The Pilot Studies And Large-scale Pilot Demonstration Of SF CWs In The Nansi Lake Basin

In this paper, the surface flow constructed wetlands (SF CWs) located at the Nansi Lake was studied to optimize the technical parameters of the constructed wetlands. Through the investigation of the large-scale wetland demonstration project as well as the evaluation of long-term performance, the study provides technical information and practical experience for the design and run of the SF CWs in the Nansi Lake or even in the areas with similar climatic.The optimization of the pilot wetlands showed that the suitable depth of SF CWs of the Nansi Lake was 50 cm and the suitable water distribution was gravel layer. The biological island was available in the open water. The water depth, the way of water distribution and the biological island all affected the purification ability of the wetlands by influencing the photosynthesis of the plants and the dissolved oxygen conditions. The plants made great contributions to the removal of nutrients. About 19-26% of nitrogen and 31-37% of phosphors were removed by the plants. The uptake of plants was the dominant way of P removal and microbial process was the main removal way of nitrogen.The flooding stress of 8 kinds of wetlands plants was also studied,and the result showed that the height of plants increased and the leaves became longer and thinner with the increasing of the water depth. And amount of adventitious roots was generated. The plant biomass and water content firstly increased with the increase of water depth and then decreased. The biomass reached the peak when the water depth was 50 cm and the water content reached the maximum at the depth of 90 cm. When the water depth was higher than 140 cm, the contents of chlorophyll a, b, carotenoids and soluble sugar reduced with the water depth increasing. It was suitable for the onion and iris when the water depth was 20 cm. The depth of 50cm was suitable to plant reeds, water onion, Jing Sparganium, Typha and Iris and depth of 90cm was suitable for planting Jing Tri, cattail, wild rice stem, iris and iris. The water peanuts would grow well when the water depth was 200 cm.The long-term performance of the wetlands was evaluated and the results showed that the purification ability of the Xinxue River's constructed wetlands was satisfied. The removal efficiencies of COD, ammonium, total nitrogen and total phosphorus were 40%,55%,50% and 34%, respectively. The water quality of the Xinxue River basically reached the standard III of the groundwater, which was satisfied with the requirement of Nansi Lake. The impact of the Xinxue River constructed wetlands on the ecological restoration was significant and the biodiversity was improved. The plant species in the demonstration area increased to more than 50, and the index of species richness, Simpson, Shannon-Wiener and Pielous reached to 10,0.7,1.5 and 0.7 from 4,0.35,0.63 and 0.47, respectively. The environmental benefit in the demonstration area was improved significantly. It removed 78.69 tons of COD,8.03 tons of ammonium,43.36 tons of TN and 0.32 tons of TP per year on average. The wetlands brought great economic benefits for increasing the income of the farmers from￥400-500 yuan to more than￥700 yuan per mu. Xinxue River's constructed wetlands provide a reliable experience for the restoration of the typical rivers in northern of China. It also made an example for the restoration of the local environment and the control of the water pollution.