The hydrodynamics within small boreal lakes have rarely been studied, yet knowing whether turbulence at the air–water interface and in the water column scales with metrics developed elsewhere is essential for computing metabolism and fluxes of climate‐forcing trace gases. We instrumented a humic, 4.7 ha, boreal lake with two meteorological stations, three thermistor arrays, an infrared (IR) camera to quantify surface divergence, obtained turbulence as dissipation rate of turbulent kinetic energy (ε) using an acoustic Doppler velocimeter and a temperature‐gradient microstructure profiler, and conducted chamber measurements for short periods to obtain fluxes and gas transfer velocities (k). Near‐surface ε varied from 10⁻⁸ to 10⁻⁶ m² s⁻³ for the 0–4 m s⁻¹ winds and followed predictions from Monin–Obukhov similarity theory. The coefficient of eddy diffusivity in the mixed layer was up to 10⁻³ m² s⁻¹ on the windiest afternoons, an order of magnitude less other afternoons, and near molecular at deeper depths. The upper thermocline upwelled when Lake numbers (L_N) dropped below four facilitating vertical and horizontal exchange. k computed from a surface renewal model using ε agreed with values from chambers and surface divergence and increased linearly with wind speed. Diurnal thermoclines formed on sunny days when winds were < 3 m s⁻¹, a condition that can lead to elevated near‐surface ε and k. Results extend scaling approaches developed in the laboratory and for larger water bodies, illustrate turbulence and k are greater than expected in small wind‐sheltered lakes, and provide new equations to quantify fluxes.

中文翻译：

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北方小湖中的湍流：空气-水气体交换的后果


北方小型湖泊内的流体动力学很少被研究，但了解空气-水界面和水柱中的湍流是否具有其他地方开发的度量标准对于计算气候强迫微量气体的代谢和通量至关重要。我们对一个占地 4.7 公顷的腐殖质北方湖进行了检测，该湖配有两个气象站、三个热敏电阻阵列、一个红外 (IR) 相机来量化表面散度，并使用声多普勒测速仪和温度获得了湍流作为湍流动能耗散率 ( ε ) ‐梯度微观结构剖面仪，并进行短期室测量以获得通量和气体传输速度（ k ）。对于0-4 ms ^-1风，近地表ε从10 ^-8到10 ^-6 m ² s ^-3变化，并遵循莫宁-奥布霍夫相似理论的预测。在风最大的下午，混合层中的涡流扩散系数高达10 ^-3 m ² s ^-1 ，比其他下午低一个数量级，并且在较深的深度接近分子。当湖泊数量（ L _N ）降至四以下时，上部温跃层上升，促进垂直和水平交换。 k根据表面更新模型使用ε计算得出，与腔室和表面散度的值一致，并随风速线性增加。日间温跃层在风速 < 3 ms ^-1的晴天形成，这种情况可能导致近地表ε和k升高。 结果扩展了实验室开发的缩放方法，适用于较大的水体，说明小型避风湖泊中的湍流和k大于预期，并提供了量化通量的新方程。