三峡前置库汉丰湖试运行年水文水质变化特征

汉丰湖是为解决三峡蓄水在重庆市开县(今开州区,下同)境内形成的38 km2消落带修建的前置库,因独特的"库中库"调控模式,季节性大范围消落区湿地、生活污染和农业面源污染源、城市和人口承载,具有特殊的水文特征及生态环境特征.2015年汉丰湖试运行期间,汉丰湖受三峡水位调控影响,兼具湖泊、河流、回水河湾等形态特征,结合水文形态变化特征和水质指标时间聚类分析,结果表明:(1)试运行年水文水质有4个特征变化时期:5~8月为T1(河流形态期),1月、3月和11~12月为T2(湖泊形态期),2月、4月和9月为T3(水位变动期),10月为T4(水华敏感期).(2)通过主成分分析和逐步回归分析发现汉丰湖水体富营养化在不同时期受不同主导成分影响,主成分累积贡献率在上述时期分别为82.93%、77.61%、78.32%、88.40%.T1时期主要水质影响指标为DP、TP、SD、pH;T2时期主要水质影响指标为TN、DN、DP、TP、NO_3~--N;T3时期主要水质影响指标为SD、NH_4~+-N、DN、T;T4时期主要水质影响指标为TN、DN、DO、NH_4~+-N、pH、高锰酸盐指数、H、NO_3~--N.(3)用主成分分析简化水质指标之间的相关性,以因子得分(score values)为自变量用于多元线性回归分析,结果发现各时期Chl-a与因子分值明显相关,T1时期Chl-a主要受水体氮含量影响,主要影响成分为PC2;T2时期Chl-a主要受水体氮、磷营养盐状态影响,主要影响成分为PC1;T3时期Chl-a主要受水深变化影响,主要影响成分为PC3;T4时期Chl-a主要受水动力影响,主要影响成分为PC3.综上所述,汉丰湖试运行期间频繁且大幅度的水位变动是其水文水质变化的重要影响因素.

Hanfeng Pre-reservoir Commissioning Time Variation Feature of the Hydrology and Water Quality in Three Gorges Reservoir

Hanfeng Pre-reservoir is very rare in the world which is specially designed to reduce the impact of Fluctuating Zone, and it is formed in Hanfeng Lake of Three Gorges reservoir. The Hanfeng Pre-reservoir has many special hydrological characteristics and ecological environment features based on its unique "pre-reservoir" control mode, the wide seasonal wetland of Fluctuating Zone, the huge life pollution and agricultural pollution, and the pressure of huge city and excessive population. HanFeng Lake has a variety of morphological features such as lakes, rivers, and other backwater bay, for the effect of water level regulation in Three Gorges, since the successful commissioning of the Hanfeng Lake pre-dam system in 2015. The change of Hanfeng Lake hydrology and water quality during the commissioning was divided into four periods by combining Hydrological and Morphological Variation characteristics with Water quality indicators time clustering analysis:May to August as T1 (river period); January, March and November to December as T2 (lake period); February, April and September as T3 (water level fluctuation period); October as T4 (algal blooms period) in 2015. Principal component analysis and stepwise regression analysis showed that Eutrophication of Hanfeng Lake was dominated by different dominant components at different times and the water quality index factor which has a significant effect on the Chl-a was also different. Cumulative contribution rates of principal components were 82.93%, 77.61%, 78.32%, 88.40% for each period, respectively. The main water quality indicators of T1 (river period) were DP, TP, SD, pH and the significant influencing index of Chl-a was PC₂, so Chl-a was mainly affected by water nitrogen content. The main water quality indicators of T2 (lake period) were TN, DN, DP, TP, NO₃^--N and the significant influencing index of Chl-a was PC₁, so Chl-a was mainly affected by water eutrophication including nitrogen and phosphorus nutrient status. The main water quality indicators of T3 (water level fluctuation period) were SD, NH₄⁺-N, DN, T and the significant influencing index of Chl-a was PC₃. so Chl-a was mainly affected by water level fluctuation. The main water quality indicators of T4 (algal blooms period) were TN, DN, DO, NH₄⁺-N, pH, permanganate index, H, NO₃^--N and the significant influencing index of Chl-a was PC₃. so Chl-a was mainly affected by flow rate and hydrodynamic conditions. As mentioned in the review, the frequent and significant water level changes during the commissioning of Hanfeng Lake were the important factors influencing the change of hydrological and water quality characteristics.