MOLECULAR COMPOSITION AND OPTICAL PROPERTIES OF NATURAL ORGANIC MATTER: CORRELATING BULK SPECTROSCOPY AND ULTRAHIGH RESOLUTION MASS SPECTROMETRY

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1 MOLECULAR COMPOSITION AND OPTICAL PROPERTIES OF NATURAL ORGANIC MATTER: CORRELATING BULK SPECTROSCOPY AND ULTRAHIGH RESOLUTION MASS SPECTROMETRY CLIMATE CHANGE AND DOM IN PEATLANDS William T. Cooper*, MalakTfaily*, Rasha Hamdan*, Anahita Zare*, Jane Elizabeth Corbett #, Jeffrey P. Chanton # *Department of Chemistry & Biochemistry # D t f E th O d At h i Si # Dept of Earth, Ocean and Atmospheric Science Florida State University

2 REACTIVE AND REFRACTORY COMPONENTS OF DISSOLVED ORGANIC MATTER IN PEATLAND SOIL POREWATERS RELATIONTO TO CLIMATECHANGE CHANGE With soil depths up to 3 to 5 meters, peatlands serve as large repositories of stored carbon, an amount representing 25 to 50% of current levels of atmospheric CO 2 The balance between net ecosystem production and decomposition (or heterotrophic respiration) of peat is thus of considerable interest. It has been proposed that peats will accumulate until the respiration of solidphase peat in the underlying column matched the rate of CO 2 uptake at the surface. Thereafter a peatland would exist in a steady statestate with respect to its carbon balance in which C fixation balanced decomposition in the soil column. Recent evidence suggests that HYDROLOGY may play an important role in establishing this steady state balance.

3 Study Sites in the Glacial Lake Agassiz Peatland (GLAP) Red Lake (RL) IV Fen and Bog Sites RL IV Fen RL II RL IV Bog

4 Bogs and Fens

5 Organic Matter Evolution IN GLAP FEN Radiocarbon distribution in Glacial Lake Agassiz Red Lake II Fen cm depth, Δ 14 C Peat DIC/ CH 4 * DOC Filled diamonds represent peat radiocarbon values, filled triangles DIC, open triangles CH 4 and filled squares, DOC. Symbols adjacent to an * are overlapping.

6 Organic Matter Evolution in GLAP BOG Radiocarbon distribution in Glacial Lake Agassiz Red Lake II Bog cm depth, Δ 14 C Peat DIC/ CH 4 DOC Filled diamonds represent peat radiocarbon values, filled triangles DIC, open triangles CH 4 and filled squares, DOC.

7 Organic Matter Evolution in GLAP FEN & BOG DOC - Δ 14 C Bogs Fens & Lawns Thus, a significant fraction of DIC & CH 4 in the BOGS are solid-phase respiration products DIC - Δ 14 C DOC radiocarbon content versus DIC radiocarbon content for sites with Carex present, fens and lawns (open triangles) and Sphagnum-woody plant dominated sites (filled diamonds). The line was drawn with a slope of 1.

8 Conclusions Part I 1. The 14 C content t of the products of respiration, CH 4 and ddic, are similar to DOC in sedge-dominated FEN peatlands. In Sphagnum-woody plant dominated BOG peatlands, however, the respiration products are intermediate between the 14 C content of the solid phase peat and the DOC. 2. Molecular-level characterization indicated qualitative differences in the DOC in sphagnum-woody plant and sedgedominated peatlands that were consistent with the variations in DOC reactivity. The aromatic-rich BOG DOC appears less reactive than DOC in the FEN. 3. The cause of this differential reactivity, and whether it is associated with production or environmental effects, is currently under investigation. Biochemical? Enzymatic? Hydrologic? Sphagnum bog Fen Chanton et al. Glob. Biogeochem. Cycles, D Andrilli et al. Org. Geochem

9 Ultrahigh Resolution and Mass Accuracy Mass Spectrometry m z = eb ω Homologous Series I Black River C27H21O16 Abu undance C26H17O17 C H O C28H25O15 Homologous Series II C29H29O14 C24H25O18 C30H33O13 C25H29O17 C31H37O12 C26H33O16 C32H41O m/z

10 Correlating Bulk Spectroscopy and Ultrahigh Resolution Mass Spectrometry Fourier-transform ion cyclotron resonance mass spectrometry (FT-ICR MS) Molecular-level characterization of DOM Excitation-emission matrix spectroscopy (EEMS) Characterizes CDOM Absorption spectroscopy Characterizes CDOM

11 Sample Characteristics Bog Fen Depth (cm) ph DOC (mm) Depth (cm) ph DOC (mm)

12 van Krevelen diagrams BOG Lipid-like Formulas UNIQUE to the Surface Deep Bog Lignin-like RL IV bog (10 cm) Tannin-like 85 % of molecular formulas in surface found at depth Lipid-like Lignin-like RL IV bog (290 cm) Tannin-like Few Compounds new compounds with high being O/C disappear formed with depth 12

13 Number of formu ulas DBE O PLOTS DBE = C (H/2) + (N/2) +1 DBE-O represents C=C bonds by subtracting out the C=O contribution: measures carbon unsaturation 300 Bog 10cm Oxygenated compounds are disappearing with 250 Bog 290cm depth; highly unsaturated t compounds are concentrated DBE-O Oxygenated compounds Carbon Unsaturation

14 van Krevelen diagrams FEN Lipid-like Formulas UNIQUE to the Surface Deep Fen Lignin-like RL IV fen (10 cm) Tannin-like 76 % of molecular formulas in surface found at depth Lipid-like Lignin-like RL IV fen (300 cm) Tannin-like Many Compounds new compounds with high appear, O/C disappears many with relatively with depth high H/C ratios 14

15 DBE O PLOTS Numbe er of form mulas Fen 10cm Fen 200cm Overall degree of unsaturation relatively unchanged with depth Oxygenated compoundsdbe-o Carbon Unsaturation 15

16 EEMS spectra Peaks A and C; Humic-like terrestrial signatures in peatland DOM Peak A: Humic-like Peak C: Fulvic-like Austnes et al. Biogeochemistry,

17 DOC Fluorescence intensity plots Dep pth (cm) Bog ( Peaks A & C) Fen ( Peaks A and C) FI/DOC (QSE/mM) Peak C Peak A Peak C Dep pth (cm) FL/DOC (QSE/mM) Peak A RL IV Bog peak A RL IV Bog peak C RL IV fen peak A RL IV fen peak C Little change in the bog with Deep fen is exhibits less depth; if any change increasing fluorescence per unit mole compared to surface fen 17

18 SUVA plots SUVA = A 254 (m -1) / [DOC] (mg C/L) = Correlated with DOM aromaticity SUVA (L mg C -1 m -1 ) % non-matching molecular formulas Fen Bog Aromaticity of bogs is slightly changing with depth, if increasing Deep fen samples show lower aromaticity consistent with normalized FI value Lower Aromaticity Higher Aromaticity 18

19 Fluorescence/Absorption Plots Bog Decreases with the decrease of aromatic/conjugated molecules Surface fen Deep fen As MW increases, the ratio decreases 19

20 DOC and C/N Plots Bog Bog Fen Fen Fen The elevated [DOC] and C/N ratios in Sphagnum and woody plant bog DOM suggest less reactivity at the bog sites 20

21 Thermal Fluorescence Quenching Fluorescence is quenched as temperature increases. The extent of thermal quenching occurs depends on the molecular composition of fthe fluorophores. Bog DOM at 100 cm 10 C 15 C 20 C 25 C 30 C 35 C 40 C 45 C Relative STDV < 3 %

22 Thermal Fluorescence Quenching FEN Peak A* Peak C* Fen 50 cm 32.9 % 30.4 % Fen 100 cm 32.2 % % Fen 200 cm % % Fen 300 cm 29.7 % 24.2 % *reduction in fluorescence at 45 o C vs. 10 o C Fen humic (peak A) thermal quenching did not change significantly with depth, suggesting only a slight change (if any) in the composition of fen peak A fluorophores throughout the depth profile. Fen fulvic (peak C) thermal quenching, on the other hand, decreased with depth, suggesting a change in the composition of fulvic like fluorophores. Observed variability of fluorescence quenching is significantly less than the observed differences in fluorescence quenching

23 Thermal Fluorescence Quenching BOG Peak A* Peak C* Bog 50 cm 33% 30% Bog 100 cm 32.8 % 30.5 % Bog 200 cm % % Bog humic like fluorescence exhibited slightly higher fluorescence quenching relative to fulvic like fluorescence. This suggests differences in their composition. Bog 290 cm 30.59% 28.6 % *reduction in fluorescence at 45 o C vs. 10 o C Humic and fulvic like fluorescence quenching in the bog did not vary much with depth. This slight change in thermal quenching suggests a slight (if any) change in the composition of DOM. Observed variability of fluorescence quenching is significantly less than the observed differences in fluorescence quenching

24 Acknowledgements FSU Chemistry NHMFL N.S.F. High-Field FT-ICR Mass Spectrometry Facility at the National High Magnetic Field Laboratory National Science Foundation; Carbon & Water Program, Earth Sciences

25 Acknowledgements The Cooper Research Group The GLAP Working Group