TRANSPORT OF HEAVY-METALS IN A SLUDGE-TREATED FORESTED AREA

Plots in a mixed hardwood forest received two separate applications of anaerobically digested sewage sludge in fall 1974 and spring 1975. Total solids loading in the low and high treatments were 12. 71 and 26-96 metric tons/ha, respectively. Copper, Zn, and Cd loadings in the high treatment were 24. 50, 28. 49, and 0. 253 kg/ha, respectively. Calculated amounts of percolate Cu, Zn, and Cd moving out of the 120-cm depth in the high treatment were 0. 3, 3. 2, and 6. 6% of the total applied levels, respectively, indicating a definite order of relative mobility for the three metals. Results also indicated that Cu applied in the sewage sludge was more extractable than the native soil Cu, Zn was only slightly more extractable, and Cd was less extractable. Of the other heavy metals only Cr and Ni increased in the 0- to 7. 5-cm depth following sludge applications.