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Sediment Quality Assessment and Management: Insight and Progress Edited by M. Munawar© 2003 Ecovision World Monograph Series Aquatic Ecosystem Health & Management Society A physico-ecological engineering system to reduce the eutrophication in Wulihu Bay, Taihu Lake, China C. Hu*, J. Qian, G. Wang, W. Hu, P. Pu Taihu Laboratory for Lake Ecosystem Research, Nanjing Institute of Geography and Limnology, Chinese Academy of Sciences, 73 East Beijing Road, Nanjing 210008 China. * Keywords: sediment remediation, aquatic macrophytes Introduction Lakes have become environmentally deteriorated as a result of increased eutrophication (such as Taihu Lake, in China) and a lot of cities are seriously short of drinking water because of pollution. The eutrophication of Wulihu Bay in the northern part of Taihu Lake in China has developed so rapidly in the last 20 years that submerged macrophytes were extinct in this lake area. The water was very turbid, with most of transparency (SD) ranging between 0.25 and 0.45 m. The lake water had very high nutrient concentration, with NH4 +-N ranging between 3 and 19 mg l-1. The annual average concentrations of TN, NH+ 4-N, TP and chla were 6.621, 3.859, 0.167 mg l-1 and 64.93 mg m-3, respectively (Wang et al., 1999a). In order to harness eutrophic lakes, many research projects have been conducted for improving water quality and controlling eutrophication, such as biomanipulation. Biomanipulation was first put forward by Shapiro in 1975, then improved by many scientists, and popularized in Europe. Many researches tackled several facets of the ecological relationships within water bodies and provided suggestions for many different way of making the trophic chain works for the improvement of the water quality. However, many successful examples were usually shortdated. When the investigation region, object and compass changed, the same results and conclusions were difficult to be made, so biomanipulation should be improved (Shapiro, 1975; Smith, 1985; McQueen et al., 1986; Cooke, 1986; Benndorf, 1987; Shapiro, 1990; Carpenter and Kitchell, 1992; DeMefo et al., 1992; Benndorf, 1995; Perrow et al., 1997; Horppila et al., 1998.). Especially, it is not suitable in eutrophic 354 lakes in China, in practice.The method how water quality can be improved gradually, continuously and inexpensively has not been found by now. A Physico-Ecological ENgineering System (PEEN) was developed to provide an effective and inexpensive method to remove nutrients using aquatic vegetation (Pu, 1993, 1995b; Pu et al., 1995a, 1998a, 1998b; Zhang et. al., 1998; Wang et al., 1999a). PEEN improves water quality by constructing an optimum artificial ecosystem using aquatic macrophyte and solar energy. From 1996 to 1998, SD was above 100 cm in the enclosures of PEEN while it was below 50 cm in the open water area of the eutrophic lake. The average concentrations of TN, TP, NH4 +-N and chla in PEEN were 1.662, 0.074, 0.388 mg l-1 and 33.92 mg m-3, respectively, only 25.1%, 44.3%, 52.3% and 10.0% of those in the open water area. It has been proven that PEEN is one of the best effective methods for improving water quality in eutrophic lake. This study reports how PEEN affects on sediment, which was carried out in Wulihu Bay. Material and methods PEEN experiment was carried out in 1994 in the intake water area of Wuxi Zhongqiao Tap Water Plant in a eutrophic Wulihu Bay, northern Taihu Lake, China (Fig.1). PEEN mainly included two parts: physical engineering and ecological engineering. The physical engineering was made up of frame and soft wall. The soft wall made of nontoxic chemical fiber cloth with floater at surface and heavy anchor at the bottom. The ecological engineering was mainly to restore and restructure some keystone species for a healthy lake ecosystem. Fifteen species of macrophytes restored in PEEN can be divided into three ecotypes: floating, leaves-floating and submerged macrophytes. Most of macrophytes were restored in the enclosures of PEEN without harvested. PEEN was formed by 10 long-rectangular enclosures, each with an area of 5×40 m2, in which the original sediment and water quality were the same as that in the control sites (open water area) with less than 0.4 m sediment thickness on the loess layer, with about 2 m water depth. The sediment was covered with polythene film only in one enclosure (Zhang et al., 1998, Wang et al., 1999a). In 1994, 1996 and 1998, 102 cores of sediment had been sampled with a specialmade...


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