Waterside convective velocity in a large and shallow lake: A case of Lake Taihu

Abstract

湖泊水体的对流混合是最基本的物理过程，其能显著影响湖泊生态系统温室气体等循环，但浅水湖泊水体对流混合的研究鲜有报道.本研究基于太湖（面积2400 km²，平均水深1.9 m）中尺度通量网的原位、高频、连续和多点的观测数据，分析该大型浅水湖泊水体对流混合速率w^*的时空特征.结果表明太湖水体w^*的均值为2.49 mm/s，因太湖的风速、水温和辐射等物理参数无空间变化，w^*也无明显的空间变化.但是研究表明w^*呈现显著的昼夜变化和季节变化，且昼夜变化幅度强于季节变化.总体上夜间w^*是白天的4倍多，冬季w^*（均值1.79 mm/s）明显低于春季（均值2.42 mm/s）、夏季（均值2.91 mm/s）和秋季（均值2.82 mm/s）.太湖w^*主要受风速和能量收支影响，白天风速是主要驱动因子，夜晚能量收支是主要驱动因子.;Waterside convective controlling aquatic greenhouse gases cycle is a common physical process in lakes. However, the physical process was less studied in shallow lakes. This study investigated the waterside convective strength, which was expressed with a waterside convective velocity scale (w^*), in a large (area 2400 km²) and shallow (mean depth 1.9 m) lake based on in-situ high-frequency monitoring data. Results showed that the w^* with an annual mean value of 2.49 mm/s was relatively uniform in space. However, the w^* had an obvious diurnal variation, the value in nighttime was about four times higher than that in daytime. Meanwhile, the w^* varied seasonally, the peak value generally occurred in summer and lowest in winter. It should be noted that the diurnal variation of w^* was more significant compared to the seasonal variation. Our results also demonstrated that daytime w^* was driven by wind speed, and nighttime w^* was driven by energy budget.