Gas bubbles in freshwater ecosystems: origin, fate, and bubble-mediated transport

游离气体以气泡的形式存在，大小从微米到厘米不等，在水生生态系统中无处不在。气泡不仅影响水的物理性质，还促进了与全球地球化学循环和气候相关的重要传输途径。在空气-水界面，气泡加速气体交换，从而影响全球碳循环。从水生沉积物中释放的气泡（沸腾）是甲烷进入大气的重要途径。此外，气泡介导的运输不仅与气体有关。上升的气泡在其表面运输颗粒、溶质和细菌。这些物质，包括碳、营养物和污染物，来源于沉积物或在气泡上升期间从水柱中清除。尽管有这种潜在的重要性，但人们对气泡及其在淡水生态系统中的特性知之甚少，现有的知识主要基于对海洋系统的观察。在这个项目中，我们调查的过程，控制淡水生态系统中的气泡的丰度和特性，沿着的作用，运输气体，溶解和颗粒物的评估。我们区分气泡产生的空气夹带在水面上，气泡成核在远洋区由于过量的溶解气体压力和气泡在水生沉积物中形成。我们假设这三种不同类型的泡沫具有不同的特性。基于现场测量和实验室实验，我们将描述控制这三种类型气泡及其输送物质的产生、老化和命运的过程和环境变量。观察结果和调查结果将与基于过程的模型相联系，以制定一个新的框架，用于评估水生生态系统中气泡介导的运输的相关性。这一新知识有望对水生研究、监测和管理的各个领域作出重要贡献。

The presence of free gas in form of bubbles ranging in size from micrometers to centimeters is ubiquitous in aquatic ecosystems. Bubbles not only affect the physical properties of water, they also facilitate an important transport pathway with relevance for global biogeochemical cycling and climate. At the air-water interface, bubbles accelerate gas exchange and therewith affect global carbon cycling. Bubbles released from aquatic sediments (ebullition) are an important pathway for methane to the atmosphere. Moreover, bubble-mediated transport is not only relevant for gases. Rising gas bubbles transport particles, solutes and bacteria on their surfaces. This material, including carbon, nutrients and pollutants, originates from the sediments or had been scavenged from the water column during bubble rise. Despite this potential importance, little is known about gas bubbles and their characteristics in freshwater ecosystems, existing knowledge is primarily based on observations in marine systems. In this project, we investigate the processes that control the abundance and characteristics of gas bubbles in freshwater ecosystems, along with an assessment of the role in transporting gases, dissolved and particulate matter. We distinguish between bubbles generated by air entrainment at the water surface, bubbles nucleating in the pelagic zone due to excess dissolved gas pressure and bubbles formed in aquatic sediments. We hypothesize that these three different types of bubbles have distinct properties. Based on field measurements and laboratory experiments, we will characterize the processes and environmental variables that govern the generation, aging, and fate of the three types of bubbles and the substances transported by them. The observations and findings will be linked to process-based models to develop a novel framework for assessing the relevance of bubble-mediated transport in aquatic ecosystems. This new knowledge is expected to make important contributions to various fields of aquatic research, monitoring and management.