金盆水库汛期高浊水径流的潜入及热分层水体水质响应

Water-quality responses of the intrusion of high-turbidity runoff to the thermal stratified Jin-pen Reservoir during flood season

以西安金盆水库为研究对象,在汛期通过对河流区至库区的水温、浊度、DO和营养盐等水质指标进行连续监测,探究降雨径流的潜入规律及热分层水体水质动态响应特性.结果表明:在外界气温变化条件下,水库出现季节性热分层现象.汛期径流的汇入导致下温跃层消亡,热分层稳定性减弱;汛期径流水体携带大量颗粒态营养盐物质和泥沙以异重流形式潜入,其流态从过渡区的底层潜流向主库区间层流转变,潜入初期间层流厚度达20m.降雨早期异重流的潜入导致中下层水体的TN、TP、TOC显著增加,水体平均TN、TP、TOC、浊度最高分别超出平时0.2,2,0.6,16倍,水质呈现短时高污染负荷.底层潜流水体水温较高,大量沉降于沉积物中的颗粒态污染物分解速率加快,內源污染负荷进一步提高,底层水体中TN、TP、TOC浓度高达1.88,0.05,4.6mg/L;汛期可通过分层取水方案和排放高浊水来保障供水安全.

To explore the intrusion pattern of rainfall runoff and the corresponding water-quality response, vertical water-quality monitoring in Jin-pen Reservoir of Xi＇an City in China was implemented daily in the flood season. The results show that the seasonal thermal stratification occurs in the reservoir due to the change of air temperature. Storm runoff events in flood season damaged the structure of thermocline in the lower layer and weakened the stability of thermal stratification. Rainfall runoff, containing a large amount of particulate nutrients and sediments, entered the reservoir in the form of density current, which changed from underflow to interflow between transition zones and lacustrine zones, and the thickness of interflow was 20m during the early period of current intrusion. The concentrations of TP, TN, TOC increased significantly due to the intrusion of density currents in the middle and lower of water, with the highest concentration of TN, TP, TOC and turbidity was 0.2, 2, 0.6 and 16times higher than that in normal condition, resulting in serious water body pollution in short time. The decomposition rate of particulate pollutants settled in sediments increased due to the intrusion of higher temperature water in bottom, leading to a continuous increase of the endogenous nutrient loads in the reservoir, i.e., the concentration of TN, TP, TOC in bottom water was up to 1.88mg/L, 0.05mg/L, 4.6mg/L, respectively. Managers can take water from different layers of the reservoir and discharge high-turbidity current to ensure drinking water quality in flood season.