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© Author(s) 2019. This work is distributed under
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© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Submitted as: research article 05 Aug 2019

Submitted as: research article | 05 Aug 2019

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

Distribution and behaviour of dissolved selenium in tropical peatland-draining rivers and estuaries of Malaysia

Yan Chang1, Moritz Müller2, Ying Wu1, Shan Jiang1, Wan wan Cao1, Jian guo Qu1, Jing ling Ren3, Xiaona Wang1, En ming Rao3, Xiao lu Wang1, Aazani Mujahid4, Mohd Fakharuddin Muhamad2, Edwin Sia Sien Aun2, Faddrine Holt Ajon Jang2, and Jing Zhang1 Yan Chang et al.
  • 1State Key Laboratory of Estuarine and Coastal Research, East China Normal University, Shanghai 200062, China
  • 2Faculty of Engineering, Computing and Science Swinburne, University of Technology, Sarawak 93350, Malaysia
  • 3Key Laboratory of Marine Chemistry Theory and Technology, Ministry of Education, Ocean University of China, Qingdao 266100, China
  • 4Faculty of Resource Science and Technology, University Malaysia Sarawak, Sarawak 93350, Malaysia

Abstract. Selenium (Se) is an essential micronutrient for many organisms. Despite its importance, our current knowledge of the biogeochemical cycling of dissolved Se in tropical estuaries is limited, especially in Southeast Asia. To gain insights into Se cycling in tropical peat-draining rivers and estuaries, samples were collected from the Rajang, Maludam, Sebuyau, Simunjan, Sematan, Samunsam, and Lunda rivers and estuaries in western Sarawak, Malaysia, in March and September 2017 and analysed for various forms of Se (dissolved inorganic and organic). Mean total dissolved Se (TDSe), dissolved inorganic Se (DISe), and dissolved organic Se concentrations (DOSe) were 2.2 nmol L−1 (range: 0.7 to 5.7 nmol L−1), 0.18 nmol L−1 (range: less than the detection limit to 0.47 nmol L−1), and 2.0 nmol L−1 (range: 0.42 to 5.7 nmol L−1), respectively. In acidic, low-oxygen, organic-rich blackwater (peatland-draining) rivers, the concentrations of DISe were extremely low, whereas those of DOSe were high. In rivers and estuaries that drained peatland, DOSe / TDSe ratios ranged from 0.67 to 0.99, showing that DOSe dominated. The positive relationship between DISe and salinity and the negative relationship between DOSe and salinity indicate marine and terrestrial origins of DISe and DOSe, respectively. The positive correlations of DOSe with the humification index and humic-like chromophoric dissolved organic matter components in freshwater river reaches suggest that peat soils are probably the main source of DOSe. Discharges of water enriched with DOSe fractions associated with peatland-derived high-molecular-weight, high-aromaticity dissolved organic matter discharged from estuaries may promote productivity in the adjoining oligotrophic coastal waters. The results of this study suggest that the impacts of Se discharges on coastal ecosystems should be evaluated in the future.

Yan Chang et al.
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Status: final response (author comments only)
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Yan Chang et al.
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Short summary
Se is an essential micronutrient for many organisms. Our knowledge of dissolved Se biogeochemical cycling in tropical estuaries is very limited. We have found that the dissolved organic selenium was the major speciation in the peat-draining rivers and estuaries. The DOSe fractions may be associated with high-molecular-weight peatland-derived carbon compounds and may photodegrade to more bioavailable forms once transported to oligotrophic coastal water, where they may promote productivity.
Se is an essential micronutrient for many organisms. Our knowledge of dissolved Se...