| Algae blooms and degradation of aquatic macrophytes are currently worldwide pollution problems of eutrophic water. Restoration of submersed vegetation is generally considered as a long-term effective approach to improve the water quality of eutrophic lakes, and chitosan-modified soil has been used to rapidly improve the water quality in the recent years. In this study, an experiment with four treatments (the control, submersed macrophyte, submersed marcophyte + soil, and soil) was carried out in the hypereutrophic water (Meiliang Bay) in Taihu Lake during May to December in 2011, with the aim to explore a macrophyte-mediated approach to improve water quality and its ecological effects. The main results are as follows:1. The indices of water quality were measured in 3-day intervals. The results showed that the soil was effective to improve the water quality, with a decrease in the contents of TP by 74.6%, TN by 20.7%, PO4-P by 31.0%, Chl.a by 80.4% and an increased SD by 90.4% as compared to the control; the submersed marcophyte+soil treatment was the most effective to decrease the contents of TP (64.0%), TN (36.2%), PO4-P (28.6%), Chl.a (71.1%) and increased the SD (76.4%). The submersed marcophyte restoration alone did not improve the water quality. The submersed marcophyte+soil treatment was also the most effective one among the three treatments to decrease the contents of TN (15.6%), TP (61.7%), PO4-P (55.8%) and NH4-N (82.8%) in the sediment interstitial water from their initial value. The study implies that restoration of submersed vegetation with the aid of chitosan-modified soil be an effective technology to improve the water quality, although the effectiveness needs to be further evaluated on a long-term basis.2. The biomass of phytoplankton and zooplankton of all the treatments were dominated by Microcystis aeruginosa and Cyclops vicinus, respectively.58.5% of the algae were removed by the chitosan-modified soil and had no significant impacts on the community structure. Due to the food supply stress and predation of juvenile fish, the zooplankton biomass decreased dramatically under the macrophyte and soil treatments, and had some community structure diversity compared with the control except for the soil enclosures. In contrast with the macrophyte enclosures, the marcophyte+soil treatment successfully restored the submersed vegetation after the experiment with the coverage of 52.33%, and it survived during the algae blooms and improved the water quality. Based on the RDA of ecological, physio-biochemical indicators of V. natans and environmental factors in two treatments and correlation analysis of all the indexes, we found that V. natans in macrophyte treatments suffered from long-term low light and high TN, TP stress, and in the sublayer water of marcophyte + soil treatment it possibly had physiological threats caused by significantly increased nutrients and such as NH4-N, etc, released from algae decomposition.3. Our experiment results showed that chitosan-modified kaolinite soil dramatically improved the TN/TP ratio to more than 29. Advisable frequency of soil treatment was effective in algae removal effect and P adsorption, then successfully restored the submersed vegetation on the deposit. Thus we proposed a novel thought of solving the lake eutrophication problem followed these effects. But during the high algae blooms it should be applied with discretion. Besides, construction of the enclosures and measures for weakening wide wave and preventing outside water was necessary in the early days. |
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