Variations in airborne bacterial communities at high altitudes over
the Noto Peninsula (Japan) in response to Asian dust events
Teruya Maki1, Kazutaka Hara2, Ayumu Iwata3, Kevin C. Lee4, Kei Kawai5, Kenji Kai5, Fumihisa Kobayashi6, Stephen B. Pointing4, Stephen Archer4, Hiroshi Hasegawa1, and Yasunobu Iwasaka71College of Science and Engineering, Kanazawa University, Kanazawa, 920-1192, Japan 2National Institute for Environmental Studies, Tsukuba, 305-8506, Japan 3Graduate school of Natural Science and Technology, Kanazawa University, Kanazawa, 920-1192, Japan 4School of Applied Sciences, Auckland University of Technology, Auckland 1142, New Zealand 5Graduate School of Environmental Studies, Nagoya University, Nagoya, 464-8601, Japan 6Graduate School of Science and Technology, Hirosaki University, Hirosaki, 036-8561, Japan 7Community Research Service Group, University of Shiga Prefecture, 2500 Hikone, 522-8533, Japan
Received: 05 Dec 2016 – Accepted for review: 18 Jan 2017 – Discussion started: 25 Jan 2017
Abstract. Aerosol particles, including airborne microorganisms, are transported through the free troposphere from the Asian continental area to the downwind area in East Asia and can influence climate changes, ecosystem dynamics, and human health. However, the variations present in airborne bacterial communities in the free troposphere over downwind areas are poorly understood, and there are few studies that provide an in-depth examination of the effects of long-range transport of aerosols (natural and anthropogenic particles) on bacterial variations. In this study, the vertical distributions of airborne bacterial communities at high altitudes were investigated and the bacterial variations were compared between dust events and non-dust events.
Aerosols were collected at three altitudes from ground level to the free troposphere (upper level: 3,000 m or 2,500 m; middle level: 1,200 m or 500 m; and low level: 10 m) during Asian dust events and non-dust events over the Noto Peninsula, Japan, where westerly winds carry aerosols from the Asian continental areas. During Asian dust events, air masses at high altitudes were transported from the Asian continental area by westerly winds, and Laser Imaging Detection and Ranging (LiDAR) data indicated high concentrations of non-spherical particles, suggesting that dust-sand particles were transported from the central desert regions of Asia. The air samples collected during the dust events contained 10–100 times higher concentrations of microscopic fluorescent particles and Optical Particle Counter (OPC) measured particles than in non-dust events. The air masses of non-dust events contained lower amounts of dust-sand particles. Additionally, some air samples showed relatively high levels of black carbon, which were likely transported from the Asian continental coasts. Moreover, during the dust events, microbial particles at altitudes of > 1,200 m increased to the concentrations ranging from 1.2 × 106 particles m−3 to 6.6 × 106 particles m−3. In contrast, when dust events disappeared, the microbial particles at > 1,200 m decreased slightly to microbial-particle concentrations ranging from 6.4 × 104 particles m−3 to 8.9 × 105 particles m−3.
High-throughput sequencing technology targeting 16S rRNA genes (16S rDNA) revealed that the bacterial communities collected at high altitudes (from 500 m to 3,000 m) during dust events exhibited higher diversities and were predominantly composed of natural-sand/terrestrial bacteria, such as Bacillus members. During non-dust periods, airborne bacteria at high altitudes were mainly composed of anthropogenic/terrestrial bacteria, (Actinobacteria), marine bacteria (Cyanobacteria and Alphaproteobacteria), and plant-associated bacteria (Gammaproteobacteria), which shifted in composition in correspondence with the origins of the air masses and the meteorological conditions. Heterogeneous bacterial populations, originating from terrestrial, marine, and plant-associated categories, were used as an indicator for the mixture levels of air masses originating from the Asian continental area, the Sea of Japan, and the Japanese islands, respectively. The airborne bacterial structures at high altitudes suggested remarkable changes in response to air mass sources, which contributed to the increases in community richness and to the domination of a few bacterial taxa.
Maki, T., Hara, K., Iwata, A., Lee, K. C., Kawai, K., Kai, K., Kobayashi, F., Pointing, S. B., Archer, S., Hasegawa, H., and Iwasaka, Y.: Variations in airborne bacterial communities at high altitudes over
the Noto Peninsula (Japan) in response to Asian dust events, Atmos. Chem. Phys. Discuss., doi:10.5194/acp-2016-1095, in review, 2017.