Changes in Heavy Metal Concentrations in Acid Soils Under Pine Stands Subjected to Repeated Applications of Biosolids

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The distribution of metals in biosolid-amended soils (as measured by acid extraction) to a depth of 53 cm was examined for evidence of translocation and possible redeposition and to determine whether downward-moving heavy metals interacted with the subsoil. The soil is a sandy acid forest soil (Dystric Cambisol) located in a high-leaching environment. The biosolid was applied twice (in 2001 and 2002) at three different loading rates, and soils were sampled in the 3 years following the first application (2002, 2003, and 2004). Zinc, chromium, nickel, and copper accumulated in the uppermost horizon (0- to 4-cm depth), and the highest concentrations corresponded to the highest doses of biosolids. The lack of cadmium accumulation in this horizon was attributed to the high mobility of this element. Between 4 and 9 cm to the 48-cm depth, and with few exceptions, there were no significant differences (P < 0.05) between the different doses of biosolids and control. The existence of both subsurface lateral flow and preferential flow may explain the lack of differences. Cadmium mainly accumulated at 48 to 53 cm, which was the depth of the water table. At this depth, an overall increase in the concentrations of the other heavy metals was also observed. This pattern was attributed to the longer time of contact between the soil-reactive surface and soil solution.

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