Impact of pasture contamination by copper, chromium, arsenic timber preservative on soil biological activity

Abstract

Contamination of grazed pasture gave 0–5 cm soil contents of 19–835 mg kg^-1 Cu, 47–739 mg kg^-1 Cr, and 12–790 mg kg^-1 As. Soil Cu, Cr, As contents were correlated and declined with depth to 30 cm. In plots with medium and high contamination buried cotton strips retained most of their original tensile strength, indicating repression of decomposition processes.Lumbricus rubellus andAporrectodea rosea were absent in plots with medium and high contamination; there was no evidence of heavy metal accumulation in earthworm tissue; soil bulk density was greater in the absence of lumbricids. Enchytraeids and nematodes were most abundant with low contamination. Nematode diversity was greater with low (0–5 cm) or medium (5–10 cm) contamination than in control plots or those with high contamination; the proportion of predators increased with contamination. Basal soil respiration was less sensitive than substrate-induced respiration to contamination. Although contamination reduced the nitrification rate, all mineral N was found as NO ^sup-_inf3 after 14 days. Sulphatase was the enzyme activity most sensitive to high contamination. Whereas contamination by 100 mg kg^-1 of Cu, Cr, and As caused little depression of soil biological activity, there was some supperssion at 400 mg kg^-1 and at 800 mg kg^-1 normal processes were inhibited and herbage production was negligible. No single measurement adequately indicated the need for site remediation.