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 μg 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.

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The transformation of landscapes from nonurban to urban land use has potential to greatly modify soil phosphorus (P) pools. There is minimal information on variation of P pools along urbanization gradients. Soils in five zones along an urban-rural land use gradient in Hangzhou city, southeast China, were analyzed for total P, Olsen-P and P fractions. Along the urban-rural land use gradient, soil P concentration and storages varied significantly. The urban and suburban areas had significantly higher soil P than the rural area. ORDER REPRINTSThe results suggest that physical disturbances and inputs of various materials by humans can alter P pools in the soils. The urban and suburban soils were enriched with P varying from 1.1 to 12.0 times for total P (TP) and 1.6-32.9 times for Olsen-P as compared with the rural soils. The relative abundance of the various P fractions in the urban and suburban soils decreased in the order of HCl-P > organic P > residual P > NaOH-IP > NaHCO 3 -IP > H 2 O-P. The HCl-P was the dominant fraction and accounted for 42.3-81.0% of TP. Compared with the rural soils, the old urban and new suburban vegetable soils had a higher TP/C ratio, and the new urban and old suburban vegetable soils had a lower TP/C ratio. In old urban zone, the maximum P soil layer appeared as buried under different depth whereas in other soils as surface.

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To evaluate muck sediments as a potential soil amendment, total and Mehlich III-extractable concentrations of Cd, Cu, Cr, Ni, Pb, Zn, and Co in 59 muck sediment samples from the St. Lucie Estuary were analyzed. A seven-step chemical fractionation procedure was used to assess the potential mobility of heavy metals. Except for Cd, the average total concentrations of the metals are lower than the reported average concentrations of these elements in municipal composts in the U.S.A. The concentrations were also below critical levels for the safe use of wastes and byproducts in agriculture, as established by the United States Environmental Protection Agency. The Cd, Cu, Cr, Ni, Pb, Zn and Co in the sediments were predominantly associated with silicate minerals in the residual form. Most metals in the muck sediments occur predominantly in weakly mobile or nonbioavailable forms. Use of mucks in neutral pH upland soils should not pose any significant hazards or risk to the environment. However, Cd, Cu, Cr, Ni, Pb, Zn, and Co, especially Zn, Cu, and Pb, could be more readily released from the muck sediments under acidic soil conditions.