Stratification and mixing characteristics in Lake Wuliangsuhai during ice-covered period and its impacts on metabolic rates

为探究寒旱区浅湖冰封期分层动态与其对湖泊新陈代谢速率的影响，于2016—2019年对乌梁素海气象与冰雪条件、冰下水体环境开展原位观测，分析水温和溶解氧变化特征、冰下混合层的出现与发展动态及其对代谢速率的影响.结果显示：观测期内乌梁素海整体水温较高（可接近10℃），冻结期水温结构主要由稳定的上部逆温层和下部弱逆温层构成，并可逐渐过渡为融化期的上部逆温层-下部混合层结构；溶解氧由上到下衰减，甚至在底部形成缺氧区域（<2 mg/L）；受盐度影响，乌梁素海中下层水温升高至一定阈值（约6~8℃）后形成冰下混合层并随辐射增加快速发展；溶解氧动态由光合产氧与呼吸耗氧平衡决定，光合和呼吸速率的时间变化主要受冰雪条件、透射辐射、水温和混合过程影响；特别是，混合过程极大地促进了光合产氧和呼吸耗氧速率，调控了水温与溶解氧结构动态.;In order to explore the development of under-ice stratification and its impacts on the lake metabolic rates, the meteorology, ice and snow processes and under-ice water temperature and dissolved oxygen (DO) were observed in Lake Wuliangsuhai during winters of 2016-2019. This paper presented the under-ice water temperature and DO dynamics, and characterized the mixing appearance and evolution and its influence on lake ecosystem metabolic rates. The results indicated that the bulk water temperature was relatively high (up to 10℃) in freezing Lake Wuliangsuhai, and the thermal structure was featured by a stable inversion layer at the top and a weak inversion layer at the middle-bottom during freezing period, but by an inversion top layer and a mixed mid-bottom layer during melting period. Because of the salinity profile, the mixing took place in the middle-bottom water when its temperature grew up over approximately 6-8℃, and from then the mixing layer expanded fast as the incident solar radiation increased. The under-ice DO roughly decreased from the top to the bottom of the water column, and even formed a bottom anoxic zone (< 2 mg/L). DO amount dynamics was governed by the balance of photosynthesis production and respiration consumption, both of which were influenced by the ice/snow conditions, radiation transmission, water temperature and mixing process. In particular, the mixing events were able to directly change the temperature stratification and accelerate photosynthesis and respiration rates, and thus change the DO structure.