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Accumulation of Heavy Metals by Wetland Plants with Different Root Systems in a Karst Mountainous Area

20 kinds of wetland plant samples and their rhizosphere sediment samples were collected from Caohai in Guizhou Province to investigate the accumulation characteristics of heavy metals including Cu, Zn, Mn, As and Hg by these plants with different root systems in a Karst mountain area. The results showed that the accumulation coefficients of Cu, Mn, Zn, As and Hg by the wetland plants with taproot systems is 1.66, 1.50, 1.52, 1.64, and 1.56 times of those by the wetland plants with fibrous root systems respectively. Potamogeton lucens showed the highest accumulation capacity to Cu, Zn and Mn among the collected wetland plants with the average accumulation coefficients of 6.42, 2.93 and 1.34, respectively. Hydrilla verticillata presented a high accumulation capacity to Hg with an average accumulation coefficient of 3.27. None of the collected wetland plants met the criterion for super-accumulation plants. The results also indicated that the accumulation capacity of the heavy metals by the wetland plants was associated with the depth of their root penetrating into the sediment.