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Open AccessArticle

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

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Department of River Ecology, Helmholtz Centre for Environmental Research—UFZ, Brückstraße 3a, 39114 Magdeburg, Germany
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Department of Lake Research, Helmholtz Centre for Environmental Research—UFZ, Brückstraße 3a, 39114 Magdeburg, Germany
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Department of Analytical Chemistry, Helmholtz Centre for Environmental Research—UFZ, Research Group BioGeoOmics, Permoserstr. 15, 04318 Leipzig, Germany
*
Author to whom correspondence should be addressed.
Water 2020, 12(2), 331; https://doi.org/10.3390/w12020331
Received: 26 December 2019 / Revised: 14 January 2020 / Accepted: 16 January 2020 / Published: 23 January 2020
Photochemical processing is an important way to transform terrestrial dissolved organic matter (DOM) but was rarely investigated by ultra-high resolution mass spectrometry. We performed an irradiation experiment with water from a shaded forest stream flowing into a lit reservoir. Bacterial activity explained only 1% of dissolved organic carbon (DOC) decline in a combined bacterial and photodegradation approach. Photodegradation decreased the DOC concentration by 30%, the specific ultraviolet (UV) absorption by 40%–50%, and fluorescence intensity by 80% during six days. The humification index (HIX) decreased whereas the fluorescence index (FI) did not change. Two humic-like components identified by parallel factor analysis (PARAFAC) of excitation–emission matrices followed the decrease of fluorescent DOM. Changes of relative peak intensities of Fourier transform-ion cyclotron resonance mass spectroscopy (FT-ICR MS) elemental formula components as a function of cumulated radiation were evaluated both by Spearman’s rank correlation and linear regression. The FT-ICR MS intensity changes indicate that high aromatic material was photochemically converted into smaller non-fluorescent molecules or degraded by the release of CO2. This study shows the molecular change of terrestrial DOM before the preparation of drinking water from reservoirs.
Keywords: photodegradation; DOC; SUVA254; 2D fluorescence; HIX; FT-ICR MS; PARAFAC; light-dark photodegradation; DOC; SUVA254; 2D fluorescence; HIX; FT-ICR MS; PARAFAC; light-dark
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MDPI and ACS Style

Wilske, C.; Herzsprung, P.; Lechtenfeld, O.J.; Kamjunke, N.; von Tümpling, W. Photochemically Induced Changes of Dissolved Organic Matter in a Humic-Rich and Forested Stream. Water 2020, 12, 331.

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