PROBLEMS ASSOCIATED WITH THE ARTIFICIAL FLOODING OF FLOODPLAIN FORESTS IN AN INDUSTRIAL REGION IN GERMANY

This paper considers problems associated with the artificial flooding of floodplain forests in an industrial region in central Germany. Duri ng the past eight centuries river regulation has reduced flooding to a n extent dependent on local conditions. The lack of flooding has cause d a new pedo-hydrological regime. Typical tree mixtures in the floodpl ain forests of oak, ash, elm and maple have changed over the last 120 years so that ash and maple now dominate. Sediments of the rivers Weis se Elster and Mulde were found to be contaminated by industrial pollut ants, especially with heavy metals such as Cd, Zn, Co and Cr. Atmosphe ric pollution and the deposition of dust and gas contaminated by heavy metals over the last 100 years have been responsible for serious soil contamination. There is a danger of the migration of these heavy meta ls through the floodplain sediments and soils into groundwater. Artifi cial flooding is one method of re-introducing natural conditions to fl oodplains and their forests. Our investigations of the migration behav iour of contaminants, using sequential leaching procedures, have demon strated that a high proportion of the stored heavy metals in the meado w loams is soluble and highly mobile. The release of heavy metals in t he soils depends on the pH-value and grain size of the soils as well a s precipitation and climatic conditions. The mobility of the heavy met als increases with rising acidification of the soils. Despite decreasi ng atmospheric deposition in the region of Bitterfeld and reduced depo sition of basic flue ashes after the year 1990, increased mobilization of metals in the hood loams is likely to take place. The migration of these chemicals to groundwater is likely to be increased by water inf iltrating from artificial flooding. Artificial flooding may therefore have previously unforeseen negative consequences.