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One of the major problems of water pollution that we faced as whole world is eutrophication. Today, more than 90% of all the lakes in China have become or becoming eutrophication. Too much nutrients in water body leads to the algae multiplying excessively, and finally causes the eutrophication. The eutrophication is the presentation of the senescence of water body and the worse of water quality. Cultivating higher plants on the water surface is one of the effective roads to purify eutrophic water bodies.The ShuangLong Lake lying in YuBei district, ChongQing, because of too much waste water inflowing, has been become eutrophication. Higher plants were transplanted on floating-bed for removing nutrients from water by absorption and adsorption of plants. The results of preliminary experiment show that purifying eutrophic ShuangLong Lake with higher plants is actable and effective. Cyperus alternifolius.L , Oenathe javanica DC. and Ipomoea aquatica Forsk grew well and the static removal rates of TN, TP and chlorophyll-a were 62.21%,59.58%,32.66%,50.58%,35.49%,10.67%,67.26%,72.28%,39.3%, respectively. In lab test, the effect of Ipomoea aquatica Forsk purifying eutrophic water was best, but in dynamic experiment the purifying ability of Cyperus alternifolius.L is stronger than Ipomoea aquatica Forsk. So Cyperus alternifolius.L is decided to renovate the ShuangLong Lake.The medial-scale experiment was carried out on the surface of ShuangLong Lake for the purpose of researching the renovation effect of Cyperus alternifolius.L farther. The results of medial-scale experiment show that Cyperus alternifolius.L was adapted to grow on the water surface, and during the period of more than 3 months, the average of weight adding rate reached 72.1%. The water purification of Cyperus alternifolius.L has an action radius. In the action radius, water quality picks up gradually as the distance decrease, in other words, the purification ability of Cyperus alternifolius.L reduces gradually as the distance growing. For example, the TN at 25m,15m and 5m far away Cyperus alternifolius.L are 3.347mg/l,3.313 mg/l and 3.263 mg/l ; the TP at 25m,15m and 5m far away Cyperus alternifolius.L are 0.257mg/l、0.241mg/l and 0.23mg/l; and the Chl-a at 25m,15m and 5m far away Cyperus alternifolius.L are 19.973mg/m3,16.721 mg/m3 and 14.083 mg/m3. Through the analysis, it can be seen that the mechanism of higher plants renovating water body includes plants absorbing nutrients, roots adsorbing<WP=6>the suspension and colloid and assisting suspension and colloid settling.
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