There is also the possibility of treating the soil with petroleum or bi tumen, thus forming complexes that bind the radioisotopes, preventing them from penetrating into the plants.
Radioecologically, contamination of river floodplains is heaviest not only downstream from nuclear power plants, but generally over the entire floodplain, although to a lesser extent. Floodplains are regions of annual deposition of soil particles washed by snowmelt from extensive land areas, and therefore concentrate radioisotopes washed off from extensive areas. The most valuable hayfields, pastures, plantations, and fields of present day floodplains may sometimes conceal greater radioactive danger than the watersheds.
In general, the geomorphological elements of the Earth's surface which are so important for the understanding of ecological properties are also important for the understanding, forecast, and control of radioecological phenomena. Distribution of radioactive fallout from the atmosphere is largely dependent upon the local geomorphology and winds.
Usually, larger amounts of fallout settle on elevations than on depres sions. This difference has been clearly demonstrated, particularly in the neighborhood of nuclear power plants /9/. In order to reduce the radioecological danger in floodplains, it is possible to stop the discharge of radioactive wastes into rivers and river floods, and to control flooding and direct inundation by snowmelt through effective drainage; floodplain soils will have to be decontaminated by techniques similar to those tentatively suggested for other sectors.
Forest ecology involves theoretical and practical problems which are both complex and difficult. The forest is a very complex phenomenon and radioecological studies of it have scarcely begun. It is quite understand able that owing to the vast area of foliage, branches, tree trunks, shrubs, the herbaceous and moss cover, litter, etc., the forest is probably an efficient trap and accumulator of radioactive isotopes from the contaminated atmosphere. The biogeochemical cycle of matter in the forest is vast and diversified and must also involve the radioisotopes. It is important to be able to understand and predict what will happen to radioisotopes in the different components of living (and sometimes of dead) forests; it is necessary to foresee the degree of radioactive danger represented by the contaminated forest as a whole, and also of its products, which include food (mushrooms, berries, game), timber, other commercial wood, and firewood (whose ash might be radioactive). A large, essential task is the
investigation of the effect of radioactive contaminations on the various forest animals ranging from insects and small fur animals to large animals such as elks and bears, as well as to birds. In addition we cannot ignore the highly specific forms of concentration, and dissemination of radioisotopes by migration of billions of windborne seeds and insects, and thousands of birds and beasts as they make their way into and out of the forest.
Methods of alleviating, stopping, and isolating these radioecological processes must be found in order to decontaminate the living or dead forest. The simplest suggestion is that such a forest together with the ad jacent protective zone should be declared a forbidden area for as long as required to achieve a safe level of radioactivity by natural decay. Yet, it would seem that suitable radioecological investigations might result in more flexible policies concerning heavily contaminated forests than com plete isolation, or a more severe measure of burning it in situ (whereby the large quantities of radioactive ashes and aerosols might be blown by winds over large distances). The danger of forest fires is high enough without their being started intentionally.
Because radioactive isotopes accumulate in the forest litter (from the shedding of leaves), forest decontamination is laborious and only partially successful. It involves collecting, removing, and burning the litter at suitable sites, and subsequent burial of the radioactive ash. A certain degree of decontamination may thus be achieved provided this process is repeated over a period of several years. A dead forest, however, does not shed leaves, and therefore much labor will be required for cutting, removing, and burning (in suitable locations) the heavily contaminated wood, and for burying large volumes of ash. There is no doubt that the ecological conditions will dictate the suitable techniques and their details in each specific case. In this connection, we must emphasize that the specific radioecological features of each contaminated sector should be determined individually.