Improved Understanding of Dissolved Organic Matter Processing in Freshwater Using Complementary Experimental and Machine Learning Approaches

Abstract

Dissolved organic matter plays an important role in aquatic ecosystems and poses a major problem for drinking water production. However, our understanding of DOM reactivity in natural systems is hampered by its complex molecular composition. Here, we used Fourier-transform ion cyclotron resonance mass spectrometry (FT-ICR-MS) and data from two independent studies to disentangle DOM reactivity based on photochemical and microbial-induced transformations. Robust correlations of FT-ICR-MS peak intensities with chlorophyll a and solar irradiation were used to define 9 reactivity classes for 1277 common molecular formulas. Germany’s largest drinking water reservoir was sampled for 1 year, and DOM processing in stratified surface waters could be attributed to photochemical transformations during summer months. Microbial DOM alterations could be distinguished based on correlation coefficients with chlorophyll a and often shared molecular features (elemental ratios and mass) with photoreactive compounds. In particular, many photoproducts and some microbial products were identified as potential precursors of disinfection byproducts. Molecular DOM features were used to further predict molecular reactivity for the remaining compounds in the data set based on a random forest model. Our method offers an expandable classification approach to integrate the reactivity of DOM from specific environments and link it to molecular properties and chemistry.

Delineating Source Contributions to Stream Dissolved Organic Matter Composition Under Baseflow Conditions in Forested Headwater Catchments

“…sources (Lechtenfeld et al, 2014;Raeke et al, 2017;Wagner et al, 2015) and transformation processes (Herzsprung et al, 2020). Moreover, the high resolution of FT-ICR-MS allows the identification of individual molecular formulas for molecules which may also contain lowabundance heteroatoms like nitrogen and sulfur (Herzsprung et al, 2016).…”

Judgement and assessment of high resolution mass spectrometry investigations of DOM – Examples for identification of biogeochemical processes in waters

“…It was identified to be photo degraded in the other experiment [12]. The photo product C 9 H 12 O 5 was evidently accumulated in the epilimnion during lake stratification whereas the photo degraded component C 17 H 18 O 6 was depleted [11].…”

“…c) Furthermore the inter sample ranks also can be used for calculation of Spearman's rank correlation with external parameters, like the fluorescence intensity [8][9] or the concentration of chorophyll a (Chla) [11]. In figure 2 top left and right significant positive and negative correlating components (p < 0.005, n = 60) are shown.…”

“…The highly significant correlating components have potentially the highest abundance (relative intensity) differences in the The rank correlation with external parameters as shown in figure 2 top left and right helps to find out components with potential large abundance differences in samples. The Rappbode Reservoir was monitored in 2016 in each eight or nine different depths and at seven different month (from January to December) [11]. The correlation to Chla was calculated because Chla is depending on light.…”

Small-scale topography explains patterns and dynamics of dissolved organic carbon exports from the riparian zone of a temperate, forested catchment

“…Molecular formulas were assigned to peaks in the range 0-750 m/z allowing for elemental compositions C 1−60 H 0−122 N 0−2 O 0−40 S 0−1 with an error range of ±0.5 ppm according to Herzsprung et al (2020). Briefly, the following rules were applied: 0 Koch et al, 2014), −10 ≤ DBE-O ≤ 10 ( Herzsprung et al, 2014), and element probability rules proposed by Kind and Fiehn (2007).…”