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https://doi.org/10.5194/bg-2019-94
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/bg-2019-94
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 10 Apr 2019

Research article | 10 Apr 2019

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

Distribution and degradation of terrestrial organic matter in the sediments of peat-draining rivers, Sarawak, Malaysian Borneo

Ying Wu1, Kun Zhu1, Jing Zhang1, Moritz Müller2, Shan Jiang1, Aazani Mujahid3, Mohd Fakharuddin Muhamad3, and Edwin Sien Aun Sia2 Ying Wu et al.
  • 1State Key Laboratory of Estuary and Coastal Research, East China Normal University, Shanghai, China
  • 2Faculty of Engineering, Computing and Science Swinburne, University of Technology, Sarawak campus, Malaysia
  • 3Faculty of Resource Science & Technology, University Malaysia Sarawak, Sarawak, Malaysia

Abstract. Tropical peatlands are one of the largest pools of terrestrial organic carbon (OCterr); however, our understanding of the dynamics of OCterr in peat-draining rivers remains limited, especially in Southeast Asia. This study used bulk parameters and lignin phenols concentrations to investigate the characteristics of OCterr in a tropical peat-draining river system (the main channel of the Rajang and three smaller rivers) in the western part of Sarawak, Malaysian Borneo. The depleted δ13C levels and lignin composition of the organic matter indicates that the most important plant source of the organic matter in these rivers is woody angiosperm C3 plants, especially in the three small rivers sampled. The diagenetic indicator ratio (i.e., the ratio of acid to aldehyde of vanillyl phenols (Ad / Al)v) increased with decreasing mean grain size of sediment from the small rivers. The selective sorption of acid relative to aldehyde might explain the variations in the (Ad / Al)v ratio. The (Ad / Al)v ratio appears to be related to the C / N ratio (the ratio of total organic carbon to total nitrogen) in the Rajang and small rivers, where slower degradation of OCterr and a higher total nitrogen percentage (TN%) were observed, compared to other river systems. Most of the OCterr discharged from the Rajang and small river systems was material derived from woody angiosperm plants with limited diagenetic alteration before deposition, and so could potentially provide significant carbon to the atmosphere after degradation.

Ying Wu et al.
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Short summary
Our understanding of terrestrial organic matter (TOM) in tropical peat-draining rivers remains limited, especially in Southeast Asia. We explored the characteristics of TOM by bulk parameters and lignin phenols of sediment in Malaysia. They elucidated that the most important plant source of the organic matter in these rivers is woody angiosperm C3 plants with limited diagenetic alteration. Such slower degradation of TOM may link to higher total nitrogen contents, especially for the small rivers.
Our understanding of terrestrial organic matter (TOM) in tropical peat-draining rivers remains...
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