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Biogeosciences An interactive open-access journal of the European Geosciences Union
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© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Submitted as: research article 20 May 2020

Submitted as: research article | 20 May 2020

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This preprint is currently under review for the journal BG.

New insights into mechanisms of sunlight-mediated high-temperature accelerated diurnal production-degradation of fluorescent DOM in lake waters

Yijun Liu1,2, Jie Yuan3, Fu-Jun Yue1,2, Si-Liang Li1,2, Baoli Wang1,2, Mohammad Mohinuzzaman1,2, Xuemei Yang1,2, Nicola Senesi4, Xinyu Lao1,2, Longlong Li1,2, Cong-Qiang Liu1,2, Rob M. Ellam5,1, and Khan M. G. Mostofa1,2 Yijun Liu et al.
  • 1Institute of Surface-Earth System Science, Tianjin University, 92 Weijin Road, Tianjin 300072, China
  • 2Tianjin Key Laboratory of Earth Critical Zone Science and Sustainable Development in Bohai Rim, Tianjin University, 92 Weijin Road, Tianjin 300072, China
  • 3Key Laboratory of Earth and Planetary Physics, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beitucheng Western Road, Chaoyang District-100029, Beijing, PR China
  • di Scienze del Suolo, della Pianta e degli Alimenti, Università degli Studi di Bari "Aldo Moro", Via G. Amendola 165/A, 70126 BARI–Italy
  • 5Scottish Universities Environmental Research Centre, Rankine Avenue, Scottish Enterprise Technology Park, East Kilbride, G75 0QF, UK

Abstract. The production of fluorescent dissolved organic matter (FDOM) produced from phytoplankton and its subsequent degradation both of which occur constantly under diurnal-day time sunlight and by night time dark-microbial processes, influence markedly several biogeochemical processes and functions in aquatic environments and can be feasibly related to global warming (GW). In this work sunlight-mediated high-temperature was shown to accelerate the production of FDOM, but also its complete disappearance over a 24-h diurnal period in July, but not in lower temperature months. In July, extracellular polymeric substances (EPS), an early-state DOM, were produced from phytoplankton in early morning (06:00–09:00), then were degraded into four FDOM components over midday (10:00–15:00), which was followed by simultaneous production and almost complete degradation of FDOM with reformation of EPS during night time (02:00–06:00). Such transformations occurred simultaneously with the fluctuating production of nutrients (NH4+, NO3, NO2, PO43− and dissolved Si), dissolved organic carbon (DOC), dissolved organic nitrogen (DON) and the two isotopes (δ15N and δ18O) of NO3. The FDOM components identified by fluorescence excitation-emission matrix (EEM) spectroscopy combined with parallel factor (PARAFAC) analysis consisted of EPS, autochthonous humic-like substances (AHLS) of C and M types distinctly, a combined form of C and M types of AHLS, protein-like substances (PLS), newly-released PLS, tryptophan-like substances (TLS), tyrosine-like substances (TYLS), a combined form of TYLS and phenylalanine-like substances (PALS), as well as their degradation products. Finally, stepwise degradation and production processes are synthesized in a pathway for FDOM components production and their subsequent transformation under different diurnal temperature conditions, which provided a broader paradigm for future impacts on GW-mediated DOM dynamics in lake water.

Yijun Liu et al.

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Yijun Liu et al.

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