Conservation and Restoration of Wetlands to Improve their Natural Purification Function: A Case Study in Chaohu Basin

Abstract: The population growth and strong demand for food have led to the cultivation of many natural wetlands into farmland. These changes increase agricultural non-point source pollution, and they also reduce the natural wetland which can be used to purify organic pollution. The joint action of the two aspects makes the pollution problem more and more prominent in river/lake basins. This paper presents a scientific solution to improve local water quality by wetland conservation and restoration. The technical principle of the programme is improving water quality through wetland purification. The arable land and inhabitants are relocated from low-lying areas of the study basin. Then high-efficient wetland water circulation flow path is designed, the wetland animals and plant ecosystems with purification functions are reconstructed. The proposed programme was applied to the Nanfeihe delta wetland in Chaohu Basin, China. The case study area is 27.6km², consisting of 5 villages, 860hm² arable land, 12,000 inhabitants and 400 hm² fish ponds. The case study area is adjacent to the Nanfeihe River, which has annual runoff of about 500 million m³. The concentration of ammonia nitrogen (NH₄-N) in river water is 2.84 mg/l, and the total phosphorus (TP) is 0.96 mg/l. They are all exceed class V of Chinese surface water standard (NH₄-N ≦2.0 mg/l, TP ≦0.4mg/l). This study relocated nearly 10000 people from five villages in the study area. The farmland, fish ponds and the original natural wetlands were arranged into 6 wetland confluence areas according to the topography, which assumed the function of purifying the water quality of Nanfeihe River. The restored wetlands include streams (high-land, 300.4 hm²), marshes (middle-wetland, 1071.6 hm²), grass ponds (low-wetland, 414 hm²), central lake (215.7 hm²), woodland & village (758.3 hm²). The total investment is 0.929 billion RMB. Through wetland conservation and restoration, the water purification capacity of the case area has been greatly improved. The maximum daily capacity for treating polluted water from Nanfeihe river reaches 1.2 million t/d. The quality of the water that flows out of the wetland is better than class IV of Chinese surface water standard, for instance, NH₄-N=1.42 mg/l, TP =0.29mg/l.

Keywords: water pollution, restoration of wetland, natural purification function, organic pollution, Chaohu Basin.