Pb and Mn mainly exist in residual fraction and oxidizable fraction in the sediment of Nansihu Lake and its main inflow rivers,which account for 95% and 70% of the content of Pb and Mn,similar to other unpolluted sediments.

• 各水体单元表层沉积物中Pb、Mn以残渣态和可氧化态为主；其含量占Pb、Mn含量的95%25、70%25左右；基本未受人为污染.