嘉兴市南湖生态环境修复工程的系统构建与效果评价

为改善嘉兴南湖水体质量，恢复湖区生态系统，实现南湖水质、生态及景观的全面提升，在分析南湖水质问题和水体浑浊成因的基础上，采取外源污染控制、内源污染清除和原位生态修复的方法，构建了南湖水下生态系统，并对南湖的生态修复效果进行评价分析。结果表明：南湖主要水质指标(COD、NH₃-N、TP)基本达到地表水Ⅲ类(湖泊标准)，湖区大部分区域水体透明度达到80 cm以上，水体颜色由黄色变为浅绿色；超磁分离一体化设备可以显著去除水体中的TP(去除率为92.61%)，对NH₃-N(去除率为37.94%)也有一定的去除作用，但是对TN、COD等的去除不明显；以“沉水植物”为主体的水下森林生态系统对悬浮型颗粒物具有明显的去除作用，沉水植物种植区域悬浮物下降值为42.09%；环保绞吸疏浚与土工管袋干化相结合的技术，减少了疏浚过程中的底泥再悬浮，土工管袋干化后的尾水采用超磁分离一体化设备二次处理，悬浮物SS指标均不超过4 mg·L⁻¹，实现了疏浚土尾水的达标排放。嘉兴南湖生态环境修复工程(一期)项目的成功实施，验证了超磁分离一体化工艺、环保绞吸疏浚与土工管袋干化、水上抛投沉水植物种植等技术的有效性。本研究成果可为平原河网水系、开放性水域、高浊度水体的城市湖泊生态修复提供借鉴和参考。

System construction and effect evaluation of Nanhu lake ecological environment restoration project in Jiaxing,China

In order to improve the water quality of Nanhu lake in Jiaxing, restore the ecosystem of the lake area and realize the overall improvement of water quality, ecology and landscape of the lake, based on the causes analysis of water quality problems and water turbidity, the underwater ecosystem of Nanhu lake was constructed by using external pollution control, internal pollution removal and in-situ ecological restoration, and the corresponding ecological restoration effect was also evaluated and analyzed. The results show that the main water quality indexes (COD, NH3-N, TP) of Nanhu lake basically met the class III (Lake standard) of surface water, the transparency of water body in most areas of the lake area reached more than 80 cm, and the color of water body changed from yellow to light green. The integrated equipment of super magnetic separation could significantly remove TP with the removal rate of 92.61%, and could also remove NH3-N with the removal rate of 37.94%, but could not obviously remove TN and COD. The underwater forest ecosystem with "submerged plants" as the main body had an obvious removal effect on suspended particulate matter. The decrease rate of suspended particulate matter in submerged plant planting area was 42.09%. The combination of environmental protection cutter suction dredging and geotube bag drying technology could reduce the resuspension of sediment in the dredging process. The tail water after geotube bag drying was treated twice by the integrated equipment of super magnetic separation, and the SS index of suspended solids was no higher than 4 mg·L−1, realizing the standard discharge of tail water from dredged soil. The successful implementation of Jiaxing Nanhu ecological environment restoration project (phase I) verified the effectiveness of the integrated process of super magnetic separation, environmental protection wringing and suction dredging and geotube bag drying, and the throwing-planting of submerged plants over water. The research results can provide a reference for the ecological restoration of water system of river network in plain, open water region and urban lake with high turbidity water.