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Biogeosciences An interactive open-access journal of the European Geosciences Union
https://doi.org/10.5194/bg-2018-64
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.
Research article
13 Feb 2018
Review status
This discussion paper is a preprint. It has been under review for the journal Biogeosciences (BG). The manuscript was not accepted for further review after discussion.
Microbial Community Structure and Activity Changes in Response to the Development of Hypoxia in a Shallow Estuary
Yunjung Park1, Sujin Kim1, Soonja Cho1, Jaeho Cha1,2, and Soonmo An3 1Department of Microbiology, College of Natural Sciences, Pusan National University, Busan 46241, Republic of Korea
2Microbiological Resource Research Institute, Pusan National University, Busan 46241, Republic of Korea
3Department of Oceanography, College of Natural Sciences, Pusan National University, Busan 46241, Republic of Korea
Abstract. We examined the effects of changing from oxic to anoxic conditions on microbial communities using both biogeochemical and molecular approaches in a semi-enclosed estuary (Jinhae Bay, Republic of Korea). Total microbial activity, represented by oxygen demand in the water column (WOD) or sediment (SOD), revealed that the respective microbial communities in the water and sediment responded differently to low dissolved-oxygen (DO) conditions. In the sediment, SOD and the total microbial abundance, as assessed by quantitative polymerase chain reaction (qPCR) analysis, decreased under low DO conditions, indicating that the microbial adaptation to anaerobic metabolism was not well established during hypoxia development. In the water column, however, neither the total abundance of microbes nor the WOD were affected by hypoxic conditions. Regardless of DO concentration, WOD showed a positive correlation with water temperature, implying that the aerobic metabolism was sustained even under hypoxic conditions, through the intermittent supply of oxygen. In addition to the spatially different responses of microorganisms, unique responses of specific groups were noted in sulfur (S) and nitrogen (N) cycling microbes. Sulfide-oxidizing prokaryotes (SOP) dominated in the water column, and no significant changes were evident in their abundance or diversity with hypoxia. However, in sediment, distinctive sulfate-reducing bacteria (SRB) were present at each sampling period during hypoxia development (a SRB succession), implying that each SRB group has varying sensitivity to DO and other electron acceptors. Our results illustrated similarities in composition and activity of N-cycling microbes between the seasonal hypoxia and permanent oxygen minimum zone (OMZ). Vertical profiles of dissolved inorganic nitrogen, including ammonium (NH4+) and nitrate (NO3), and changes in archaeal abundance indicated that the NH4+-oxidizing archaea (AOA) varied spatially and temporally, depending on NH4+ and oxygen availability in the water column, under mature hypoxic conditions. The intriguing N dynamics recently discovered in the OMZ might also be important in the coastal hypoxic zone.
Citation: Park, Y., Kim, S., Cho, S., Cha, J., and An, S.: Microbial Community Structure and Activity Changes in Response to the Development of Hypoxia in a Shallow Estuary, Biogeosciences Discuss., https://doi.org/10.5194/bg-2018-64, 2018.
Yunjung Park et al.
Yunjung Park et al.

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Short summary
Our work addresses the influences of hypoxia on microbes in three independent aspects (activity, abundance and community structure). The activity and community structure in water column were less affected compared to the sediment (an interesting SRB (sulphate reducing bacteria) succession happened in sediment). Our results also illustrated that the intriguing N dynamics recently discovered in the OMZ (such as AOA dynamics) might also be important in the hypoxic zone.
Our work addresses the influences of hypoxia on microbes in three independent aspects (activity,...
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