Seasonally different precipitation infiltration under monsoon humid areas may drive changes of groundwater flow systems and possible nitrate transformation processes in groundwater. In this study, dissolved greenhouse gases, noble gases concentrations (N₂ and Ar) and isotopes of N₂O were used to quantitively identify nitrification and denitrification to reveal spatial and temporal characterization of nitrate transformation in typical groundwater flow profiles in the Qingyi River basin, east China. In dry and wet seasons, the recharge altitudes of groundwater were distinctive and dominant nitrate transformation processes differed spatially and temporally. According to the N₂-Ar estimation, the recharge altitudes of groundwater in dry season were higher than those in wet season, indicating obviously less proportion of precipitation from lower altitudes and relatively increased proportion of recharge from regional recharge areas in dry season, whereas local groundwater flow systems were preferentially developed in wet season. Denitrification is commonly observed in groundwater during the dry season, with positive Excess-N₂ concentrations and phenomena that N₂O concentrations initially accumulate with progress of denitrification but later decrease due to enhanced N₂O reduction. In the wet season, nitrification is the dominant process in groundwater, with only a small portion of groundwater exhibiting denitrification, resulting in positive Excess-N₂ concentrations. In this case, N₂O concentrations initially increase during nitrification but later decline due to incomplete denitrification. Quantitative results based on δSP-N₂O isotopes indicated that the maximum contribution of nitrification in groundwater during the wet season ranged from 52.8% to 100%, with an average of 77.3%. The contributions from denitrification and N₂O reduction in wet season are limited, which is consistent with results identified by nitrate and ammonium isotopes. Spatially, due to more reducing redox environment in regional groundwater flow systems, the denitrification progress (DP) in most groundwater in discharge zones exceeds 99%, with denitrified NO₃⁻ concentrations reaching up to 25.72 mg/L, significantly higher than the average DP values in recharge zones (27.7%) and transition zones (31.6%).

How to cite: Huang, X.: Identification of nitrification and denitrification along groundwater flow paths using dissolved N2, Ar, and N2O in typical groundwater flow systems in the Qingyi River basin, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-1233, https://doi.org/10.5194/egusphere-egu25-1233, 2025.

Organic inputs in grasslands are known to enhance soil carbon sequestration. However, it remains unclear whether long-term organic inputs lead to greenhouse gas (GHG) emissions, specifically methane (CH₄) from livestock and nitrous oxide (N₂O) from soils, that outweigh the benefits of carbon sequestration. Addressing this issue is crucial, as it directly impacts the evaluation of organic farming practices for sustainable land management and climate change mitigation. In this study, we employed the process-based Denitrification-Decomposition (DNDC) model to estimate the fluxes of major greenhouse gases (GHGs) in a long-term grassland silage experiment established in 1969. The model was validated against measured data, effectively capturing the dynamics of N₂O emissions, soil temperature, biomass, and soil organic carbon (SOC). Simulations under different IPCC Shared Socioeconomic Pathway (SSP) scenarios of altered temperature, CO₂ concentrations, and radiative forcing were conducted. Treatments with high levels of cattle manure and pig manure under the SSP1-2.6 scenario exhibited a net GHG sink, whereas conventional fertilization resulted in a net GHG source under both SSP1-2.6 and SSP2-4.5. Grass yields decreased under conventional fertilization in both SSP2-4.5 and SSP5-8.5 scenarios. However, the application of organic matter inputs resulted in yield increases across all scenarios. These findings highlight the potential of organic farming practices, especially with high organic inputs, to mitigate GHG emissions and enhance productivity in grassland ecosystems. Therefore, adopting organic farming practices with adequate organic inputs could serve as a sustainable strategy for balancing food production and environmental conservation.

How to cite: Meng, X., Khalil, I., and Osborne, B.: Enhancing crop yield, carbon sequestration, and greenhouse gas mitigation through organic matter inputs: long-term grassland farming observations and DNDC model predictions, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-20890, https://doi.org/10.5194/egusphere-egu25-20890, 2025.

An accurate representation of biomass burning aerosol emissions is essential in climate and Earth System Models to capture aerosol properties and their interactions. The sources of regional smoke plumes include the widespread prevalence of numerous small fires, which are  common across Savanahs, and larger more episodic wildfires, such as the extreme Californian wildfire event of September 2020. Capturing emissions from such a diverse range of fire activity is a major challenge and some atmospheric models, including the UK Earth System Model (UKESM) have scaled up aerosol emissions to ensure modelled AOD match observations. Past evaluations have struggled to provide a clear answer as to how to reconcile emissions and modelled aerosols, with contrasting outcomes for different regions and/or assessments of seasonal means versus individual smoke plumes. Our modelling study leverages observational data from the unprecedented wildfires in September 2020 to identify potential issues in capturing the aerosol from large / extreme wildfires in the global modelling system of UKESM. Running in nudged mode and with daily emissions from GFED4.1s emissions enables a realistic simulation of the thick smoke plumes that ensued across the continent and out into the Pacific, with little overall bias in AODs between UKESM and co-located observations (AERONET, VIRS, MAIAC). However, scaling emissions by a factor of 2 provides better agreement globally and across regions dominated by smaller fires. We therefore develop a means of differentiating between small and large fires based on the daily dry matter (fuel) consumption and apply this to enable scaling of emissions from small fires that seem to otherwise be underestimated in the model, whilst avoiding scaling those from large fires. Our results indicate a way forward to ensure a global simulation of biomass burning aerosol and fidelity in modelling extreme events.

How to cite: Johnson, B., Quaze, L., and Haywood, J.: Evaluating aerosol emissions from wildfires in the UK Earth System Model: What we have learnt from modelling the extreme wildfires in California during September 2020 , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-18758, https://doi.org/10.5194/egusphere-egu25-18758, 2025.

Open-cast lignite mining significantly disrupts cultivated soils. Restoration and re-cultivation processes enable the conversion of these disturbed areas back into productive land. These processes involve mixing original topsoil (~20%) with parent material loess (~80%), diluting the organic carbon (C) and nitrogen (N) pools, as well as the soil's biological parameters. To restore soil fertility and physical structure, Phase I includes the cultivation of alfalfa to replenish C and N, re-establish biological functions, and the addition of mineral fertiliser (N:P:K, 15:15:15 kg ha^-1). Following two to three years of Phase I, the restoration transitions to Phase II for three to five years, with an initial application of green waste compost (30 t ha^-1) and annual basal mineral fertiliser (N:P:K, 200:80:60 kg ha^-1). Phase III then involves returning the land to farmers with a typical rotation including sugar beet-winter wheat and a mix of organic and mineral fertilisation.

Previous studies have shown that soil C recovery and several key biological functions have only partially recovered, even after more than 50 years since re-cultivation. However, the evolution of P cycling, especially microbial-mediated P cycling, along this gradient remains unknown. This study aims to investigate interactions between soil P, soil microorganisms, and soil properties that affect microbial P cycling and P availability to plants following mining activity.

Hedley fractionation was employed to estimate various P pool sizes, while ion-exchange kinetics (IEK) assessed P exchangeability and reactivity in eight soils (soils restored from 2022 – year 0 – Phase I, 2020 – year 2 – Phase I, 2018 – year 5 – Phase II, 2014 – year 9 – Phase III, 2006– year 17 – Phase III, 1979 – year 44 – Phase III and 1964 – year 59 – Phase III and an original soil undisturbed). In three key soils (year 0 - Phase I; year 59 - Phase III; original undisturbed soil), ¹⁸O-labeled water was used in incubation to determine the degree of ¹⁸O integration within microbial biomass and in various P fractions.

In Phase I, a decrease in the relative size of the most labile-P pool was observed. In Phases II and III, this proportion increased, notably with a larger NaOH-extractable-P increase. P exchangeability decreased during Phase I, then significantly increased in older soils, surpassing that of the original undisturbed soil. Preliminary results indicate microbial P processing is highly correlated with total soil organic C. For instance, microbial P processing was nearly non-existent in newly formed soil (organic C: 0.54 g kg^-1) and was found to be twice as low in 59-year-old soil (organic C: 1.24 g kg^-1) compared to the original soil (organic C: 1.62 g kg^-1).

The current findings demonstrate that despite measured P levels surpassing those of the original soil in the oldest soils, biologically-driven P cycling has not fully recovered more than 50 years after soil re-cultivation.

How to cite: Raymond, N. S., Tamburini, F., Oberson, A., Reichel, R., and Mueller, C. W.: Microbial phosphorus processing in a gradient of agricultural soil development following mining activity, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-8511, https://doi.org/10.5194/egusphere-egu25-8511, 2025.

Bound biomarkers, which are covalently linked to kerogen or asphaltene macrostructures, exhibit enhanced stability against mixing effects, contamination, and biodegradation. Although previous studies have noted that the results of bound and free biomarkers in assessing sedimentary environment and maturity are not exactly consistent, specific criteria for assessing bound biomarkers have not been proposed. In this study, microscale sealed vessel catalytic hydrogenation (MSSV-Hy) was used to extract bound biomarkers from shale and compare them with free biomarkers. The study demonstrates the reliability of bound biomarkers indices in evaluating depositional environments and maturity, and it systematically compares the differences between bound and free biomarkers. The results revealed that the maturity assessment of bound biomarkers is lower than that of free biomarkers. Additionally, C29 regular steranes are selectively consumed during rapid heating, resulting in a decrease in the input parameters from terrigenous sources. Adjusted criteria for bound biomarkers can more accurately evaluate the sedimentary environment and maturity of shale.

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How to cite: Yuan, L.: Application of Bound Biomarkers in the Evaluating the Deposition Environment and Maturity of Shale, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-7582, https://doi.org/10.5194/egusphere-egu25-7582, 2025.

Plant-insect herbivore interactions are essential in shaping forest ecosystem health. The resource availability hypothesis (RAH) and the leaf economics spectrum (LES) theory predict that species in high-resource environments tend to adopt a "fast" strategy but are more susceptible to herbivory. However, this contradicts reports of increased insect herbivory in the context of global drought intensification, and hinders accurate prediction about how different plant species respond to herbivorous insect feeding.

To fill this knowledge gap, we conducted an observational study in two temperate forests dominated by Quercus mongolica and Betula platyphylla in eastern China to compare their leaf herbivory patterns and explore possible mechanisms. We measured three leaf herbivory proxies (consumed leaf area, percent consumed, and herbivory frequency), some leaf traits (leaf area, specific leaf area, leaf water content, leaf nitrogen, phosphorus and non-structural carbohydrate contents), and soil properties (pH, soil water content, soil organic carbon content, soil nitrogen and phosphorus contents).

We found that Q. mongolica, growing in poorer soil environments with lower water and nutrient contents, experienced higher leaf herbivory than B. platyphylla. Regarding leaf traits, Q. mongolica had a higher leaf area and non-structural carbohydrate content, but lower specific leaf area, leaf nutrient and water contents than B. platyphylla. At the leaf level, leaf area, rather than specific leaf area, of both tree species was positively correlated with leaf herbivory. At the tree level, species-specific patterns emerged, i.e., leaf herbivory of B. platyphylla was positively related to leaf area and negatively related to leaf nitrogen and water contents and soil phosphorus content, whereas that of Q. mongolica was only positively affected by soil phosphorus content.

These findings challenge the predictions of RAH and LES theory, as Q. mongolica that grows in resource-poorer soil environments with a conservative strategy suffers higher leaf herbivory than B. platyphylla, shedding some light on the proverb that trouble follows the needy. Moreover, water-related factors (i.e., leaf and soil water contents) and leaf area showed an important effect on driving interspecific and intraspecific leaf herbivory variations here, implying that climate-induced droughts may exacerbate herbivore pressure in temperate forests.

How to cite: Zhao, C. and Tian, D.: Trouble follows the needy: more severe leaf herbivory in the resource-poorer temperate oak forest than in the birch forest, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-17774, https://doi.org/10.5194/egusphere-egu25-17774, 2025.

Many dioecious plants are dominant foundational species (e.g., grasses, poplars, ginkgoes) that structure ecosystems and provide essential resources for diverse ecological communities. Due to their higher nutrient demands and reproductive costs, female plants generally appear more sensitive to environmental changes, such as increased temperatures and drought conditions. The soil ecosystem is critical for providing the substrate, nutrients, and habitat for terrestrial plant communities to exist. Male and female plants are likely to interact with the soil environment differently, with implications for ecosystem functioning. Recent research has shown that female and male plants differ in their soil microbial diversity and community composition. However, how plant sex affects soil communities is still unknown. This study investigated how female and male plants of Ilex vomitoria differ in fungal diversity and composition and subsequent cascading effects on soil arthropods. Fungal operational taxonomic units (OTUs) were identified from DNA sequencing data, and arthropods were extracted and identified from 91 soil samples collected under the canopies of female and male Ilex vomitoria individuals across three locations in southeastern Texas, USA. We found that male plants of I. vomitoria exhibit higher fungal diversity compared to female plants, with both sexes associating with distinct fungal communities. Conversely, soil arthropod diversity and community composition were affected by location but not plant sex. Our results provide valuable insights into the ecological interactions of dioecious plants, emphasizing the role of plant sex as a key trait that influences soil biodiversity and the associated functioning of ecosystems.

How to cite: Bradley Jimenez, R.: Ecological interactions in dioecious plants: implications for soil fungi and arthropods, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-13963, https://doi.org/10.5194/egusphere-egu25-13963, 2025.

Disturbances resulting from anthropogenic global change pose ongoing threats to plant biodiversity. Functional trait-based approaches enable ecologists to observe species-level stress responses with implications for community-level adaptations to disturbances. DRAGNet (Disturbance and Resources Across Global Grasslands) leverages grassland restoration to explore the mechanisms driving disturbance recovery and community assembly. In this single-site study, we examine how plant composition and traits vary across disturbance (tillage) and soil resource (NPK+) gradients. Plant composition will be surveyed in 28 plots, with root and soil samples extracted for trait analysis and soil nutrient testing. We predict that plants in disturbed, nutrient-enriched plots will exhibit divergent functional traits, including reduced root biomass and specific root length, alongside changes in above-ground traits. Preliminary data illustrates the impact disturbance can have on community composition, particularly by promoting invasive species (PERMANOVA, p = 0.0576). This finding underscores the influence of disturbance on plant community assembly and highlights the potential vulnerability of restored grasslands to invasive species proliferation under human-induced disturbances. This study aims to uncover the root functional traits driving the recovery of a restored grassland across both soil disturbance and resource gradients.

How to cite: Campbell, A., Sullivan, L., Celestin, M., and McCary, M.: Getting Out from Under: The Belowground Response of a Restored Grassland to Soil Disturbance and Resource Addition, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-14964, https://doi.org/10.5194/egusphere-egu25-14964, 2025.

Forested upstream watersheds support clean freshwater and maintaining stable hydrological conditions of ecosystem services. The associations between vegetation growth and climatic variations play a vital role on hydrological regimes that are region-dependent, but the associations of climate-phenology-hydrology have rarely been investigated in tropical/subtropical regions particularly. In this analysis, the hydroclimate records (1991-2020) at two long-term studied forest watersheds, Fushan (FS) and Leinhuachi (LHC) experimental forest, Taiwan were used, and showed that the incidences of meteorological and hydrological droughts are becoming prominent after 2001. We further investigated the effects of monthly climate variables (temperature and precipitation) on vegetation growth using monthly PV (photosynthetic vegetation fraction) of a watershed derived from MODIS (Moderate Resolution Imaging Spectroradiometer), and examined the effects of spring and summer rainfall on the variations of vegetation phenological patterns and subsequent watershed streamflow during 2001–2020. The PV and temperature showed a linear relationship without time-lag effect (R² = 0.51-0.57, p < 0.001), whereas PV and precipitation exhibited no time-lag in FS but a log-linear relationship with 2-month lag (R² = 0.15-0.59, p < 0.001) existed in LHC, indicating the accumulation of rainfall during relatively dry season (winter-spring) was critical for vegetation growth. Structural equation modeling (SEM) revealed that earlier start of growing season (SOS) caused by relatively high spring rainfall (February-March) led to longer growing season (LOS) and higher P-Q deficit (precipitation minus runoff) during the growing season in LHC. Nevertheless, the large amount of precipitation during growing season has no effect on the end of growing season (EOS), LOS and P-Q deficit. Neither EOS has influence on LOS and P-Q deficit. However, these patterns were not found in FS. Understanding the vegetation responses to climatic variations is required for future hydrologic regime projections, especially under changing climate.

How to cite: Chang, C.-T., Lee, J.-Y., Chiang, J.-M., Wang, H.-C., Huang, C., and Huang, J.-C.: Hydrological responses to vegetation-climate interactions at two subtropical forested watersheds of Taiwan, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-2383, https://doi.org/10.5194/egusphere-egu25-2383, 2025.

The increasing frequency and intensity of drought events make them a growing threat for plants that are sensitive to water scarcity. It is therefore important to understand how plants react to drought stress. The willow trees from the short-rotation coppices (SRC) on the DTU-Risø Campus in Denmark (DK-RCW) are particularly sensitive to water shortage as they are rainfed. We address the following question: how do extremely dry conditions affect the willows growth? We study the plants response mechanisms to periods of water scarcity and examine how these responses impact their gross primary productivity (GPP). There is a particular relevance to this in the current context of global warming, where the SRC are used to produce bioenergy and can store carbon to mitigate climate change.

Field measurements were carried out at the DK-RCW site to gather information on canopy structure (leaf area index). These results were integrated into a modelled relationship with carbon flux data from an eddy covariance flux tower located onsite and providing continuous CO₂ and H₂O flux data in more than 10 years. The simple empirical model was used to contrast the GPP’s sensitivity to stomatal and non-stomatal processes by comparison of extreme drought conditions (summer 2018 in Denmark) and wetter conditions (summers 2015 and 2021). These years represent the same stage of the rotational cycle.

This new model enables us to highlight two complementary responses to drought: the trees immediately react by adapting their physiology (stomatal resistance, increased sensitivity to vapour pressure deficit under drought), but also by changing the canopy structure as the drought increases (reduction of the leaf area index) and other responses on canopy photosynthetic capacity. High vapour pressure deficit and the reduction of the leaf area index both reduced the photosynthesis of willow trees under dry conditions. The simulated data imply limited drought recovery after the dry period had ended. For these reasons, the carbon uptake by the willow SRC is lower during droughts and thus limits the SRC productivity and carbon sink strength. We conclude from the very clear results from this case study that different drought response mechanisms must be considered when trying to understand and predict plant responses to extreme drought.

How to cite: Jaujay, M. and Ibrom, A.: Drought sensitivity of gross primary productivity in willow: effects from physiological versus structural responses, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-10635, https://doi.org/10.5194/egusphere-egu25-10635, 2025.

Abstract
Peatlands are important global terrestrial carbon (C) sink. Most of Irish peatlands have been 
influenced in past by anthropogenic management, primarily through drainage for forestry, 
agriculture, or energy and horticultural extraction. Given the recent Irish peatland restoration 
activities, it is essential to deepen our understanding of the key drivers of peatland C-dynamics 
and to improve methodologies for reporting and verifying terrestrial CO₂ removals/emissions 
from drained and restored peatlands. The dependency of CO₂ fluxes on water-table (WT) levels 
in peatland ecosystems, under different land-use (LU), has been recognised in existing literature 
[1], indicating on the importance of accounting for WT variable in predictive models. This study 
focuses on assessing the application of random forest (RF) to predict WT in total eight Irish 
peatland sites under different LU (natural, rewetted, forest, grassland), which were monitored - 
i.e. low-level Irish blanket-bog sites from Co. Mayo and raised-bog sites from Co. Offaly [2]. The 
RF was chosen due to its ability to effectively manage mixed-data (numerical and categorical) and 
to provide robust predictions without the need for extensive data-preprocessing. Used were the 
data from ca. 2017 to 2020 on-site measurements [2], as well as the selected geospatial data 
derived from E-OBS daily grided-meteorological dataset [4]. The RF was applied to a number of 
numerical and categorical variables, by splitting the data into training- and testing-datasets. 
Hyperparameter tuning was done using ‘caret’ R-package [5]. Model evaluation (using 
performance metrics) was conducted on WT-predictions from testing-dataset. While findings 
from this study on selected eight Irish peatland sites indicate a relatively good potential of RF to 
predict WT (R² = 0.78), the work highlights the importance of assessing the ‘variable importance’ 
to reduce the number of variables in the model for practical applicability purposes, as well as to 
include more sites.

Acknowledgements
The authors are grateful to the Irish Environmental Protection Agency (EPA) for funding projects 
CO2PEAT (2022-CE-1100) and AUGER (2015-CCRP-MS.30) [EPA Research Programmes 2021-
2030 and 2014–2020], and to University of Limerick funding.

References
[1] Tiemeyer, B., et al., 2020. A new methodology for organic soils in national greenhouse gas inventories: Data synthesis, derivation and application,
Ecological Indicators, Vol. 109, 105838,  https://doi.org/10.1016/j.ecolind.2019.105838.
[2] Renou-Wilson, F., et. al, 2022. Peatland Properties Influencing Greenhouse Gas  Emissions and Removal (AUGER Project) (2015-CCRP-MS.30), EPA Research Report, Irish Environmental Protection Agency (EPA) https://www.epa.ie/publications/research/climate-change/Research_Report_401.pdf.
[3] Premrov, A., et.al, 2023. Insights into the CO2PEAT project: Improving methodologies for reporting and verifying terrestrial CO₂ removals and emissions from Irish peatlands. IGRM2023, Belfast, UK. https://www.researchgate.net/publication/369061601_Insights_into_the_CO2PEAT_project_Im
proving_methodologies_for_reporting_and_verifying_terrestrial_CO2_removals_and_emissions
_from_Irish_peatlands.
[4] Copernicus Climate Change Service, Climate Data Store, (2020): E-OBS daily gridded meteorological data for Europe from 1950 to present derived from in-situ observations. Copernicus Climate Change Service (C3S) Climate Data Store (CDS). https://doi.org/10.24381/cds.151d3ec6.
[5] Kuhn, M. 2008. Building Predictive Models in R Using the caret Package. Journal of Statistical Software, 28(5), 1–26. https://doi.org/10.18637/jss.v028.i05.

How to cite: Premrov, A., Yeluripati, J., Renou-Wilson, F., Walz, K., Byrne, K. A., Wilson, D., Hyde, B., and Saunders, M.: Assessing the application of random forest (RF) to predict water-table (WT) in selected Irish peatlands, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-5122, https://doi.org/10.5194/egusphere-egu25-5122, 2025.

Surfactants are extensively utilized across agriculture, pharmaceuticals, and environmental remediation due to their ability to modify surface and interfacial properties. In horticulture, wetting agents and synthetic surfactants are commonly employed to mitigate water repellency in organic growing media, particularly peat-based substrates. These agents are known to aid the substrate’s wettability and improve physical and hydraulic properties, optimizing plant growth and productivity. However, environmental persistence and the potential ecotoxicity of synthetic surfactants have raised significant concerns, highlighting the need for sustainable alternatives. Biosurfactants, particularly rhamnolipids, have gained considerable attention for their biodegradability and surface-active properties both at the scientific and commercial levels. Despite their potential, a comprehensive understanding of the interaction between rhamnolipid and peat essential for assessing its environmental fate and behavior is inadequate. In this regard, the main objective of this study is to quantify the sorption and desorption dynamics of rhamnolipid in peat using batch equilibrium and kinetic experiments to evaluate its suitability as a surfactant for horticultural systems, optimize application strategies, and assess the transport behavior and environmental implications of residual surfactants. Kinetic analysis revealed rapid initial adsorption followed by a gradual approach to equilibrium, with the adsorption and desorption kinetics being well described by the Elovich equation, indicating a chemisorption-dominated process. Furthermore, desorption followed both the Elovich and pseudo-first-order models, illustrating a complex and rate-dependent release process likely influenced by heterogeneous retention of rhamnolipid on the peat surface. Equilibrium analysis demonstrated that the adsorption data were best fitted by the Freundlich model, reflecting the heterogeneous nature of the peat surface and the complexity of its adsorption sites. Sequential desorption experiments exhibited notable hysteresis with reduced desorption efficiency, suggesting strong retention of rhamnolipid on the peat particles. These findings highlight the potential of rhamnolipid as a sustainable alternative to synthetic surfactants for mitigating water repellency in peat-based growing media. Equilibrium and kinetic modeling results will be presented with a comprehensive discussion of their practical implications, providing critical insights into their environmental significance and potential applications in horticultural systems.

Keywords: Water repellant peat, sorption, rhamnolipid biosurfactant

How to cite: Duggireddy, R. and Arye, G.: Sorption Behavior of Rhamnolipid Biosurfactant on Peat, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-2449, https://doi.org/10.5194/egusphere-egu25-2449, 2025.

Nitrous oxide (N₂O) is the most important stratospheric ozone-depleting gas of the 21^st century. Most N₂O emissions occur in soils and are associated with agricultural activities. Ammonia (NH₃) is not a greenhouse gas, but it can indirectly contribute to greenhouse gas emissions. NH₃ volatilization is an important indirect N₂O emission pathway in agricultural systems. In addition, NH₃ can have significant effects on both human health and the natural environment, and its emissions negatively affect biodiversity. A meta-analysis was conducted to evaluate NH₃ and N₂O losses and the effectiveness of adding urease and nitrification inhibitors on direct N₂O emissions and NH₃ volatilization. Data were used from 14 separate studies that simultaneously investigated direct N₂O emissions and NH₃ volatilization from irrigated wheat. All studies were conducted on irrigated wheat in semi-arid climates and on calcareous soils with urea application. The average direct N₂O emission factor for irrigated wheat was 0.4%. Our results showed that, on average, nitrification inhibitors reduced direct N₂O emissions by 35% and increased NH₃ volatilization by 29%. The average NH₃ emission factor was 32% and urease inhibitors reduced NH₃ volatilization by 41%. The results showed that indirect N₂O emissions from NH₃ volatilization should be considered in these conditions.

How to cite: Mirkhani, R., Jabbari Malayeri, M., Naserian Khiabani, B., Mousavi, S. M., Ghafariyan, M. H., Ghavami, M. S., Dercon, G., Shorafa, M., and Kheng Heng, L.: Meta-analysis of direct nitrous oxide emissions and ammonia volatilization from irrigated wheat in calcareous soils under semi-arid conditions, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-1026, https://doi.org/10.5194/egusphere-egu25-1026, 2025.

Climate change is expected to alter the frequency and intensity of extreme events, modifying the natural disturbance regimes to which ecosystems are currently adapted. Here, we present a spatially explicit risk index for mangroves and their associated biodiversity and ecosystem services based on projected frequency changes of tropical cyclone wind speeds and rates of relative sea level rise under SSPs 245, 370 and 585 by 2100.

To compute the risk index, we calculate the relative change of tropical cyclone frequency across different wind speed intensity categories based on probabilistic tropical cyclone tracks downscaled from 3 different CMIP6 models of varying climate sensitivity. This data is then combined with thresholds of sea level rise which are estimated to exceed mangrove adaptive capacity and mapped onto global mangrove extents.

Globally, approximately half of the total mangrove area (40-56% depending on the SSP) will be at high to severe levels of risk due to climate-modified tropical cyclone disturbance regimes. Further, we find mangrove areas with high levels of biodiversity and ecosystem services provision, including coastal protection for people and assets, carbon sequestration, and fishery benefits, are at proportionally higher levels of risk than mangrove forests generally. We also identify mangrove areas which are projected to experience non-analog tropical cyclone disturbances in the future. Our findings emphasize the need to anticipate changes in natural disturbance regimes to adapt ecosystem management, sustain ecosystem services in the future, and fully realize mangroves’ potential as nature-based solutions (NBS).

How to cite: Hülsen, S., Dee, L., Kropf, C., Meiler, S., and Bresch, D.: Mangroves and their services are at risk from climate-modified tropical cyclones and sea level rise , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-1419, https://doi.org/10.5194/egusphere-egu25-1419, 2025.

The seagrass meadows are critical for organic carbon storage and play a significant role in mitigating climate change. However, the ongoing degradation of the seagrass meadows in Thailand reduces their ability to sequester carbon effectively, potentially contributing to greenhouse gas (GHG) emissions. This study examines variations in carbon storage, carbon metabolism, and GHG emissions across degraded, healthy seagrass and bare sand areas along Andaman Sea, Thailand. The average carbon storage within the surface sediment (top 10 cm) varies across seagrass conditions, with the highest carbon storage in heavy degraded (365.2 ± 206 g C m^-2), followed by bare sand (289.5 ± 236 g C m^-2) and healthy seagrass (86.47 ± 5.8 g C m^-2). Furthermore, degraded seagrass and bare sand exhibited heterotrophic ecosystem functions with an average NCP value of 0.44 ± 0.49 and -0.13 ± 0.79 mmol C m⁻² d⁻¹, respectively. Conversely, healthy seagrass maintained autotrophic ecosystem functions with NCP 1.30 ± 0.508 mmol C m⁻² d⁻¹. The average total carbon sink varied among seagrass conditions, with the highest in degraded seagrass (4328 ± 2395 CO₂-eq m⁻² d⁻¹), compared to bare sand (3981 ± 4120 CO₂-eq m⁻² d⁻¹) and healthy seagrass (1630 ± 0 CO₂-eq m⁻² d⁻¹). The study also revealed that CH₄ emissions dominated GHG fluxes in all seagrass conditions, with the highest mean CH₄ fluxes recorded in degraded seagrass (1.16 ± 0.51 µmol m⁻² h⁻¹), followed by bare sand (1.02 ± 0.41 µmol m⁻² h⁻¹) and healthy seagrass (0.48 ± 0.07 µmol m⁻² h⁻¹). On the other hand, the CO₂ emissions remained consistently low in both seagrass meadows (healthy and degraded) and bare sand areas. These findings are important to indicate and provide the baseline of GHG emissions for healthy and degraded tropical seagrass meadows.

Keywords: Blue carbon, Climate Change, Emission, Greenhouse gas, Seagrass meadows

How to cite: Halim, M., Stankovic, M., and Prathep, A.: Estimating the Potential Greenhouse Gas Emission from Degraded Seagrass Meadows: A Case Study from Thailand's Seagrass Ecosystems, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-7982, https://doi.org/10.5194/egusphere-egu25-7982, 2025.

Seagrass ecosystems are vital for coastal resilience, biodiversity, and as critical carbon sinks. With global seagrass declines, restoration has emerged as a key strategy for ecological and carbon recovery. Although through seagrass restoration, various ecosystem services return, there is a lack of information on the return of the carbon sequestration and accumulation. This study aims to assess the potential recovery of blue carbon benefits through seagrass restoration across various sites in Thailand. We analyzed carbon stocks and accumulation rates in restored Enhalus acoroides meadows at four sites, evaluating spatial variability in carbon recovery in restored versus natural meadows and unvegetated sediment. Despite successful seagrass establishment, the organic carbon (OC) content (%) within the surface sediment (top 20 cm) was not significantly different among restored, natural seagrass meadows, and bare sand, averaging 0.8 ± 0.1%, 0.9 ± 0.2%, and 0.9 ± 0.2% respectively. Although significant differences in OC content (%) were observed between sites, no differences were noted between the habitat types within each site. Predominantly sandy sediment (over 90%) with minimal mud content (1% or less) were found at all sites. The highest organic carbon stock in surface sediment was in unvegetated sediment, averaging 16.8 ± 3.4 Mg C ha^-1. Significant differences in OC stocks were also observed across all site comparisons, with higher stocks generally found in bare sand compared to restored and natural seagrass meadows. Sediment accumulation profiles, indicated by the absence of excess ²¹⁰Pb, suggest a lack of net fine sediment accumulation over the past decade or mixing of the upper sediment, precluding reliable sedimentation rate estimation. These findings suggest that these restored meadows are not forming depositional environments contributing to significant additional carbon sequestration, as evidenced by the minimal increase in OC stocks across the sites. Additionally, the low OC content (%) and minimal mud presence suggest overall low sedimentation rates, even in natural seagrass meadows. These results highlight the complexity of achieving carbon sequestration goals through seagrass restoration, emphasizing the need for site-specific restoration strategies that consider local sediment dynamics and ecological conditions to enhance carbon storage capabilities.

Keywords: organic carbon, carbon additionality, carbon accumulation, seagrass, restoration

How to cite: Stankovic, M., Kaewsrikhaw, R., Masqué, P., Vanderklift, M. A., Upanoi, T., and Prathep, A.: Lack of blue carbon recovery in restored tropical seagrass ecosystems, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-14608, https://doi.org/10.5194/egusphere-egu25-14608, 2025.

Dredging of the fairway in the Ems estuary was driven by the need to accommodate the increasing draft of ships. This modification has had negative effects on the sediment balance and ecology of the estuary. The fairway deepening results in strong alterations of the tidal dynamics, such as tidal amplitude and duration, as well as hydrodynamics such as current velocity and turbulence. This results in increased fine sediment input, which, at high suspended sediment concentrations, contributes to the formation of fluid mud—a mixture of silt, clay, and organic matter. The dynamics of fluid mud, particularly the differences between spring and neap tides, are not yet fully understood.

We investigated the formation, dispersion, and entrainment of fluid mud during the semi-diurnal tidal cycle. Therefore, the influence of flow velocity and salinity at different water depths, and the differences between spring and neap tides based on two dedicated measurement campaigns in 2023 was analyzed using high-resolution spatiotemporal monitoring data. Salinity data were used as an indicator of stable stratification. Additionally, sediment samples have been collected using a sediment corer to analyze the composition and properties of the fluid mud layer.

Our Spring-neap tide analysis showed a reduction of the flow cross-section during neap tide leading to differences in hydrodynamics between spring and neap tide driven by high sediment concentrations and fluid mud occurrence. During neap tide fluid mud was found to cover a larger fraction of the water column than during spring tide. This further highlights the strong influence of flow velocity on the dynamics of fluid mud and the need to include spring-neap considerations for future sediment management plans for the Ems.

How to cite: Lehn, J., Slabon, A., Holthusen, D., Rovelli, L., Fiskal, A., Hoffmann, T., and Borgsmüller, C.: Spring-neap tidal variation of fluid mud occurrence in the hyper-turbid Ems estuary , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-19333, https://doi.org/10.5194/egusphere-egu25-19333, 2025.

The accelerated pace of urbanization, population growth, and extensive land-use changes has significantly disrupted the ecological balance and functionality of riverine wetland ecosystems, leading to substantial degradation of wetland health. This study evaluates the health and resilience of the Upper Ganga Riverine Wetland (UGRW) in India, which has experienced significant land-use transformations over the past two decades. The analysis highlights the wetland's resilience to various natural and anthropogenic stresses and its ability to sustain critical ecosystem services, including provisioning, regulating, cultural, and supporting services. The findings reveal drastic land-use and land-cover (LULC) changes, with built-up areas increasing by 245%, while forest and wetland areas decreased by 41% and 8%, respectively, between 2000 and 2020. These transformations have led to a marked decline in ecosystem resilience (23%) and a substantial reduction in ecosystem service values (ESVs), which decreased from 2138.28 million USD in 2000 to 1769.16 million USD in 2020—an overall loss of 18%. Urban expansion, deforestation, and wetland fragmentation have further exacerbated the decline in wetland health, diminishing its ecological balance and capacity to deliver vital services. This study underscores the urgent need for integrated environmental management strategies to mitigate the impact of LULC changes, conserve wetland ecosystems, and enhance their resilience. By assessing ecosystem services and their dependence on sustainable land use, this research provides critical insights for policymakers and stakeholders. It emphasizes the necessity of balancing developmental priorities with ecological preservation, offering a strategic framework to foster sustainability and resilience in one of India’s most vital riverine landscapes.

How to cite: Yadav, A., Kansal, M. L., and Singh, A.: Wetland Health in Transition: Resilience and Ecosystem Services Amid Urbanization and Land-Use Change, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-885, https://doi.org/10.5194/egusphere-egu25-885, 2025.

The field of Blue Carbon research has traditionally focused on the carbon sequestration capacity of coastal vegetated habitats, despite these habitats comprising only a small fraction of oceanic sediment. However, continental shelf sediments also play a significant role in carbon sequestration and represent a significantly larger surface area. While the majority of organic carbon deposited in the shelf sediment is initially fixated by phytoplankton, and then potentially cycled through other marine organisms, some of it is originated from coastal and terrestrial producers, such as marine macroalgae, then transported, deposited and sequestered into shelf sedimentary basins. In this study, we investigated the sedimentary organic carbon (OC) stocks and sequestration rates at two sites of the continental shelf of Portugal, each adjacent to major wetland systems dominated by saltmash and seagrasses: the northern site is located off the Sado estuary at the Arrábida coast where macroalgae forests are also present, and the southern site off the Ria Formosa coastal lagoon. We also assessed the contributions of marine and terrestrial primary producers to sedimentary OC using various proxies such as C/N ratios, carbon isotopic signature (δ13 C), magnetic susceptibility, lipid contents and sedimentary DNA metabarcoding. Our findings revealed similar OC sequestration rates at both sites (23.3 ± 7.1 g OC m⁻² yr⁻¹ and 20.9 ± 5.7 g OC m⁻² yr⁻¹ for the northern and southern sites, respectively) and comparable OC stocks in the top 25 cm of sediment (29.5 ± 2.33 g OC cm⁻² and 21.1 ± 3.01 g OC cm⁻², respectively). Clear differences were observed on the contributions of terrestrial versus marine sources to the sediment organic matter, with the northern site showing lower terrestrial contribution as opposed to the southern site. This conclusion is supported by the different proxies used. For example, the northern site consistently exhibited higher OC contents at comparable particle sizes, indicative of a greater deposition rate of organic carbon not adhered to sediment particles, typical of oceanic primary productivity. Sedimentary DNA metabarcoding detected seagrass and saltmarsh genetic material in sedimentary organic matter from both sites, indicating that detritus from the two wetlands are being exported to the continental shelf. Further investigation is needed to quantify the relative magnitude of this export. Understanding this process is essential to accurately assess the role of coastal vegetated habitats in the global carbon cycle, as current estimates focus solely on in-situ sequestration and often overlook the potential contribution of exported organic matter. Our study highlights the need to expand our perspective on the interconnectedness of coastal and oceanic carbon dynamics.

How to cite: Martins, M., Magalhães, V., Salgueiro, E., Cordeiro, L. G., Abrantes, F., Masqué, P., de los Santos, C. B., and Santos, R.: Carbon accumulation, storage and provenance in the Portuguese continental shelf , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-19205, https://doi.org/10.5194/egusphere-egu25-19205, 2025.

Alkalinity enhancement in rivers is a proposed carbon dioxide removal strategy which leverages physical and biogeochemical properties of rivers to promote uptake of atmospheric carbon dioxide. Robust monitoring, reporting and verification of carbon dioxide removal is necessary to instill trust in carbon credits and market activity stemming from river alkalinity enhancement. Rivers have the unique characteristic of reflecting integrated watershed characteristics along a one-dimensional trajectory. Depending on the size of the river, alkalinity dosing location and quantity, transit distance to the ocean and availability of monitoring locations, carbon dioxide uptake can be quantified through a hybrid approach leveraging direct measurements and models. In this poster, we propose a flexible, multiscale quantification framework which can be adapted to a wide range of rivers and deployment scenarios. 

How to cite: Yin, J., He, J., Sutherland, K., and Gill, S.: A flexible, multiscale quantification framework for river alkalinity enhancement, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-14511, https://doi.org/10.5194/egusphere-egu25-14511, 2025.

Tidal Marshes are wetland ecosystems at the marine-terrestrial interface which serve as strong sinks for atmospheric carbon dioxide and large reservoirs of soil organic carbon (SOC). However, tidal marsh soils also produce and emit the potent greenhouse gas methane (CH₄). Previous work has demonstrated that CH₄ flux is inversely related to salinity, and that methane flux is negligible compared to carbon dioxide (CO₂) uptake in marshes with salinities of >18 parts per thousand (ppt). However, in lower salinity tidal marshes, CH₄ flux is highly variable, and can spike sharply following the depletion of sulfate supply. In order to better understand drivers of methane flux across a range of salinities, we established three transects along estuarine gradients in Rhode Island and Connecticut, USA. At landward and seaward sites along each transect, we measured methane flux, salinity, and conducted various porewater and soil chemical analyses. We found that methane flux was significantly higher and more variable in marshes where salinity is < 18 ppt. The highest magnitude methane fluxes occurred when sulfate was nearly depleted in marsh porewater, indicating that sulfate abundance dampens methane production, but demonstrating the need for further investigation into processes governing sulfate depletion and replenishment in salt marshes, and the degree to which salinity is a reliable proxy for sulfate concentration. Additionally, the lack of spatial data products which delineate tidal marshes according to salinity complicates efforts to estimate methane budgets in tidal estuaries. Our results indicate that spatial differences in salinity should inform wetland mapping in order to facilitate estimations of greenhouse gas budgets, but more high-resolution monitoring of salinity is needed to accurately delineate map units.

How to cite: Norton, M., Moseman-Valtierra, S., and Stolt, M.: Greenhouse Gas Flux in Coastal Salt Marshes: Field Measurements along Estuarine Gradients in Northeastern USA, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-14217, https://doi.org/10.5194/egusphere-egu25-14217, 2025.

Global Ecosystem Dynamics Investigation (GEDI) mission, operating from International Space Station, is a full-waveform LiDAR measuring vertical 3-dimensional structure of terrestrial ecosystems. The vertical canopy cover (CC) available from the GEDI L2B product has applications in forest ecosystem, forest health and climate change studies, and management practices. Some studies have assessed the accuracy and uncertainty of the GEDI vertical canopy cover profile product using aerial LiDAR scans and in-situ measurements. However, in-situ measurements taken using angle-of-view effectively produces canopy closure whereas GEDI measures vertical CC. Cajanus tube, regarded as ideal canopy cover measurement technique, is time consuming and impractical for larger areas. In this study, suitable in-situ canopy cover measurement methodologies were assessed alongside GEDI vertical CC. Canopy cover measurements were taken under GEDI footprints in the Indian Western Himalayan region using spherical densiometer, hemispherical photographs and digital canopy photographs with narrow angle-of-view. The plot dimensions were adjusted to accommodate horizontal geolocation uncertainty of GEDI version 2 data products. Following data collection, measurement techniques were assessed based on R-squared, RMSE and MAE.

How to cite: Paygude, A., Pande, H., and Tiwari, P. S.: Assessment of In-situ Canopy Cover Measurement Techniques and GEDI Vertical Canopy Cover in the Indian Western Himalayan Region, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-7236, https://doi.org/10.5194/egusphere-egu25-7236, 2025.

There is interest in biogeochemical cycling and ecosystem functioning in the Clarion Clipperton Zone (CCZ, equatorial Pacific) due to the possibility in the near future of deep sea mining of polymetallic nodules. A set of important processes and ecosystem services relate to the fixation, export and deposition in sediment of organic carbon (C). This is important to understand both as a mechanism for C sequestration, and also as a set of processes which feeds deep sea biological communities. However, due to the remote nature of the CCZ, and the considerable resource required, it has rarely been possible to directly observe the coupling between processes from the sea surface all the way through the water column to the fate of organic C in sediments, nor how those linked processes vary over time or in response to mining disturbance.

Here we present data on C fixation, export, sediment composition and relationships with benthic community biomass. We show clear coupling between surface productivity, export and sinking flux, but that sediment organic C concentrations are not always closely coupled to water column processes. Repeated measurements over a period of ~18 months show inter-annual variability at the seafloor, rather than a stable seasonal pattern. Organic C delivery to the sediment is reflected in the biomass of faunal groups, with different temporal responses in the different groups (macrofauna, metazoan meiofauna and foraminifera) linked to factors such as competition, predation pressure and life cycle differences. Changes in sediment total organic carbon following a mining vehicle test will also be considered.

How to cite: Woulds, C., Lough, A., and Homoky, W. and the Carbon fixation, export, sedimentation and utilisation Team: Temporal variability in organic carbon fixation, export, sedimentation and utilisation in the Clarion Clipperton Zone, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-21501, https://doi.org/10.5194/egusphere-egu25-21501, 2025.

The dynamics of dissolved inorganic carbon (DIC), stable carbon isotopes of DIC (δ¹³C_DIC), and anthropogenic CO₂ (CO_2ant) in the upper 500 m of the water column were examined in two upwelling-favourable regions: the Sri Lankan Dome (SLD) and the central Bay of Bengal (BOB) in the Northern Indian Ocean over the period 1995 to 2016. This study aimed to investigate the spatiotemporal variability of these carbon parameters and assess the influence of CO_2ant in these oceanic environments. Data from the GLODAPv2.2022 database, including cruise-based biogeochemical bottle measurements, were utilized to examine temporal trends in DIC and δ¹³C_DIC. The TrOCA (Tracer combining Oxygen, Carbon, and Alkalinity) approach was employed to calculate CO_2ant. Although DIC concentrations showed minimal variability across the water column in both the SLD and central BOB, significant fluctuations in CO_2ant and δ¹³C_DIC were observed in the upper 50 m in both regions between 1995 and 2016. Specifically, δ¹³C_DIC values in the upper 50 m decreased by 0.45 ‰ (at a rate of 0.021 ‰ yr^-1) in the SLD and by 0.41 ‰ (at a rate of 0.02 ‰ yr^-1) in the central BOB over the study period. This decline is likely attributable to the combined effects of upwelling of remineralized DIC and increased CO_2ant invasion in the upper 50 m of these oceanic regions, occurring at rates of 0.93 µmol kg^-1 yr^-1 in the SLD and 1.97 µmol kg^-1 yr^-1 in the central BOB. Additionally, a weaker correlation between δ¹³C_DIC and CO_2ant was observed in the central BOB, whereas a stronger correlation in the SLDsuggests that the invasion of isotopically lighter CO_2ant contributed significantly to the observed depletion of δ¹³C_DIC in both regions from 1995 to 2016. These findings underscore the significant role of anthropogenic CO₂ in influencing carbon dynamics in the upper ocean of these upwelling-prone regions.

How to cite: Kaluthotage, P., Silva, A., Dheerasinghe, M., and Kokuhennadige, H.: Temporal variability in dissolved inorganic carbon, δ13CDIC, and anthropogenic CO2 in the North Indian Ocean from 1995 to 2016: assessing the influence of anthropogenic CO2, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-14051, https://doi.org/10.5194/egusphere-egu25-14051, 2025.

The variability of iron (Fe) isotopes during the Paleoproterozoic is a topic of debate due to the complex pathways involved in isotopic fractionation. Similarly, the expansion of ocean oxygenation during the late part of the Great Oxygenation Event (GOE)―the ∼2.22–2.06 Ga Lomagundi Event (LE) that represents Earth’s most pronounced and longest-lived carbon isotope excursion―remains controversial. Here, we present new Fe isotope data on bulk samples from a range of lithologies of the Francevillian Group, Gabon, including marine carbonates, black shales, thin sedimentary pyrite beds, early diagenetic pyrite and carbonate nodules. We also analyse pyritized Francevillian biota that were further combined with data obtained from in situ Fe isotope analyses on early diagenetic pyrite nodules (pyritized Francevillian biota and non-fossil pyrite). The δ⁵⁶Fe values from this study vary from highly positive values, up to +1.71‰, in non-fossil pyrite nodules, to highly negative values, down to –3.14‰, in pyritized Francevillian biota. The near-to-zero δ⁵⁶Fe values notably characterize primary carbonates, black shale, thin pyrite beds and carbonate concretions. The near-to-zero δ⁵⁶Fe values are interpreted to reflect complete oxidation and quantitative removal of dissolved Fe²⁺ from seawater, in the Paleoproterozoic oceans, followed by complete reduction of Fe³⁺ in the sediments akin to previously described modern-like Fe biogeochemical cycle which is proposed to have kicked off only from ca. 1.7 Ga. In contrast, positive δ⁵⁶Fe values are linked to equilibrium isotope fractionation, favoured by the high S/C ratios during early diagenesis, while the negative values reflect the kinetic isotope effect driven by a high organic carbon content of the Francevillian biota. The Francevillian Group massive manganese deposition is devoid of concomitant and significant Fe precipitation in the Francevillian shelf environments which is in stark contrast to early GOE Mn-ore deposits in southern Africa. The data thus suggests that the marine Fe²⁺ reservoir was already exhausted in the Paleoproterozoic oceans during the late part of the GOE. In this scenario, and considering the observation of Fe-lean Mn deposits, the Paleoproterozoic oceans were likely oxygenated enough to quantitatively oxidize and remove Fe²⁺ from seawater during the LE. However, extensive oxidation of Fe²⁺ may have been an important O₂ buffer that contributed to maintaining low redox thresholds (e.g., low Eh) in the deep Paleoproterozoic oceans, which ultimately prevented it from reaching oxidizing conditions that require the stability of Mn (oxyhydr)oxides and other elements of similar redox thresholds, i.e., nitrate and selenate. Oxidizing conditions to quantitatively oxidize Mn²⁺ or to significantly build up a pool of oxyanions stable at much higher redox thresholds (e.g., nitrate and selenate) were only reached in the photic zone where the rate of oxygenic photosynthesis was significantly enhanced as a consequence of intense oxidative weathering during the LE. The findings highlight moderately oxygenated Paleoproterozoic oceans with habitats capable of sustaining complex aerobic ecosystems only restricted in shelf environments during the immediate aftermaths of the GOE.

How to cite: Ajagunjeun, A., Ossa Ossa, F., Kleinhanns, I. C., Marin-Carbonne, J., Hofmann, A., Al Suwaidi, A., and Schoenberg, R.: Expanded aerobic iron biogeochemical cycle in the Paleoproterozoic oceans during the ca. 2.22-2.06 Ga Lomagundi Event, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-15990, https://doi.org/10.5194/egusphere-egu25-15990, 2025.

Understanding how climate and biology changed during and after Snowball Earth events - global glaciations which coincided with major shifts in the ocean-atmosphere state - is critical for understanding the evolution of life on Earth. New observations of the Neoproterozoic Sturtian glaciation pose challenges to the Snowball paradigm. Precision geochronology shows that the Sturtian lasted ~56 Myr, and the lack of sulfur-MIF signals observed indicates that the atmosphere remained oxygenated throughout. A source of O₂ is required to maintain an oxygenated atmosphere for ~56 Myr, but in the canonical Snowball scenario, primary production shuts down completely. Here, we model the carbon and oxygen cycles during the Snowball to investigate this challenge. We propose that photosynthesis in melt holes on the equatorial glacier surface was sufficiently productive to provide the missing O₂ source, and that accumulation of aeolian dust sustained these melt holes and supplied them with nutrients. We argue that primary production was limited by phosphorus availability and photosynthetically active surface area, and show that only a dust-supported supraglacial ecosystem could satisfy both conditions.

How to cite: Minsky, C., Wordsworth, R., and Johnston, D.: Supraglacial biological niches as a solution to the Sturtian oxygenation problem, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-14396, https://doi.org/10.5194/egusphere-egu25-14396, 2025.