洞庭湖近30年水环境演变态势及影响因素研究

水量、泥沙和污染物交换作为河流与湖泊之间的关键过程，对湖泊生态环境演变具有复杂而深远的影响.以长江中游典型通江湖泊洞庭湖为研究对象，着眼于“江湖”“河湖”“人湖”三重作用关系变化，从水文情势、水质、富营养化3个层面剖析了近30年洞庭湖水环境演变态势及主控因素.结果表明:①“江湖”关系变化影响了洞庭湖水沙交换及其年内分配，是湖泊枯水期提前和延长、水沙关系突变等现象的主控因素；“河湖”“人湖”关系变化协同加剧了该现象.②“河湖”关系的失衡和“河湖”统筹管理措施缺位，造成入湖河流长期输送大量营养物质，是湖体氮磷污染较重的根源；“江湖”“人湖”关系变化协同影响着营养盐分布格局，但影响范围及程度有限.③在“江湖”“河湖”作用关系复合影响下，藻类生长条件更为有利，增加了洞庭湖富营养化及水华风险.为保障洞庭湖水环境安全，建议:针对“江湖”作用主导的低枯水位问题，以水资源调控为核心，推进长江与流域上游水库联合生态调度，保障湖泊生态流量；针对“河湖”作用主导的水质恶化问题，以水污染防治为核心，强化流域污染控制，统筹“河湖”一体化监测管理模式，保障湖泊水环境质量；对于“人湖”作用主导的生态破坏问题，以生态空间管控为核心，划定并坚守生态红线，保障生态空间. 

Trend and Driving Factors of Water Environment Change in Dongting Lake in the Last 30 Years

As a key process between rivers and lakes, the exchange of water, sediment and pollutant has a complex and profound impact on the ecological environment evolution of a lake. In this study, we chose Dongting Lake, a typical river connected lake in the middle reaches of the Yangtze River, as the research area. With a focus on the alteration of the 'Yangtze River-lake' 'tributaries-lake' 'human-lake' relationships, we tried to analyze the evolution trend and casual factors of the water environment in Dongting Lake during the past three decades from three aspects: hydrological regimes, water quality and eutrophication. The results indicated that: (1) The alteration of 'Yangtze River-lake' relationship has influenced the water and sediment exchange and its annual distribution progress in Dongting Lake, which is the main casual factor for an earlier and longer dry period, as well as the mutation of water and sediment relationship. Meanwhile, this phenomenon is aggravated by the change of 'tributaries-lake' 'human-lake' relationships. (2) The imbalance of 'tributaries-lake' relationship and the lack of integrated management measures of 'tributaries-lake' has led to the transport of large amount of nutrients from rivers to lakes for a long time, resulting in serious nitrogen and phosphorus pollution in Dongting Lake. Although changes in the relationship between the 'Yangtze River-lake' 'human-lake' have a synergistic effect on the distribution pattern of nutrients, the scope and extent of the impact are limited. (3) Under the combined influence of the 'Yangtze River-lake'tributaries-lake' interactions, the conditions for algae growth are more favorable. This increases risk of eutrophication and water blooms in Dongting Lake. In view of the problems of the lower water level that is mainly caused by the 'Yangtze River-lake' interaction, taking water resource regulation as the core, it is suggested to promote the joint ecological operation of the reservoirs in the upper reaches of the Yangtze River and tributaries to ensure the ecological flow of Dongting Lake. As to the water quality deterioration caused by the 'tributaries-lake' interaction, we should focus on water pollution prevention, strengthen the pollution control in river basin, and coordinate the integrated monitoring and management model of tributaries and lake to ensure the environment quality of the lake. For the ecological damage problem dominated by 'human-lake' interaction, it is suggested to take the ecological space management as the core, delineate and adhere to the ecological red line to ensure ecological space.