BG1.10 | Molecular and Isotopic Tracers across Environmental Interfaces: The Carbon Cycle, Pyrogenic and Natural Organic Matter
EDI
Molecular and Isotopic Tracers across Environmental Interfaces: The Carbon Cycle, Pyrogenic and Natural Organic Matter
Co-organized by SSS5
Convener: Marcus SchiedungECSECS | Co-conveners: Franziska Lechleitner, Jutta Niggemann, Carsten SimonECSECS, Blanca Ausin, Anna GuninaECSECS, Philipp MaurischatECSECS
Orals
| Fri, 19 Apr, 08:30–12:30 (CEST), 14:00–15:45 (CEST)
 
Room 1.14
Posters on site
| Attendance Fri, 19 Apr, 16:15–18:00 (CEST) | Display Fri, 19 Apr, 14:00–18:00
 
Hall X1
Posters virtual
| Attendance Fri, 19 Apr, 14:00–15:45 (CEST) | Display Fri, 19 Apr, 08:30–18:00
 
vHall X1
Orals |
Fri, 08:30
Fri, 16:15
Fri, 14:00
Understanding the partitioning of carbon in different reservoirs on Earth, and the sensitivity of these reservoirs to climatic and anthropogenic factors, remains a key challenge in predicting future responses to global warming. A lot of this uncertainty stems from the inherent complexity of the carbon cycle, where physical, chemical, and biological processes interact on different temporal and spatial scales. Thus, a wide variety of tracers are needed to unravel individual processes and assess their sensitivity to climatic and anthropogenic influences.

Natural Organic matter (OM) is globally ubiquitous and a keystone interactive medium in environmental ecosystem functioning. The vast molecular diversity of natural OM may be both a symptom or a cause of its mediating role in various processes essential for life on Earth, such as nutrient retention and resupply, or climate stability. Dissolved organic matter (DOM) forms the main carbon and energy source for microbial life, still it accumulates in the oceans to one of the biggest carbon reservoirs on Earth. Pyrogenic organic matter (PyOM) is an important component of OM and is characterized by its condensed aromatic composition. It originates from natural (e.g., wildfires) and anthropogenic sources (e.g., biochar) and despite the importance of PyOM in the environment, its processing and fate remain largely unknown.

In this session, we aim to bring together the latest insights into the partitioning and size of all reservoirs of the global carbon cycle and the processes governing fluxes of carbon between these reservoirs. We invite contributions from process- to field-scale approaches and method development for a detailed understanding of isotopic and molecular composition of individual carbon reservoirs, as well as their active role within ecosystem functioning. We are interested in studies showing new field data, laboratory experiments and modeling that use geochemical tracers (e.g., 14C, biomarkers, stable and non-traditional isotopes, trace elements) combined with geomorphic and hydrological tools to unravel controls on the carbon cycle from the local to the global scale. Modern analytical tools and their combination are crucial in advancing this research field, encompassing a variety of spectroscopic and mass spectrometric techniques (AMS, NIR, MIR, NMR, XPS, py-GC-MS, HR-MS, LC-MS-MS, EEMs-PARAFAC, PTR-MS, etc.) as well as new computational approaches.

Orals: Fri, 19 Apr | Room 1.14

Chairpersons: Franziska Lechleitner, Blanca Ausin
08:30–08:35
08:35–08:45
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EGU24-5444
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ECS
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On-site presentation
Chen Li, Zhimin Jian, and Haowen Dang

As a vital component of the global carbon cycle, the ocean’s biological carbon pump determines the amount of carbon fixed by primary production in the surface waters. The efficiency of this biological pump is closely interconnected with the nitrogen cycle, which regulates nutrient inventory and primary productivity rates. Additionally, the structure of the upper ocean ecosystem influences the efficiency of the biological pump by determining how much fixed carbon is exported to the deep ocean. Compound-specific nitrogen isotope (δ15NAA) is a novel proxy that could provide valuable insights into both aspects of these questions. The δ15NAA could unravel isotopic information of source nitrogen and show δ15N changes associated with trophic processes. This study generates sedimentary δ15NAA, as well as bulk sediment δ15N and organic δ15N records from a western equatorial Pacific site (MD10-3340) covering the last 140 kyr. Our results demonstrate an overall agreement among three proxies, all indicating distinct precessional variations in source nitrate δ15N and potential changes in nutrient inventory. More importantly, the δ15NAA signatures suggest an inverse relationship between animal trophic activity in the surface water and the degradation of organic matter precipitating through the water column. Higher ecosystem trophic position is found during glacial periods, accompanied by inactive organic matter recycling, which implies a greater potential for carbon burial in deep reservoirs. Together, we suggest that the δ15NAAsignatures can provide a detailed picture of carbon cycle coupled with nitrogen cycle.

How to cite: Li, C., Jian, Z., and Dang, H.: Efficiency of Biological Carbon Pump: Insights from Compound-Specific Amino Acid δ15N, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5444, https://doi.org/10.5194/egusphere-egu24-5444, 2024.

08:45–08:55
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EGU24-17503
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ECS
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On-site presentation
Sara Campderrós, Leopoldo D. Pena, Jaime Frigola, Ester Garcia-Solsona, Eduardo Paredes, Negar Haghipour, Heather M. Stoll, and Isabel Cacho

The Iberian Margin is a dynamic margin, affected by complex sedimentary and oceanographic processes. The Mediterranean Outflow Water (MOW) is a prominent water mass that flows along the Iberian margin and interacts with the sediment on the slope. However, more information about how MOW interacts with sediment delivery, distribution, deposition along the margin is needed. In this study we combine Nd, Sr and Pb isotopes on fine-grained detrital sediments (< 63 μm) and 14C measurements in planktonic foraminifera (G. bulloides) in 25 coretop sediment samples collected along the entire Iberian Margin (from the Gulf of Cadiz to the “Cachucho” mount in the Cantabrian Sea). Nd, Sr and Pb isotopes were used to (i) identify the main source areas of terrigenous sediments coming from the Iberian Peninsula and (ii) trace the distribution of these sediments along the Iberian Margin. Additionally, 14C data in planktonic foraminifera were used to obtain radiocarbon ages, that allowed us to date the coretop sediments. Results from Nd, Sr and Pb isotopes allow us to identify three main terrigenous sediment source provinces in the Iberian margin, depicting a prominent south to north gradient. Moreover, large age discrepancies in coretop sediments are strongly associated with the main pathway of MOW, thus suggesting erosion and lateral transport of sediments along the main path of the MOW.

How to cite: Campderrós, S., Pena, L. D., Frigola, J., Garcia-Solsona, E., Paredes, E., Haghipour, N., Stoll, H. M., and Cacho, I.: Sediment source and transport along the Iberian Margin, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17503, https://doi.org/10.5194/egusphere-egu24-17503, 2024.

08:55–09:05
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EGU24-1180
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ECS
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On-site presentation
Rakesh Kumar Rout, Gyana Ranjan Tripathy, Satyabrata Das, and Santosh K. Rai

Oxidation of pyrites plays a key role in global chemical and climatic cycles. In particular, interaction of sulfuric acid produced through this process with carbonates releases CO2 to the atmosphere. This CO2 source counterbalances the CO2 consumed during silicate weathering in river basins, and hence, may influence earlier-suggested linkage between silicate weathering and global cooling events. In this study, we have investigated the dissolved major ions and sulfur isotopes of Indus headwaters to quantify the net effect of sulfide oxidation on the CO2 budget. This research is an attempt to evaluate the coupling between global Cenozoic cooling event and Himalaya weathering - ­a hypothesis which overlooked the CO2 supply via sulfide and organic oxidation. Towards this, we have employed sulfur isotopes (δ34S) as a proxy for riverine sulfate sources, mainly due to its distinct composition for the two major end-members [pyrite (~ -12 ‰) and gypsum (~ 17 ‰); [1]]. The average sulfate concentrations for the Indus headwaters are found to be higher than the regional rainfall, global average for rivers, and other major Himalayan rivers (e.g., Ganga and the Brahmaputra). Consistently, the mean δ34S for the Indus headwaters is also depleted with respect to that reported for the Ganga (~ 2 ‰) and Brahmaputra (~ 4 ‰) outflows [1-5]. Also, the sulfur isotopic values for the Indus headwaters are systematically depleted by 3 to 4 ‰ than that reported earlier for Indus mainstream [3]. These lighter δ34S values for the headwaters hint at relatively higher sulfide oxidation in the northwestern (NW) Himalaya compared to central and eastern Himalayas. Also, these processes are found to be more intense in the mountainous regions than in the floodplains. These observations are consistent with the basin lithology dominated by Paleozoic carbonates and organic-rich shales, and higher glacial coverage. Estimation of sulfide-derived cations from carbonate weathering and silicate-derived cations indicate that the chemical weathering in the Indus headwaters serve as a net source of CO2 to the atmosphere. This finding is in contrast with previous suggestion of significant CO2 removal during the Himalaya weathering and hence, challenges the role of land surface processes in the NW Himalaya in regulating the Cenozoic cooling event.

 

 

References

[1] Burke et al., (2018), Earth Planet. Sci. Lett., 496, 168-177.

[2] Chakrapani et al., (2009), J. Asian Earth Sci., 34, 347-362.

[3] Karim and Veizer, (2000), Chem. Geol., 170, 153-177.

[4] Kemeny et al., (2021), Geochim. Cosmochim. Acta, 294, 43-69.

[5] Turchyn et al., (2013), Earth Planet. Sci. Lett., 374, 36-46.

How to cite: Rout, R. K., Tripathy, G. R., Das, S., and Rai, S. K.: Net CO2 release during chemical weathering in the north-western Himalaya: A dominant role of pyrite oxidation, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1180, https://doi.org/10.5194/egusphere-egu24-1180, 2024.

09:05–09:35
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EGU24-11285
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solicited
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On-site presentation
Timothy Eglinton and the Bomb-spike team

The Earth’s carbon cycle encompasses myriad processes that connect different reservoirs containing diverse forms of carbon that turnover and exchange on a wide range of spatial and temporal scales. Increased atmospheric CO2 from anthropogenic perturbation of the carbon cycle associated with fossil fuel combustion and land-use change reflects the release of carbon from stable, slow-cycling reservoirs.  Much current research seeks to quantify carbon transfer from slow to fast cycling reservoirs, as well as the ability of different carbon reservoirs, particularly the terrestrial biosphere and the oceans, to compensate for these increased CO2 emissions through carbon uptake and storage. Determination of the turnover time and rate of transfer of carbon between reservoirs is crucial in this regard. Radiocarbon, 14C, represents a powerful tool to address this question by virtue of its ~ 5700-year half-life that allows processes occurring on centennial to millennial timescales to be resolved. Superimposed on natural abundance 14C variations, above-ground nuclear weapons testing during the mid-20th Century created an abrupt spike in atmospheric radiocarbon (“bomb spike”) that has subsequently permeated into and moved through various Earth surface carbon reservoirs, serving as a useful tracer of carbon cycle processes occurring on annual to decadal timescales. Numerous studies have exploited this signal for assessment of turnover or transit times within and through carbon pools, atmospheric and oceanic circulation, ecosystem functioning and source attribution. However, much 14C data currently tends to be compartmentalized, with a focus on specific reservoirs or geographic locations.

In this study, we evaluate the global expression of the radiocarbon bomb spike across the different Earth surface active carbon reservoirs (terrestrial biosphere, soils, freshwater aquatic systems, and marine carbon reservoirs). We compile 14C data from existing and nascent databases as well as new measurements, including direct observations and records from natural archives spanning the pre-bomb period to the present, to develop an overview of the general features of 14C (timing, amplitude and character of the bomb peak) within each reservoir over this time interval.  In addition to using this information to refine our understanding of the interactions between different reservoirs, this study seeks to (i) identify gaps and biases in data with a view to motivating further 14C studies, (ii) underline the value of systematic data reporting, as well as careful archiving of samples for future 14C analysis, (iii) inform isotope-enabled carbon cycle and earth system models, and (iv) serve as benchmark against which to gauge future carbon cycle changes.

How to cite: Eglinton, T. and the Bomb-spike team: Global expression of bomb radiocarbon in Earth's surface carbon reservoirs, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11285, https://doi.org/10.5194/egusphere-egu24-11285, 2024.

09:35–09:45
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EGU24-19642
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On-site presentation
Rienk Smittenberg, Valerie Schwab, Hans Sanden, Iso Christl, Frank Hagedorn, Irka Hajdas, Lukas Wacker, Negar Haghipour, Susan Trumbore, Xiaomei Xu, and Stefano Bernasconi

The ecosystem carbon balance of high latitude and high altitude ecosystems is particularly sensitive to climate change, where increasing temperatures generally lead to a rise of the ecosystem carbon storage, but also increasing carbon turnover times. In this study, we investigated the carbon dynamics of the 150-year long Damma Glacier forefield chronosequence, Switzerland. Specifically, we performed radiocarbon analysis of a range of organic matter fractions, sampled in 2007, 2017 and 2022 from soils developing on areas having been exposed for 20-150 years due to the retreat of the glacier. To characterize the age spectrum of material making up the bulk soil carbon, we isolated a range of different fractions, from supposedly 'stable' carbon pools (fine mineral-bound, and peroxide-resistant carbon), microbially ‘labile’ respired CO2, dissolved soil organic carbon (DOC), hydrophobic leaf wax-derived alkanes, and microbial-derived fatty acids. Comparison of our results with the penetration of the radiocarbon bomb spike and the increase of soil and ecosystem carbon over the both the chronosequence (space-for-time) and over the sampling period (time-for-time) allowed us to make the following inferences: (i) A small but persistent contribution of ancient carbon is present in the forefield area exposed by the glacier, which is particularly visible in the hydrophobic leaf wax 14C data. From this we conclude that this old carbon pool is at least in part a remnant of ancient soil carbon from a previous warm and glacier-free period, potentially adding to contributions of fossil-fuel derived black carbon deposition. (ii) There is a significant portion of soil carbon with a decadal-scale carbon turnover rate, and (iii) mineral-bound carbon clearly has a slower turnover time. (iv) Microbial lipids, soil CO2 and DOC 14C content reflect different carbon sources: in younger soils, relatively low 14C contents indicate a higher relative contribution of ancient carbon decomposition, while in older soils this signal is swamped by decomposition of freshly photosynthesized organic matter.

How to cite: Smittenberg, R., Schwab, V., Sanden, H., Christl, I., Hagedorn, F., Hajdas, I., Wacker, L., Haghipour, N., Trumbore, S., Xu, X., and Bernasconi, S.: Insight in high alpine soil carbon dynamics from compound-specific and soil fraction radiocarbon analysis on a glacier forefield chronosequence , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19642, https://doi.org/10.5194/egusphere-egu24-19642, 2024.

09:45–09:55
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EGU24-11885
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On-site presentation
Margot White, Benedict Mittelbach, Timo Rhyner, Negar Haghipour, Thomas Blattmann, Martin Wessels, Nathalie Dubois, and Timothy Eglinton

Climate change and other anthropogenic impacts such as nutrient pollution result in perturbations to freshwater systems that alter aquatic carbon cycling. In the alpine Rhine basin, for example, long-term monitoring over the past four decades has documented increasing water temperatures that cause a decrease in the solubility of CO2. However, this same dataset records a small increase in the concentration of dissolved inorganic carbon (DIC) over the same period. This requires increasing inputs of DIC to aquatic systems and an acceleration of the carbon cycle, but the source of this additional carbon is not clear. Possible explanations include increased weathering of bedrock or increased soil organic matter respiration, with sharply contrasting implications for carbon storage and turnover. Radiocarbon (14C) is an ideal tool to distinguish between these different scenarios, as bedrock weathering will contribute 14C-depleted (fossil) DIC whereas increased soil respiration will contribute DIC that is more 14C-enriched (younger). Furthermore, large changes in the atmospheric radiocarbon content over the past century resulting from the testing of nuclear weapons provide a strong signal with which to track the exchange between aquatic and atmospheric carbon pools by examining how lake water DI14C changes through time. Here we focus on Lake Constance, a large peri-alpine lake fed mostly by the alpine Rhine River. We measured natural abundance radiocarbon in archived fish scales collected from Lake Constance over the past 100 years to reconstruct changes in lake water DI14C. These fish scales come from young fish caught in the lake who feed primarily on phytoplankton and thus reflect the 14C of the lake DIC pool. Preliminary measurements of fish scales from the pre-bomb period were 0.78 to 0.79 Fm, reflecting the addition of 14C dead rock-derived carbon from the dissolution of carbonate rocks within the catchment. These values are 14C-depleted compared to present day water column DIC values of 0.82 to 0.84 Fm, where the bomb spike signal persists. Results from fish scales will ultimately be compared with other archives of water column DI14C currently in development, including 14C of chlorophyll degradation products and zooplankton exoskeletons isolated from varved lake sediments. These records permit us to investigate how carbon cycling in the lake and its catchment has responded to anthropogenic perturbations such as warming and nutrient pollution over the past century, with the eventual goal of calibrating isotope enabled carbon cycle models.

How to cite: White, M., Mittelbach, B., Rhyner, T., Haghipour, N., Blattmann, T., Wessels, M., Dubois, N., and Eglinton, T.: Radiocarbon measurements of archived fish scales reconstruct past carbon cycle changes in a peri-alpine lake, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11885, https://doi.org/10.5194/egusphere-egu24-11885, 2024.

09:55–10:05
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EGU24-11112
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ECS
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On-site presentation
Sarah Rowan, Marc Leutscher, Sönke Szidat, and Franziska Lechleitner

We know that the concentrations of CO2 and DIC in the subsurface are often magnitudes higher than in the soil zone, and therefore we need to understand this reservoir and its vulnerability to change. Understanding the critical zone in the context of CO2 input, cycling dynamics, and export is essential as this carbon is particularly vulnerable to changes in water table rise which may result in rapid release of CO2 into the atmosphere. Cave environments provide an accessible natural window into the critical zone as they connect meteoric water, soils, the unsaturated vadose zone, and saturated zone. We conducted a two year monitoring campaign at Milandre cave in northern Switzerland, analyzing pCO2, d13CO2, and 14CO2 at various environmental interfaces, including the soil zone, within the epikarst, and in the cave itself. Forest soils maintained stable, modern 14C signatures and low d13C indicating year-round contribution of CO2 from C3 tree and plant root respiration. Conversely, meadow soils exhibited notable seasonality in F14C, suggesting a dominance of respiration from older soil pools in the winter months. Distinct variations in CO2 concentrations were observed within the cave, influenced by temperature driven ventilation dynamics. Keeling plot analysis revealed a consistent contributing endmember of C3 vegetation. However, similarities between the F14C of the meadow soils and cave CO2 suggests a significant contribution of meadow soil CO2 into the cave. These findings offer vital insights into the nuanced dynamics of CO2 sources and cycling processes within the critical zone of Milandre Cave, shedding light on the influences of seasonal variation and ecological influences of critical zone carbon and the export of carbon from terrestrial ecosystems.

How to cite: Rowan, S., Leutscher, M., Szidat, S., and Lechleitner, F.: Exploring CO2 Cycling in Karst Critical Zones: Lessons from Milandre Cave, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11112, https://doi.org/10.5194/egusphere-egu24-11112, 2024.

10:05–10:15
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EGU24-15535
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ECS
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On-site presentation
Gang Xue, Yanjun Cai, Peng Cheng, Franziska Lechleitner, Haiwei Zhang, Yanhong Zheng, Yingying Wei, Shouyi Huang, Ling Yang, Xing Cheng, Yanbin Lu, Jie Zhou, Le Ma, Hai Cheng, and Lawrence Edwards

The complexity of processes affecting soil organic carbon (SOC) turnover on spatio-temporal scales often hinders the extrapolation of results from specific sites to larger scales. This study presents Holocene speleothem U-Th ages paired with 14C ages of carbonate and dissolved organic carbon (DOC) through three caves located on a north-south transect through China. The deviations of speleothem 14CDOCages from the U-Th ages show clearly spatial variability, and they are positively correlated with mean ages of modern SOC and soil turnover time, suggesting that deviations can be used to infer the SOC turnover. We further demonstrate that slow SOC turnover (large deviation) was associated with weak monsoon (low temperature/less precipitation) on temporal scales. Our findings reveal that climate dominates the speleothem 14CDOCages and SOC turnover. As global warming likely will intensify, the accelerated turnover of SOC, particularly at higher latitude areas, may partially offset the existing soil carbon stock. 

How to cite: Xue, G., Cai, Y., Cheng, P., Lechleitner, F., Zhang, H., Zheng, Y., Wei, Y., Huang, S., Yang, L., Cheng, X., Lu, Y., Zhou, J., Ma, L., Cheng, H., and Edwards, L.: The climate control of soil organic carbon dynamics inferred from speleothem radiocarbon ages, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15535, https://doi.org/10.5194/egusphere-egu24-15535, 2024.

Coffee break
Chairpersons: Carsten Simon, Philipp Maurischat, Jutta Niggemann
10:45–10:50
10:50–11:10
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EGU24-19168
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solicited
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On-site presentation
Nicholle Bell, Ezra Kitson, Gianluca Trifiro, and Richard York

Peatlands are organic matter rich (with over 60% organic matter) ecosystems that act as ‘carbon sinks’, storing many times the carbon stored by Earth’s forests. Peatlands act as sponges storing excess water from rain events and releasing it slowly, a mechanism that not only mitigates floods but also filters drinking waters. However, peatlands can only conduct these vital services when healthy and functioning, with a near surface water table and anoxic acidic conditions below the surface. Unfortunately, 80% of UK peatlands have been assessed as damaged mainly via drainage for repurposing the land for other uses. Rewetting peatlands by installing dams is one of the most common methods to restore these damaged bogs. While there is a large amount of evidence that rewetting restores the water table, questions remain whether rewetting successfully restores peatlands to their full health. To answer this question, we need to know what is happening below the surface and examine the roles of key players in peat formation and carbon cycling, namely the microbes and the carbon-containing molecules. It is not clear which of these players is more important, or how they depend on each other. To address this question, we are using the latest technologies (DNA/RNA sequencing, NMR spectroscopy and FT-ICR mass spectrometry) to uncover who they are, how they interact and how they are impacted by drainage and rewetting. The task is not easy as peat is an uncharacterised complex mixture on a molecular and microbial level and the key players could be found in different phases (solid or liquid). In this presentation, I will provide a brief overview of what insights the technologies we are using provide for below the surface characterisation of UK peatlands.

How to cite: Bell, N., Kitson, E., Trifiro, G., and York, R.: Molecules and microbes: monitoring peatland health below the surface, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19168, https://doi.org/10.5194/egusphere-egu24-19168, 2024.

11:10–11:20
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EGU24-14728
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On-site presentation
Laura Meredith, Juliana Gil Loaiza, Adrian Castro, Antonette DiGuiseppe, Gemma Purser, Zhaoxin Zhang, Qunli Shen, Kolby Jardine, Romy Chakraborty, Eoin Brodie, and Malak Tfaily

Volatile organic compounds (VOCs) are diverse and prevalent metabolites exchanged in microbial systems but are often overlooked as vectors of soil organic matter (SOM) transformations. Roots, litter, aboveground vegetation, and microbial metabolism are all sources of VOCs to soil; however, little is known about how they can contribute to soil carbon (C) cycling. VOCs have been shown to contribute to key soil C pools including microbial biomass, dissolved organic matter, particulate organic matter, and mineral-associated organic matter (MAOM), suggesting that they can participate in critical soil C stabilization pathways such as the microbial necromass conduits to MAOM. Yet, we still lack an understanding of the specific VOC-induced transformations in SOC, hindering the characterization of this process across soil and volatile compounds.

 

To address this research gap, we conducted a soil incubation study to evaluate the contributions of VOCs to SOM composition. We hypothesized that VOCs would impact SOM composition and soil carbon pool magnitudes. We evaluated whether the diversity and quality of soil metabolites change in response to weekly additions of five individual VOCs over a 3-month period: methanol, acetone, acetaldehyde, isoprene, and alpha-pinene. In our study, we utilized soil matrices from a semi-arid agroecosystem, alongside sterile (irradiated) soil controls and silica controls, enabling us to distinguish between biotic and abiotic interactions. We monitored CO2 concentrations regularly as a proxy for microbial activity. Destructive triplicate samples were harvested each month for metabolite extraction and high-resolution SOM analysis by Fourier-transform ion cyclotron resonance mass spectrometry (FTICRMS). We found that VOCs stimulated SOM transformations and generally increased the number of lipids and amino sugars—markers of microbial biomass. VOCs a-pinene, acetaldehyde, and methanol had the most unique compounds, suggesting that these VOCs may support biomass production and its transformation, while isoprene and acetone had no unique compounds and may have predominantly been used for catabolic, CO2-producing processes. With this study, we aim to grow understanding of the role of VOCs in soil C cycling and their contribution to soil ecological and metabolic interactions related to carbon stabilization.

How to cite: Meredith, L., Gil Loaiza, J., Castro, A., DiGuiseppe, A., Purser, G., Zhang, Z., Shen, Q., Jardine, K., Chakraborty, R., Brodie, E., and Tfaily, M.: Transformations of soil organic matter induced by volatile organic compounds, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14728, https://doi.org/10.5194/egusphere-egu24-14728, 2024.

11:20–11:30
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EGU24-815
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ECS
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On-site presentation
Alexander Zherebker, Oliver Babcock, Roman Vasilevich, and Chiara Giorio

Natural organic matter (NOM) is a complex mixture of thousands of organic molecules that reflects environmental conditions and chemical transformations occurring nowadays or in the past. Fourier transform mass spectrometry (FTMS) resolves isobaric constituents and it is widely applied to obtain aquatic, terrigenous and aerosol NOM fingerprints. Traditionally, comparison of mass peak intensities is used to make a distinctive conclusion about samples behavior, but it has the limitation of omitting structural information on the corresponding ions. Due to the stochastic character of NOM synthesis, drastically different samples may appear as resembling, which hampers mechanistic study of NOM dynamics and its attribution to the source. Here we present how implementation of chemical and isotopic tagging in combination with FTMS helps to overcome this issue. The developed approach provides an upper boundary for the presence of specific structural features, e.g. functional groups, in individual NOM components. This facilitates a clear distinction between different NOM samples, which would share isobaric ions, and provides insights on isomeric complexity of these ions. The advantages of the method were demonstrated on two sets of samples. Firstly, we collected permafrost peat cores from different depths in the European Arctic region, which varied in corresponding botanical conditions, peat degradation and oxidation states. Selective deuteromethylation and bromination coupled to FTMS enabled to capture structural differences between shared ions, which differed in carboxylic functionality and aromaticity. Surprisingly, structural differences were found for ions, which abundance positively correlated with peat characteristics and geo-temporal conditions. The second set included aerosol particles collected in marine, rural and urban areas. Application of in-source H/D exchange for FTMS analysis of extracted NOM enabled to enumerate functional groups in shared ions and point molecular constituents with similar and distinct structural features. The observed trends serve to better understand aerosol formation processes and accompanied conventional formula-based statistical analysis including better understanding of Kendrick mass defect series.

How to cite: Zherebker, A., Babcock, O., Vasilevich, R., and Giorio, C.: From sediments to the atmosphere: a mass spectrometry approach revealing structural dissimilarities of common NOM components, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-815, https://doi.org/10.5194/egusphere-egu24-815, 2024.

11:30–11:40
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EGU24-16215
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ECS
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On-site presentation
Shuxian Gao, Elaine Jennings, Limei Han, Boris Koch, Peter Herzsprung, and Oliver Lechtenfeld

Ultrahigh resolution mass spectrometry (UHRMS) routinely detects and identifies thousands of molecular formulas (MFs) in natural organic matter (NOM). However, multiple assignments (MultiAs) occur when the several chemically plausible MFs are assigned to one single mass peak. MultiAs for a mass peak consist of one common core MF but different “formula residuals”, or replacement pairs, and increase as more heteroatoms and isotopes are being considered during the assignment process. This poses a major problem for the reliable interpretation of NOM composition in a biogeochemical context. A number of approaches have been proposed to rule out false assignments based on structural constraints or isotopologue detection and intensity ratios. But this becomes increasingly challenging for low abundance mass peaks or when stable isotope labeling (e.g. with 15N, 2H) is employed. Here, we present a new approach based on mass error distributions for the identification of true and false-assignments among MultiAs. An automatic workflow was developed for the detection and exclusion of false assignments in MultiAs based on their recurring replacement pairs and Kendrick mass defect values. The workflow can validate MFs for mass peaks that are close to detection limit or where naturally occurring isotopes are rare (e.g. 15N) or absent (e.g. P, F), substantially increasing the reliability of MFs assignments and broadening the applicability of UHRMS in characterization of NOM, e.g. for organic nitrogen and organic phosphorus in different environmental compartments, which are key components for global elemental cycles.  

How to cite: Gao, S., Jennings, E., Han, L., Koch, B., Herzsprung, P., and Lechtenfeld, O.: Detection and exclusion of false molecular formula assignments via mass error distributions in ultrahigh resolution mass spectra from natural organic matter., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16215, https://doi.org/10.5194/egusphere-egu24-16215, 2024.

11:40–11:50
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EGU24-1957
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ECS
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On-site presentation
Erika Andersson, Lars Tranvik, Marloes Groeneveld, Anders Tunlid, Per Persson, and Ulf Olsson

Dissolved organic matter (DOM) is a major carbon pool and considered the most bioavailable and most mobile fraction of organic matter. DOM is generally defined as the organic matter passing a filter pore size of 0.2 or 0.45 µm, and this size cut off means that DOM not only contains dissolved molecules but also colloidal objects and aggregates up to a few hundred nanometres. The properties of this colloidal DOM fraction, such as for example size, shape, and surface charge, will affect its actual bioavailability and mobility in the environment. Although previously not well studied, there has recently been a growing interest in this colloidal fraction of DOM.

We have studied DOM extracted by water from a boreal spruce forest soil, filtered through a 0.2 µm pore size. By using a combination of spectroscopy techniques, such as NMR, and light (SLS, DLS), X-ray (SAXS) and neutron (SANS) scattering techniques, we can access chemical and physical information on both the molecular and colloidal fractions of DOM.

Our results show that the colloidal DOM has a homogenous chemical composition, and that carbohydrates is the dominating chemical component in both the colloidal and molecular DOM. The colloids have a mass fractal structure which does not change upon dilution and they are electrostatically stabilised against aggregation. In a lab scale study, we investigated the bacterial decomposition of this DOM during a two-month incubation. The molecular fraction of DOM was quickly decomposed. However, no change was observed for the colloidal DOM, constituting ca. 50% of the carbon, indicating that it persisted bacterial decomposition.

Our results suggest that colloidal properties could be an important but hitherto overlooked aspect to the central question of what dictates organic matter reactivity and persistency in different environments and across different time scales. Our current work extends from soil solution to aquatic ecosystems, to assess the ubiquity of the colloidal fraction of DOM.

How to cite: Andersson, E., Tranvik, L., Groeneveld, M., Tunlid, A., Persson, P., and Olsson, U.: Bacterial decomposition of dissolved organic matter: including the colloidal perspective, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1957, https://doi.org/10.5194/egusphere-egu24-1957, 2024.

11:50–12:00
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EGU24-6629
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ECS
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On-site presentation
Grace Abarike, Simone Brick, Bert Engelen, and Jutta Niggemann

Dissolved organic matter (DOM) is diverse in composition and serves as substrate for microbial metabolism. Within subterranean estuaries (STEs), DOM is introduced from different sources along the groundwater flow paths. These different DOM sources make it challenging to disentangle degradation pathways, especially in high-energy beaches with dynamic porewater advection and changing redox conditions. We performed sediment incubations in flow-through reactors (FTRs) to investigate how DOM from different sources is transformed by STE microbial communities. We used sediment and groundwater from the STE of a high-energy beach on Spiekeroog Island (Germany). Intertidal beach sediments were incubated for 13 days in FTRs with groundwater of low (~1.6) and high salinity (~29.1) as marine and terrestrial endmember, respectively, in triplicate setups, and additional control FTRs with artificial seawater of respective salinities. The FTRs ran under oxic conditions with recirculating advective flow. Porewater samples were taken daily for quantification of dissolved organic carbon (DOC) and nutrient concentrations, and samples from the start and the end of the incubation were taken for the analysis of microbial community composition, microbial cell numbers, and DOM composition. DOM samples were isolated through solid phase extraction and molecularly characterized via ultrahigh-resolution Fourier-transform ion cyclotron resonance mass spectrometry. Over the course of the incubation, DOC concentrations increased, presumably from sediment leaching and potentially also by primary production in light-exposed parts of the setup, as oxygen concentrations also increased. The DOM composition of the porewater samples at start and end of the incubation was highly diverse, with a total of up to 2900 different molecular formulae detected in each sample. As expected, the low salinity porewater had a more terrestrial DOM signature with a higher proportion of aromatic compounds compared to the DOM in the high salinity porewater. In all setups, the DOM composition changed significantly from start to end. We observed an increase in DOM lability in both endmember setups indicating the mobilization of fresh DOM from sediments and/or microbial activity, including primary production. Interestingly, the changes observed were similar for both DOM endmembers. Our results indicate that the microbial communities of the high-energy beach STE thrive on a similar fraction of DOM, independent of its source.

How to cite: Abarike, G., Brick, S., Engelen, B., and Niggemann, J.: Different dissolved organic matter (DOM) sources sustain microbial life in beach subterranean estuary, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6629, https://doi.org/10.5194/egusphere-egu24-6629, 2024.

12:00–12:10
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EGU24-21439
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ECS
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On-site presentation
Katherine Shek, James Stegen, Alan Roebuck, Amy Goldman, Mikayla Borton, Kelly Wrighton, and Adam Wymore

Inferring linkages between microbial metabolism and dissolved organic matter (DOM) across environmental gradients is a promising avenue to improve biogeochemical predictions at large spatial scales. Despite decades of metagenomic studies identifying microbial functional trait-environment patterns at small spatial scales, general patterns at continental or global scales that may improve large-scale models remain unresolved. Recent influx of multi-omics datasets that represent diverse environmental conditions has enabled scalable analyses linking microbial metabolic niche breadths with key environmental processes, such as carbon and nutrient transformations.

Here, we leveraged publicly available microbial metagenome assembled genomes (MAGs) derived from the Worldwide Hydrobiogeochemistry Observation Network for Dynamic River Systems (WHONDRS) data paired with metabolomic (FTICR-MS) and sediment chemistry data to link microbial metabolic potential with organic chemistry. We annotated 1,384 MAGs representing 65 sites using the R tool microTrait, which categorizes functional traits under the YAS (growth yield-resource acquisition-stress tolerance) framework. Following Hutchinsonian niche theory, we modeled microbial trait combinations as n-dimensional hypervolumes and observed trait-DOM patterns at the continental scale, showing microbial functional tradeoffs along gradients of organic carbon. We expect that at the continental scale, microbial trait profiles will be distinct across climatic regions, and that niche breadth (i.e. the size of individual hypervolumes in trait space) will correlate with DOM/metabolite diversity. The results of this work will distill generalizable patterns of microbe-DOM availability and diversity at large spatial scales, thus identifying information to improve current biogeochemical models.

How to cite: Shek, K., Stegen, J., Roebuck, A., Goldman, A., Borton, M., Wrighton, K., and Wymore, A.: Modeling microbial functional trait-environment interactions at the continental scale, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-21439, https://doi.org/10.5194/egusphere-egu24-21439, 2024.

12:10–12:20
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EGU24-3667
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ECS
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On-site presentation
Bingbing Wei, Michael Seidel, Gesine Mollenhauer, Hendrik Grotheer, Jenny Wendt, Thorsten Dittmar, and Moritz Holtappels

Deepwater formation in the North Atlantic Ocean is a major gateway for dissolved organic matter (DOM) transport into the deep ocean. Despite focusing on vertical mixing, lateral transport of DOM from productive shelf regions is underexplored. Previous research suggested substantial offshore DOM transport on the Irish and Hebrides Margin via the bottom Ekman Drain. Our in-depth bottom water DOM analyses of carbon isotopes in combination with ultrahigh-resolution mass spectrometry (FT-ICR-MS) indicated that downwelling in this region leads to higher DOM concentrations (by 7–11 μM) and younger radiocarbon ages (by 190–330 yrs) compared to DOM of the central Northeast Atlantic at similar depths. During downslope transport, conservative mixing shapes the molecular composition of recalcitrant DOM, while minor particulate organic matter degradation contributes to producing less-refractory DOM with terrigenous signals. Consequently, the bottom Ekman transport emerges as a rapid and efficient channel for transporting fresh DOM into the deep North Atlantic Ocean, acting as a crucial carbon sink for atmospheric CO2.

How to cite: Wei, B., Seidel, M., Mollenhauer, G., Grotheer, H., Wendt, J., Dittmar, T., and Holtappels, M.: Rapid lateral transport of fresh dissolved organic matter to the deep ocean in the NE Atlantic, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3667, https://doi.org/10.5194/egusphere-egu24-3667, 2024.

12:20–12:30
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EGU24-5586
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On-site presentation
Catherine Moody, Nicholle Bell, Logan Mackay, and Ezra Kitson

DOM from peatlands is a collection of complex molecules, but also a significant source of carbon to aquatic pathways. It has a wide impact on aquatic ecosystems, providing an energy source for microbes and buffering capacity for water chemistry changes. The composition of DOM in drinking water reservoirs also impacts on chemical and energy demands of treatment processes, and is an area of growing concern for UK drinking water providers.

DOM was extracted from water collected from peatland headwater streams and reservoirs in the UK. The DOM was analysed with elemental analysis and FT-ICR MS to determine how the composition changes as water moves through the catchment. A combination of spatial and temporal sampling strategies allowed seasonal and catchment characteristics to be investigated (from 2018-2021, and 53-61°N).

There were significant trends in DOM composition metrics across a north/south gradient, with higher lipid content, and lower carbohydrate and peptide content in northern sites than southern sites. Samples collected in 2021 had several significant composition differences to other years. Monthly sampling showed the largest changes in DOM composition coincided with the end of the growing season (September in the UK).

These results show variable DOM in headwaters can be, and how reservoirs act to buffer the most extreme changes, resulting in more stable DOM compositions in reservoirs. Understanding how DOM composition is impacted by season, climate and catchment characteristics will have important ramifications for drinking water providers, and will help catchment managers plan land use changes and timing of water draw-off from peatland reservoirs.

How to cite: Moody, C., Bell, N., Mackay, L., and Kitson, E.: Temporal and spatial changes in DOM revealed by FT-ICR MS, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5586, https://doi.org/10.5194/egusphere-egu24-5586, 2024.

Lunch break
Chairpersons: Jutta Niggemann, Anna Gunina, Marcus Schiedung
14:00–14:05
14:05–14:15
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EGU24-10047
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On-site presentation
Mary Zeller, Bryce Van Dam, Amy McKenna, Christian Lopes, Christopher Osburn, James Fourqurean, Kominoski John, and Michael Böttcher

Carbonate-associated organic matter (CAOM) is the organic matter associated with carbonate minerals, and a survey of carbonate-rich surface sediments suggests that it is incorporated at a consistent amount scaling with the internal surface area of the carbonate grains. As the carbonate sediment is sensitive to changes in saturation state due to benthic biogeochemical processing, we predicted that CAOM could exhibit interesting biogeochemical cycling, based on its potential to bridge particulate and dissolved pools of organic matter. Here, we report on a study in a seagrass meadow in central Florida Bay, USA. We utilize a combination of inorganic stable isotope (C, S, O) and high resolution mass spectrometry (21T FT ICR-MS) techniques to explore the carbon and sulfur cycles here, with a particular emphasis on dissolved organic matter (DOM) characterization. CAOM is examined similar to standard solid phase extraction (SPE-DOM) methods, after first washing carbonate sediment and dissolving it incompletely under a mild hydrochloric acid treatment. The δ34S and δ18O of sulfate, as well as the δ13C of dissolved inorganic carbon (DIC), suggest that the promotion of sulfide oxidation in the seagrass rhizosphere drives rapid carbonate dissolution and re-precipitation cycles. Sulfide oxidation, as well as elevated sulfide concentration, promotes sulfurization of CAOM, which is more sulfurized than porewater and surface water, as 42% of CAOM formulas vs 28% of surface water are sulfurized. Furthermore, a substantial quantity of molecular formulas present in the overlaying surface waters (90% of formulas, 97% by relative abundance) are also present in CAOM. Despite the CAOM sample containing nearly twice the number of formulas compared to surface water, due in part to its higher dissolved organic carbon concentration, these shared formulas make up 75% of the abundance of CAOM formulas. We argue that repeated coupled sulfur and inorganic carbon cycles, intensified by seagrasses, leads to increased sulfurization and release of CAOM, affecting DOM quality in the broader aquatic system. We estimate that approximately 9% of the particulate organic carbon (POC) stored in the sediments of this site are CAOM. Our results suggest that CAOM here is a form of “dissolvable” organic carbon which cycles much more rapidly than POC more broadly.

How to cite: Zeller, M., Van Dam, B., McKenna, A., Lopes, C., Osburn, C., Fourqurean, J., John, K., and Böttcher, M.: Carbonate-associated organic matter: A form of “dissolvable” organic matter?, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10047, https://doi.org/10.5194/egusphere-egu24-10047, 2024.

14:15–14:25
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EGU24-7317
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ECS
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On-site presentation
Irina Zweig and Alexey Kamyshny

The presence of organic molecules containing sulfur-sulfur bonds was identified in both water columns and sediments of natural aquatic systems. While processes leading to formation of these compounds were intensively studied during recent decades, the kinetics and mechanisms of reactions responsible for their decomposition remain poorly understood. This study focuses on the kinetics and products of the reactions of dimethyl disulfide, dimethyl trisulfide, and cyclic polysulfide lenthionine (1,2,3,5,6-pentathiepane) with hydrogen sulfide at the pH and temperature ranges typical of environmental conditions. The findings reveal that under environmental conditions (pH≥5), the overall reaction rates are primarily controlled by the reaction of bisulfide anion (HS-) rather than hydrogen sulfide. The activation energy and the order of the reaction with respect to bisulfide anion is dimethyl disulfide < dimethyl trisulfide < lenthionine, while the order of the reaction with respect to organosulfur compounds is lenthionine < dimethyl trisulfide < dimethyl disulfide. The rates of the reactions between linear dimethyl polysulfides with bisulfide anion were found to be higher than the rates of their reactions with cyanide and hydroxyl anions, but lower than the rates of their photodecomposition. These results suggest that rapid decomposition of organosulfur compounds in sulfidic aphotic natural aquatic systems should be controlled by HS- decomposition pathway. Products of the decomposition of dimethyl disulfide and dimethyl trisulfide include methanethiol, higher dimethyl polysulfides, and inorganic polysulfides. The cyclic polysulfides were shown to be more stable than their linear analogs, resulting in their preferential preservation during the maturation process.

How to cite: Zweig, I. and Kamyshny, A.: Reactivity of hydrogen sulfide toward organic compounds with sulfur-sulfur bonds, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7317, https://doi.org/10.5194/egusphere-egu24-7317, 2024.

14:25–14:35
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EGU24-6501
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On-site presentation
Pablo Lodeiro, Joao C. A. Macedo, Calin David, Carlos Rey-Castro, Jaume Puy, María Martínez-Cabanas, Roberto Herrero, Manuel E. Sastre de Vicente, and José L. Barriada

The binding properties of dissolved organic matter (DOM) play a crucial role in the biogeochemical cycles of trace metals and carbon. The composition of DOM is anticipated to exert influence over the magnitude and distribution of the intrinsic ion binding affinities that occur over a continuum of values, referred to as the affinity spectra. These spectra encompass many different organic acid groups that contribute to the nuanced binding characteristics of DOM. The total proton binding capacity represents the maximum sites available for other chemical species that may compete with protons for the same DOM binding sites, particularly in the case of metals. Consequently, the study of proton binding by DOM becomes the initial step to investigate deeper into metal binding mechanisms. Here, we research the variability in proton binding exhibited by DOM extracted from the Ebro and Mero Rivers (NNE and NW of Spain), and at the Atlantic Ocean and Mediterranean Sea. Our approach combines the non-ideal competitive adsorption (NICA) isotherm, offering insights into chemical binding on heterogeneous ligands, with the Donnan electrostatic model, which accounts for polyelectrolytic effects, i.e., the non-specific binding. This methodology enables us to pinpoint potential shifts in DOM binding affinities and derive a comprehensive set of intrinsic binding parameters for DOM. Importantly, these parameters are thermodynamically consistent and remain independent of the specific conditions of the samples, enhancing the extrapolation to future environmental changes.

 

Acknowledgements: Authors thank Agencia Española de Investigación for the financial support through the research projects PID2020-117910GB-C21 and -C22/AEI/10.13039/501100011033. P.L. acknowledges current support from the Ministerio de Ciencia, Innovación y Universidades of Spain and University of Lleida (Beatriz Galindo Senior award number BG20/00104)

References:

[1] Lodeiro, P., Rey-Castro, C., David, C., Humphreys, M. H., Gledhill, M., 2023. Proton Binding Characteristics of Dissolved Organic Matter Extracted from the North Atlantic. Environmental Science & Technology 57, 21136–21144.

[2] Waska, H., Brumsack, H.-J., Massmann, G., Koschinsky, A., Schnetger, B., Simon, H., Dittmar, T., 2019. Inorganic and organic iron and copper species of the subterranean estuary: Origins and fate. Geochimica et Cosmochimica Acta 259, 211–232.

[3] Heerah, K. M.,  Reade, H. E., 2023. Towards the identification of humic ligands associated with iron transport through a salinity gradient. Scientific Reports 12:15545.

How to cite: Lodeiro, P., Macedo, J. C. A., David, C., Rey-Castro, C., Puy, J., Martínez-Cabanas, M., Herrero, R., Sastre de Vicente, M. E., and Barriada, J. L.: Variations in binding properties of dissolved organic matter along river-ocean continuum, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6501, https://doi.org/10.5194/egusphere-egu24-6501, 2024.

14:35–14:45
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EGU24-16483
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ECS
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On-site presentation
Linn Speidel, Negar Haghipour, Thomas Blattmann, Lisa Bröder, Julie Lattaud, Alysha I. Coppola, and Timothy I. Eglinton

Black carbon (BC) is a fraction of organic carbon resulting from the incomplete combustion of biomass and fossil fuels. The production and fate of BC is a topic of great interest in the context of ongoing climate change, as the intensity and severity of fires is increasing. The recalcitrant nature enables BC to buffer these changes by removing biomass-derived carbon into longer cycling pools. BC is mainly produced on land and a portion is transported in both particulate and dissolved form by the rivers to the oceans. Dissolved BC (DBC) cycles on millennial timescales, thereby storing BC as fraction of Dissolved Organic Carbon (DOC) in the marine DOC pool before deposition to sediments or complete degradation. However, there is currently limited information on the cycling, transport and evolution of modern riverine DBC, and how it contributes to the deep ocean DOC pool.
The arctic and boreal regions are well recognized as a nexus for climate change, given amplified rates of change in average temperatures and summer precipitation, which exacerbate carbon cycle feedbacks, including enhanced BC production by intensified wildfire seasons. The Beaufort Sea in the Arctic Ocean is composed of different water masses, with Pacific water masses entering from the Chukchi Sea, and arctic rivers - in particular the Mackenzie River - being the major source of freshwater that delivers both terrestrial DOC and DBC. Presently, information on the sources and fate of BC in the Arctic Ocean remains sparse.
Here, we report DBC concentrations and Δ14C values in the Beaufort Sea during early winter conditions. Distinct water masses were sampled, including the outflow of the Mackenzie River and the Pacific water jet on the shelf break, during two cruises in 2021 and 2022 that spanned the coast of north Alaska to the Amundsen Gulf. Preliminary radiocarbon results show that DBC on the shelf break is up to five millennia old. We discuss our findings in the context of regional hydrography and carbon cycle processes.

How to cite: Speidel, L., Haghipour, N., Blattmann, T., Bröder, L., Lattaud, J., Coppola, A. I., and Eglinton, T. I.: Radiocarbon signatures of dissolved black carbon in early winter water masses from the Beaufort Sea, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16483, https://doi.org/10.5194/egusphere-egu24-16483, 2024.

14:45–15:05
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EGU24-18669
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solicited
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On-site presentation
Matthew Jones, Alysha Coppola, and Cristina Santín

Fires play a critical role in modulating the quantity and quality of carbon (C) stored in the terrestrial biosphere, including in aboveground vegetation and soils. Via riverine transport routes, fires also affect the quantity and quality of C delivered to the global oceans.

The mission of this talk is to set the scene on the multifaceted ways in which fire impacts the global C cycle, with a special focus on the widely-overlooked role of pyrogenic C.

We will begin by summarising how fires impact on terrestrial stores of C, starting with natural cycles of disturbance and recovery that influence total stocks of C on the terrestrial landscape. We will then demonstrate how shifting fire regimes, related to climate change and changes in land use, are perturbing the cycle of C and influencing the quantity of C stored on the landscape. Increased fire frequency and intensity generally promotes a loss of C from landscapes, especially in cases where vegetation cannot recover completely in the shortening time available between disturbance events.

Set within the broader cycle of biogenic C is a sub-cycle of highly recalcitrant ‘pyrogenic’ C – a by-product of incomplete combustion during fires. We will highlight how the special properties of this pyrogenic C promote its longevity in terrestrial stores in a manner that can offset (or ‘buffer’) losses of total C. The process of pyrogenic C storage has been widely overlooked in models of the global C cycle leading to C accounting errors, however we will highlight some recent examples of its implementation in land surface models and the lessons learned from doing so.

Due to its exceptional longevity in terrestrial pools, pyrogenic C has enhanced odds of reaching the global oceans via rivers. We will discuss the disproportionate export of pyrogenic C to the global oceans (relative to biogenic C) and how this leads to an unusual potential for long-term C sequestration.

Finally, we will provide an overview of the current understanding of the global budget of pyrogenic C, integrating best estimates for the fluxes of C to and from terrestrial stores and to and from marine stores. We will also highlight how uncertainties in the magnitude of fluxes in the C cycle lead to poor understanding of whether pyrogenic C currently acts as a sink or source of C to the atmosphere. We will underscore the particular need to constrain the decomposition rates and residence times of pyrogenic C in soils and marine stores if we are to build a complete picture of its role in the global C cycle.

How to cite: Jones, M., Coppola, A., and Santín, C.: Pyrogenic carbon: Is it a sink in the global carbon cycle? And why we can’t be sure., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18669, https://doi.org/10.5194/egusphere-egu24-18669, 2024.

15:05–15:15
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EGU24-11446
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ECS
|
On-site presentation
Minerva García-Carmona, Cristina Santín, and Stefan Doerr

Wildfires play an important role in the carbon cycle, influencing both atmospheric carbon concentrations and terrestrial carbon storage. Pyrogenic carbon (PyC) derived from incomplete biomass combustion during wildfires is currently considered a relevant carbon sink at the global level. In order to assess the quantitative importance of PyC production, accurate data on PyC generation in different ecosystems and under a range of fire conditions are needed. In this study, we focus on the fire-prone continent of Australia, specifically on eucalypt forests, which are the most common type of native forests. Eucalypt forests, subjected frequently to both wildfires and human-prescribed fires, provide an important context for understanding PyC dynamics.
We conducted comprehensive pre-fire and postfire fuel inventories and quantified all pyrogenic materials generated in three representative eucalypt forests in Sydney, Melbourne, and Perth. Experimental fires, simulating low to medium-severity wildfires, were used to quantify PyC conversion rates in the main fuel components: forest floor, understory, down wood, and overstory (comprising only tree bark as these fires did not affect the crowns).
Our results show an average pyrogenic carbon conversion rate of 24% for eucalypt forests. This translates to 9 t C ha-1 of the carbon affected by the fire being emitted to the atmosphere, while 3 t C ha-1 is transformed into PyC, underscoring the relevance of PyC in carbon budgets from eucalypt forest fires. The conversion rates varied substantially among fuel components, with the bark component exhibiting the highest conversion rate, at approximately 40%, and the down wood component displaying the lowest rate at around 15%. Intermediate conversion values were reported for forest floor and understory components. 
Given the recurrent nature of fires in eucalypt forests in Australia, both naturally and under human-prescribed conditions, our findings suggest that PyC production plays a significant role in the carbon cycle, of sufficient magnitude to be considered in global carbon budget estimations.

How to cite: García-Carmona, M., Santín, C., and Doerr, S.: Pyrogenic Carbon production in eucalypt forests: implications for the carbon cycle in fire-prone ecosystems, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11446, https://doi.org/10.5194/egusphere-egu24-11446, 2024.

15:15–15:25
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EGU24-1109
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ECS
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On-site presentation
Oliver Donnerhack, Patrick Liebmann, Philipp Maurischat, and Georg Guggenberger

Forest fires are among the most influential disturbances in ecosystems and have varying effects on the soil depending on fire intensity and biomass consumption. The significant decline in biodiversity in European forests due to centuries of non-sustainable forest management, combined with worsening drought from climate change, has greatly increased vulnerability to wildfires. Incomplete combustion during fires leads to the formation of black carbon (BC), a group of substances known for their persistence in soil. However, studies suggest that medium-condensed BC species may have lower chemical and spatial stability and are therefore potentially more mobile and consequently only serve as temporary carbon sinks.

In order to assess the mobilization of BC, we investigate short-term changes in BC under field conditions, particularly of the low-condensed BC, and call into question the established concept of the general stability of BC pools. We investigated the dynamics of BC alterations during the post-fire period within one winter, following a late summer forest fire. We selected two comparable sites featuring spruce-dominated forest stands with different geologic parent material and weather conditions, particularly with respect to the amount of precipitation during the observation period. We sampled soil profiles down to 40 cm depth shortly after the fire event in late summer and after a 6-month period in late spring. After performing density fractionation to separate the mineral associated organic matter (MAOM) from particulate organic matter (POM), we analysed the BC content in the MAOM fraction using benzene polycarboxylic acids (BPCA) analysis.

The results show a high content of low to medium condensed BPCAs directly after fire, which decreased, especially the medium condensed BPCA marker, during the observation period. Taking into account the fast change in medium BPCA values in the MAOM fraction, we conclude that the general assumption that BC is in principle a stable, long-term carbon sink needs to be addressed more carefully.

How to cite: Donnerhack, O., Liebmann, P., Maurischat, P., and Guggenberger, G.: Post fire Black Carbon alteration: Rapid changes in a supposedly inert pool, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1109, https://doi.org/10.5194/egusphere-egu24-1109, 2024.

15:25–15:35
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EGU24-16551
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ECS
|
On-site presentation
Johanne Lebrun Thauront, Severin Luca Bellè, Marcus Schiedung, Amicie Delahaie, Marija Stojanova, François Baudin, Pierre Barré, and Samuel Abiven

Pyrogenic carbon (PyC) is a continuum of aromatic and condensed organic molecules. It represents about 15 % of organic carbon in soils and sediments1. However, there is a discrepancy in the literature regarding quantification of PyC: different methods that are currently considered as reference differ largely in their results1,2. Indeed, most methods used to quantify PyC are based on different operational principles (e.g. chemical, thermal or physical stability of PyC, molecular markers) and consequently, they do not cover the same range of the PyC continuum2. In addition, most of them are expensive and/or time consuming. Here, we propose a new PyC quantification method based on Rock-Eval® thermal analysis, thought to be rapid, inexpensive and comparable to the previous methods toolbox. Rock-Eval® thermal analysis has been successfully introduced to the field of soil carbon analysis in the last two decades and allowed to distinguish between various pools of soil carbon (inorganic carbon, stable and active organic carbon) using a single analysis of combined pyrolysis and thermal oxidation3,4. In this study, we formulate the hypothesis that Rock-Eval® thermal analysis in combination with predictive modelling is suitable to quantify PyC in soil matrices.

To build and validate such a model, we chose soil samples originating from contrasting climate zones and parent material and with varying properties including clay content and mineralogy, iron oxide speciation and content, pH, cation-exchange capacity and organic carbon content. We measured PyC using a set of established methods (i.e. CTO-375, BPCA and HyPy) and acquired Rock-Eval® thermograms. Then, we identified the relevant features for PyC quantification in the thermograms by applying several machine-learning approaches. This work adds a new soil carbon pool to the ones already accessible from Rock-Eval® thermal analysis and allows an efficient and rapid quantification of PyC in soils, which is needed for large-scale studies of soil carbon pools.

(1) Reisser, M.; Purves, R. S.; Schmidt, M. W. I.; Abiven, S. Pyrogenic Carbon in Soils: A Literature-Based Inventory and a Global Estimation of Its Content in Soil Organic Carbon and Stocks. Front. Earth Sci. 2016, 4 (August), 1–14. https://doi.org/10.3389/feart.2016.00080.

(2) Hammes, K.; Smernik, R. J.; Skjemstad, J. O.; Schmidt, M. W. I. Characterisation and Evaluation of Reference Materials for Black Carbon Analysis Using Elemental Composition, Colour, BET Surface Area and 13C NMR Spectroscopy. Appl. Geochemistry 2008, 23 (8), 2113–2122. https://doi.org/10.1016/j.apgeochem.2008.04.023.

(3) Disnar, J. R.; Guillet, B.; Keravis, D.; Di-Giovanni, C.; Sebag, D. Soil Organic Matter (SOM) Characterization by Rock-Eval Pyrolysis: Scope and Limitations. Org. Geochem. 2003, 34 (3), 327–343. https://doi.org/10.1016/S0146-6380(02)00239-5.

(4) Cécillon, L.; Baudin, F.; Chenu, C.; Houot, S.; Jolivet, R.; Kätterer, T.; Lutfalla, S.; Macdonald, A.; Van Oort, F.; Plante, A. F.; Savignac, F.; Soucémarianadin, L. N.; Barré, P. A Model Based on Rock-Eval Thermal Analysis to Quantify the Size of the Centennially Persistent Organic Carbon Pool in Temperate Soils. Biogeosciences 2018, 15 (9), 2835–2849. https://doi.org/10.5194/bg-15-2835-2018.

How to cite: Lebrun Thauront, J., Luca Bellè, S., Schiedung, M., Delahaie, A., Stojanova, M., Baudin, F., Barré, P., and Abiven, S.: Prediction of soil pyrogenic carbon contents from Rock-Eval® thermal analysis: a machine-learning based model, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16551, https://doi.org/10.5194/egusphere-egu24-16551, 2024.

15:35–15:45
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EGU24-2117
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On-site presentation
Kristiina Karhu, Subin Kalu, Aino Seppänen, Kevin Mganga, Outi-Maaria Sietiö, and Bruno Glaser

Biochar can increase long-term soil organic carbon (SOC) storage due to its polyaromatic structure. In addition to the recalcitrant carbon (C) contained in the biochar itself, biochar can also increase SOC storage by adsorption or organic matter on its surfaces, and reduced decomposition rate of native SOC (negative priming). Limited number of studies have looked at how biochar affects decomposition and stabilization of fresh C inputs, and native SOC decomposition. To fill this knowledge gap, we conducted a laboratory incubation study, where we followed the fate of added 13C-labeled glucose in a fine-textured agriculturally used soil (Stagnosol) amended with two different biochar levels corresponding to 15 and 30 Mg ha-1 in field conditions. Biochar addition reduced mineralization of SOC and added 13C glucose, while increasing microbial biomass and microbial carbon use efficiency (CUE). Most of the added biochar, as well as remaining 13C were found in the free particulate organic matter (POM) fraction after 6 months, indicating that added 13C glucose was preserved within the biochar particles. Our closer study of 13C amino sugar fraction extracted from the biochar particles revealed that the microbes that had efficiently grown on the added 13C glucose in the presence of biochar, were retained as dead microbial residues inside the biochar pores. This microbial route could provide a way for additional formation of rather recalcitrant C in the form of microbial residues in the presence of biochar, which could with time contribute to building SOC stock in biochar amended soils beyond the C present in biochar itself. We found that biochar also increased the portion of occluded POM in the treatments without 13C glucose addition, demonstrating that increased soil occlusion following biochar addition reduced SOC mineralization. The effects were found to be dose-dependent, i.e. higher biochar application rate resulted in lower mineralization rate of native SOC and of added 13C-glucose.

How to cite: Karhu, K., Kalu, S., Seppänen, A., Mganga, K., Sietiö, O.-M., and Glaser, B.: Biochar enhanced microbial carbon use efficiency, while reducing mineralization of added and native soil organic carbon, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2117, https://doi.org/10.5194/egusphere-egu24-2117, 2024.

Posters on site: Fri, 19 Apr, 16:15–18:00 | Hall X1

Display time: Fri, 19 Apr 14:00–Fri, 19 Apr 18:00
Chairpersons: Blanca Ausin, Anna Gunina, Philipp Maurischat
The Global Carbon Cycle: Reservoirs and Fluxes
X1.1
|
EGU24-416
|
ECS
Keito Aonuma, Yusuke Yokoyama, Yosuke Miyairi, Masayuki Chimura, Tomonori Hamatsu, Osamu Sakai, and Guido Plaza

The inner ear of fish contains calcium carbonate (CaCO3)-based crystals called otoliths, which play an essential role in hearing and balance. During otolith formation, new calcium carbonate is deposited in layers on the surface of the existing part and the part is no longer affected by metabolism. This feature means that each layer of the otolith retains the trace element ratios and isotope ratios it had at the time of formation. By analysing this preserved information, it is possible to make estimates about the environment and habitat at that time.

The stepwise acid dissolution method has been used in several studies as a technique for analysing the radiocarbon isotope ratios preserved in otoliths. In this method, phosphoric acid is used to dissolves the otolith from the outermost to the innermost layers. It has the advantage that a large amount of carbon can be collected from a single otolith, compared to the mechanical methods for the calcium carbonate sampling from each layer of the otolith.

However, this method involves dissolving the otolith in acid and the pattern of dissolution cannot be controlled minutely by the experimenter. Pacific cod (Gadus macrocephalus) otolith used by us is flattened and the dissolution pattern of such otoliths is not yet known. Furthermore, no direct observation of the otolith dissolution process has been made in relation to previous studies.

In this study, we dissolved three Pacific cod otoliths in phosphoric acid to directly confirm the process of otolith dissolution in the stepwise acid dissolution method. We removed each otolith from the acid one or more times during the dissolution process, weighed it and observed the change in the shape of the otolith and the layer structure exposed on the otolith surface. As the dissolution progressed and the otoliths became smaller, we polished them to check that the internal layered structure had not been destroyed by acid penetration.

As a result, we found that the serrated structures present on the outer edges of the otoliths are maintained when they are dissolved from the outside by acid. We also confirmed that acid dissolution from the outside does not destroy the inner layer structure, even microstructures such as daily rings. The validity of the stepwise acid dissolution method would be strengthened by these results. On the other hand, the otoliths were thinner as a result of acid dissolution, exposing the more inner layers on the flat surface. This is due to the thin vertical thickness of the flattened otoliths. This observation suggests that the collected carbon may be mixed with the carbon collected from more inner layer. This carbon mixing is able to be taken into account with future work. In addition, care should be taken when using this method near the nucleus, as the final stage of dissolution results in multiple holes in the otolith.

How to cite: Aonuma, K., Yokoyama, Y., Miyairi, Y., Chimura, M., Hamatsu, T., Sakai, O., and Plaza, G.: The dissolution pattern of the flattened otolith of Pacific cod using the stepwise acid dissolution method, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-416, https://doi.org/10.5194/egusphere-egu24-416, 2024.

X1.2
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EGU24-7593
Marco A. Bolandini, Daniele De Maria, Negar Haghipour, Lukas Wacker, Jordon D. Hemingway, Timothy I. Eglinton, and Lisa Bröder

Radiocarbon (14C) measurements provide a powerful tool to deconvolute sources and dynamics of organic matter in the environment. However, interpretation of conventional bulk-level 14C data is challenging due to the myriad components comprising organic matter in soils and sediments. Thermally ramped oxidation provides one approach for overcoming this limitation, and involves subjecting a sample to gradually increasing temperatures, serially oxidizing the OC to CO2. Collected over prescribed temperature ranges ('thermal fractions'), this CO2 is then analyzed for 14C content using accelerator mass spectrometry (AMS). While effective, current ramped oxidation methods are mostly 'offline', involving manual collection and subsequent AMS analysis of evolved CO2, hindering sample throughput and reproducibility.

Here, we introduce a compact, online ramped oxidation (ORO) setup in which CO2 from discrete thermal fractions is directly collected and measured for 14C by AMS equipped with a gas ion source. The setup comprises two modules: (i) an ORO unit with two sequential furnaces - the first, ramped from room temperature to 900 °C, holds the sample; the second, maintained at 900 °C, includes a catalyst ensuring complete oxidation to CO2; and (ii) a dual-trap interface (DTI) collection unit with two parallel molecular sieve traps alternately collecting and releasing CO2 from a given fraction for direct injection into the AMS.

Preliminary results indicate reproducible data, evident in both thermograms and F14C results. Analysis of natural reference samples reveals that measured 14C values and their associated uncertainties align with those reported in the literature using conventional “off-line” ramped oxidation methods, affirming the utility of the new ORO-DTI-AMS setup.

Our goal is to apply this new method for comprehensive investigation of a range of natural samples, with a particular focus on the improved understanding of the fate of OC held in permafrost soils in the context of on-going climate and carbon cycle change in high latitude ecosystems.

How to cite: Bolandini, M. A., De Maria, D., Haghipour, N., Wacker, L., Hemingway, J. D., Eglinton, T. I., and Bröder, L.: Towards an online ramped oxidation approach for thermal dissection and serial radiocarbon measurement of complex organic matter, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7593, https://doi.org/10.5194/egusphere-egu24-7593, 2024.

X1.3
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EGU24-10209
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ECS
Meng Yu, Timothy Eglinton, Pengfei Hou, Negar Haghipour, Hailong Zhang, Zicheng Wang, and Meixun Zhao

The balance between remineralization and sedimentary burial of terrestrial organic carbon (OCterr) in large river-dominated marginal seas influences atmospheric CO2 inventory on a range of timescales. Here we systematically investigate the evolution of OCterr along the river-estuary-coastal ocean continuum for three fluvial systems discharging to the Chinese marginal seas. The 14C-depleted characteristics of bulk OC and molecular components of riverine suspended sediments and marine sediments suggest that the Chinese marginal seas are a significant sink of pre-aged OCterr. Lower plant-wax fatty acid 14C contents suggest selective degradation of labile OC within estuaries, resulting in apparent aging of OCterr, followed by an apparent rejuvenation in OCterr in shelf sediments, the latter likely reflecting inputs from proximal sources that contribute younger OCterr. This selective degradation, aging and rejuvenation of OCterr along the continuum confounds the use of plant wax lipid 14C to constrain lateral transport times, and sheds light on more complex OCterr dynamics in marginal seas.

How to cite: Yu, M., Eglinton, T., Hou, P., Haghipour, N., Zhang, H., Wang, Z., and Zhao, M.: Apparent Aging and Rejuvenation of Terrestrial Organic Carbon Along the River-Estuary-Coastal Ocean Continuum, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10209, https://doi.org/10.5194/egusphere-egu24-10209, 2024.

X1.4
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EGU24-11886
Negar Haghipour, Charlotte Schnepper, Thomas Blattmann, Kayley Kundig, Maxi Castrillejo, Nuria Casacuberta, Timothy I. Eglinton, and Margot E. White

An increasing demand for radiocarbon analysis of small samples has led to the development of various methods to further improve and simplify the CO2 extraction needed for accelerator mass spectrometer (AMS) measurements. Here, the performance of a direct feeding system of CO2 from dissolved inorganic carbon (DIC) from small water samples (<6 ml) and direct AMS measurement via a gas ion source coupled to a gas interface system (GIS) is presented and compared to the conventional preparation by graphitization that demands significantly larger samples (> 60 ml).

Seawater samples collected from Sargasso Sea, southeast of and lake water samples collected from Lake Constance have been prepared by both methods. The extraction of CO2 gas from samples for GIS measurement is performed using a carbonate handling system (CHS-Ionplus AG) through purging the headspace, acidifying the water, and sparging out the CO2. The preparation time is greatly reduced compared to conventional analysis that requires the labor-intensive graphitization step. The yielded 14C results from the direct CO2 measurements are in good agreement with values obtained from graphite measurements. The observed deviation between the two methods is below the uncertainty of radiocarbon gas measurement (~7‰).

This new approach will facilitate understanding of carbon cycle dynamics in many different environments and applications where a high throughput (up to 80 sample/day) is required. The new method is suitable for groundwater, pore water, seawater, freshwaters from lakes, rivers and glacial settings. Furthermore, it enables the analysis of small milliliter-scale samples and those containing low DIC concentrations.

How to cite: Haghipour, N., Schnepper, C., Blattmann, T., Kundig, K., Castrillejo, M., Casacuberta, N., Eglinton, T. I., and White, M. E.: Direct radiocarbon measurements of dissolved inorganic carbon from environmental water using a gas ion source , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11886, https://doi.org/10.5194/egusphere-egu24-11886, 2024.

X1.5
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EGU24-19501
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ECS
Prabodha Lakrani Hewage, Luz María Mejía, Negar Haghipour, Mariem Saavedra-Pellitero, Ben Trundley, Timothy Eglinton, David Hodell, and Blanca Ausín

Coccolithophores are calcifying marine phytoplankton whose blooms can be seen from space and play an important, yet complex, role in the global carbon cycle. On one hand, coccolithophores sequester atmospheric CO2 to the deep ocean via photosynthesis contributing to the biological pump. On the other hand, coccolithophores increase aqueous CO2 via precipitation of tiny calcite scales named coccoliths (i.e., carbonate counter pump), which are a major component of marine sediments. Coccoliths are generally in the 2-20 µm size range, and thus they can be winnowed by strong currents and transported to distal locations. Here, we show the first coccoliths radiocarbon (14C) ages and explore the influence of size-dependent coccolith sorting and transport, redistribution, and fate in marine sediments. Because the coccolith depends on the species, we have separated and 14C dated four coccolith size fractions: 8-11 µm, 5-8 µm, 3-5 µm, and 2-3 µm, in  five depth intervals on a sediment core recovered from SHAK06-5K site, off the Iberian Margin. Coccolith separation was achieved by a combination of dry sieving, microfiltration, centrifugation, and settling experiments. Energy Dispersive Spectroscopy (EDS) images of selected size fractions were used to estimate the relative contribution of coccolith and non-coccolith carbonate. A relationship between coccolith 14C age and grain size is apparent in all samples, with the smallest size class recording the youngest ages and the largest coccoliths being the oldest. The latter suggests that hydrodynamic sorting largely influences coccolith redistribution in marine sediments, where larger coccoliths result in increased mobility, as they are prone to resuspension than coccoliths in 2-3 µm size fraction that tend to show cohesive behaviour. The 14C ages of coccoliths are older than those of co-deposited planktic foraminifera, bulk organic carbon (OC), long-chain fatty acids (LCFA), and alkenones. Coccoliths within the 2-3 µm size class show 14C ages comparable to those of OC in all samples. Such a pattern indicates similar transport mechanisms for both the smallest coccoliths and OC, and that the majority of carbonate in the 2-3 µm size fraction, including the non-coccolith particles, is predominantly derived from marine primary production and thus, of biogenic origin. Our study has implications for palaeoceanographic studies using coccoliths as paleo-productivity and geochemical proxies.

How to cite: Hewage, P. L., Mejía, L. M., Haghipour, N., Saavedra-Pellitero, M., Trundley, B., Eglinton, T., Hodell, D., and Ausín, B.: Inorganic biogenic carbon redistribution and transport in marine sediments, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19501, https://doi.org/10.5194/egusphere-egu24-19501, 2024.

X1.6
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EGU24-6516
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ECS
Nora Gallarotti, Bernhard Peucker-Ehrenbrink, Sophia Johannessen, Lisa Bröder, Reto Wijker, Britta Voss, Negar Haghipour, and Timothy Eglinton

Rivers play a key role in the global carbon cycle by transferring organic carbon (OC) from the terrestrial biosphere to marine sediments, which act as an important long-term carbon sink. Associations between biospheric OC and mineral phases can alter OC stability and hydrodynamic properties, thereby influencing its transport and storage patterns within a river basin and dictating the fate of terrestrial biospheric OC discharged to the ocean. While research has mainly investigated the formation of these associations within soils, open questions remain on how these interactions evolve over space and time.

The Fraser River Basin in British Columbia, Canada drains regions with distinctive lithological and climatic gradients allowing the simultaneous study of leaf-wax-specific isotopic compositions (δ2H, δ13C) and inorganic geochemical signatures (εNd) of sediments as tracers of the provenance of biospheric OC and detrital mineral phases, respectively. In addition, bulk radiocarbon (D14C) serves as a tool to constrain biospheric OC residence times. Here, to investigate seasonal variations in the geochemical signatures of OC and its mineral host in sediments exported by the Fraser River to the Strait of Georgia using samples from a time-series sediment trap deployed cover the course of a year adjacent to the river mouth.

Both εNd and D14C follow a seasonal pattern by which aged OC (-176 to -140‰) is mostly transported during high discharge events such as the freshet in June and heavy rainstorms occurring in the upper basin in fall. During the former event, the geochemical signature (εNd: -9.2 to -7.2) points towards the Coastal Range affecting the detrital mineral composition more strongly, which shifts towards a greater proportion of Rocky Mountains-sourced sediment (εNd: -11.7 to -9.1) during the second high discharge event. Biomarker specific δ2H will further elucidate the extent to which the provenance of biospheric OC coincides with the mineral detrital load. Further, comparison with geochemical signatures of fluvial sediments within the Fraser basin, together with corresponding signatures in river-proximal sediments deposited in the Strait of Georgia allow for OC-mineral interactions to be assessed from a source-to-sink perspective.

This coupled investigation of organic and inorganic tracers provides new insights into terrestrial organic carbon export and the role of organo-mineral interactions on riverine organic carbon dynamics. These findings also have important ramifications for the interpretation of sedimentary archives.

How to cite: Gallarotti, N., Peucker-Ehrenbrink, B., Johannessen, S., Bröder, L., Wijker, R., Voss, B., Haghipour, N., and Eglinton, T.: Spatio-temporal dimensions of organic carbon-mineral interactions in a source-to-sink system, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6516, https://doi.org/10.5194/egusphere-egu24-6516, 2024.

X1.7
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EGU24-14130
|
ECS
Wet atmospheric depositional fluxes of organic carbon: Global Dynamics of Fossil Derived Brown Carbon
(withdrawn after no-show)
Min-Young Lee and Tae-Hoon Kim
Natural Organic Matter
X1.8
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EGU24-16627
Oliver Lechtenfeld, Jan Kaesler, Elaine Jennings, and Boris Koch

Marine dissolved organic matter (DOM) is an important component of the global carbon cycle, yet its intricate composition and the sea salt matrix pose major challenges for chemical analysis. The current view on marine DOM as assessed with ultrahigh resolution mass spectrometry (UHR-MS) is largely based on SPE-extracts known for its consistent underestimation of e.g. the mean nominal oxidation state of carbon (NOSC) and molecular weight as compared to bulk measurements. We introduce a direct injection, reversed-phase liquid chromatography Fourier-transform ion cyclotron resonance (FT-ICR) MS approach to analyze marine DOM without the need for solid-phase extraction. Effective separation of salt and DOM is achieved with a large chromatographic column and an extended isocratic aqueous step. Post-column dilution of the sample flow with buffer-free solvents and implementing a counter gradient reduced salt buildup in the ion source and resulted in excellent repeatability. With this method over 5,500 unique molecular formulas were detected from just 5.5 nmol of carbon in 100 µL filtered Arctic Ocean seawater. We observed highly linear detector response for variable sample carbon concentrations and a high robustness against the salt matrix. We could demonstrate the bias of SPE in marine DOM on a molecular level leading to a predominant detection of less polar DOM, while neglecting a large fraction of polar, heteroatom-rich DOM. In addition, a substantial fraction of terrestrial-derived DOM was previously overlooked in solid-phase extracted marine DOM. Overall, the direct analysis of seawater offers fast and simple sample preparation and avoids fractionation introduced by extraction. The method facilitates studies in environments, where only minimal sample volume is available e.g. in marine sediment pore water, ice cores, or permafrost soil solution. The small volume requirement also supports higher spatial (e.g. in soils) or temporal sample resolution (e.g. in culture experiments). Chromatographic separation adds further chemical information to molecular formulas, enhancing our understanding of marine biogeochemistry, chemodiversity, and ecological processes.

How to cite: Lechtenfeld, O., Kaesler, J., Jennings, E., and Koch, B.: Direct analysis of marine dissolved organic matter using LC-FT-ICR MS, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16627, https://doi.org/10.5194/egusphere-egu24-16627, 2024.

X1.9
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EGU24-13692
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ECS
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Livia Vieira Carlini Charamba, Tobias Houska, Klaus Kaiser, Klaus-Holger Knorr, Stephan Krüger, Tobias Krause, Huan Chen, Pavel Krám, Jakub Hruška, and Karsten Kalbitz

Dissolved organic matter (DOM) is crucial for various ecological processes, playing essential roles in carbon and nutrient cycling. In forested catchments, litter input contributes to soil organic matter, influencing DOM composition in surface waters. The transition of DOM from soil organic matter to the dissolved state significantly impacts ecological balance and highlights the role of specific soil horizons in the catchment for stream water. DOM fingerprints, reflecting variations and similarities, act as valuable indicators for identifying primary DOM sources. The increasing trend in dissolved organic carbon (DOC) concentrations in surface waters underscores the urgency to understand contributing sources comprehensively. This study aims to characterize DOM along the terrestrial-aquatic continuum, identifying sources in stream water.

Soil, soil water, and stream water samples were collected biweekly for approximately two years at various depths in the Sosa drinking water reservoir catchment (Ore Mountains, Saxony, Germany). Two sub-catchments (one with a significant peatland component and one with predominantly mineral soils) were considered, each with two streams. The soil and soil water samples included four different soil types that characterize the entire catchment, i.e., intact and degraded peatland, cambisol, podzol. Pyrolysis gas chromatography-mass spectrometry (Py-GC-MS) was employed to characterize DOM in both solid and aqueous samples. Rstudio was used as a semiautomatic data processing aiming to achieve consistent compound identification. A principal component analysis (PCA) and cluster analysis were used to identify DOM sources in stream water.

PCA results showed a clear distinction between solid and aqueous samples. Overlaps were observed among soil water and stream water samples, revealing shared organic compound sources and potential transfer pathways. Fluctuations and degradation patterns were noted across seasons, especially for soil water samples. Cluster analysis revealed that soil water DOM from peat horizons predominantly influenced upstream stream water DOM in peatland-dominated areas. Downstream, the DOM composition changed and was influenced by soil water from the cambisol and the podzol (mineral soils). Concerning the sub-catchment composed mainly of mineral soils, stream water reflected DOM of deep mineral horizons of cambisols and podzols. Forest floor soil water from cambisol had no to very little effect in both sub-catchments, however, soil water of the podzol forest floor slightly contributed to the streams located in the mineral soil-dominated sub-catchment. Thus, the results show that the primary source of DOM in the Sosa catchment came from soil water of deep mineral soil horizons and that stream proximity was a primary factor influencing the influx of allochthonous DOM into stream water.

The research emphasized that DOM composition in the four streams closely resembled soil water DOM and analyzing the composition of the solid organic soil horizons did not help to identify the potential DOM source of the streams. Therefore, although recognizing intrinsic stream processes is important, successful source identification requires analysis of DOM in soil water from major catchment soil types. Proximity to stream water played a critical role as the predominant factor contributing to the introduction of allochthonous DOM into stream water.

How to cite: Vieira Carlini Charamba, L., Houska, T., Kaiser, K., Knorr, K.-H., Krüger, S., Krause, T., Chen, H., Krám, P., Hruška, J., and Kalbitz, K.: Unveiling the role of soil water: Identifying primary sources of dissolved organic matter in surface waters, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13692, https://doi.org/10.5194/egusphere-egu24-13692, 2024.

X1.10
|
EGU24-3355
Peter Herzsprung, Carolin Waldemer, Matthias Koschorreck, and Oliver Lechtenfeld

Natural organic matter (NOM) was widely investigated in natural waters, sea water, river water, lake water, groundwater. The highest molecular resolution of NOM can be achieved by Fourier-transform ion cyclotron resonance mass spectroscopy (FT-ICR-MS). This analytical tool generates molecular formulas (MF) for thousands of NOM components. By coupling liquid chromatography to FT-ICR-MS insights into the polarity (hydrophilic versus hydrophobic) of NOM compounds can be achieved.

Anthropogenic inputs have an imprint on NOM and it changes its overall composition. Aquaculture is one of the fastest growing sectors of food production by covering over 8 Mio ha. The consequences of fish farming for the organic matter quality in fish pond waters and sediments are poorly understood. Here we investigated the stages of pollution by comparison the water extractable organic matter (WEOM) in the sediment at the main site of fish feed application and open water sediments at different distances (transect) to the feeding site.

Full profile HPLC-FTICR-MS chromatograms were segmented into approx. one-minute wide segments between 10 and 15 Min (five segments), the main eluting region of WEOM. MF were calculated for the mass range 150 - 1000 Da with an error threshold of 1 ppm using in-house software considering the following carbon (C), hydrogen (H), oxygen (O), nitrogen (N) and sulphur (S) elements: 12C0–60, 13C0–1, 1H0–122, 16O0–40, 14N0–8, 32S0–3, and 34S0–1.

For all retention times, N3, N4, N5, N6, N7 (CHNO) MF with 0.2 < O/C < 0.5 and 1.5 < H/C < 2.0 showed relative higher intensities in the feeding center compared to the distant sites. For some MF like C20H37N5O7, C22H39N5O7, C24H42N6O10 the intensity was more than five times higher in the center compared to open water site. Such components can be suggested to be oligopeptides (Leu-Asn-Thr-Ile, Glu-Pro-Lys-Ile, Leu-Leu-Asp-Ser-Gln as possible isomeric solutions). The sediment in the feeding center exhibited a prevalence of CHNOS and CHOS2 MF, whereas N1, N2, CHOS1, and CHO displayed relatively uniform intensities along the transect, with some instances of slightly higher intensities observed away from the feeding site. The number and abundance of CHNOS MF decreased with increasing retention time (decreasing polarity). Notably, these compounds appear to be inherently hydrophilic, characterized by predominantly low molecular weights (< 400 Da).

The results obtained suggest the following biogeochemical processes: Initially, the protein-rich fish feed undergoes hydrolysis, leading to the formation of oligopeptides. Subsequent partial desamination of these molecules facilitates their interaction with inorganic sulphides, resulting in the formation of CHNOS MF. Notably, the component C8H13N1O3S1, exhibiting a five-fold intensity at the feeding site, appears to correspond to one of the possible metabolites (Sulfanylpropanoyl-proline).

The results indicate a potential overfertilization with easily biodegradable protein-rich substances. The WEOM quality seems highly affected by additional input of CHNO, CHNOS and CHOS.

How to cite: Herzsprung, P., Waldemer, C., Koschorreck, M., and Lechtenfeld, O.: NOM quality differences in sediments of land based aquacultures – insights by liquid chromatography-high resolution mass spectrometry, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3355, https://doi.org/10.5194/egusphere-egu24-3355, 2024.

X1.11
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EGU24-5028
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ECS
A Novel Method for Analyzing Dissolved Organic Matter in Soils
(withdrawn after no-show)
Shuchai Gan, Faming Wang, and Ying Wu
X1.12
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EGU24-15782
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ECS
Johann Wurz, Anika Groß, Kai Franze, and Oliver Lechtenfeld

As the volume and complexity of data in environmental sciences continue to grow, the need for data management and reproducible processing methods becomes increasingly crucial. In the specific research domain of natural organic matter (NOM), there is currently no standardized tool for data processing, particularly for the management of data and its respective metadata. We developed and present the Lambda-Miner - a semi-automatic web application for data processing of ultrahigh-resolution mass spectrometry data of NOM. The platform provides an end-to-end data processing pipeline and supersedes manual steps via standardized data and metadata management. It empowers users to execute interactive workflows for mass spectra calibration, assignment of molecular formulas by specific rules to peak masses, and validation of these formulas according to specific sets of rules. Peak data as well as sample and measurement metadata are stored in a relational database management system (RDBMS). The Lambda-Miner thus facilitates reproducible, standardized data processing which builds a common repository for mass data, metadata (such as sample type and geolocation), intermediate, and final results in a format suitable for subsequent analyses. The combination of this information in one place enables meta-analyses such as long-term quality control studies and software optimization assays. The Lambda-Miner supports domain-specific requirements for research data management and contributes to achieving FAIR data principles in the domain of NOM analytics. The Lambda-Miner allows researchers to process their ultrahigh-resolution mass spectrometry data of NOM within minutes and linking it to features such as extraction efficiency, accumulation time, and relation of total assigned current to total ion current. Processed data can be downloaded in an interoperable format, facilitating individual data processing or visualization. The current implementation of the Lambda-Miner is designed for studying NOM with Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) allowing formula assignments with widely used elemental compositions of NOM in the mass range from 0 to 1000 Da. But its modular structure makes it easy to adjust and extend the implementation for other kind of analyses or instrumentations. With its adaptability and focus on reproducibility, the Lambda-Miner introduces a valuable tool for advancing standardized data storage, processing, and analysis in the study of Natural Organic Matter.

How to cite: Wurz, J., Groß, A., Franze, K., and Lechtenfeld, O.: Lambda-Miner: Enhancing Reproducible Natural Organic Matter Data Processing with a Semi-Automatic Web Application , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15782, https://doi.org/10.5194/egusphere-egu24-15782, 2024.

Dissolved Organic Matter
X1.13
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EGU24-3890
|
ECS
Muhammed Fatih Sert, Knut Ola Dølven, Sebastian Petters, Timo Kekäläinen, Janne Jänis, Jorge Corrales-Guerrero, and Bénédicte Ferré

Cold seeps and cold water corals (CWCs) coexist on Northern Norway's continental shelf at the Hola trough between Lofoten and Vesterålen. Here, cold seeps release methane from the seabed, yet only a limited amount reaches the atmosphere. The remaining methane dissolves and disperses in nearby seeps. Methane is unreactive for most microorganisms in the water column, yet it is a unique energy and carbon source for methane-oxidizing bacteria (MOB). MOBs metabolize methane and release carbon dioxide as the end product of oxidation. Increasing carbon dioxide may constrain pH-sensitive CWCs in the region. We investigated the biogeochemistry of carbon, carbon isotopes, nutrients, dissolved organic matter (DOM) compositions and microbial diversity through water column profiles and water samples collected in June 2022. Preliminary results indicated that elevated methane increases dissolved inorganic carbon concentrations and modifies carbon isotopic compositions. Additionally, DOM compositions implied a positive correlation between prokaryotic diversity and protein-like DOM components at cold seeps and the entire water column near CWCs, suggesting analogous microbial modifications. Our preliminary conclusion suggests cold seeps and CWCs symbiotically coexist in Northern Norway continental shelves; however, enhanced water temperatures and consequent increase in methane release at cold seeps may mitigate the functioning of CWCs in future.

This study is supported by the Research Council of Norway, project number 320100, through the project EMAN7 (Environmental impact of Methane seepage and sub-seabed characterization at LoVe-Node 7).

How to cite: Sert, M. F., Dølven, K. O., Petters, S., Kekäläinen, T., Jänis, J., Corrales-Guerrero, J., and Ferré, B.: Carbon cycling in coexisting marine ecosystems: Cold seeps and coral reefs in Northern Norway, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3890, https://doi.org/10.5194/egusphere-egu24-3890, 2024.

X1.14
|
EGU24-15386
|
ECS
Dariya Baiko, Thorsten Dittmar, Philipp Böning, and Michael Seidel

Coastal vegetated ecosystems (CVEs) are highly productive habitats whose role in coastal biogeochemical cycles cannot be understated. The high productivity of salt marshes, seagrass meadows, and mangrove forests is channeled into the sediments and into the sea in form of particulate and dissolved organic matter (DOM). While labile DOM is degraded within a short time frame, recalcitrant DOM compounds can remain in the oceanic water column for hundreds to thousands of years. However, so far, DOM has received little consideration in carbon sequestration approaches. In sulfidic porewater of CVEs, DOM can undergo abiotic sulfurization, producing dissolved organic sulfur (DOS), which may render it resistant to biodegradation. Thus, the formation of DOS in CVEs can act as a link between labile and recalcitrant pools of DOM and provide the means of carbon transport across and beyond ecosystem boundaries. We analyzed DOM as well as inorganic nutrients in samples from temperate (German) and tropical (Malaysian) mesotidal CVEs. Unprecedentedly high porewater DOC concentrations were found in both temperate salt marshes as well as in tropical mangroves. High proportions of DOS in the DOM pool demonstrated accumulation of sulfurized compounds in the porewater. Molecular DOM patterns deduced from ultrahigh-resolution mass spectrometry (FT-ICR-MS) analysis indicated that up to 50% of the several thousand molecular formulas identified were characteristic of the analyzed CVEs. Adjacent habitats shared a substantial proportion of DOM molecular formulas indicating lateral transfer of organic material. This emphasizes that the potential for carbon dioxide removal of CVEs extends beyond the areas with above-ground biomass.

How to cite: Baiko, D., Dittmar, T., Böning, P., and Seidel, M.: Dissolved Organic Matter from Coastal Vegetated Ecosystems Through the Lens of Carbon Sequestration, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15386, https://doi.org/10.5194/egusphere-egu24-15386, 2024.

X1.15
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EGU24-8750
Hannelore Waska and Hanne Banko-Kubis

Subterranean estuaries underlying high-energy beaches are efficient turnover sites for dissolved organic matter (DOM) and nutrients from marine and terrestrial waters. In addition, leaching of beach wrack during tidal inundation and precipitation can contribute to DOM and nutrient loads. However, the combined impact of diverse environmental settings on the release of DOM and nutrients from beach wrack has so far not been studied, although e.g., salinity oscillations and temporary exposure to sunlight are common in high-energy beach subterranean estuaries. Here, we present the results of an extensive beach wrack leaching experiment taking beach wrack type, age, sunlight exposure, and leaching matrix into consideration. A combination of UVA irradiation, advanced wrack age, and leaching by low-salinity artificial rainwater resulted in high dissolved organic carbon (DOC) and total dissolved nitrogen (TDN) releases of mmoles- to moles per kg dry weight in the macroalga Fucus sp. Furthermore, jellyfish wrack released millimoles of TDN in artificial seawater incubations. Ultra-high-resolution analyses of DOM revealed a prevalence of molecular formulae resembling biochemical building blocks such as sugars, amino acids, and vitamins, indicating that the released DOM could be of substantial nutritional value for the heterotrophic microbial communities on and near beach wrack. An interesting finding was the high abundance of aromatic and humic-like DOM released from macroalgal beach wrack, which may impact typically used marine and terrestrial source- and sink proxies. As such, beach wrack DOM and nutrients could further complicate biogeochemical distribution patterns in the subterranean estuary.

How to cite: Waska, H. and Banko-Kubis, H.: Experimental comparison of dissolved organic matter and nutrients leached from beach wrack by sea- and rainwater: A nutritional boost for the sandy beach subterranean estuary, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8750, https://doi.org/10.5194/egusphere-egu24-8750, 2024.

X1.16
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EGU24-12381
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ECS
Danielle Green, Fereidoun Rezanezhad, Scott Smith, Stephanie Slowinski, and Philippe Van Cappellen

Dissolved organic carbon (DOC) is an important contributor to both carbon cycling and other biogeochemical processes in aquatic ecosystems. The biodegradable fraction of DOC can be microbially degraded over time, producing carbon dioxide (CO2), a greenhouse gas. In addition, microbial degradation-resistant DOC can accumulate in water bodies, causing chemical and physical changes to aquatic systems. Although biodegradable DOC (BDOC) is widely studied, there is no agreed-upon standard method for assessing its biodegradability. Here, we aimed to develop and evaluate a new method for determining BDOC in freshwater samples. Our method includes filtering water samples to below 0.22 µm, to remove existing microbial cells, prior to inoculating the samples with a concentrated microbial inoculum produced by stepwise isolation of microbial cells from a peat sample. In addition, we added solutions containing nitrogen and phosphorus (in the forms of NH4NO3 and K2HPO4, respectively) to ensure that the microbes were not nutrient-limited. The samples were then capped with foam stoppers and incubated in the dark at 25⁰C on a shaker for 28 days to allow constant aeration during BDOC degradation. When applied to five freshwater samples collected from rivers, stormwater ponds, and a lake, and a glucose control, we observed that the amount of BDOC in the natural samples ranged from 15% to 53% and was 90% in the glucose control. Rates of BDOC degradation were calculated from DOC measurements at six sampling time points between days 0 and 28. We found that the DOC trends with time were best explained by two successive phases for BDOC degradation in all of the samples: an initial, fast, phase of BDOC degradation followed by a second, slower, phase of BDOC degradation where the rate constant for the second phase was between 5.57 and 565 times slower than for the initial phase. Changes in chemical characteristics of DOC measured using absorbance and fluorescence parameters including specific ultraviolet absorbance at 254 nm (SUVA254), humification index (HIX), and parallel factor analysis (PARAFAC) at each sampling time revealed that the initial, fast, phase of BDOC degradation often represents the utilization of small, non-aromatic compounds while the later, slower, phase of BDOC degradation often represents the utilization of more complex, aromatic compounds. The presented method provides a new approach to measure and characterize BDOC degradability and degradation kinetics that can be applied to future studies on biogeochemical processes in aquatic ecosystems.

How to cite: Green, D., Rezanezhad, F., Smith, S., Slowinski, S., and Van Cappellen, P.: Assessing the biodegradability of dissolved organic carbon in freshwater systems: A method evaluation study, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12381, https://doi.org/10.5194/egusphere-egu24-12381, 2024.

X1.17
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EGU24-14981
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ECS
Spatial and temporal exploration of lake-water humic DOM quality - from the Northern hemisphere
(withdrawn)
Cathrine Brecke Gundersen, Kar Austnes, and Heleen A. de Wit
X1.18
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EGU24-3292
Yaojin Xiong

Elevated concentration levels of geogenic ammonium in groundwater arise from the mineralization of nitrogen-containing natural organic matter in various geological settings worldwide, especially in alluvial-lacustrine and coastal environments. However, the difference in enrichment mechanisms of geogenic ammonium between these two types of aquifers remains poorly understood. To address this knowledge gap, we investigated two representative aquifer systems in central Yangtze (Dongting Lake Plain, DTP) and southern China (Pearl River Delta, PRD) with contrasting geogenic ammonium contents. The use of optical and molecular characterization of DOM combined with hydrochemistry and stable carbon isotopes has revealed differences in DOM between the two types of aquifer systems and revealed contrasting controls of DOM on ammonium enrichment. The results indicated higher humification and degradation of DOM in DTP groundwater, characterized by abundant highly unsaturated compounds. The degradation of DOM and nitrogen-containing DOM was dominated by highly unsaturated compounds and CHO+N molecular formulas in highly unsaturated compounds, respectively. In contrast, the DOM in PRD groundwater was more biogenic, less degraded, and contained more aliphatic compounds in addition to highly unsaturated compounds. The degradation of DOM and nitrogen-containing DOM was dominated by aliphatic compounds and polyphenols and CHO+N molecular formulas in highly unsaturated compounds and polyphenols, respectively. As DOM degraded, the ammonium production efficiency of DOM decreased, contributing to lower ammonium concentrations in DTP groundwater. In addition, the CHO+N(SP) molecular formulas were mainly of microbial-derived and gradually accumulated with DOM degradation. In this study, we conducted the first comprehensive investigation into the patterns of groundwater ammonium enrichment based on DOM differences in various geological settings.

How to cite: Xiong, Y.: Characteristics of Dissolved Organic Matter Contribute to Geogenic Ammonium Enrichment in Coastal versus Alluvial-lacustrine Aquifers, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3292, https://doi.org/10.5194/egusphere-egu24-3292, 2024.

Pyrogenic Organic Matter
X1.19
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EGU24-12192
Cristina Santin, Carmen Sánchez-García, Minerva García-Carmona, Tercia Strydom, Philippa Ascough, and Stefan H. Doerr

Southern African savanna fires account for ~30% of the annual global carbon (C) emissions from vegetation fires, but their impact on the global C cycle extends beyond direct emissions During fire, part of the C burnt is converted to pyrogenic carbon (PyC), which is more resistant to degradation than original biomass and acts as a buffer to global fire C emissions when stored in soils or sediments. Despite its recognized importance for the C cycle, how much PyC is produced and how much of it stays in savanna ecosystems is still not well known, with no information yet for Southern African savannas. To address this research gap, we quantified how much PyC was produced during four fires in Kruger National Park (South Africa) and how much PyC was stored in surface soils. We also characterized the chemical and thermal recalcitrance of this PyC. Our results will be discussed in the broader context of C emissions from savanna fires as well as the role PyC plays as a C sequestration mechanism through its accumulation in soils, redistribution and ex-situ transport.

How to cite: Santin, C., Sánchez-García, C., García-Carmona, M., Strydom, T., Ascough, P., and Doerr, S. H.: There to remain? Pyrogenic carbon production of savanna fires, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12192, https://doi.org/10.5194/egusphere-egu24-12192, 2024.

X1.20
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EGU24-12504
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ECS
Carmen Sánchez-García, Cristina Santín, Tercia Strydom, and Stefan Doerr

Herbivores play a vital role in the functioning of savanna ecosystems. They ingest plants, modifying the vegetation cover, and disperse nutrients across the landscape in the form of dung. Fire in savanna is also a key nutrient recycling pathway, making elements readily available through the resultant ash and smoke. Wildfire ash, known for its susceptibility to be transported by wind and water, plays a key role in redistributing pyrogenic organic matter and nutrients across the landscape. However, our level of understanding of ash characteristics from burnt dung is very low. In addition, and due to its high carbon content, dung also adds to the wildland fuels for fires, alongside vegetation. Given that savannas are the dominant source of global Cemissions from fires, assessing the role of burnt dung in C dynamics is, therefore, also crucial for more accurate estimations of the overall C released during savanna fires.

We quantified C losses from dung combustion during fire in four savanna sites burnt by experimental fires in Kruger National Park (South Africa). We also analysed chemical properties, including major nutrients and metals, of dung and dung-derived ash. The studied dung came from large herbivores (zebra, elephant, giraffe, buffalo and wildebeest). The concentration of carbon and nitrogen in burnt dung was significantly lower than unburnt dung (carbon: 41 and 4.1%, nitrogen: 1.1 and 0.3% in unburnt and burnt dung, respectively). The carbon released from dung burning accounted for up to 6% of the carbon released from vegetation burning, emphasizing the substantial role of dung in carbon emissions during savanna fires. Our results also highlight burnt dung as a hotspot for minerals and nutrients with chemical characteristics different to those found in vegetation ash (e.g., phosphorus: 9,195 and 6,158 mg kg-1, copper: 55.8 and 28.1 mg kg-1 in dung-derived and vegetation ash respectively). This is likely to affect local soil physical and chemical properties and hence enhance ecosystem diversity.

How to cite: Sánchez-García, C., Santín, C., Strydom, T., and Doerr, S.: Burning poop: carbon dynamics in herbivore dung during southern-African savanna fires, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12504, https://doi.org/10.5194/egusphere-egu24-12504, 2024.

X1.21
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EGU24-17520
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ECS
Stephen Boahen Asabere, Ankit Ankit, Tino Peplau, Simon Drollinger, Christopher Poeplau, Daniela Sauer, and Axel Don

Pyrogenic carbon (PyC) is produced by the incomplete combustion of biomass. It is chemically inert and nutrient-deficient, making it relatively stable in soils. PyC can thus form an important pool of total soil organic carbon (TOC) for C preservation in soils. Despite its significance, data on the nature, level, and relative contribution of PyC to TOC in tropical urban agroecosystems is largely non-existent. In this study, we aim to determine the content and chemical composition of PyC in urban arable soils of Kumasi, a rapidly expanding city in Ghana, West Africa. PyC is likely enriched in these soils, mainly due to soot deposition from traffic, combined with widespread burning of household waste and use of charcoal for cooking.

We sampled topsoils (0–10 cm) from arable fields under four levels of urbanisation intensity (UI), from low to high UI. We employed a range of analytical techniques including visual, chemothermal, thermogravimetric, and biomarker analysis, as well as fourier transformed infrared (FTIR) and nuclear magnetic resonance (NMR) spectroscopy. Visual assessment indicated that ≥80% of all bulk soil samples contained charred macro particles, pointing to PyC enrichment in the urban arable soils. Separating TOC into particulate organic C (POC, ≥63 µm particle size) and mineral-associated organic C (MAOC, <63 µm), chemothermal assessment revealed that PyC contributed less than 0.1% to each fraction under all urban intensity conditions. These PyC levels increased notably along with increasing UI in both TOC fractions. Thereby, median PyC levels in the MAOC fraction (7.8–20.4 mg kg-1) were markedly higher compared to those of the POC fraction (0.1–0.3 mg kg-1). This finding highlight a noticeable PyC contribution to TOC preservations in Kumasi’s tropical urban arable soils, although overall contribution is low. Ongoing thermogravimetric, FTIR spectroscopy, NMR spectroscopy, and biomarker analysis will further detail the amount and chemical composition of PyC in these soils. For instance, we will integrate diagnostic ratios of polycyclic aromatic hydrocarbons with masoccharide anhydrides in order to decouple the relative amount of PyC from biomass and that of fossil fuel.

By characterising the chemical nature of PyC with this wide range of analytical techniques, insights into the source and transformation of PyC in a tropical urban agricultural context can be provided. This will lead to better understanding of the role of PyC in the urban soil carbon cycle and its implications for urban sustainability and global C sequestration efforts.

How to cite: Asabere, S. B., Ankit, A., Peplau, T., Drollinger, S., Poeplau, C., Sauer, D., and Don, A.: A multi-method approach to characterise and quantify pyrogenic carbon in tropical urban agroecosystems. , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17520, https://doi.org/10.5194/egusphere-egu24-17520, 2024.

X1.22
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EGU24-9643
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ECS
Long-term effects of biochar application on soil quality and yields under field conditions in Switzerland
(withdrawn)
Samuel Schlichenmaier and Markus Steffens
X1.23
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EGU24-1546
Vera Samburova, Eric Schneider, Christopher Rüger, Brad Sion, Lukas Friederici, Yasaman Raeofy, Markus Berli, Palina Bahdanovich, Hans Moosmüller, and Ralf Zimmermann

In the past decade, the size, frequency, and severity of wildfires have increased around the world, especially in forests of the western United States, where ecosystems are dominated by dry conifer forests. It is known that fires can greatly affect not only air quality, climate, forest, and fauna, but also soil. The heat from fires can alter soil chemistry and change soil water repellency (SWR). SWR can reduce soil infiltration, which can increase surface runoff, erosion, and the potential for flooding and mud and debris slides. The increased frequency and intensity of western U.S. wildfires due to the rapidly changing climate poses an important question: What are the short- and long-term effects of wildfires on soil’s hydrologic responses, including SWR, and what is the role of fire-induced chemistry in SWR?

In the summer and fall of 2021 and 2022, there were four mega-wildfires (Caldor, Dixie, Beckwourth Complex, and Mosquito) in the Eastern Sierra Nevada mountains (California, USA). These wildfires provided us an opportunity to collect post-fire soil and ash samples and study the effects of fires on the physical and chemical properties of soils. We collected over 80 samples and performed multiple water-droplet penetration time (WDPT) tests in the field and, in the laboratory, apparent contact angle (ACA) measurements with the goniometer technique. For all four fires, a significant increase in SWR was observed between unburned and burned soils, with WDPT increasing from <1 s to 600 s (maximum measured value) and ACA values increasing between 1.1 and 9 times (p-value < 0.001). Our WDPT and ACA measurements of the samples collected 6 months and 1 year after the 2021 megafires (Dixie, Caldor, and Beckwourth Complex megafires) showed no significant changes in SWR for unburned and burned soils. The chemical analysis of organic constituents of unburned and burned soils with ultra-high-resolution mass spectrometry (thermogravimetry atmospheric pressure photoionization in combination with Fourier transform ion cyclotron resonance mass spectrometry or TG APPI FT-ICR MS) suggests that burned soils became water-repellent due to the formation and/or deposition of aromatic organic species (e.g., polycyclic aromatic hydrocarbons or PAHs) on the soil surface during fires. We found a positive correlation (R2 = 0.813) between the ACA values of analyzed fire-affected samples and aromaticity derived from the TG APPI FT-ICR MS spectra.

These results of our research highlight the importance of future research on the chemical composition of post-fire soils and the need to study the long-term effects of fires on soil properties.

How to cite: Samburova, V., Schneider, E., Rüger, C., Sion, B., Friederici, L., Raeofy, Y., Berli, M., Bahdanovich, P., Moosmüller, H., and Zimmermann, R.: Soil chemistry and hydrophobicity caused by four 2021-22 western U.S. megafires., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1546, https://doi.org/10.5194/egusphere-egu24-1546, 2024.

X1.24
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EGU24-7088
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ECS
Kate Kingston, Zhihong Xu, Chris Pratt, Brendan Mackey, Paul Petrie, and Yihan Li

The increased frequency and intensity of climate extremes challenges vineyards to adapt and mitigate to ensure the survival of grape vines (Vitis vinifera) to meet the growing demand for quality wine.  Regenerative Viticulture (RV) is a novel approach with a strong focus on increasing soil carbon (C) stocks to regenerate vineyard soil that is largely degraded and in poor health.  When soil health and fertility is low, this impacts vine health and reduces its ability to fight disease and pests and withstand extreme climatic events. We hypothesised that biochar would increase nitrogen (N) cycling and retention and that these would differ in relation to the distinct physiochemical properties of the two vineyard soils.   Conscious of contributing to a sustainable circular economy, we utilised viticulture industry waste to produce biochar’s to compare with standard pine biochar.  Biochar was produced with three feedstocks at different pyrolysis temperatures, grape marc (475°C), vine pruning (450°C) and pine (600°C).  Soil (0 - 10 cm depth) was collected from under vines from vineyards at the South Burnett (heavy texture) and Granite Belt (sandy texture) regions in Queensland, Australia. We used a novel 15N natural abundance approach in a laboratory incubation experiment to investigate the potential of using biochar, a C-dense material produced by high temperature pyrolysis of organic materials in limited oxygen conditions as a suitable climate smart RV method for vineyard soils.  A short three-day laboratory incubation followed by microdiffusion was conducted to quantify the impacts of the three biochars on N transformations in the two soils.  Soil moisture was controlled at 60% and 90% water holding capacity (WHC) and biochar applied at 0% and 10% (w/w), with samples harvested on incubation days 0 and 3. Preliminary results indicate that in the short term for both experimental soils, biochar stimulated microbial activity, increased N availability and water use efficiency and reduced N loss through denitrification.  The results indicate that fungicides use in vineyards impacted the underlying soil health and microbial communities and influencing N cycling.  For the long term impact, the potential to use biochar for increase biodiversity and ecosystem recovery as a climate smart RV method in vineyards needs to be trialled in the field.  This is to establish the long-term effects of C accumulation and improved N cycling on soil health, biodiversity, vine resilience under extreme natural weather events, and on wine grape quality and quantity.

How to cite: Kingston, K., Xu, Z., Pratt, C., Mackey, B., Petrie, P., and Li, Y.: Using a novel N-15 natural abundance approach to quantify soil nitrogen transformations in biochar-treated vineyard soils., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7088, https://doi.org/10.5194/egusphere-egu24-7088, 2024.

Posters virtual: Fri, 19 Apr, 14:00–15:45 | vHall X1

Display time: Fri, 19 Apr 08:30–Fri, 19 Apr 18:00
Chairpersons: Marcus Schiedung, Anna Gunina
vX1.1
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EGU24-1595
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ECS
Yasaman Raeofy, Vera Samburova, Markus Berli, Brad Sion, and Hans Moosmüller

Recently, wildfire activity and intensity in the western U.S. have greatly increased, mainly due to a warming climate, population growth, land use changes, and fuel accumulation. Disastrous effects during fires include loss of human lives and infrastructure, ecosystem disturbances, and emissions of carbon dioxide and air pollutants. In addition, wildfires modify physical and chemical soil properties and can cause Fire-Induced Soil Hydrophobicity (FISH), which reduces water infiltration into the soil and accelerates runoff during precipitation events. This may induce cascading disasters including flooding, landslides, and deterioration of water quality. To predict and mitigate such disasters, FISH is generally quantified at a few fire-affected locations using a manual infiltration test. However, this limited spatial coverage poorly represents FISH on a watershed scale as needed for prediction and mitigation purposes.

Watershed-wide, high-resolution monitoring of FISH is only practical using airborne or satellite-based remote sensing, for example utilizing solar reflectance spectra to characterize and monitor physical and chemical properties of fire-affected soils. Such spectra depend on light scattering and absorption at the soil surface. For this study, we have sampled ash, burned, and unburned soils, fresh (0 month), 1 year, and 2 years after three recent California (US) megafires: the Dixie (2021, 3,890 km2), Caldor (2021, 897 km2), and Beckwourth Complex (2021, 428 km2) fires. We studied the optical, chemical, and physical properties of all our samples. Optical hyperspectral reflectance spectra (350–2,500 nm) were obtained using natural solar (blue sky) illumination and a spectroradiometer (ASD FieldSpec3), operated in reflectance mode.  For all three fires, the results show that 700 nm wavelength reflectance of ash samples collected 1 and 1.5 years after the fire decreased between 36% and 76% compared to that of samples collected right after the fires. Additionally, significantly higher visible reflectance has been found for unburned compared to burned soil samples in each fire region that was studied. Fourier-transform infrared (FTIR) measurements were used to characterize the carbonate content of soil and ash samples demonstrating a positive relationship between carbonate content and visible reflectance, indicating a possible contribution of carbonate to the reflectance of soil/ash samples.

How to cite: Raeofy, Y., Samburova, V., Berli, M., Sion, B., and Moosmüller, H.: Hyperspectral Reflectance of Pre- and Post-Fire Soils: Toward Remote Sensing of Fire-Induced Soil Hydrophobicity, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1595, https://doi.org/10.5194/egusphere-egu24-1595, 2024.