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Biogeosciences An interactive open-access journal of the European Geosciences Union
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© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 18 Dec 2018

Research article | 18 Dec 2018

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

Composition and cycling of dissolved organic matter from tropical peatlands of coastal Sarawak, Borneo, revealed by fluorescence spectroscopy and PARAFAC analysis

Yongli Zhou1, Patrick Martin1, and Moritz Müller2 Yongli Zhou et al.
  • 1Asian School of the Environment, Nanyang Technological University, Singapore 639798 Singapore
  • 2Swinburne University of Technology, Faculty of Engineering, Computing and Science, 93350 Kuching, Sarawak, Malaysia

Abstract. Southeast Asian peatlands supply ~ 10 % of the global flux of dissolved organic carbon (DOC) from land to the ocean, but the biogeochemical cycling of this peat-derived DOC in coastal environments is still poorly understood. Here, we use fluorescence spectroscopy and parallel factor (PARAFAC) analysis to distinguish different fractions of dissolved organic matter (DOM) in peat-draining rivers, estuaries, and coastal waters of Sarawak, Borneo. The terrigenous fractions showed high concentrations at freshwater stations within the rivers, and conservative mixing with seawater across the estuaries. The autochthonous DOM fraction, in contrast, showed low concentrations throughout our study area at all salinities. The DOM pool was also characterized by a high degree of humification in all rivers and estuaries up to salinity 25. These results indicate a predominantly terrestrial origin of the riverine DOM pool. Only at salinities > 25 did we observe an increase in the proportion of autochthonous relative to terrestrial DOM. Natural sunlight exposure experiments with river water and seawater showed high photolability of the terrigenous DOM fractions, suggesting that photodegradation may account for the observed changes in DOM composition in coastal waters. Nevertheless, we estimate based on our fluorescence data that at least 20 %–25 % of the DOC at even our most marine stations (salinity > 31) was terrestrial in origin, indicating that peatlands likely play an important role in the carbon biogeochemistry of Southeast Asian shelf seas.

Yongli Zhou et al.
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Yongli Zhou et al.
Yongli Zhou et al.
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Short summary
We found that peatlands in coastal Sarawak, Borneo are exporting extremely humified organic matter, which dominates the riverine organic matter pool and conservatively mixes with seawater while the freshly produced fraction is low and stable in concentration at all salinities. We estimated that terrigenous fractions, which showed high photo-lability, still account for 20 % of the coastal dissolved organic carbon pool, implying the importance of peat-derived organic matter in coastal carbon cycle.
We found that peatlands in coastal Sarawak, Borneo are exporting extremely humified organic...