Abstract: Agricultural nonpoint source nitrogen (N) and phosphorus (P) losses are one of the major factors resulting in surface waters eutrophication, while understanding the fluxes and chemical forms of N and P in runoff is critical to control the eutrophication of water bodies. Vegetable field is a main land use pattern in Taihu Lake region, but its N and P losses haven’t been reported. In this paper, a field monitoring study of N and P losses with surface runoff was conducted, and the effects of grass buffer strip on reducing the export of N and P from vegetable field was investigated. The results showed that the runoff export of N and P from vegetable fields during the period from October 24, 2004 to August 17, 2005 was 3 010.9 g·hm^-2 and 695.0 g·hm^-2, respectively. In the runoff, particle N and P were the predominant fractions, which accounted for 64% and 75%, and NH₄⁺-N and H₂PO₄^- were the major forms of soluble N and P, occupying 50% and 87%, respectively. The average filtering efficiency of N and P was 42%-91% and 30%-92%, respectively, and the removal efficiency of particle N and P was higher than that of soluble N and P. The present study indicated that grass buffer strip could effectively control the N and P losses with runoff from vegetable fields.

Key words: Copper tailings, Heavy metal, Chemical forms, Zoysia japonica, Trifolium pratense