太湖流域源头南苕溪河口生态工程恢复及其初期水质净化效应

针对太湖流域源头溪流农业面源污染严重和生态拦截净化较弱的问题,采用生态工程措施于南苕溪人青山湖水库河口处对河道进行恢复.综合考虑山溪性河流水文水动力特征,通过构建、稳定和保护河口与滨岸带生态系统实现河道恢复目标.所采用关键技术包括:合金钢网石兜抛石技术、深潭-浅滩/塘-洼地组合净化技术、分流沙嘴技术、T-型乱石抛筑透水坝技术、河岸侵蚀面防侵蚀的浅滩沙洲场技术、植被缓冲带技术、水生植物恢复技术等.对河口生态工程区进行连续9个月的监测结果显示,工程区上段浅滩及分流沙嘴区能有效复氧,提升pH值并降低电导率,同时对总磷、活性磷和悬浮颗粒物有较好的去除效果;中段深潭区通过强化的微生物活性能有效去除铵态氮与亚硝态氮;下游T-型坝能较好地拦截并沉积河口冲刷物质,但需对其定期清理以防引发二次污染.河口生态工程运行初期较好地改善了河道结构并提升了河流自净能力,对河流生态恢复最具指示作用的水质指标溶解氧饱和度、铵态氮去除率在工程实施后较工程实施前平均分别提高了14.5％、14.7％.

Ecological engineering restoration at the confluence of South Tiaoxi Stream in the upper Taihu Lake and its water quality improvement

Headwater streams of Taihu Lake suffer from severe agricultural diffuse pollution and decreased ecological purification function. To improve this situation, several ecological restoration measures were implemented at the confluence of South Tiaoxi Stream in front of Qingshanhu Reservoir. Based on the hydrological and hydraulic characteristics of the stream, a design to establish stabilized ecosystems at the interior corridor and riparian zones was adopted. The techniques used in the program include alloy-steel wire gabion wrapping riprap, pool/riffle and pond/swale combinations, diverging barrier spit, permeable dam with riprap of T-type stones, sandbar field for prevention of riparian erosion, vegetated buffer strip, and aquatic macrophyte restoration. Monitoring of the water quality in the program area for nine months showed that the upstream riffle and overflow weir area effectively reoxygenated the water, increased the pH, reduced electrical conductivity, and removed suspended solids, soluble reactive phosphorus and total phosphorus. The middle pool area removed ammonium and nitrite well via enhanced microbial activity. With periodic cleaning, the downstream T-bars intercepted and deposited the floating materials and sediments from the confluence area. Overall, the confluence ecological engineering measures improved the river corridor structure and enhanced its self-purification capability, as indicated by the increased dissolved oxygen saturation degree of 14.5% and ammonia nitrogen removal rate of 14.7% at the confluence.