中国北方再生水修复河道的水文变化及其生态效应

Using reclaimed water to recharge rivers is an effective measure to alleviate the ecological crisis for urban rivers and lakes. Rapid changes of water quality and quantity for river restoration caused by reclaimed water inevitably have significant impacts on river environment and aquatic ecosystems. The project selects Miyun, Huairou and Shunyi in the Chaobai River, Beijing as the study areas to (1) analyze the spatial and temporal evolutions of the surface water hydrology and environment of rivers restored by reclaimed water, (2) clarify the influences to the groundwater table and water quality due to river restoration by reclaimed water, (3) reveal migration and transformation mechanism of the typical pollutants in the river sediments and vadose zone media, (4) simulate the changes of hydrological processes through the quality and quantity coupling models, (5) establish the ecological response relationships between reclaimed water quality and aquatic organisms and reveal the ecological response relationship and interaction mechanism between physicochemical indexes and aquatic organisms for river restoration by reclaimed water, and (6) determine the ecological flow and nutrient thresholds for river health, and thus propose an ecological restoration mode of "ecological flow + aquatic organisms→ecosystem health assessment" for river restoration using reclaimed water. This study could provide scientific basis for river ecological restoration and water resource sustainable use.

利用再生水补给河道是缓解城市河湖生态危机问题的有力措施。再生水用于修复河道引起的水质水量快速变化，必然对河道水环境和水生态系统产生显著影响。本项目选择北京潮白河密云、怀柔、顺义段为研究区域，分析再生水修复河道的地表水水文水环境时空演变过程；阐明再生水修复河道对地下水水位、水质的影响行为；揭示再生水特征污染物在河床底质及包气带介质中的迁移转化机理；通过水量-水质-水生态耦合模型，模拟再生水修复河道的水文变化过程；建立再生水水质与水生生物之间的生态响应关系，揭示再生水修复河道的理化指标与水生生物之间的生态响应关系和作用机制；确定再生水修复河道的生态流量和营养盐阈值，进而提出再生水修复河道的“生态流量+水生生物→生态系统健康评价”的生态修复模式，通过本项目的研究，为河道生态修复和水资源可持续利用提供科学依据。

利用再生水补给河道是缓解城市河湖生态危机问题的有力措施。再生水用于修复河道引起的水质水量快速变化，必然对河道水环境和水生态系统产生显著影响。本项目选择北京潮白河密云、怀柔、顺义段为研究区域，分析再生水修复河道的地表水水文水环境时空演变过程；阐明再生水修复河道对地下水水位、水质的影响行为；揭示再生水特征污染物在河床底质及包气带介质中的迁移转化机理；通过水量-水质-水生态耦合模型，模拟再生水修复河道的水文变化过程；建立再生水水质与水生生物之间的生态响应关系，揭示再生水修复河道的理化指标与水生生物之间的生态响应关系和作用机制；确定再生水修复河道的生态流量和营养盐阈值，进而提出再生水修复河道的“生态流量+水生生物→生态系统健康评价”的生态修复模式。重要结果包括：（1）Chl-a河道沿程分布主要受控于河道水力条件，空间上Chl-a与河水NO3-N、pH存在强互馈关系，藻类生长显著影响河道地表水水质；（2）提出了基于潜在水源同位素线（PWL）的河岸带柳树茎水氢同位素偏移的校正方法；（3）再生水补给增加了底泥反硝化细菌，表层底泥主要通过有机氮合成去除NO3-N，深层底泥主要通过反硝化反应去除NO3-N；（4）再生水补给对受水区水质影响明显，含水层深度越浅，影响越大；距离北部水源地越近，影响越大。（5）再生水影响了芦苇C、N计量特征的空间变化，相较于根和茎，芦苇叶对环境的响应最为显著，且再生水主要影响了鲫鱼肌肉的δ15N值；（6）再生水修复河道典型断面藻华发生的阈值条件为TP > 0.035 mg/L和NH4-N > 0.17 mg/L，当河水NO3−N浓度高于20 mg/L时，河岸带地下水将面临氮污染风险，地表水、地下水、底泥的生态风险熵大于1，对水生生物具有高生态风险。通过本项目的研究，为河道生态修复和水资源可持续利用提供科学依据。