Soil microbial biomass and organic C in a gradient of zinc concentrations in soils around a mine spoil tip

Soil microbial biomass carbon (biomass C) and its activity were measured in soil from Gabuzkoa (Spain) contaminated with heavy metals from a mine spoi l tip. Soil was collected along a natural gradient of heavy metal contamina tion characterized by different organic C contents, clay contents, cultivat ion and topography. Biomass C and ninhydrin-N were measured by fumigation-e xtraction (FE), substrate induced respiration (SIR) and by soil ATP content . Microbial activity was measured by CO2 production and the arginine ammoni fication rate. The maximum soil concentration of zinc (about 6500 mu g Zn g (-1) soil) was up to 27 times current European Union (EU) limits far agricu ltural soils. Microbial biomass, arginine ammonification rate and biomass C as a percentage of soil organic C decreased with increasing soil Zn concen tration, while CO2 production and specific respiration rate increased. Soil biomass C was negatively (% variance accounted for = 45) and CO2 evolution positively (% variance accounted for = 72) significantly correlated with Z n concentration, in exponential relationships. Both biomass specific respir ation rate (% Variance accounted for = 83) and biomass as percentage of soi l organic C (% variance accounted for = 76) were more significantly correla ted to soil Zn concentration than was biomass alone. It was concluded that both biomass and activity measurements could serve as indicators of environ mental stress due to metals in non-experimental sites. Additionally, these 'linked' measurements generally provided more sensitive indicators of envir onmental stress by heavy metals than either biomass C or CO2 evolution alon e. (C) 1999 Elsevier Science Ltd. All rights reserved.