Temporal and spatial variation of water quality in Yuqiao Reservoir induced by water diversion project

Abstract

研究输水对水库水质时空变化的影响有助于科学预测水体富营养化及防控水华暴发.本文以于桥水库为例，基于2011-2015年实测资料分析入库水质——水温、总氮（TN）、总磷（TP）与流量的相关关系；并以2012年为典型年，运用平面二维水动力-水质数学模型模拟库区水质变化随入库流量的响应关系.研究表明：（1）11月-次年4月水库水温受气温控制，入库与库区水温差异不明显；5-10月，非输水期库区上游水温最高，输水期入库温差随流量增大呈线性升高趋势，库区上游水温明显降低且出现谷值；（2）营养物（TN、TP）浓度变化规律全年基本一致，非输水期入库TN浓度高、TP浓度低，营养物在果河段汇集，库区营养物衰减浓度降低且浓度梯度平缓；输水期入库TN浓度随流量增大呈幂函数降低趋势、TP浓度呈线性升高趋势，营养物被输移至库区上游导致库区TN、TP浓度升高且浓度梯度增大；（3）库区水温谷值及TN、TP浓度峰值均滞后于果河流量变化，且库区南岸比北岸更易受果河来流影响污染更严重.;Studying the temporal and spatial variation of water quality in a reservoir is beneficial for forecasting water eutrophication and preventing algal bloom. Taking Yuqiao Reservoir (YQR) as a case in this paper, the relationship between the inlet water quality -temperature, total nitrogen (TN), total phosphorus (TP) and the inlet discharge was analysed according to the observed data from 2011 to 2015. The response of the water quality in YQR to the inlet discharge was also modelled during the 2012, by utilizing a 2D hydrodynamic and water quality model. The results indicate that from November to April, the water temperature is controlled by the atmosphere, and there is no obvious difference between the inlet temperature and the temperature in YQR. From May to October, during non-water-diversion period, the temperature in the upstream of YQR is the highest. During water-diversion period, the temperature difference presents a linear increasing trend along the inlet discharge, and the temperature in the upstream of YQR decreases and reaches the minimum value. The variation of the nutrients (TN & TP) concentrations is basically consistent throughout the year. During non-water-diversion period, there is a high concentration of TN with a low concentration of TP in Guoheqiao. Meanwhile, the nutrients gather in Guohe section, but decay in YQR with a small concentration gradient. During water-diversion period, the TN concentration presents a decreasing trend of power function, but TP concentration presents a linear rising trend. At the same time, the nutrients are transported to the upstream of YQR, which causes the TN & TP concentrations and the concentration gradient increasing in YQR. In addition, the minimum value of water temperature and the peak values of TN & TP concentrations lag behind the change of the discharge from Guohe River. The south bank is more vulnerable to the incoming flow of Guohe River than the north bank, where has suffered more serious pollution.