Bioavailability of heavy metals in aquaculture pond sediments with submerged plants

Abstract:

This paper is aimed at restoration of aquaculture pond sediments with submerged plants. We chose plastic boxes to make a terrarium and selected three kinds of submerged plants, namely Vallisneria, Potamogeton crispus and Hydrilla verticillata to plant on sediments.Then we investigated the total contents and occurrence characteristic of heavy metals(Cu, Zn, Pb, Cd, Hg, As, Cr) in sediments and analyzed their bioavailabilities. Results showed that the contents of heavy metals in aquaculture pond sediments were rather high, which may lead to high ecological risk. After planting submerged plants, we found that the contents of heavy metals in sediments were lower and their ecological risks were reduced. Compared with all heavy metal elements, we discovered that submerged plant restoration showed a good removal effect on Cu, Pb, Cd and Hg, while it appeared poor to Cr in sediments. There are different restoration effects between submerged plants which lived in different seasons. Cluster Analysis showed that submerged plants that grew in spring and summer can obtain a better restoration effect to Cd, As, Cu, Zn, Pb, while overwintering plant can reduce the content of Cr more efficiently. Speciation analysis on heavy metal in sediment reflected that bioavailability fraction contents of Cu, Cd and their mobility factor(MF) were higher before planting submerged plants. After restoration, the bioavailability fraction contents and MF of Cu, Cd increased significantly compared with the others. Besides, it showed extremely significant correlation(P<0.01) between the bioavailability fraction contents of heavy metals and their MF to the removal rate of heavy metal. In conclusion, the bioavailability and MF of heavy metals in sediment can effectively characterize the removal effect of heavy metal restoration with submerged plants.