Equilibrium analysis of dissolved oxygen in Lake Wuliangsuhai during ice-covered period

Abstract

为探明中国北方浅水湖泊乌梁素海冰封期水体溶解氧平衡的内在机理，于2021年1—2月在湖心处布设了一台水质在线监测浮标，收集到包括溶解氧等在内的水质数据. 通过对溶解氧数据的小波降噪处理，结合气象资料，模拟分析了冰生长及稳定期内水体溶解氧的变化趋势，定性分析了水体溶解氧的平衡机理. 结果表明：湖泊的日均最高产氧速率为7.19 mg/(L ·d)，最低产氧速率为2.01 mg/(L ·d); 日均最高耗氧速率为7.13 mg/(L ·d)，最低耗氧速率为2.37 mg/(L ·d). 24 h的单位时间平均最高产氧速率为0.55 mg/(L ·h)，最低产氧速率为0 mg/(L ·h); 单位时间平均最高耗氧速率为0.36 mg/(L ·h)，最低耗氧速率为0.08 mg/(L ·h). 由此说明小时间尺度下溶解氧的补充消耗不均衡导致了大时间尺度下的溶解氧不平衡，进而产生了冬季湖泊的亏氧现象. 通过进一步溶解氧驱动因素与水环境因子响应关系的分析发现，浊度、水温与产氧速率呈显著负相关，叶绿素a与产氧速率和耗氧速率均呈显著正相关，表明了这些限制性水环境因子在一定程度上影响了冰下水体的溶解氧平衡.;In order to probe into the internal mechanism of dissolved oxygen (DO) equilibrium in the shallow Lake Wuliangsuhai in Northern China during the ice-covered period, a set of online water monitoring buoys were arranged in the center of lake for collection of water quality data from January to February, 2021. Upon the wavelet denoising processing of DO and based on the meteorological data, the DO changes during the growth and stability period of ice was simulated and analyzed, followed by a qualitative analysis of the mechanism of the DO equilibrium. Results show as follow: The lake's maximum daily average oxygen production rate was 7.19 mg/(L ·d); the minimum was 2.01 mg/(L ·d). The maximum daily oxygen consumption rate was 7.13 mg/(L ·d) and the minimum was 2.37 mg/(L ·d). The maximum 24-hour per-unit-time average oxygen production rate was 0.55 mg/(L ·h) and the minimum was 0 mg/(L ·d). The maximum per-unit-time average oxygen consumption rate was 0.36 mg/(L ·h) and the minimum was 0.08 mg/(L ·h). This study indicates that the disequilibrium between the DO production and consumption on small time scales results in DO disequilibrium on large time scales, causing oxygen deficiency in the lake in winter. Further analysis on the relationship between DO driving factors and water environment factors suggests a negative correlation between turbidity, water temperature and oxygen production rate and a positive correlation between chlorophyll-a and oxygen production and consumption rate, which indicates that these restrictive water environmental factors influence the DO equilibrium in water body under ice.