Long-term effects on soil microbial properties of heavy metals from industrial exhaust deposition

Soil samples were taken at 0-10 cm and 10-20 cm depth from 7 clay-marsh sites used as grassland close to Nordenham in the north of Lower Saxony, Germany. The sites had been contaminated by deposition of heavy metals from industrial exhausts, the level of contamination varying according to their distances from a lead factory. The soils were analyzed to assess the depth-specific effects of NH4NO3 extractable and total amounts of Zn, Pb, and Cu on basal respiration, adenylates, ergosterol, and biomass C estimated by fumigation extraction (FE) and substrate-induced respiration (SIR). Most of the chemical and biological properties studied decreased with depth, but depth-specific differences in the relationships between these properties rarely occurred. The biomass C/soil organic C ratio was at a relatively high level, but most consistently reflected pollution as a decrease with increasing heavy metal load, independently of the method used for biomass C estimation. However, the SIR estimates were on average 44 % lower than those of FE, mainly due to pH effects. The metabolic quotient SIR-qCO(2) increased with increasing NH4NO3 extractable and total heavy metal contents, but also with decreasing pH, whereas the FE-qCO(2) remained unaffected by heavy metals and pH. The ATP/FE-biomass C ratio was on average 8.2 mumol g(-1) and negatively affected by soil plc, but also by total Zn, NH4NO3 extractable Zn and Cu. The ergosterol/FE-biomass C ratio was on average 0.29 %, i.e. at a very low level, and increased with increasing heavy metal content, This indicates a change in the community structure towards fungi.