深型水库溶解氧分层规律及其机制探究——以万安水库为例

溶解氧（DO）是衡量生态状况的重要指标,对生态系统的平衡至关重要。为探究深型水库DO分层的规律及其影响机制,于2022年监测了九龙江万安水库的理化指标及营养元素的垂向分布,并分析库区的DO分层规律及影响因素。结果表明：2月属万安水库混合期,呈贫营养状态,DO垂向平均浓度高达6.70 mg/L,DO变化受浮游植物分布及“翻库”影响;5月属热分层形成期,处中营养状态,水体在内源产氧减少和原位DO消耗驱动作用下出现温跃层溶解氧极小值,36 m以下水体处于缺氧状态;8月为热分层稳定期,处中度富营养化,表层DO最大浓度达12.00 mg/L以上,在35 m深度出现DO极大值,水体热分层阻碍DO补充、内源产氧减弱是造成热分层稳定期水体上层大范围缺氧的主要原因;10月为热分层消退期,呈中营养状态,DO垂向平均浓度仅为0.77 mg/L,水深2.79 m以下水层皆处于缺氧状态。热分层时期DO垂向变化受到水体热分层、营养水平、污染状态及浮游植物生长分布等因素的影响,热分层从物理角度影响DO分层,营养水平及污染状态可以影响DO的产耗机制,而库区水体浊度通过影响浮游植物的垂向分布进而对DO浓度产生影响。本研究探明了水层缺氧及变温层DO极小值等现象出现的原因,深入探讨了DO变化规律与营养元素生物地球化学循环间的关系,为维护库区水生态健康提供科学依据。

Stratification of dissolved oxygen in deep reservoirs and its mechanism: A case study of Wanan Reservoir

Dissolved oxygen (DO) is an important indicator to measure the ecological condition and is vital to the balance of the ecosystem. To study the pattern of DO stratification and its influenced mechanism in deep-type reservoirs, the vertical distribution of physical and chemical indicators and nutrient element indicators in Wanan Reservoir of Jiulong River was monitored in 2022, and the pattern of DO stratification and influencing factors in the reservoir area were analyzed. The results showed that: February was the mixing period of Wanan Reservoir, which was in an anaerobic state, and the average vertical concentration of DO was as high as 6.70 mg/L, and the change of DO was affected by the distribution of phytoplankton and the "turning of the reservoir"; May was the period of thermal stratification, which was in a mesotrophic state, and the water body appeared in the thermocline under the driving effect of the reduction of endogenous oxygen production and the depletion of in-situ DO. Dissolved oxygen is very small, and the water body below 36 m is in anoxic state; August is the stable period of thermal stratification, in moderate eutrophication, the maximum concentration of DO in the surface layer reaches more than 12.00 mg/L, and DO is very large at a depth of 35 m. The thermal stratification of the water body hinders DO replenishment, and the weakening of the endogenous oxygen production is the main cause of the large-scale anoxicity of the water body in the upper layer during the stable period of thermal stratification; October is the period of the receding of the thermal stratification, and it is a mesotrophic state, with the vertical average of DO in the middle layer. In October, when the thermo-stratification period subsided, the mesotrophic state was observed, and the average vertical DO concentration was only 0.77 mg/L, and all the water layers below 2.79 m depth were in anoxic state. The DO vertical change during the thermal stratification period was affected by the thermal stratification, nutrient level, pollution status and phytoplankton growth distribution, etc. The thermal stratification affected the DO stratification from the physical point of view, the nutrient level and the pollution status could affect the DO production and consumption mechanism, and the turbidity of the water body in the reservoir area affected the vertical distribution of the phytoplankton and then affected the DO concentration. In this study, the reasons for the phenomena of anoxia and DO minima in the water layer were analyzed, and the relationship between DO change law and biogeochemical cycle of nutrients was explored. This will provide scientific basis for the maintenance of water ecological health in the reservoir area.