Vertical transport caused by mixing is essential for understanding physical processes in lakes. However, mixing processes in shallow lakes are not well understood because of the lack of turbulence measurements. This study presents observations of vertical mixing and oxygen flux in a shallow lake, Lake Kitaura of the Lake Kasumigaura continuous lake system, which is located along the central eastern coast of the Japanese mainland. Mooring and microstructure surveys were conducted in August 2020. The vertical eddy diffusivity was estimated from the Ellison scale using high-frequency sampled temperature data from the mooring location, and the estimations were consistent with those observed from the microstructure profiler. The estimated eddy diffusivity revealed a mixing structure and oxygen flux in the lake during the study period. The daily cycle of stratification and mixing was caused by daily heating due to solar radiation and by winds from daily sea breezes, respectively. The daily stratification maximum occurred around noon, which suppressed vertical mixing. Vertical mixing was intensified due to sea breezes in the afternoon, which led to movement of oxygen from the surface layer to the bottom layer. The maximum vertical mixing was observed at 18:00. The oxygen concentration did not increase during nighttime when the negative surface heat flux was observed; thus, nighttime cooling may not primarily contribute to the vertical oxygen supply.

混合引起的垂直传输对于了解湖泊中的物理过程至关重要。然而，由于缺乏湍流测量，浅湖中的混合过程尚不清楚。本研究介绍了位于日本大陆中东部沿海的 Kasumigaura 湖连续湖泊系统的 Kitaura 浅湖的垂直混合和氧气通量的观察结果。系泊和微结构调查于 2020 年 8 月进行。垂直涡流扩散系数是使用来自系泊位置的高频采样温度数据从埃里森尺度估计的，估计值与从微结构剖面仪观察到的一致。估计的涡流扩散率揭示了研究期间湖中的混合结构和氧气通量。分层和混合的日常循环分别是由太阳辐射引起的日常加热和日常海风带来的风引起的。每日分层最大值出现在中午左右，这抑制了垂直混合。下午由于海风的作用加强了垂直混合，导致氧气从表层移动到底层。在 18:00 观察到最大垂直混合。观测负地表热通量时，夜间氧浓度没有增加；因此，夜间降温可能不会主要促进垂直供氧。下午由于海风的作用加强了垂直混合，导致氧气从表层移动到底层。在 18:00 观察到最大垂直混合。观测负地表热通量时，夜间氧浓度没有增加；因此，夜间降温可能不会主要促进垂直供氧。下午由于海风的作用加强了垂直混合，导致氧气从表层移动到底层。在 18:00 观察到最大垂直混合。观测负地表热通量时，夜间氧浓度没有增加；因此，夜间降温可能不会主要促进垂直供氧。