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Photochemically Induced Changes of Dissolved Organic Matter in a Humic-Rich and Forested Stream
Open AccessArticle

Quality of Dissolved Organic Matter Driven by Autotrophic and Heterotrophic Microbial Processes in a Large River

1
Department of River Ecology, Helmholtz—Centre for Environmental Research—UFZ, Brückstraße 3a, D-39114 Magdeburg, Germany
2
Department of Analytical Chemistry and ProVIS—Centre for Chemical Microscopy, Helmholtz Centre for Environmental Research—UFZ, Permoserstr. 15, 04318 Leipzig, Germany
3
Department of Lake Research, Helmholtz Centre for Environmental Research—UFZ, Brückstraße 3a, 39114 Magdeburg, Germany
*
Author to whom correspondence should be addressed.
Water 2020, 12(6), 1577; https://doi.org/10.3390/w12061577
Received: 7 May 2020 / Revised: 28 May 2020 / Accepted: 29 May 2020 / Published: 31 May 2020
Rivers are regarded as important sites for processing of dissolved organic matter (DOM) from terrestrial sources on its way to the ocean. However, little is known about the longitudinal change of DOM molecular composition in large rivers. Here we performed a Lagrangian sampling in the lower part of the Middle Elbe at low discharge conditions to test how DOM composition changes along the river stretch and how this is related to microbial processes. The concentration of dissolved organic carbon and fluorescence indices showed only subtle longitudinal differences. In contrast, ultra-high-resolution mass spectrometry analysis of riverine DOM detected pronounced changes in molecular composition. Also, chlorophyll a concentration, bacterial abundance, and bacterial production all increased downstream. The three microbial parameters were positively related to intensities of CHO and CHNO molecular formulas with high hydrogen/carbon and low oxygen/carbon ratios but negatively to several CHOS surfactants. To disentangle the role of autotrophic and heterotrophic processes, we developed a new approach and compared slopes from linear regression of DOM compound intensities versus chlorophyll a concentration and bacteria abundance. As a result, most of the positive related DOM compounds were produced by bacteria. In conclusion, longitudinal changes of river DOM seemed to be largely driven by microbial processes. View Full-Text
Keywords: dissolved organic matter (DOM); fourier transform-ion cyclotron resonance mass spectroscopy (FT-ICR MS); phytoplankton; bacteria; bacterial production dissolved organic matter (DOM); fourier transform-ion cyclotron resonance mass spectroscopy (FT-ICR MS); phytoplankton; bacteria; bacterial production
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MDPI and ACS Style

Kamjunke, N.; Lechtenfeld, O.J.; Herzsprung, P. Quality of Dissolved Organic Matter Driven by Autotrophic and Heterotrophic Microbial Processes in a Large River. Water 2020, 12, 1577.

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