鄱阳湖水量平衡变化的水环境效应与调控

Since the 21st century, concomitantly impacted by the drought condition with low precipitation and the water impoundment of the Three Gorges reservoir, Poyang Lake continuously presented extremely-low water levels, decreasing water environmental pollutant-carrying capacity and water quality deterioration. These issues will potentially influence the water supply safety in the Poyang Lake area and the mid-lower Yangtze River reaches. This study will be initiated from the point of view of the relationships between hydrological regime and nutrients' spatio-temporal distribution among the Poyang Lake, "Five rivers" and the Yangtze River. Based on the analyses of the dynamic relationships between the dry-wet conditions induced by climate and water levels of the Poyang Lake, the alterations of water balance and water level in the Poyang Lake within different types of hydrological years will be investigated. With the monitoring of river-lake hydrology, hydrodynamics and water quality, this study will also reveal the changes of nutrients in-out, detention and deposition processes affected by altered water balance of the Poyang Lake. Considering the water level, water velocity, water renewal time period and nutrient sources, the effects on spatial distribution of nutrients and their magnitude induced by these factors' interaction will be disclosed. A hydrodynamic and water quality model will be set up for the Poyang Lake. The responses of nutrient spatial distribution and algae growth to the alteration of water balance will be simulated and evaluated. The dominant factors triggering the water quality change will be indicated, on the basis of which some scenarios will be established for water regulation. The amount of nutrient reduction will be quantified, and the pattern and intensification of water environment influenced by water level regulation of lake mouth will be disclosed. Integrated strategies for maintaining the pre-defined water functions will be formed for Poyang Lake.

在干旱少雨气候背景和三峡蓄水运行共同影响下，21世纪以来鄱阳湖出现了持续超低水位，导致水环境容量下降和水质恶化，对鄱阳湖地区以及长江中下游供水安全造成威胁。本研究从鄱阳湖与"五河"及长江的水文与营养盐联系出发，分析气候丰枯与鄱阳湖水位变化特征，开展河湖水文、水动力和水质监测，研究不同类型水文年鄱阳湖的水量平衡过程及水位变化特点，测算水量平衡影响下鄱阳湖营养盐收支平衡与降解特征，综合分析鄱阳湖水位、流速、换水周期、营养盐来源对营养盐浓度空间分布的影响，建立水动力与水质模型，模拟并评估鄱阳湖营养盐分布及藻类生长对水量平衡变化的响应过程，揭示近年来鄱阳湖水质变化的主控因素，并通过设定情景探讨营养盐污染削减量与湖口水位调控对水环境的影响方式和强度，提出保障鄱阳湖水功能目标的综合优化方案。

在干旱少雨气候背景和三峡蓄水运行共同影响下，21 世纪以来鄱阳湖出现了持续超低水位，导致水环境容量下降和水质恶化，对鄱阳湖地区以及长江中下游供水安全造成威胁。因此迫切需要揭示鄱阳湖水文条件变化对水环境变化的影响机制，解释当前鄱阳湖水环境变化原因以及预估未来可能的变化。本研究采用气象和水文时间序列统计，河湖水文、水动力和水质监测，水文和水动力建模等方法，开展水量平衡变化对鄱阳湖水质的影响研究，结果显示： 2003年以来干旱少雨叠加长江上游水利工程共同影响导致鄱阳湖水文节律发生显著变化，江湖水量交换变化并导致鄱阳湖枯水期延长。鄱阳湖流域“五河”入湖氮污染物量占82%，2000年以来生活污水等点源有增长趋势，面源未呈现增长趋势。由于枯水期湖泊水位低、降解能力弱，水环境容量少，加之点源污染增加，是枯水期延长背景下水质下降的主要原因。鄱阳湖作为长江通江湖泊，水文和水量平衡可分枯水期（11月-次年2月）、涨水期（3-7月）、丰水期（8-10月）三个阶段，综合分析鄱阳湖水位、流速、换水周期、营养盐来源对湖体营养盐浓度空间分布关系，揭示出枯水期低水位且流速快，呈现河流相特征，水体更新速率较快，虽然氮磷污染指标高，但藻类生长受低温和流速快抑制；涨水期高水位且流速快，水体更新速度进一步加快，氮磷污染浓度仍然较高，但高流速和快速换水不利于藻类生长和累积；丰水期高水位流速慢，但入湖氮磷少，藻类生长受到氮磷低营养的抑制，这种组合特点形成了通江湖泊对藻类水华的抑制机制。维持鄱阳湖通江的特点对鄱阳湖藻类水华控制具有重要意义，建闸增加春季蓄水，减少湖流流速，而同期氮磷污染浓度最高，有可能会引发富营养化加剧和藻类水华爆发的问题。