Abstract:

To understand the change characteristics of heavy metal concentrations in farmland drainage and their influencing factors, the representative farmlands of paddy field, orchard, vegetable field and nursery field were selected from Hangzhou. The authors sampled and analyzed the concentrations of water-soluble cadmium, cobalt, chromium, copper, iron, nickel, lead, zinc and manganese in the runoff drainage caused by rainstorm, and compared them with the status of heavy metals in urban runoff drainage. The analysis results showed that the soluble concentrations of different kinds of heavy metals in the farmland runoff water during the rainstorm were quite different. The average concentrations of the metals were as follows: cadmium (0.19 μg/L) < cobalt (0.46 μg/L) < chromium (1.04 μg/L) < nickel (1.73 μg/L) < lead (4.98 μg/L) < copper (88.47 μg/L) < zinc (184.52 μg/L) < manganese (609.52 μg/L) < iron (1135.21 μg/L). The concentrations of copper, zinc, manganese and iron in the runoff water were significantly higher than those of other metal elements. Except manganese and iron, the concentrations of heavy metals in farmland runoff water were low, which could basically meet the requirements of Class I and II surface water quality. Statistical analysis showed that the concentrations of soluble heavy metals in surface runoff water were affected by land use. The concentrations of iron and manganese were the highest in paddy field runoff, the concentration of copper was the highest in orchard runoff, and the concentrations of cadmium, cobalt, chromium, nickel, lead and zinc were the highest in the urban regions runoff. The correlation analysis showed that the concentrations of heavy metals in the surface runoff water were mainly negatively related to soil pH, and positively related to the total and water-soluble contents of the soil heavy metals, but they were not significantly related to the soil cation exchangeable capacity, organic matter content and clay content of the soils. The contents of heavy metals in the surface runoff were mainly affected by the degree of soil heavy metal pollution and pH. The concentration of heavy metals in the surface runoff from the normal farmland did not have a significant impact on the surface water quality.

Key words: Farmland, Surface Drainage, Heavy Metals, Land Use, Soil Acidity