Unravelling the Contribution of Turbulence and Bubbles to Air-Water Gas Exchange in Running Waters

Aquatic ecosystems exchange gases with the atmosphere and this exchange is critical for many ecosystem processes and the global greenhouse gas cycle. However, it is difficult to determine how fast gases exchange with the atmosphere, especially in running waters where bubbles can speed up the exchange of certain gases. Here, we provide a data set on air-water gas exchange velocities, collected during an outdoor flume experiment. We used experimental stream channels to create a wide range of flow conditions, and tested how these conditions effect the rate at which different gases in the water exchange with the atmosphere. Besides gas exchange velocities for direct air-water exchange and exchange mediated by bubbles, the data set also contains data on, among others, flow conditions, turbulent kinetic energy dissipation rate, bubble flux rate and ambient underwater sound pressure signatures. The experimental design and data are described in articles by Vingiani et al. (2021) and Klaus et al. (2022).

main data contributions:
(1) Gas exchange velocity estimates based on mass balance of various gases in flume water
Concentrations of helium, xenon, argon och methane were measured in the in- and outlet water of the flumes using mass-spectrometry . A mass balance of the gases yielded air-water gas exchange velocities.
(2) turbulent kinetic energy dissipation estimates based on Acoustic Doppler Velocimetry
Three-dimensional flow velocities were measured at 24 locations per flume using an Acoustic Doppler Velocity meter. Spectral analysis was applied to derives turbulent kinetic energy dissipation rates.
(3) sound pressure signatures derived from Hydrophone and microphone recordings
Ambient sound was recorded at 12 locations per flume using a hydrophone and a microphone. Spectral analysis was used to derive sound signatures associated with water flow / turbulence and air bubbles.

水生生态系统可与大气进行气体交换，该交换过程对诸多生态系统过程及全球温室气体循环至关重要。然而，精准测定气体与大气的交换速率颇具挑战，尤其在存在气泡可加速特定气体交换的流水生境中。本数据集提供了户外水槽实验中测得的水气气体交换速率数据：研究人员通过实验流槽构建了一系列不同的水流条件，以此探究这些条件对水体中不同气体与大气间交换速率的影响。除直接水气交换以及气泡介导的气体交换速率数据外，本数据集还包含水流条件、湍动能耗散率（turbulent kinetic energy dissipation rate）、气泡通量率（bubble flux rate）以及水下环境声压特征（ambient underwater sound pressure signatures）等多类数据。本实验设计与相关数据已在Vingiani等人（2021）及Klaus等人（2022）发表的论文中详述。

主要数据贡献：
(1) 基于水槽水体中多种气体质量平衡的气体交换速率估算：研究人员采用质谱法对水槽进水与出水口中的氦气、氙气、氩气以及甲烷浓度进行了测定，通过气体质量平衡计算得到水气气体交换速率。
(2) 基于声学多普勒测速法（Acoustic Doppler Velocimetry）的湍动能耗散率估算：研究人员使用声学多普勒测速仪在每个水槽的24个测点处测量了三维流速，通过频谱分析推导得到湍动能耗散率。
(3) 基于水听器（hydrophone）与麦克风（microphone）录制数据的声压特征：研究人员在每个水槽的12个测点处使用水听器与麦克风录制了环境声信号，通过频谱分析得到与水流/湍流及气泡相关的声压特征。