Division S-6-soil & water management & conservation

Heavy metal accumulation in agricultural soils increases export potential of the metals to the environment. The concentrations of dissolved heavy metals (Cd, Co, Cr, Cu, Fe, Ni, Pb, Zn, Mn, and Mo) in surface runoff were monitored over a 2-yr period at 11 sites of vegetable farms and citrus groves in Florida. A total of 1277 surface runoff samples were analyzed for dissolved metals and extractable metals in the surface soils of each field site were determined. Concentrations of the metals in the runoff ranged widely from nondetectable level to 2.80, 18.5, 14.1, 1475, 9227, 39.3, 30.4, 1401, 2118, and 15.0 mug L-1 for Cd, Co, Cr, Cu, Fe, Ni, Pb, Zn, Mn, and Mo, respectively. Spatial and temporal variations in the concentrations of heavy metals and runoff discharge were noted among the different sites. Ninety-four, 96, 55, 32, 93, and 61% of the samples had metal concentrations below the detection limits for Cd, Co, Cr, Ni, Pb, and Mo, respectively, whereas 0.62, 30, and 23% of the samples had Cu, Fe, and Mn higher than their drinking water standards. Annual loads of dissolved metals in the runoff varied widely among monitoring sites and were different between the year 2001 and 2002. The concentrations of heavy metals in the surface runoff were associated with the accumulation of the metals in the soils. The 0.01 M CaCl2 extractable Cu, Fe, Zn, and Mn in soil were found to significantly correlate with Cu, Fe, Zn, and Mn concentrations in the surface runoff.