Use of FT ICR MS to characterize seasonal and spatial variability of dissolved organic matter in a small forested catchment

Inland water process large amounts of dissolved organic matter (DOM), representing an important component in the global carbon cycle. Locally, DOM has an important ecological and biogeochemical role that may vary according to its quality (e.g. composition). Land use, season and hydrologic regime are some factors that possibly will influence the changes in DOM composition. State-of-the art technique to study the molecular chemical composition of DOM is Fourier transform ion cyclotron resonance mass spectrometry (FT ICR MS). The analysis of changes in DOM quality by FT ICR MS allows conclusions to be drawn about the sources and mobilization processes of the organic material. In this study we investigate the changes in DOM quality over a period of 1.5 year in a small forested catchment composed of two different zones: wetland (zone A) and steep slope areas (zone B). The catchment is located in the National Park Bayerischer Wald in Southern Germany. This offers a natural environment unaffected by direct anthropogenic influence. Therefore, only indirect anthropogenic effects and natural vegetation disturbances and possible interactions between them can affect DOM dynamics. Monthly samples were taken along the rivers (1st and 2nd order) from September 2018-November 2018 and from April 2019-November 2019 with a total of 124 samples. The samples were analyzed by FT ICR MS, total organic carbon analyzer and UV/VIS spectrometer. Our results showed that the concentration of dissolved organic carbon between the sampling points is similar, but differs over the year at normal discharge conditions. FT ICR MS analysis indicated that the main molecular composition of DOM was CHO (38-47%), with the majority of the composition consisting of highly unsaturated compounds. Conversely, samples in zone A had more aliphatic compounds and nitrogen formulas than the ones sampled in zone B during the year. UV/VIS data also indicated that DOM is more aromatic in the zone B. The results suggest that DOM coming mainly from ground water is the dominant pool of organic matter in the wetland during the year, while in the steep zone a contribution from fresh-plant derived DOM is expected. We also found predominantly low averaged molecular weight DOM in summer in the catchment, suggesting that biological activity plays an important role during this season in DOM quality. We conclude that understanding the dynamic and mobilization mechanisms of DOM in catchments with low human impact are important for the conceptual understanding of natural DOM regulation mechanisms.

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

Water ◽

10.3390/w12020331 ◽

2020 ◽

Vol 12 (2) ◽

pp. 331 ◽

Cited By ~ 4

Author(s):

Christin Wilske ◽

Peter Herzsprung ◽

Oliver J. Lechtenfeld ◽

Norbert Kamjunke ◽

Wolf von Tümpling

Keyword(s):

Organic Matter ◽

Dissolved Organic Matter ◽

High Resolution Mass Spectrometry ◽

Rank Correlation ◽

Ion Cyclotron Resonance ◽

Molecular Change ◽

Spearman’S Rank Correlation ◽

Forest Stream ◽

Ft Icr Ms ◽

Ft Icr

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.

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A molecular perspective on the ageing of marine dissolved organic matter

Biogeosciences ◽

10.5194/bg-9-1935-2012 ◽

2012 ◽

Vol 9 (6) ◽

pp. 1935-1955 ◽

Cited By ~ 119

Author(s):

R. Flerus ◽

O. J. Lechtenfeld ◽

B. P. Koch ◽

S. L. McCallister ◽

P. Schmitt-Kopplin ◽

...

Keyword(s):

Organic Matter ◽

Dissolved Organic Matter ◽

Thermohaline Circulation ◽

Solid Phase ◽

Amino Sugar ◽

Ion Cyclotron Resonance ◽

Magnitude Comparison ◽

Degradation Rates ◽

Ft Icr Ms ◽

Ft Icr

Abstract. Dissolved organic matter (DOM) was extracted by solid-phase extraction (SPE) from 137 water samples from different climate zones and different depths along an eastern Atlantic Ocean transect. The extracts were analyzed with Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) with electrospray ionization (ESI). Δ14C analyses were performed on subsamples of the SPE-DOM. In addition, the amount of dissolved organic carbon was determined for all water and SPE-DOM samples as well as the yield of amino sugars for selected samples. Linear correlations were observed between the magnitudes of 43 % of the FT-ICR mass peaks and the extract Δ14C values. Decreasing SPE-DOM Δ14C values went along with a shift in the molecular composition to higher average masses (m/z) and lower hydrogen/carbon (H/C) ratios. The correlation was used to model the SPE-DOM Δ14C distribution for all 137 samples. Based on single mass peaks, a degradation index (IDEG) was developed to compare the degradation state of marine SPE-DOM samples analyzed with FT-ICR MS. A correlation between Δ14C, IDEG, DOC values and amino sugar yield supports that SPE-DOM analyzed with FT-ICR MS reflects trends of bulk DOM. DOM weighted normalized mass peak magnitudes were used to compare aged and recent SPE-DOM on a semi-quantitative molecular basis. The magnitude comparison showed a continuum of different degradation rates for the detected compounds. A high proportion of the compounds should persist, possibly modified by partial degradation, in the course of thermohaline circulation. Prokaryotic (bacterial) production, transformation and accumulation of this very stable DOM occur primarily in the upper ocean. This DOM is an important contribution to very old DOM, showing that production and degradation are dynamic processes.

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Molecular insights into the unique degradation trajectory of natural dissolved organic matter from surface to groundwater

10.5194/egusphere-egu21-1845 ◽

2021 ◽

Author(s):

Liza McDonough ◽

Megan Behnke ◽

Robert Spencer ◽

Christopher Marjo ◽

Martin Andersen ◽

...

Keyword(s):

Organic Matter ◽

Surface Water ◽

Organic Carbon ◽

Dissolved Organic Matter ◽

Molecular Properties ◽

Marine Environments ◽

Groundwater Environment ◽

Ft Icr Ms ◽

Over Time ◽

Ft Icr

Dissolved organic matter (DOM) comprises a large and complex range of molecules with varying mass, elemental arrangements, conformation, and polarity. These diverse molecules interact with the environment resulting in changes to their molecular character and reactivity over time. Significant advances in our understanding of the molecular character of reactive and recalcitrant DOM have been made throughout the past decade, largely due to the development of ultra-high resolution techniques such as Fourier-transform ion cyclotron resonance mass spectrometry (FT-ICR MS). This understanding, however, is almost entirely based on surface water environments. Here, we investigate how the molecular properties of DOM change due to reactions occurring in a groundwater environment over time. We use FT-ICR MS combined with liquid chromatography organic carbon detection (LC-OCD), fluorescence and radiocarbon (14C) dissolved organic carbon (DOC) for a range of groundwater DOM samples, including the oldest DOC reported from a site which is not impacted by sedimentary organic carbon inputs (25,310 &#177; 600 years BP). Our results indicate that polarity and nominal oxidation state of carbon (NOSC) play a major role in the reactivity of groundwater DOM, with a preferential removal of hydrophilic, high oxygen to carbon (O/C) ratio molecules over time (rs = 0.91, p = 2.4 x 10-6). We also note an increase in likely bio-produced molecules containing low numbers of O atoms in deep methanogenic groundwater environments. These molecular formulae appear to accumulate due to the prolonged anoxic conditions which would not be experienced by surface water DOM. The decline in NOSC with increasing average bulk groundwater DOC age contrasts with findings from marine environments where NOSC has been reported to increase over time. Furthermore, the proportion of specific molecular formulae which are stable in marine waters, decline in groundwater as 14CDOC decreases (rs = 0.68, p = 6.9 x 10-3) suggesting that current indicators of DOM degradation state derived from marine environments are not applicable to groundwater environments. Our research shows that the molecular character of reactive DOM in groundwater differs from that of surface water due to exposure to different environments and processing mechanisms, suggesting that it is the interaction between external environmental factors and intrinsic DOM molecular properties which control DOM recalcitrance.

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A molecular perspective on the ageing of marine dissolved organic matter

Biogeosciences Discussions ◽

10.5194/bgd-8-11453-2011 ◽

2011 ◽

Vol 8 (6) ◽

pp. 11453-11488 ◽

Cited By ~ 5

Author(s):

R. Flerus ◽

B. P. Koch ◽

O. J. Lechtenfeld ◽

S. L. McCallister ◽

P. Schmitt-Kopplin ◽

...

Keyword(s):

Organic Matter ◽

Dissolved Organic Matter ◽

Thermohaline Circulation ◽

Solid Phase ◽

Relative Mass ◽

Ion Cyclotron Resonance ◽

Degradation Index ◽

Single Mass ◽

Ft Icr Ms ◽

Ft Icr

Abstract. Dissolved organic matter (DOM) was extracted with solid phase extraction (SPE) from 137 water samples from different climate zones and different depths along an Eastern Atlantic Ocean transect. The extracts were analyzed with Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) with electrospray ionization (ESI). Δ14C analyses were performed on subsamples of the SPE-DOM. In addition, the amount of dissolved organic carbon was determined for all water and SPE-DOM samples as well as the yield of amino sugars for selected samples. Linear correlations were observed between the magnitudes of 43 % of the FT-ICR mass peaks and the extract Δ14C values. Decreasing SPE-DOM Δ14C values went along with a shift in the molecular composition to higher average masses (m/z) and lower hydrogen/carbon (H/C) ratios. The correlation was used to model the SPE-DOM Δ14C distribution for all 137 samples. Based on single mass peaks a degradation index was developed to compare the degradation state of marine SPE-DOM samples analyzed with FT-ICR MS. A correlation between Δ14C, degradation index, DOC values and amino sugar yield supports that SPE-DOM analyzed with FT-ICR MS reflects trends of bulk DOM. A relative mass peak magnitude ratio was used to compare aged SPE-DOM and fresh SPE-DOM regarding single mass peaks. The magnitude ratios show a continuum of different reactivities for the single compounds. Only few of the compounds present in the FT-ICR mass spectra are expected to be highly degraded in the oldest water masses of the Pacific Ocean. All other compounds should persist partly thermohaline circulation. Prokaryotic (bacterial) production, transformation and accumulation of this very stable DOM occurs probably primarily in the upper ocean. This DOM is an important contribution to very old DOM, showing that production and degradation are dynamic processes.

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