Pietsch Renee B, Grothe Hinrich, Hanlon Regina, Powers Craig W, Jung Sunghwan, Ross Shane D, Schmale Iii David G
Biological Sciences, Virginia Polytechnic Institute and State University (Virginia Tech), Blacksburg, VA, United States of America.
School of Plant and Environmental Sciences, Virginia Polytechnic Institute and State University (Virginia Tech), Blacksburg, VA, United States of America.
PeerJ. 2018 Sep 26;6:e5663. doi: 10.7717/peerj.5663. eCollection 2018.
Natural aquatic environments such as oceans, lakes, and rivers are home to a tremendous diversity of microorganisms. Some may cross the air-water interface within droplets and become airborne, with the potential to impact the Earth's radiation budget, precipitation processes, and spread of disease. Larger droplets are likely to return to the water or adjacent land, but smaller droplets may be suspended in the atmosphere for transport over long distances. Here, we report on a series of controlled laboratory experiments to quantify wind-driven droplet production from a freshwater source for low wind speeds. The rate of droplet production increased quadratically with wind speed above a critical value (10-m equivalent 5.7 m/s) where droplet production initiated. Droplet diameter and ejection speeds were fit by a gamma distribution. The droplet mass flux and momentum flux increased with wind speed. Two mechanisms of droplet production, bubble bursting and fragmentation, yielded different distributions for diameter, speed, and angle. At a wind speed of about 3.5 m/s, aqueous suspensions of the ice-nucleating bacterium were collected at rates of 283 cells m s at 5 cm above the water surface, and at 14 cells m s at 10 cm above the water surface. At a wind speed of about 4.0 m/s, aqueous suspensions of were collected at rates of 509 cells m s at 5 cm above the water surface, and at 81 cells m s at 10 cm above the water surface. The potential for microbial flux into the atmosphere from aquatic environments was calculated using known concentrations of bacteria in natural freshwater systems. Up to 3.1 × 10 cells m s of water surface were estimated to leave the water in potentially suspended droplets (diameters <100 µm). Understanding the sources and mechanisms for bacteria to aerosolize from freshwater aquatic sources may aid in designing management strategies for pathogenic bacteria, and could shed light on how bacteria are involved in mesoscale atmospheric processes.
海洋、湖泊和河流等自然水生环境是种类繁多的微生物的家园。一些微生物可能会随着液滴穿过气-水界面并进入空气中，有可能影响地球的辐射收支、降水过程和疾病传播。较大的液滴可能会回到水中或邻近的陆地，但较小的液滴可能会悬浮在大气中进行长距离传输。在此，我们报告了一系列控制实验室实验，以量化低风速下淡水源中风驱动的液滴产生情况。液滴产生速率在临界值（10米等效风速5.7米/秒）以上随风速呈二次方增加，在该临界值时液滴开始产生。液滴直径和喷射速度符合伽马分布。液滴质量通量和动量通量随风速增加。液滴产生的两种机制，即气泡破裂和破碎，产生了不同的直径、速度和角度分布。在风速约为3.5米/秒时，在水面上方5厘米处，冰核细菌的水悬浮液收集速率为283个细胞/米²·秒，在水面上方10厘米处为14个细胞/米²·秒。在风速约为4.0米/秒时，在水面上方5厘米处，水悬浮液收集速率为509个细胞/米²·秒，在水面上方10厘米处为81个细胞/米²·秒。利用天然淡水系统中已知的细菌浓度，计算了水生环境中微生物进入大气的通量。估计高达3.1×10⁵个细胞/米²·秒的水面会以潜在悬浮液滴（直径<100微米）的形式离开水体。了解细菌从淡水水生来源气溶胶化的来源和机制，可能有助于设计致病细菌的管理策略，并有助于揭示细菌如何参与中尺度大气过程。
