour in the environment. Existing models are charac- terised by a variety of approaches. The above can be illustrated by the models, developed in the framework of the Agreement for International Collaboration on the Consequences of the Chernobyl Accident between the European Commission and Ministries for Chernobyl A!airs in Belarus, Russia and the Ukraine (Shaw, Mamik- hin, Dvornik & Zhuchenko 1996a), and early models (for example: Olson, 1963; Anokhin, 1974; Crout Neil, Beresford, Howard & Unsworth, 1990; Van Voris, Cowan, Cataldo, Wildung & Shugart, 1990; Muller & Prohl, 1993; Alexakhin, Ginsburg, * Corresponding author. E-mail address: mam@tikh.soils.msu.su (S.V. Mamikhin) 0265-931X/99/$ - see front matter  1999 Elsevier Science Ltd. All rights reserved. PII: S 0 2 6 5 - 9 3 1 X ( 9 9 ) 0 0 0 2 5 - 9