Structural dynamics of a vegetative soil cover for waste rock dumps

Abstract

Most waste rock dumps of Uranium mining in the Eastern German Ore Mountains near Schlema site are covered with an 80 cm compacted loam sublayer and a vegetated 20 cm top layer by mixing of compost and mineral soil (vol. 50%/vol. 50%). The cover is quite fertile and leads to a considerable reduction of water infiltration into the heaps. However, soil forming processes alter the physical properties of the cover affecting soil hydrology, stability and growth conditions. Within 6 years after placement self-compaction increased dry bulk density of the top soil (10 – 20 cm depth) from 1.15 – 1.35 g cm−3. As a consequence, the air filled macropores decreased from >20 vol.-% to 8 vol.-%, whereas the water storing medium pores increased by 9 vol.-%. In contrast, dry bulk density of the pre-compacted mineral sublayer remained unchanged at 1.72 g cm−3. Nevertheless, even in 30 – 60 cm depth, a significant increase in plant available water-holding capacity occurred. Initial soil dynamics are likely to improve the hydrological efficency and stability of the cover system. On the other hand, there is already some evidence for structural cracks and preferential water flow, which counteract the positive effects of self-consolidation and therefore requires further research.