Preliminary results of afforestation of brackish sludge mounds

High population density and intensive use of land in Flanders (Northern Bel gium) have resulted in a shortage of land to dump dredged sediments. In sea rch of an area efficient solution, a mound was constructed and afforested; 50-114% more dredged sediment per unit area could be discarded by construct ing mounds with a height of 6.6 m compared to conventional disposal sites. To prevent erosion, the mound was afforested. Preliminary results of tree g rowth and changes in soil conditions are demonstrated. Tree survival and he ight growth are highest in the dominant wind direction sc. the SW-NE axis. On the slopes, parallel with the dominant wind direction, tree mortality up to 80% was observed. The increase of the soil organic carbon content from 3.1 to 3.8% could be partly put down to the growth of tree roots. This incr ease in organic carbon has far-reaching consequences for potential soil san itation. The high amount of CaCO3 in the soil protects the mound from inter nal or external acidification for the next centuries. After four growing se asons, electric conductivity was reduced to the threshold for salt sensitiv e plants. (C) 2001 Elsevier science B.V. All rights reserved.