底泥疏浚对太湖内源及底栖生物恢复的影响

底泥疏浚对湖泊内源削减具有重要的作用,是富营养化湖泊内源治理的重要技术之一.以太湖疏浚区为对象,估算了近十余年疏浚对内源负荷的削减量,并评估了太湖北部竺山湖和梅梁湖的底泥疏浚效果.结果表明,太湖累计疏浚的4 200万m³底泥,共计清除了底泥中氮约6.26万t,总磷约1.83万t,有机质约117万t,相当于清除了蓄积于底泥中二十余年的外源污染物输入量.对于外源控制较好的梅梁湖,底泥疏浚后5 a内水质改善明显,随后出现反弹,但仍有效削减了表层底泥总氮和总磷含量.相反,对于外源输入仍较大的竺山湖,疏浚十余年后,底泥内源又回复到浚前水平.对竺山湖疏浚区开展了长达6 a的底栖生物群落跟踪评估,发现疏浚初期对底栖生物群落具有一定的影响,但浚后2 a,底栖生物密度与生物量等指标已接近浚前水平. 6 a后,疏浚区与未疏浚区的底栖生物群落多样性指数已无差别.结果也表明,底泥疏浚对湖体内源具有较好的控制效果,且疏浚效果维持程度与外源输入强度密切相关.此外,长期来看,疏浚区底栖生物群落依靠自恢复能力可达到浚前水平,疏浚不会对底栖生物群落结构造成影响.

Effects of Sediment Dredging on the Reduction in Sediment Internal Loading of Lake Taihu and the Self-recovery Ability of Benthic Organism

Sediment dredging has a great effect on the control of lake internal loading and is one of the important methods for lake internal loading management. In this study, the dredged area of Taihu Lake was used as the main object. An estimation of the reduction in whole lake internal loading of Taihu Lake in decade years was carried out. At the same time, we evaluated the effect of sediment dredging on the control of internal loading in the northern area of Taihu Lake (Zhushan Bay and Meiliang Bay). The results indicated that a total of 42 million cubes of sediment was dredged from Taihu Lake, and the total nitrogen, total phosphorus, and organic matter in the dredged sediment was estimated to be approximately 6.26×10⁴ tons, 1.83×10⁴ tons, and 11.7×10⁵ tons, respectively. This was roughly equal to the 20 years of external loading pollution accumulated in Taihu Lake. From a long-term perspective, sediment dredging could effectively increase the water quality of Meiliang Bay within five years and that where the external loading has been controlled effectively. However, the water quality of Meiliang Bay subsequently rebounded, but dredging still reduced the nitrogen and phosphorus content in surface sediment. On the contrary, dredging could not effectively control the internal loading of Zhushan Bay, which still had a large input of external loading. The amount of sediment internal loading recovered to the original level of the pre-dredging period. In a six-year-long period of continuous monitoring of the benthic organism community of Zhushan Bay, the results indicated that sediment dredging could cause negative effects on sediment dredging initially, but the density and biomass of the benthic organisms in the dredged area had later been recovered to the un-dredged level. There was no difference between the dredged and un-dredged areas with regard to the diversity indices of benthic organisms. The results of this study indicated that sediment dredging can effectively control the lake internal loading. However, the maintenance period of dredging effects was related closely to the input intensity of the external loading. In addition, sediment dredging did not have a large influence on the benthic organism community and could recover to the original level depending on self-recovery.