Department of Geosciences and Environment, Universidad Nacional de Colombia, Medellín, Antioquia, Colombia.
Institute for Environmental Sciences, University of Kaiserslautern-Landau, Landau, Rhineland-Palatinate, Germany.
PLoS One. 2024 Mar 12;19(3):e0299998. doi: 10.1371/journal.pone.0299998. eCollection 2024.
Gas fluxes from aquatic ecosystems are a significant component of the carbon cycle. Gas exchange across the air-water interface is regulated by near-surface turbulence and can be controlled by different atmospheric forcing conditions, with wind speed and surface buoyancy flux being the most recognized drivers in empirical studies and modeling approaches. The effect of rainfall on near-surface turbulence has rarely been studied and a consistent relationship between rain rate and near-surface turbulence has not yet been established. In this study, we addressed some limitations still present in the quantitative understanding of the effect of rain rate on near-surface turbulence and on the resulting gas transfer velocity in freshwater. We performed controlled laboratory experiments over a wide range of rain rates (7 to 90 mm h-1) and estimated gas transfer velocities from high-resolution measurements of O2 concentration, while rain-induced turbulence was characterized based on particle image velocimetry. We found that the rain-induced dissipation rates of turbulent kinetic energy declined with depth following a consistent power-law relationship. Both energy dissipation rates and gas transfer velocity increased systematically with the rain rate. The results confirm a causal relationship between rainfall, turbulence, and gas exchange. We propose a power-law relationship between near-surface turbulent dissipation rates and rain rate. In combination with surface renewal theory, we derived a direct relationship between gas transfer velocity and rain rate, which can be used to assess the importance of short-term drivers, such as rain events, on gas dynamics and biogeochemical cycling in aquatic ecosystems.
水生生态系统的气体通量是碳循环的重要组成部分。空气-水界面的气体交换受近表面湍流控制，并且可以通过不同的大气强迫条件进行控制，其中风速和表面浮力通量是经验研究和建模方法中最公认的驱动因素。降雨对近表面湍流的影响很少被研究，并且降雨率与近表面湍流之间尚未建立一致的关系。在这项研究中，我们解决了在定量理解降雨率对近表面湍流和淡水气体转移速度的影响方面仍然存在的一些限制。我们在广泛的降雨率范围内（7 至 90mm h-1）进行了受控的实验室实验，并通过对 O2 浓度的高分辨率测量来估计气体转移速度，同时根据粒子图像测速法来描述降雨引起的湍流。我们发现，降雨引起的湍流动能耗散率随深度呈一致的幂律关系下降。能量耗散率和气体转移速度都随着降雨率系统地增加。结果证实了降雨、湍流和气体交换之间的因果关系。我们提出了近表面湍流动能耗散率与降雨率之间的幂律关系。结合表面更新理论，我们推导出了气体转移速度与降雨率之间的直接关系，该关系可用于评估短期驱动因素（如降雨事件）对水生生态系统气体动力学和生物地球化学循环的重要性。
