| Water pollution is a main factor causing short water supply, and water eutrophication is a worldwide phenomenon, become the most difficulty in environmental remediation for water pollution. Understanding the mechanisms of eutrophication of water body and develop feasible remediation technology is the frontier and hot research field in plant nutrition and environmental ecology. As a new, cheap and ecological sound technology, phytoremediation of eutrophicated water system attract many scientists all over the world . The objectives of this study were : to analyze the factors causing eutrophication in Mu Ge Hu resevoir of Thai Lake catchment, investigate on the strategies for controlling and remediating water eutrophication in Mu Ge Hu resevoir, compare the effectiveness of different aquatic plant species on remediating eutrofication water body under simulated conditions. The aquatic plants species used included: Eichhornnia crassipes, Ceratophyllum demersum L., Myriophyllum verticillatum L, Potamogeton maackianus A.Bennett, Potamgeton malaianus Miq., Vallisneria spiralis L The major comparisons and observations made were: 1) The efficiency of growing aquatic plants on decontaminating the eutrophicated in low temperature season; 2) The changes and transfer of nutrients in the soil-plant-water system; 3) Effects of growing aquatic plants on the regulation of nutrient release from the lake sediment; 4) The seasonal change of aquatic plants in low or high temperature season; 5) The key techniques for phytoremediation on the eutrophicated water sysytem. The main results obtained are summarized as follows:1. By survey and investigation on the causes of eutrophication in Mu Ge Hu reservoir, it was found that the degradation of eco-system of the catchment was the main cause of eutrophication in the rswervoir. The major factors causing eutrophication of Mu Ge Hu Reservoir included N and P non-point pollution from agricultural practices, industry pollution and daily life pollution. The industry pollution may be controlled by changing their structureand move out the pollution township-industries. The pollution caused by daily life and agriculture must be controlled by ecological engineering technology, including setting up the healthy eco-system, recovering the forest and the river eco-system, as well as introducing physical-ecological engineering on the water system. It was observed that the best time for the physical-ecological engineering to apply in the catchment was during the abundant water period. After application of physical-ecological engineering, the contents of nitrogen and phosphorus at the 2 stations were lower than that before application. The content of total nitrogen in the entrance and the center of the reservoir decreased to 86.3 % and 48.9% , and the phosphorus content decreased to 31.8%t and 53.5 % of that before application, separately.2. In low temperature season, all the 6 aquatic plant species showed effective ability in decreasing total nitrogen, nitrate nitrogen and phosphorus in the eutrophicated water body. Different plant species had different effectiveness. The values of COD decreased in short period (10 days) but recovered afterwards. Growing aquatic plants in the eutrophicated water body increased water transparency and improved the water quality in the low temperature season. These results indicated that aquatic plants can decontaminate the polluted water. Selecting suitable plant species is critical. In this 'study, Myriophyllum verticillatum L. ,Potamogeton maackianus A.Bennett ,Ceratophyllum demersum L.) can survive in winter, which could be firstly chosen for phytoremediation engineering.3. The aquatic plants could also control nitrogen release from the sediment. In the polluted water system, the nitrogen release from the sediment could resulted in the increase of total nitrogen in water body. Sediment rapped by plastic sheet could stop nitrogen release in short period, but could not in longer time period, and N release peaked after the sediment was covered for 20 days. Either with... |
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