[Bioremediation efficiency of applying Daphnia magna and submerged plants: a case study in Dishui Lake of Shanghai, China].

From April 2007 to January 2008, a bioremediation experiment was conducted in a diversion channel of D-port pilot area of Dishui Lake (the channel length is 950 m, and its water volume is 10000 m3). Daphnia magna was first introduced to filter the high biomass of phytoplankton and other particulate organic matter, and then, five submerged plant species Elodea canadensis, Vallisneria spiralis, Hydrilla verticillata, Potamogeton lucens, and Potamogeton crispus were transplanted. Water samples were collected monthly to monitor the water quality and to investigate the bioremediation efficiency. Ten months monitoring data showed that in the remediation area, the water body's total nitrogen (TN), ammonium nitrogen (NH4(+)-N), nitrate nitrogen (NO3(-)-N), nitrite nitrogen (NO2(-)-N), total phosphorus (TP), and reactive phosphate (PO4(3-)-P) concentrations and chemical oxygen demand (COD) were significantly lower (P < 0.01), dissolved oxygen (DO) was increased by 50.4%, and the Secchi depth (SD) reached to an average of 3.4-3.7 m. Overall, the water quality was up to grades II or III of state water quality standards for surface water. In March 2008, the established submerged plant community was used to test its effectiveness in improving the eutrophicated water body from Dishui Lake, and the results showed that after 7-day treatment, except biological oxygen demand (BOD), the TN, TP, NO3(-)-N, NO2(-)-N, NH4(+)-N, and PO4(3-)-P concentrations and COD of the eutrophicated water were all decreased significantly, the DO was increased by 17.98%, and the SD was increased by 30 cm. The present study demonstrated the effectiveness of introducing D. magna and transplanting submerged plants in improving the water quality of Dishui Lake.