潘家口水库热分层期溶解氧垂向分布及影响因素

为探究水库热分层对溶解氧垂向分布的影响，2019年8月在潘家口水库设置监测平台，分别采用YSI-EXO2监测仪和NISKIN采样器进行监测和水样采集，测定库区水温、溶解氧、pH、浮游植物等水质指标的垂向分布，分析水体热分层期溶解氧垂向分布的影响因素及溶解氧极小值（MOM）的形成原因。结果表明：潘家口水库8月存在显著热分层现象，水温呈混合层-温跃层-滞温层结构。混合层溶解氧浓度大于6.5 mg/L；温跃层受热分层等影响显著，层内出现MOM，梯度明显增大，浓度显著减小；滞温层溶解氧逐渐恢复。相关性分析表明：溶解氧与水温和浮力频率显著相关，热分层是MOM形成的主要物理因素；溶解氧与浮游植物生物量和pH呈正相关，温跃层浮游植物的呼吸作用、营养物质的积累和有机物质的氧化分解等生物和化学因素在一定程度上促进了MOM的发展。

Vertical distribution and influencing factors of dissolved oxygen during thermal stratification in Panjiakou Reservoir

In order to explore the effect of reservoir thermal stratification on the vertical distribution of dissolved oxygen(DO), a monitoring platform was set up in Panjiakou Reservoir in August 2019. For monitoring purposes, YSI-EXO2 monitor and NISKIN sampler were used to collect water samples and to measure the vertical distribution of water quality indicators such as water temperature, dissolved oxygen, pH and phytoplankton in the reservoir. Then, the influencing factors of the distribution of dissolved oxygen and the formation causes responsible for the metalimnetic oxygen minimum(MOM) during the thermal stratification period were analyzed based on the measurements. The results showed that Panjiakou Reservoir has undergone significant thermal stratification in August, 2019 and the water temperature presented epilimnion-metalimnion-hypolimnion structure. The concentration of dissolved oxygen in the epilimnion was higher than 6.5 mg/L, whereas in the metalimnion it was reduced significantly with a large gradient, where MOM appeared because of the thermal stratification. The concentration of dissolved oxygen in the hypolimnion gradually recovered partly. Correlation analysis indicated that dissolved oxygen was significantly correlated with water temperature and buoyancy frequency, and the thermal stratification was the main physical factor for the formation of MOM. Dissolved oxygen was positively correlated with phytoplankton biomass and pH, which was mainly associated with photosynthesis and respiration of phytoplankton. The development of MOM was promoted by the biological and chemical factors such as the respiration of plankton, the accumulation of nutrients and the oxidative decomposition of organic matters to some extent.