IMPACT OF PASTURE CONTAMINATION BY COPPER, CHROMIUM, AND ARSENIC TIMBER PRESERVATIVE ON SOIL MICROBIAL PROPERTIES AND NEMATODES

Microbial properties and nematode abundance were measured along a grad ient of increasing Cu, Cr, and As concentrations (50-1300 mg Cr kg-1) in the top 5 cm of a pasture soil contaminated by runoff of preserving liquor from an adjacent timber-treatment plant. Microbial biomass C a nd N were significantly (P<0.05) lower in contaminated than uncontamin ated soils. The amount of microbial biomass C as a percentage of total organic C declined significantly (r 2 value with Cr 0.726) with incr easing contamination, and the ratio of respired C to biomass C was sig nificantly (P<0.05) higher with contamination. Substrate-induced respi ration, microbial biomass P, and denitrification declined (r2 value wi th Cr 0.601, 0.833, and 0.709*, respectively) with increasing contami nation. Increasing contamination. had no effect on prokaryote substrat e-induced respiration but eukaryote: eukaryote substrate-induced respi ration declined significantly (r2 value with Cr 0.722). Accordingly, the ratio of prokaryote substrate-induced respiration increased signif icantly (r2 value with Cr 0.799) with contamination. There was a sign ificant (r2 value with Cr 0.872) hyperbolic relationship between sulp hatase activity and contamination, with activity declining by approxim ately 80% at > 1000 mg Cr kg-1. Increasing contamination had no effect on basal respiration, dimethyl sulphoxide reduction, and phosphatase, urease, and invertase activities. Numbers of plant-associated nematod es declined significantly (r2 value with Cr 0.780) with contamination . On a percentage basis, plant-feeding nematodes predominated in less contaminated soils, whereas bacterial-feeding and predatory nematodes predominated in heavily contaminated soils. The use of the fumigation- incubation procedure for measurement of microbial biomass C in heavy-m etal contaminated soils is discussed.