Beitrag zur Schwermetalldynamik auf aufgeforsteten Standorten im Einflussbereich der ehemaligen August-Bebel-Hütte in Helbra (Mansfelder Land)

Abstract

Fornacon, C.; Frühauf, M.; Schumann, H.: Comparison of heavy metal dynamics in afforested areas in the surrounding of the former copper metallurgical plant in Helbra (Mansfelder Land). – Hercynia N.F. 38 (2005): 197–207.The smelting of the August-Bebel-Hütte (ABH) in Helbra was part of the copper shales mining period in the Mansfelder Land. The ABH was closed in 1990 but its 110 years working period resulted in very high contaminated soils in the immediate agricultural dominated vicinity. The afforestation of the highest contaminated areas started in the beginning of the seventies and continued until in the nineties. In the study five differentially afforestated areas (poplar - 31 to 33 years – profile 1/ poplar, aspen - 17 years – profile 2/ poplar, sycamore maple, ash leaf maple, robinia - 15 years – profile 6/ ash, sycamore maple, lime tree - 12 years – profile 3/ larch - 12 years – profile 4) were compared with two adjacent agricultural areas (profile 5, 7) in order of determine the dynamics of the heavy metals Pb, Cu, Zn and Cd. The seven soil profiles were vertical sampled and analysed on texture, pH value, soil organic matter, total carbonate content, total content of heavy metals with aqua regia dissolution and the plant available fraction using NH4NO3-solution. High and very high contaminations of the soils were only found at the O- and A-horizons of the soils. Total contents of heavy metals depended on the distance to and the main wind direction from the ABH. NH4NO3-soluble topsoil fractions of the afforestated areas showed an added mobilisation of heavy metals when compared to the agricultural samples. Low pH-values resulted in higher heavy metal mobilisation. In the profiles highest mobilisation for Cd the lowest for Pb was found. In contrast no relation to the pH-value was observed for Cu that might be due to lightly soluble Cu-complexes formed with carbonates and phosphates. In conclusion the afforestations have a considerable influence on the mobilisation of heavy metals. Highest mobilisation was found in profile 1 with the highest total contents of heavy metals. But in spite of lower total contents of heavy metals than profile 2 the second highest mobilisation were found in profile 4 with the lowest pH-values because of the coniferous afforestation. Trees with high C/N-ratios are available to reduce pH-value in topsoil in a very short time and enhance the mobilisation of heavy metals.