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https://doi.org/10.5194/bg-2019-214
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/bg-2019-214
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 11 Jun 2019

Research article | 11 Jun 2019

Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Biogeosciences (BG).

Biogeographical distribution of Microbial Communities along the Rajang River-South China Sea Continuum

Edwin Sien Aun Sia1, Zhuoyi Zhu2, Jing Zhang2, Wee Cheah3, Jiang Shan2, Faddrine Holt Jang1, Aazani Mujahid4, Fuh-Kwo Shiah5, and Moritz Müller1 Edwin Sien Aun Sia et al.
  • 1Faculty of Computing, Engineering and Science, Swinburne University of Technology, Sarawak Campus, Jalan Simpang Tiga, 93350, Kuching, Sarawak, Malaysia
  • 2State Key Laboratory of Estuarine and Coastal Research, East China Normal University, Zhongshan N. Road 3663, Shanghai, 200062, China
  • 3Institute of Ocean and Earth Sciences, University of Malaya, 50603 Kuala Lumpur, Malaysia
  • 4Department of Aquatic Science, Faculty of Resource, Science and Technology, University Malaysia Sarawak, 93400 Kota Samarahan, Sarawak, Malaysia
  • 5Research Center for Environmental Changes, Academia Sinica, Taipei 11529, Taiwan

Abstract. Microbial community composition and diversity in freshwater habitats, especially in lotic environments, are much less studied compared to marine and soil communities. The Rajang River is the main drainage system for central Sarawak in Malaysian Borneo and passes through peat domes whereby peat-rich material is being fed into the system and eventually into the southern South China Sea. Microbial communities found within peat-rich systems are important biogeochemical cyclers in terms of methane and carbon dioxide sequestration. To address the critical lack of knowledge about microbial communities in tropical (peat-draining) rivers, this study represents the first seasonal assessment targeted at establishing a foundational understanding of the microbial communities of the Rajang River-South China Sea continuum. This was carried out utilizing 16S rRNA gene amplicon sequencing via Illumina MiSeq in size-fractionated samples (0.2 and 3.0 μm GF/C filter membranes) covering different biogeographical features/sources from headwaters to coastal waters. The microbial communities found along the Rajang river exhibited taxa common to rivers (i.e. the predominance of β-Proteobacteria) while estuarine and marine regions exhibited taxa that were common to the aforementioned regions as well (i.e. predominance of α- and γ-Proteobacteria). This is in agreement with studies from other rivers which observed similar changes along the salinity gradients. In terms of particulate versus free-living bacteria, nonmetric multi-dimensional scaling (NMDS) results showed similarly distributed microbial communities with varying separation between seasons. Distinct patterns were observed based on linear models as a result of the changes in salinity along with variation of other biogeochemical parameters. Alpha diversity indices indicated that microbial communities were higher in diversity upstream compared to the marine and estuarine regions whereas anthropogenic perturbations led to increased richness but less diversity. Despite the observed changes in bacterial community composition and diversity that occur along the Rajang River to sea continuum, the PICRUST predictions showed minor variations. The results provide essential context for future studies such as further analyses on the ecosystem health in response to anthropogenic land-use practices and probable development of biomarkers to improve the monitoring of water quality in this region.

Edwin Sien Aun Sia et al.
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Short summary
Microbial community composition and diversity in freshwater habitats are much less studied compared to marine and soil communities. This study presents the first assessment of microbial communities of the Rajang River, the longest river in Malaysia, expanding our knowledge of microbial ecology in tropical regions. Areas surrounded by oil palm plantations showed the lowest diversity and other signs of anthropogenic impacts included the presence of CFB-groups as well as probable algal blooms.
Microbial community composition and diversity in freshwater habitats are much less studied...
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