Drainage and irrigation ditches are hotlines of greenhouse gas (GHG, including CH₄, CO₂, and N₂O) emissions. These emissions are particularly high from agricultural ditches, due to inputs of organic and inorganic nutrients from land management. However, the total GHG emissions from agricultural ditches and their contribution to regional and national budgets remains largely unknown, due to a twin data gap of measured GHG fluxes and mapped ditch areas. Here, we estimated diffusive GHG emissions from agricultural ditches across the North China Plain (~141,000 km²), one of the most intensive agricultural regions worldwide, based on three regional-scale field campaigns on 36 ditch-river systems, each of which included collector ditches (CD), branch ditches (BD), main ditches (MD), and a connected river, in 2023. The results found that ditches emitted diffusive greenhouse gas emissions five times larger than their area share over the North China Plain.

How to cite: Yan, Z. and Ge, Z.: Regional-scale comparisons of greenhouse gas emissions from ditches and cropland soils , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-1604, https://doi.org/10.5194/egusphere-egu26-1604, 2026.

CH₄ is the one of the most important greenhouse gases (GHGs) with a higher global warming potential than carbon dioxide. Increasing evidence suggests that riverine networks surrounding urban landscapes are considered important hotspots for CH₄ emissions. However, the factors influencing the spatial pattern of riverine CH₄ emissions in heavily urbanised areas remains unclear. Here, we investigated the spatial variability of diffusive CH₄ fluxes across the water-air interface (fCH₄) and dissolved CH₄ concentrations in the water column (dCH₄) in river reaches that drain multiple land covers (i.e., urban, agricultural and mixed landscapes) in a major urban river in the Yangtze River Delta, eastern China. fCH₄ were measured using a portable infrared gas analyser combined with a floating chamber, dCH₄ were determined by the headspace equilibration technique, and various water quality parameters were analysed in the laboratory. Our results showed that almost all sampling sites in the river were oversaturated with dissolved CH₄. Rivers in urbanised areas were identified as CH₄ emission hotspots, with mean fluxes of 3.76±4.58 mmol·m^-2·d^-1 and mean concentrations 6.91±6.95 μmol·L^-1, corresponding to 6.4 and 3.2 times of those from river reaches in non-urban areas, respectively. Factors related to the high CH₄ emissions in urban rivers included nutrient supply (e.g., NO₃-N, NH₃-N, TP), carbon input and hypoxia. Overall, these findings highlight the need for greater awareness regarding the role of urban river networks in contributing to global warming, especially given ongoing urban expansion.

How to cite: Zhou, J., Peacock, M., and Zhao, P.: Spatial patterns and drivers of riverine methane (CH4) emissions in highly urbanised areas: A case study in Yangtze River Delta, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-3762, https://doi.org/10.5194/egusphere-egu26-3762, 2026.

Benthic bioturbation in coastal wetlands may substantially alter greenhouse gas (GHG) emissions by reshaping scalar transport and redox conditions, yet its net effect and mechanistic pathways remain poorly constrained. We develop a three-dimensional LES--Darcy reactive-transport framework that couples overlying flow, burrow-driven ventilation, and porewater biogeochemical reactions to quantify CO₂, CH₄, and N₂O exchange from crab-burrowed sediments. We designed an ensemble of simulations spanning a broad range of hydrodynamic forcing, surface topography, and bioirrigation conditions, including contrasts in burrow depth and ventilation strength. Time-series results show a consistent response sequence: CO₂ fluxes are elevated at the onset of ventilation and relax toward a quasi-steady level that remains above the flat-sediment baseline; CH₄ fluxes are generally enhanced, with the strongest amplification early in the simulations when flushing can export reduced gases faster than they are oxidized; and N₂O exhibits a pronounced transient pulse as the oxic--anoxic structure reorganizes around the burrow. At quasi-steady state, CO₂ and CH₄ fluxes are enhanced by up to ~12-fold and ~3-fold relative to undisturbed sediments. Across scenarios, burrow depth and bioirrigation intensity emerge as the dominant, synergistic controls on multi-gas fluxes, whereas external hydrodynamic forcing and mound-scale relief exert secondary, context-dependent effects. These results provide a process-based foundation for incorporating fauna-driven ventilation into blue-carbon budgets and wetland restoration planning by linking burrow-scale transport--reaction dynamics to ecosystem-scale GHG emissions.

How to cite: Huang, Y. and Liu, Y.: Bioturbation Amplifies Greenhouse Gas Emissions from Coastal Wetlands: Insights from a 3D Reactive Transport Model, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-3554, https://doi.org/10.5194/egusphere-egu26-3554, 2026.

The dynamics of the oceanic partial pressure of CO₂ (pCO₂) are governed by the combined influence of thermal effects, driven by temperature variability, and non-thermal processes related to several processes such as biology, and air–sea gas exchange. The relative contribution of these components can be quantified using the decomposition framework proposed by Takahashi et al. (1993, 2002, 2009). Here, this methodology is applied to high-frequency in situ pCO₂ observations from 17 fixed-position open-ocean moorings (Sutton et al., 2019), providing an Eulerian view of surface ocean carbon variability across a range of oceanic regions. This approach allows us to isolate the non-thermal component of pCO₂ variability and to investigate its statistical properties beyond mean or seasonal signals. The impact of non-thermal processes is examined using probability density function (PDF) analyses and PDF-quotient diagnostics (Xu et al., 2007). These analyses reveal that non-thermal forcing plays a key role in shaping the distribution of pCO₂ variability, with a particularly strong influence on extreme values relative to the core of the distribution. Such extremes are often underestimated when variability is characterized using low-frequency or climatological approaches. Despite the generally lower variability of open-ocean environments compared to coastal regions, our results demonstrate that non-thermal processes significantly contribute in these environments to short-term pCO₂ fluctuations and extremes. This highlights the importance of sustained, high-frequency pCO₂ observations for improving air–sea CO₂ flux estimates and for reducing uncertainties in regional and global ocean carbon budgets.

References:

Takahashi et al. (1993), Seasonal variation of CO₂ and nutrients in the high-latitude surface oceans: A comparative study. Global Biogeochemical Cycles, 7 (4), 843–878. doi: 10.1029/93GB02263

Takahashi et al. (2002), Global sea–air CO₂ flux based on climatological surface ocean pCO₂, and seasonal biological and temperature effects. Deep Sea Research Part II: Topical Studies in Oceanography, 49 (9), 1601–1622. doi: 10.1016/S0967-0645(02)00003-6308

Takahashi et al. (2009), Climatological mean and decadal change in surface ocean pCO₂, and net sea–air CO₂ flux over the global oceans. Deep Sea Research Part II: Topical Studies in Oceanography, 56 (8), 554–577. doi: 10.1016/j.dsr2.2008.12.009313

Sutton et al. (2019), Autonomous seawater pCO₂ and pH time series from 40 surface buoys and the emergence of anthropogenic trends. Earth System Science Data, 11 (1), 421–439. doi: 10.5194/essd-11-421-2019295

Xu et al. (2007), Curvature of Lagrangian Trajectories in Turbulence. Physical Review Letters, 98 (5), 050201. doi: 10.1103/PhysRevLett.98.050201324

How to cite: Robache, K. and Schmitt, F. G.: Statistical characterization of non-thermal open ocean pCO2 variability, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-4928, https://doi.org/10.5194/egusphere-egu26-4928, 2026.

Greenhouse gas (GHG) emissions from inland waters exhibit pronounced spatial and seasonal variability, yet the role of groundwater discharge in regulating these dynamics remains insufficiently constrained. In reservoirs located in topographically complex regions, strong hydraulic gradients can induce substantial groundwater–surface water exchange, potentially altering carbon and nitrogen inputs as well as biogeochemical conditions that govern GHG production and emission.
Here, we investigate the seasonal influence of groundwater discharge on CH₄, CO₂, and N₂O emissions in a subtropical reservoir using an integrated approach combining multi-season field observations and controlled microcosm experiments. Groundwater discharge rates were quantified using a radon-222(²²²Rn) mass balance framework, revealing marked seasonal variability, with enhanced discharge during winter and moderate but persistent inputs during spring and autumn. Dissolved GHG concentrations in groundwater were consistently elevated relative to surface water, indicating groundwater as a direct source of atmospheric GHGs.
Across seasons, groundwater discharge contributed substantially to reservoir-scale emissions, accounting for approximately one-third of CH₄ and CO₂ fluxes and a smaller but non-negligible fraction of N₂O emissions. However, the relationship between discharge intensity and GHG fluxes was non-linear. Field observations and incubation experiments demonstrate that moderate groundwater inputs during transitional seasons enhanced CH₄ and CO₂ production by increasing carbon availability, modifying dissolved organic matter composition, and reducing oxygen availability at the water–sediment interface. In contrast, higher discharge rates in winter altered C/N ratios and microbial activity in ways that partially constrained GHG production despite increased groundwater inflow.
Our results highlight groundwater discharge as a dynamic regulator of aquatic GHG emissions rather than a simple source term. By linking seasonal hydrological exchange to biogeochemical responses, this study provides process-based constraints on groundwater-driven GHG emissions from reservoirs and underscores the importance of incorporating groundwater–surface water interactions into regional and global assessments of inland-water GHG budgets.

How to cite: Qian, C., Wang, Q., Gilfedder, B. S., Frei, S., Yu, J., and Yu, Z.-G.: Mechanisms of Groundwater–Surface Water Interactions on Ecosystem Greenhouse Gas Emissions, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-2104, https://doi.org/10.5194/egusphere-egu26-2104, 2026.

Riverine N₂O and N₂ fluxes, key components of the global nitrogen budget, are known to be influenced by river size (often represented by average river width), yet the specific mechanisms behind these effects remain unclear. This study examined how environmental and microbial factors influence sediment N₂O and N₂ fluxes across rivers with varying widths (2.8 to 2,000 meters) in China. Sediment acted as sources of both N₂O and N₂ emissions, with both N₂ fluxes (0.2 to 20.8 mmol m^-2 d^-1) and N₂O fluxes (0.7-54.2 μmol m^-2 d^-1) decreasing significantly as river width increased. N₂ fluxes were positively correlated with denitrifying bacterial abundance, whereas N₂O fluxes, when normalized by the abundance of denitrifying bacteria, were negatively correlated with N₂O-reducing microbes. Water physicochemical factors, particularly temperature and nitrate, were more important drivers of these fluxes than sediment factors. Nitrate significantly increased denitrifying bacterial abundance, whereas higher temperatures enhanced cell-specific activity. Lower N₂O and N₂ emissions in wider rivers were attributed to decreased denitrifying microbial abundance and lower denitrification rates, in addition to the commonly assumed reduction in exogenous N₂O and N₂ inputs. Rolling regression analysis showed that nitrate concentration had a stronger effect on sediment N₂O and N₂ fluxes in narrower rivers, whereas temperature was more influential in wider rivers. This difference is attributed to more stable nitrate concentrations and decreased nitrogen removal efficiency in wider rivers, while temperature variation remained consistent across all river widths. Beyond sediments, temperature had a greater effect on excess N₂O concentrations than nitrate in the overlying water of wider rivers (>165 meters), highlighting its broader impact. This study provides new biogeochemical insights into how river width influences sediment N₂O and N₂ fluxes and highlights the importance of incorporating temperature into flux predictions, particularly for wider rivers.

How to cite: Zhang, S. and Xia, X.: Temperature has an enhanced role in sediment N2O and N2 fluxes in wider rivers, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-9294, https://doi.org/10.5194/egusphere-egu26-9294, 2026.

Lakes play a critical role in estimating global greenhouse gas (GHG) emission budgets. Various human activities, such as agricultural practices, reclaimed water containing nutrients, and other point and non-point pollution, have led to significant nutrient loading and consequently elevated GHG emissions. As a result, research has increasingly focused on GHG flux patterns from these human-impacted lakes. However, this poses a challenge for global estimates: a significant mismatch may exist between the number of lakes with GHG flux measurements and the total number and area of lakes across lake types. Due to the contrasting lake formation processes and varying degrees of human disturbance, lakes can be classified into distinct types, such as human-impacted urban and non-urban lakes and natural permafrost and non-permafrost lakes. These types exhibit distinct characteristics in size and nutrient concentrations. Therefore, accounting for lake type is as essential as lake area for accurate global estimates. Yet, the extent to which lake classification influences global lake GHG emission estimates remains poorly understood. Here, we addressed this gap through a meta-analysis. We observed distinctive patterns in physicochemical properties and GHG measurements across lake types, and identified varied relationships between GHG fluxes and lake area among the four lake types. We classified global lakes into the four types described above based on the population-lake volume ratio or cropland-lake volume ratio, urban coverage, and permafrost coverage within 3 km of the lake. We then estimated GHG emissions from global lakes based on both lake type and size, demonstrating that global lakes emitted 813.0 (Q1–Q3: 575.7–1235.9) teragram CO₂-equivalents year^-1, which is one-third of the latest estimate without considering lake type. Human-impacted lakes contribute significantly to global lake GHG emissions, with disproportionately high emissions relative to their surface area. Our results provide new insights for improving the accuracy of global lake GHG emission estimates.

How to cite: Zhang, Z. and Xia, X.: The critical role of lake classification in refining global lake greenhouse gas emission estimates, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-7138, https://doi.org/10.5194/egusphere-egu26-7138, 2026.

Long-term anoxic conditions enable natural peatlands to accumulate carbon in peat soils over millennia and are generally described as CO₂ sinks and CH₄ sources. Drainage of these ecosystems is known to reduce CH₄ emissions from soils. However, drainage ditches can partly offset this reduction by acting as hotspots for CH₄ emission. Many of these ditches are periodically cleaned to maintain their drainage efficiency. The effect of this procedure on ditch CH₄ fluxes is unclear.

To address this knowledge gap, we measured CH₄ fluxes from forestry drainage ditches before and after ditch cleaning between April and October 2025 at 58 measuring points across four drainage system catchments in western Estonia. The peat layer at the study sites was approximately 2 meters thick and underlain by clay, resulting in multiple locations where clay was exposed in the ditch bottom after cleaning. The clay-bottom ditches were filled with sediment prior to cleaning. No significant change in CH₄ emissions was observed within the full dataset. However, when separating the data by ditch bottom substrate, peat-bottom ditches showed a nearly fivefold increase in CH₄ fluxes (from 9.01 to 45.07 nmol m^-2 s^-1), while fluxes from clay-bottom ditches remained similar (12.95 to 11.37 nmol m^-2 s^-1). Prior to ditch cleaning, CH₄ emissions did not differ significantly between peat- and clay-bottom ditches.

The mechanisms for this separation post-cleaning are unclear. Firstly, ditch water parameters (depth, pH, dissolved oxygen, redox potential, electrical conductivity, temperature) measured alongside fluxes showed no significant differences between uncleaned and cleaned ditches. Furthermore, a multiple linear regression model based on measured water parameters explained nearly 40% of the variability in peat-bottom ditch CH₄ fluxes prior to cleaning. This explanatory power was lost following ditch cleaning, indicating a change in mechanism. Increased lateral inflow of dissolved CH₄ may contribute to post-cleaning fluxes. Although neither CH₄ fluxes nor dissolved concentrations increased further downstream with greater catchment size, the contribution of lateral transport cannot be excluded. In clay-bottom ditches, where most organic substrate was removed during cleaning, a substantial proportion of CH₄ emissions may originate from lateral inputs rather than in situ methanogenesis. The removal of vegetation and sediment during cleaning may have disrupted a long-established stability in the system, enhancing methanogenesis in peat-bottom ditches while suppressing in situ methanogenesis in clay-bottom ditches due to substrate limitations.

How to cite: Truupõld, J., Sarjas, J., Tamm, I., Pindus, M., Yıldız, K., and Kasak, K.: Methane emission responses to drainage ditch cleaning in forested peatlands, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-6522, https://doi.org/10.5194/egusphere-egu26-6522, 2026.

Seasonally ice-covered lakes are significant sources of methane (CH₄) and carbon dioxide (CO₂), with substantial emissions during spring and autumn turnover. During these events, gases accumulated in the hypolimnion are released to the atmosphere, with turnover accounting for 26–59% of CH₄ and 15–30% of CO₂ in some lakes. Climate change is altering ice cover duration and mixing regimes, affecting greenhouse gas (GHG) dynamics: reduced ice cover prolongs the ice-free period, increasing opportunities for GHG production and release, while shifts in turnover timing and duration can modify both the magnitude and seasonality of emissions, potentially generating climate feedbacks. Although the effects of climate change on ice cover and mixing are increasingly studied, the combined impacts on greenhouse gas production and release under future warming scenarios are still not well quantified.
We simulated projected changes in ice cover, turnover periods, and GHG dynamics in Lake Kuivajärvi, a small boreal lake in Finland, under future warming scenarios using outputs from five general circulation models and the LAKE model. LAKE reproduces temperature, horizontal velocities, O₂, CO₂, and CH₄ using a horizontally averaged transport equation, including sediment interactions and a snow-ice module.
Our results show substantial inter-model differences in ice cover length, and turnover timing and duration. Trends in ice cover duration and spring turnover are generally consistent—ice cover is decreasing (-14 ± 6 days per decade) and spring turnover is starting earlier and lasting longer (~3.6 days per decade)—whereas changes in autumn turnover are highly uncertain, with low model agreement and high variability. Lake Kuivajärvi is projected to experience occasional years with a monomictic regime by the late 21st century. Alongside changes in ice cover and turnover timing, CH₄ and CO₂ emissions are increasing during extended ice-free periods and altered mixing events.

How to cite: Fregona, M., Jansen, J., Li, X., and Mammarella, I.: Future climate warming prolongs spring mixing and increases annual greenhouse gas emissions in a boreal lake, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-10552, https://doi.org/10.5194/egusphere-egu26-10552, 2026.

Glacial streams export organic matter (OM) derived from various sources, including atmospheric deposition, overridden soils, and in situ microbial production. In most inland freshwater systems, this OM is mineralised by microbial respiration, resulting in net CO₂ evasion to the atmosphere.
Here, we show that the glacier-fed stream Virkisá (Iceland) deviates from this paradigm and acts as a net carbon sink, sequestering atmospheric CO₂.

Using self-constructed, low-cost CO₂ chambers, we quantified CO₂ fluxes between the stream and the atmosphere at six sites along a 3 km transect downstream from the glacier terminus. Over four seasons (154 measurements conducted between March 2023 and August 2025), CO₂ uptake fluxes ranged from an average of -18.76 ± 13.87 mg m^-2 h^-1 at the glacier outlet to -4.48 ± 3.53 mg m^-2 h^-1 further downstream. CO₂ uptake was strongest in spring, weaker during summer and autumn, and decreased with distance from the glacier. Measurements from four additional glacial streams (Skaftafellsá, Svínafellsá, Kvíárjökull, and Fjallsá) consistently identified glacial streams as CO₂ sinks.

A strong correlation between CO₂ fluxes and pH indicates that negative CO₂ fluxes were primarily driven by enhanced chemical carbonate and silicate weathering, with electrical conductivity serving as a proxy for weathering intensity. Freshly eroded, highly reactive basaltic sediments originating from beneath the glacier may promote rapid weathering reactions, increasing pH and thereby consuming CO₂, overriding the biological and abiotic processes that typically dominate in non-glacierized catchments.

In contrast, chamber measurements using the same methodological principle reveal that these glacial streams act as sources of CH₄.

Overall, our findings highlight the role of glacial streams as significant carbon sinks and underscore the need for further investigation, particularly in the context of ongoing glacier retreat and the increasing exposure of reactive glacial sediments.

How to cite: Wild, A.-K., Fasching, C., Boodoo, K., and Chifflard, P.: Glacial streams in Iceland as CO2 sinks and CH4 sources, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-12177, https://doi.org/10.5194/egusphere-egu26-12177, 2026.

Peatlands represent a dominant global soil carbon pool, but their role here is vulnerable to climate change and land use pressures. Peatland streams are known conduits of terrestrial carbon loss, rapidly transferring CO₂ and CH₄ from peat soils to the atmosphere. Despite their recognised contribution to global river greenhouse gas emissions, the hydroclimatic drivers here remain obscured across spatiotemporal gradients.

To address these research needs, we applied a novel isotopic framework (radiocarbon, δ¹³C, δD, δ¹⁸O), to constrain age and sources of peatland stream CO₂ and CH₄, alongside constraints on hydrological flow paths and CH₄ oxidation mechanisms. Over four seasonal visits, we sampled eight catchments on the Isle of Lewis, Scotland, spanning gradients of catchment areas, geomorphology, and land use. The Lewis Peatlands represent one of Europe’s largest continuous blanket bogs, and our catchments capture 30% of their surface area. All sites were subject to the same climate and underlying geology, enabling us to isolate spatiotemporal drivers across catchments.

Chamber-based emissions (flux) measurements reveal high variability of both CO₂ (–4.17 ± 2.35 to 106.73 ± 11.26 mmol m^-2 d^-1) and CH₄ (0 to 2.44 ± 0.34 mmol m^-2 d^-1), with inconsistent coupling in the magnitude of CO₂ and CH₄ emissions, suggesting independent supply controls. We explore these catchment-specific patterns considering their geomorphological attributes. We find that both CO₂ and CH₄ fluxes decrease exponentially with catchment area. Surface moisture indices derived using remote sensing show stronger CH₄ emissions in wetter catchments, while the magnitude of CO₂ emissions was more strongly linked to temperature. Preliminary radiocarbon data hint that CO₂ tends to become younger in drier catchments associated with summer sampling, validating the observed seasonal controls of CO₂ dynamics. While stronger CO₂ and CH₄ fluxes generally aligned with younger carbon turnover, these pathways also act as a significant export mechanism for older carbon, with some of the highest fluxes formed of older carbon.

Preliminary stable isotope data indicate greater inter-catchment variability in stream CH₄ sources than CO₂. Pending isotopic data will enable us to track these patterns over one year of sampling. Globally, only six published datasets report coupled river ¹⁴C-CO₂ and ¹⁴C-CH₄, making this one of the first studies to track these paired data over time. Combined with geochemical context and geospatial analyses, this framework will enable us to better constrain what are clearly highly dynamic and variable processes and avoid missing hotspots and key drivers of these peatland carbon loss mechanisms.

How to cite: Baldwin, C., Dean, J., Garnett, M., Cronwright, H., Smith, A., Mena-Rivera, L., Day, C., Dasari, S., Sulikova, S., and Hilton, R.: Complex hydroclimatic drivers of peatland stream CO2 and CH4 emissions revealed from a multi-catchment temporal study, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-14359, https://doi.org/10.5194/egusphere-egu26-14359, 2026.

Methane (CH₄) emissions from tropical reservoirs are sensitive to hydroclimatic and biogeochemical pressures, yet the dominant controls remain poorly quantified. Here, we combine satellite-derived chlorophyll-a (Chl-a) with a Bayesian upscaling model trained on a global CH₄–Chl-a dataset to estimate long-term (2012–2024) diffusive and ebullitive CH₄ emissions from Volta Lake in Ghana, the world’s largest artificial reservoir by surface area. Modeled emissions show substantial interannual variability and a pronounced post-2016 decline. Annual diffusive emissions ranged from 30.2 - 72.8 Gg CH₄-C yr⁻¹, ebullitive emissions from 109.1 - 211.9 Gg CH₄-C yr⁻¹, yielding combined emissions of 139.2 - 284.7 Gg CH₄-C yr⁻¹. Interannual CH₄ variability closely followed changes in lake-mean Chl-a, consistent with productivity-linked organic matter supply as a key constraint on methanogenesis. In contrast, annual associations between Chl-a (and modeled CH₄) and rainfall, evapotranspiration, or radiation were weak and not statistically significant, suggesting that hydroclimatic influence may operate primarily through seasonal watershed–lake biogeochemical coupling rather than year-to-year mean climate anomalies. These results highlight the sensitivity of Volta Lake methane emissions to long-term shifts in productivity, with implications for reservoir greenhouse gas budgets under changing hydroclimate.

How to cite: Asilevi, P. J., Pickard, A. E., Kitson, E., Quansah, E., and Spears, B. M.: Hydroclimatic Drivers of Modeled Methane Emissions over Volta Lake, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-14398, https://doi.org/10.5194/egusphere-egu26-14398, 2026.

It is now recognised that freshwater ecosystems are active components of the global carbon cycle, and that human activities have greatly modified natural aquatic biogeochemical processes. In some inland waters, this has led to large greenhouse gas (GHG) emissions to the atmosphere. However, these emissions are highly variable in time and space and are consequently hard to measure at scales required to inform GHG budgets. High-frequency, field-scale monitoring techniques such as eddy covariance offer the potential to capture these important but poorly understood emissions. A network of eddy covariance towers has been established across four UK inland waters, encompassing a Scottish loch, a Northern Irish lough, an English lake and a Welsh reservoir. High temporal resolution methane and carbon dioxide flux data from the respective water bodies have been generated from 2022 onwards.  Fluxes of carbon dioxide exhibited strong seasonality, with uptake occurring in the summer and release to the atmosphere in the winter. Seasonality was less clear for methane fluxes, though highest emissions to the atmosphere generally occurred in the spring and summer. Methane fluxes were positively correlated with chlorophyll-a at sites where supporting water quality data were available, with a statistically significant correlation evident at one site, indicating productivity as a key control on emissions. All sites were net sinks for carbon dioxide and net sources of methane over the monitoring period. This network of eddy covariance flux towers is generating new scientific understanding concerning the processes that drive aquatic fluxes of carbon dioxide and methane, and the contribution of inland waters to national GHG budgets.

How to cite: Pickard, A., Helfter, C., Barry, C., Belcher, A., Mackay, E., Riutta, T., van den Berg, M., Yeung, K., and Evans, C.: Eddy covariance measurement of carbon dioxide and methane fluxes from UK inland waters, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-16881, https://doi.org/10.5194/egusphere-egu26-16881, 2026.

Aquaculture ponds, among the fastest-growing inland water bodies, are hotspots of carbon emissions. However, the carbon emissions from aquaculture ponds exhibit significant variability under different management practices, complicating carbon flux quantification. By conducting year-round monthly observations in a fishpond (P1) and a shrimp pond (P2) in subtropical Hong Kong, this study examined their carbon emissions and influencing factors under different management practices. Our results showed that under different management practices, the main drivers of carbon emissions were different. For P1 with low artificial disturbance and increased ecosystem stability, increasing temperature has indirectly reduced CO2 emissions by enhancing photosynthetic intensity while directly promoting CH4 emissions. In comparison, adjustment of water depth and fertilizer application have largely regulated carbon emissions from P2. Consequently, P1 exhibited high primary productivity and functioned as a net CO₂ sink ( -42.33 ± 18.91 mmol m−2 d−1). However, the absence of draining-drying and the presence of a thicker sediment layer in P1 led to stronger CH4 emissions (29.41 ± 27.53 mmol m−2 d−1). Conversely, intensive artificial management practices in P2, including draining, drying, and refilling, have significantly disrupted its primary productivity and shifted it to a CO2 source (62.89 ± 106.61 mmol m−2 d−1) while substantially reducing its CH₄ emissions, especially CH4 ebullition. The total CO2-eq emission flux for P2 was approximately 62% lower than that for P1. This study underscores the substantial impact of human disturbance, especially the draining-drying-refilling practice, on carbon cycle in aquaculture ponds, which should be fully incorporated into future carbon flux estimations.

How to cite: Yang, Q., Li, Y., Liu, J., and Ran, L.: CO2 and CH4 emissions from subtropical aquaculture ponds under different management practices, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-17284, https://doi.org/10.5194/egusphere-egu26-17284, 2026.

Serpentinising systems are among the most plausible environments for life’s emergence, where reactions between water and ultramafic rocks generate hydrogen, methane, and simple organics that could have fuelled early metabolisms. These reactions create highly alkaline fluids and steep pH–redox gradients that persist today, sustaining diverse microbial processes that regulate greenhouse gas fluxes. Here, we examined subsurface fluids from the Samail Ophiolite (Oman), the world’s largest and best-exposed terrestrial serpentinising system, to characterise greenhouse gas dynamics and their interconnections across contrasting geochemical conditions. CH₄ concentrations increased markedly with pH and were highly supersaturated (up to 48,000× atmospheric equilibrium) in reduced, hyperalkaline fluids (pH > 11), indicating strong net production. In contrast, CO₂ concentrations decreased with pH, consistent with substantial CO₂ consumption and carbonate precipitation under hyperalkaline conditions, whereas CO₂ remained elevated in pH-neutral, oxidised fluids. N₂O concentrations were low (0.001–1.5 μM) and showed strong net consumption under hyperalkaline, reducing conditions. However, addition of CH₄ alongside ¹⁵N-nitrite stimulated N₂O production — up to 72-fold higher in hyperalkaline fluids, revealing a mechanistic link between CH₄ and N₂O cycling. Isotopic data (⁴⁵N₂O, ⁴⁶N₂O) further indicated depth- and pH-dependent shifts in dominant N₂O pathways. Our findings show that interactions between geological and microbial processes control the balance of greenhouse gas production and consumption in serpentinising systems. These insights illuminate how life and geochemistry interact under extreme conditions, with implications for modern CO₂ storage strategies and ancient Earth environments.

How to cite: Si, Y., Stocker, M., Shannon, J., Matter, J., and Lam, P.: Coupled CH4, CO2, and N2O cycling in a subsurface serpentinising system, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-19847, https://doi.org/10.5194/egusphere-egu26-19847, 2026.

Groundwater is increasingly recognised as a significant source of carbon dioxide (CO₂) to streams. However, the fate of this terrestrial CO₂, whether it is released locally to the atmosphere or transported downstream, remains unclear. This uncertainty stems from the difficulty of quantifying groundwater inflows on a fine spatial and temporal scale. In this study, we examine the fate of groundwater-derived CO₂ along a 400 m reach of a boreal headwater stream by combining high-resolution measurements of groundwater CO₂ inputs, CO₂ evasion, and downstream CO₂ export during the ice-free period (April to September). Groundwater CO₂ inputs exhibited strong spatial heterogeneity, spanning more than two orders of magnitude across gaining stream segments (median: 13 g C m^-2 d^-1, interquartile range (IR): 0.00 – 50 g C m^-2 d^-1). This variability was primarily driven by differences in groundwater inflow rates associated with local catchment characteristics, such as stream slope. Over time, groundwater CO₂ inputs varied by more than one order of magnitude, with pronounced peaks in late April (108 g C m^-2 d^-1, IQR: 58 – 126 g C m^-2 d^-1) and late July (136 g C m^-2 d^-1, IQR: 46 – 175 g C m^-2 d^-1). In contrast, groundwater CO₂ inputs remained consistently low during baseflow conditions in mid-July (10 g C m^-2 d^-1, IQR: 7.1 – 18 g C m^-2 d^-1) and late August (16 g C m^-2 d^-1, IQR: 6.6 – 31 g C m^-2 d^-1). The seasonal variability in groundwater CO₂ inputs was driven by two contrasting mechanisms: a spring peak mainly caused by increased groundwater discharge during snowmelt, despite relatively low CO₂ concentrations in the groundwater, and summer and autumn peaks linked to rainfall events and higher CO₂ concentrations in the groundwater, likely reflecting increased soil respiration. Throughout the study period, the median value of groundwater CO₂ inputs exceeded the median value of CO₂ evasion (3.0 g C m^-2 d^-1, IQR: 1.9 – 3.0 g C m^-2 d^-1) by a factor of 20 and was of the same order of magnitude as downstream CO₂ export (76 g C m^-2 d^-1, IQR: 46 – 300 g C m^-2 d^-1). These results demonstrate that a substantial proportion of the CO₂ derived from groundwater in headwater streams is not immediately emitted, but instead redistributed along the stream network, where it can contribute to downstream emissions or biogeochemical processing. Our findings highlight the need for integrative assessments of CO₂ fluxes, which explicitly account for groundwater inflows, atmospheric emissions, and downstream export, particularly in the context of climate-driven changes to hydrology and terrestrial carbon cycling.

How to cite: Olid, C., Hauptmann, D., Karlsson, J., and Klaus, M.: Export, not evasion: the fate of groundwater-derived CO2 in a boreal stream, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-17625, https://doi.org/10.5194/egusphere-egu26-17625, 2026.

The shallow East Siberian Arctic Shelf (ESAS) is the World’s largest shelf sea system and overlies a complex sedimentary drape that includes thawing subsea permafrost, methane hydrates, and gas and oil reservoirs. Uncertain estimates suggest that the ESAS releases as much methane to the atmosphere as the rest of the World Ocean; yet the relative contributions from different sources are poorly constrained—a prerequisite for anticipating future release trajectories. Here, multi-year source-diagnostic triple-isotopic compositions (δ¹³C, δ²H, and Δ¹⁴C) of seawater-dissolved and ebullitive methane show that methane contributions vary greatly across the ESAS, with the subsea permafrost-associated biogenic methane pools only standing for one-tenth (Outer Laptev Sea), three-tenths (East Siberian Sea), and six-tenths (Inner Laptev Sea) of the total methane releases. For the East Siberian Sea and the Outer Laptev Sea, distinct fossil gas seeps of different origins were identified. Multi-year constancy in each regime’s isotopic fingerprints of ebullitive and dissolved methane and concentration patterns suggests that bubble dissolution is the primary source of elevated methane levels below and above the pycnocline. Furthermore, the high methane concentrations in bubbles reaching the sea surface (80±22%) indicate direct release of methane from the seabed into the atmosphere via ebullition, thereby going past potential microbial degradation. While it is complicated to include both ebullition and the diversity of methane sources in methane budgets, it appears critical for predicting methane release trajectories in the ESAS region and, consequently, their contribution to the increasing atmospheric methane pool.

How to cite: Brussee, M., Holmstrand, H., Wild, B., Kosmach, D., Chernykh, D., Kurilenko, A., Shakhova, N., Semiletov, I., and Gustafsson, Ö.: Triple-isotopic source fingerprinting of dissolved and bubble-held methane across the East Siberian Arctic Shelf Seas, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-20599, https://doi.org/10.5194/egusphere-egu26-20599, 2026.

Inland aquatic ecosystems, including rivers, lakes, and reservoirs, play an active but still poorly constrained role in the global carbon cycle by acting as both sources and sinks of greenhouse gases such as CO₂, CH₄, and N₂O. Quantifying these emissions remains difficult because aquatic biogeochemical processes vary strongly over short spatial and temporal scales, while commonly used monitoring approaches—such as infrequent manual sampling or costly stationary installations—often fail to resolve rapid changes associated with diel cycles, hydrological events, or transient mixing conditions that can contribute disproportionately to annual fluxes. To overcome these limitations, we developed a scalable, open-architecture Internet of Things (IoT) monitoring system for continuous, high-resolution observation of aquatic greenhouse gas dynamics, built around a Raspberry Pi–based edge-computing unit coupled with calibrated gas sensors (NDIR for CO₂ and a semiconductor-based sensor for CH₄) and supporting environmental sensors for temperature, pressure, and relative humidity. Data are transmitted in near real time to a cloud-based dashboard, enabling remote system diagnostics, immediate visualization, and rapid identification of anomalous events, rather than relying on delayed, site-based data retrieval. Initial field deployments show that this high-frequency approach captures short-term variability in gas concentrations that is largely missed by discrete sampling, highlighting the importance of temporal resolution for inland water GHG assessments. By providing a flexible and cost-effective alternative to conventional reference stations, this system offers a practical route toward denser observation networks, improved model validation, and more reliable carbon budget estimates in heterogeneous freshwater environments.

How to cite: Bara, A., Gaur, S., and Dwivedi, S. B.: Advancement in Smart Monitoring of Greenhouse Gases: An IoT Approach for Inland Waterbodies, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-20871, https://doi.org/10.5194/egusphere-egu26-20871, 2026.

The CO₂ emissions from inland waters in Amazon Basin constitute a critical, yet often underrepresented, component of the global carbon budget. While the region is widely recognized as a vital carbon sink due to its vast forests, its extensive aquatic networks, particularly floodplains, act as significant natural sources of atmospheric CO₂. However, current process-based biogeochemical models usually fail to capture the temporal extent of floodplains. This limitation propagates into substantial uncertainties in the estimated CO₂ emissions from Amazonian inland waters, particularly from floodplains. In this work, we are using the satellite-observations-based product GIEMS-D3 to take a deep dive into Amazon floodplain dynamics. Through comparison with the process-based model ORCHILEAK, we aim to explore which and to what extent biotic and abiotic factors have impacts on the floodplain dynamics and associated CO₂ emissions. The findings from this study will provide key constraints for refining biogeochemical models, leading to more accurate representations of inland water CO₂ emissions and a better-constrained global carbon budget.

How to cite: Roessler, A., Yan, Y., Ma, M., and Regnier, P.: Assessing the Impact of Amazon Floodplain Dynamics on CO2 Emissions: A Satellite-Model Synthesis, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-665, https://doi.org/10.5194/egusphere-egu26-665, 2026.

Headwater streams are increasingly recognized as hotspots of greenhouse gas (GHG) emissions within river networks, driven by strong land–water interactions, high biological activity, turbulence, and groundwater inputs. Despite their disproportionate contribution to atmospheric fluxes of CO₂, CH₄, and N₂O, the processes linking GHG emissions to dissolved organic matter (DOM) dynamics along the soil–water continuum remain insufficiently understood, particularly under varying hydrological conditions and land-use change.

This study investigates the interactions between stream GHG emissions and DOM quantity and quality in a forested headwater catchment. The research is conducted in the Wüstebach catchment, located in the Eifel National Park (Germany) and part of the TERENO long-term environmental observation network. Here, we present preliminary results focusing on how hydrology and land cover influence the coupling between GHG dynamics and DOM characteristics.

Water chemistry and GHG samples are collected bi-weekly over one year along about 500 m stream reach, from the source to the gauging station, at ten locations along the main stem and three locations along a nearby control stream. Sampling points are spaced approximately every 100 m and positioned upstream and downstream of tributaries, allowing assessment of spatial variability, tributary inputs, and land-use effects on GHG concentrations and fluxes.

Preliminary results reveal pronounced seasonal and hydrological controls on GHG emissions. Mean CO₂ and N₂O fluxes are higher during winter and autumn, whereas CH₄ fluxes peak during summer. Increasing discharge is associated with enhanced CO₂ and N₂O fluxes in both streams, while CH₄ fluxes show no consistent relationship with discharge. Both dissolved concentrations and atmospheric fluxes of CO₂, CH₄, and N₂O are consistently higher in the clearcut stream compared to the reference stream. In the clearcut area, elevated dissolved organic carbon (DOC) concentrations correlate positively with increased CO₂ concentrations in stream water. In contrast, CO₂ emissions show the expected negative relationship with DOM aromaticity (SUVA₂₅₄) in the reference stream, but this relationship is absent in the clearcut stream, indicating altered DOM processing and carbon turnover following land-use change.

How to cite: Batsatsashvili, M., Bol, R., Gettel, G., Kalbitz, K., and Pütz, T.: Effect of vegetation reestablishment on greenhouse gas emissions from a small headwater stream, Eifel/Lower Rhine Valley (TERENO Network, Germany), EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-16631, https://doi.org/10.5194/egusphere-egu26-16631, 2026.

Methane emissions from reservoirs are dominated by ebullition, which accounts for up to 88 % of global methane emissions from reservoirs. Due to the sporadic nature of ebullition, it is difficult to measure its persistence through an annual cycle. Short-term manual sampling approaches, often consisting of 24-hour floating chamber deployments, cannot adequately capture the long-term patterns and variability in these emissions rates. This induces higher uncertainty when scaled to system-wide total emissions estimates. To address this, three low-cost automated real-time floating chambers, the Monitub system, were deployed in the Borumba Creek inflow arm of Lake Borumba, a sub-tropical reservoir in Queensland, Australia, to monitor emissions over an annual cycle. Monitoring of chlorophyll, temperature and bed pressure was also conducted to explore links to flux rates.

This long-term high temporal resolution data has revealed the presence of ebullition year-round, rather than it being dependent on seasonality. Statistical analysis of the hourly and daily averages shows rates follow a log-normal distribution. Preliminary results show the fit stabilises 6 – 8 months after deployment. This finding provides insight into minimum deployment timelines required for more accurate characterisation of temporal emission patterns.

These insights would not be attainable through traditional manual sampling techniques, but rather a long-term automated monitoring system is required. These systems can capture sporadic events, reduce required labour, and provide higher statistical understanding of methane emissions. These advances can improve total emissions estimates and inform future monitoring programs, which will lead to higher understanding of the contribution of ebullitive rates.

How to cite: Duncan, B., Deering, N., Fluggen, K., and Grinham, A.: Year-long real-time monitoring of methane emissions from a sub-tropical reservoir show the persistence of ebullition, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-17038, https://doi.org/10.5194/egusphere-egu26-17038, 2026.

The eutrophication and deoxygenation of coastal systems can severely impact the biogeochemistry of surface sediments, and can lead to oxygen limitation and sulfide accumulation. Changes in oxygen and sulfide availability may have large effects on the sedimentary dynamics of the potent greenhouse gas nitrous oxide (N₂O), and thus on N₂O fluxes between sediments and the overlying water column. Here, we used a combination of porewater and microsensor measurements, batch incubations, and metagenome and metatranscriptome analyses to assess the effect of oxygen and sulfide on N₂O production and consumption processes in surface sediments of a seasonally euxinic coastal system. In spring, our study system (Lake Grevelingen, The Netherlands) is characterized by oxygenated bottom waters and surface sediments, while water column stratification in summer leads to euxinic bottom waters and highly sulfidic surface sediments (mM concentrations). An absence of net N₂O production in spring sediment was consistent with an in situ limitation of oxygen and NO_x. Batch incubations showed that despite this in situ limitation, the microbial community maintained the potential for nitrification and N₂O production through denitrification. The nosZ gene, which is responsible for N₂O consumption, was present and expressed by a diverse microbial community dominated by clade II nosZ-possessing Flavobacteriia. Sulfidic summer conditions were simulated in batch incubations via sulfide additions. At low mM sulfide concentrations N₂O consumption was enhanced, while higher sulfide concentrations halted most of the studied nitrogen cycling processes. Hence, restoration of coastal systems by re-oxygenation could affect N₂O dynamics by changing oxygen, NO_x and sulfide availability, which would have implications for the role these sediments play in N₂O exchange with overlying waters.

How to cite: van Erk, M. R., Rigutto, I. M. L., Leão, P., Slomp, C. P., and Jetten, M. S. M.: N2O dynamics in surface sediments of a seasonally euxinic coastal basin, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-18186, https://doi.org/10.5194/egusphere-egu26-18186, 2026.