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

Research article 18 Jun 2019

Research article | 18 Jun 2019

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

Distribution and Flux of Dissolved Iron of the Rajang and Blackwater Rivers at Sarawak, Borneo

Xiaohui Zhang1, Moritz Müller2, Shan Jiang1, Ying Wu1, Xunchi Zhu3, Aazani Mujahid4, Zhuoyi Zhu1, Mohd Fakharuddin Muhamad4, Edwin Sien Aun Sia2, Faddrine Holt Ajon Jang2, and Jing Zhang1 Xiaohui Zhang et al.
  • 1State Key Laboratory of Estuarine and Coastal Research, East China Normal University, 200241 Shanghai, China
  • 2Swinburne University of Technology, Faculty of Engineering, Computing and Science, 93350 Kuching, Sarawak, Malaysia
  • 3School of Ecological and Environmental Sciences, East China Normal University, 200241 Shanghai, China
  • 4Faculty of Resource Science & Technology, University Malaysia Sarawak, 94300 Sarawak, Malaysia

Abstract. Dissolved iron (dFe) is essential for biogeochemical reactions in oceans, such as photosynthesis, respiration and nitrogen fixation. Currently, large uncertainties remain on riverine dFe inputs, especially for tropical rivers in Southeast Asia. In the present study, dFe concentrations and distribution along the salinity gradient in the Rajang River in Malaysia, and three blackwater rivers draining from peatlands, including the Maludam River, the Sebuyau River, and the Simunjan River, were determined. In the Rajang River, the concentration of dFe in fresh water (salinity < 1) in the wet season (March 2017) was higher than that in the dry season (Auguest 2016), which might be related to the resuspension of sediment particles and soil erosions from cropland in the watershed. In the Rajang Estuary, an intensive removal of dFe in low salinity waters (salinity < 15) was observed, likely due to the salt-induced flocculation and the absorption onto suspended particulate matters (SPM). However, dFe concentration enhancements in the wet season occured in some sampling sites, which may be related to the desorption from SPM and agriculture activities. On the other hand, dFe was conservatively distributed in high salinity waters (salinity > 15), which may result from the association between dFe and pelagic organic matters. In the blackwater rivers, concentrations of dFe reached 44.2 μmol L−1, indicating a great contribution from peatland. The dFe flux derived from the Rajang Estuary to the South China Sea was (6.4 ± 2.3) × 105 kg yr−1. For the blackwater river, the dFe flux was approximately (1.1 ± 0.5) × 105 kg yr−1, in the Maludam River. The anthropogenic activities may play an important role in the dFe yield, such as the Serendeng tributary of the Rajang River, and Simunjan River, where intensive oil palm plantations were observed.

Xiaohui Zhang et al.
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Xiaohui Zhang et al.
Xiaohui Zhang et al.
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Short summary
This study offered detailed information on dFe concentrations, distribution and the magnitude of flux in the Rajang River, i.e. the largest river in Malaysia. Three blackwater rivers, draining from peatlands, were also included in our study. Compared with the Rajang River, the dFe concentrations and yield from three blackwater rivers were much higher. Anthropogenic activities in the watershed, such as palm oil plantation, may markedly increase the concentration dFe in these tropical rivers.
This study offered detailed information on dFe concentrations, distribution and the magnitude of...