Different sources of heavy metals and their long-term effects on soil microbial properties

We analysed soils of Lower Saxony, Germany, variously contaminated with sewage sludge, sediment, and dump material from mining and factory residues, to assess the effects of different sources of heavy metals and different metal species (total, EDTA and NH sub(4)NO sub(3) extractable) on activity (basal respiration), biomass (microbial C, adenylates) and community structure (ergosterol) of soil microorganisms in relation to important chemical soil properties. The contents of biomass C, adenylates and ergosterol did not necessarily decrease with increasing heavy metal content, reflecting the importance of other environmental factors, e.g. differences in C input. The biomass C/soil C ratio ranged from 0.19 to 2.10% and decreased in the order: sludge>sediment>dump contamination, in accordance with the increasing heavy metal load. The ergosterol/biomass C ratio, which in contrast increased in the orders/sludge