Shallow lake limnology and control of eutrophication in Lake Taihu

自2007年无锡暴发饮用水危机事件以来，太湖经历了前所未有的高强度、大规模治理，各种治理措施累计投资已经超过千亿元.监测显示，在治理初期太湖的氮、磷浓度下降明显，水质有所好转，但最近几年关键水质指标总磷与浮游植物叶绿素a浓度出现了波动，蓝藻水华有所反弹.研究表明，太湖的外源负荷并没有减少，这与城镇用水量增加、污水排放标准偏低、面源污染削减不足有很大的关系；同时，内源负荷也因为蓝藻水华的持续而加重，浅水湖泊水深浅、扰动强的特点强化了磷的循环利用效率，加剧了内源负荷对湖泊富营养化和蓝藻水华的影响.气候变暖叠加营养盐富集的复合效应、流域风速下降以及暴雨事件频次和强度增加等气象水文条件变化，都促进了太湖蓝藻水华的暴发；蓝藻水华的时空分布特征则受湖泊水动力的决定性影响.太湖治理的曲折过程，凸显了大型浅水湖泊湖沼学研究的不断深入与发展，未来需要继续加强多学科交叉研究，特别是基于湖泊-流域系统的气象水文、生物地球化学和生物生态学的学科交叉.对于太湖生态环境的综合治理和管理，既要注重湖泊与流域相结合，更需要重视自然科学和人文科学的有机融合，才能真正达到控制太湖富营养化、维护流域水环境安全与社会经济可持续发展的目标.;Unprecedented high intensity and large-scale restoration have been conducted in Lake Taihu since 2007 when the water crisis happened in Wuxi, and the cumulative investment of various governance measures has exceeded 100 billion RMB. As the long-term monitoring indicated, the nitrogen and phosphorus concentration in Lake Taihu decreased significantly and the water quality improved during the first few years. However, the water quality fluctuated and cyanobacteria bloom rebounded during the recent years. Studies implied that the external loading of nutrients did not decrease in Lake Taihu, which was largely related to the increase of urban water consumption, low sewage discharge standard and insufficient reduction of non-point source pollution. Meanwhile, the internal loading was aggravated by continuous cyanobacteria blooms. In addition, the impact of internal loading on lake eutrophication and cyanobacteria blooms was hence exacerbated in the case that the characteristics of shallow lakes as small water depth and strong disturbance are in favor of the efficiency of phosphorus cycling and uptake. The intensity and frequency of cyanobacteria blooms, of which the spatial and temporal distribution is determined by lake hydrodynamics, were aggravated by the combined effects of climate warming and nutrient enrichment, and changes in meteorological and hydrological conditions such as the decrease in wind speed over the lake catchment and the increase in the intensity and frequency of rainstorm events. In order to control the eutrophication of Lake Taihu, ensure the water environment security and maintain the sustainable development of society and economy, we should combine the lakes and basins as a whole, and should be conscious of importance to the combination of natural science and technology, the humanities and management.