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https://doi.org/10.5194/bg-2019-7
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/bg-2019-7
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 08 Feb 2019

Research article | 08 Feb 2019

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

Dissolved inorganic nitrogen in a tropical estuary at Malaysia: transport and transformation

Shan Jiang1, Moritz Müller2, Jie Jin1, Ying Wu1, Kun Zhu1, Guosen Zhang1, Aazani Mujahid3, Tim Rixen4, Mohd Fakharuddin Muhamad3, Edwin Sien Aun Sia2, Faddrine Holt Ajon Jang2, and Jing Zhang1 Shan Jiang et al.
  • 1State Key Laboratory of Estuaries and Coastal Research, East China Normal University, 200062, Shanghai, China
  • 2Faculty of Engineering, Computing and Science Swinburne, University of Technology, Sarawak Campus, Malaysia
  • 3Faculty of Resource Science & Technology, Universiti Malaysia Sarawak, 94300 Kota Samarahan, Sarawak, Malaysia
  • 4Leibniz Centre for Tropical Marine Research, Fahrenheitstr. 6, 28359 Bremen, Germany

Abstract. Dissolved inorganic nitrogen (DIN), including nitrate, nitrite and ammonium, frequently acts as the limitation for primary productivity. Our study focused on the transport and transformation of dissolved inorganic nitrogen in a tropical estuary, i.e. Rajang river estuary, in Borneo, Malaysia. Three cruises were conducted in August 2016, February–March and September 2017, covering both dry and wet seasons. Before entering the coastal delta, decomposition of the terrestrial organic matter and the subsequent soil leaching was assumed to be the main source of DIN in the river water. In the estuary, decomposition of dissolved organic nitrogen was an additional DIN source, which markedly increased DIN concentrations in August 2016 (dry season). In the wet season (February 2017), ammonium concentration showed a relatively conservative distribution during the mixing and nitrate addition was weak. In September 2017 (dry season), La Niña induced high precipitation and discharge rates, decreased reaction intensities of ammonification and nitrification and hence the distribution of DIN species in the estuary water was similar with the trend found in the wet season. The magnitude of riverine DIN flux varied between 77.2 and 101.5 ton N d-1, which might be an important support for the coastal primary productivity.

Shan Jiang et al.
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Status: final response (author comments only)
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Shan Jiang et al.
Shan Jiang et al.
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Short summary
Three cruises were conducted in the Rajang river estuary, Malaysia. The results revealed that the decomposition of terrestrial organic matter and the subsequent soil leaching was the main source for dissolved inorganic nitrogen (DIN) in the fresh river water. Pore water exchange and ammonification enhanced DIN concentration in the estuary water, while intensities of DIN addition varied between seasons. The riverine DIN flux could reach 101.5 ton(N)/d, supporting the coastal primary productivity.
Three cruises were conducted in the Rajang river estuary, Malaysia. The results revealed that...
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