Orals: Wed, 30 Apr | Room L1
Inland waters (streams, rivers, lakes, and reservoirs) are important sources of greenhouse gases (GHGs), including carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O), to the atmosphere. Their importance has been acknowledged in the IPCC assessment reports and in the regional and global greenhouse budgets coordinated by the Global Carbon Project (GCP). In the framework of the 2nd phase of the REgional Carbon Cycle Assessment and Processes (RECCAP-2) initiative of the GCP, a comprehensive synthesis of existing estimates of regional to global inland water GHG emissions was conducted (Lauerwald et al., 2023a, 2023b) to support the inclusion of these emissions in (sub-)continental GHG budgets. Although that synthesis was published only two years ago, a number of new global estimates have been published since. Here, we present an updated synthesis of recent, global inland water GHG emissions estimates. Moreover, we go beyond the scope of the RECCAP2 synthesis by analyzing regional patterns in more detail, and summarizing the state of knowledge about long-term trends of inland water GHG emissions in response to changes in climate, land use, wastewater management and river damming. Based on that, we discuss how contemporary inland water GHG emissions are impacted by anthropogenic activities and how they may evolve over the 21st century.
We estimate that global inland water GHG emissions have a combined warming potential of 8 (5–13) Pg CO2-eq. yr⁻¹ for a 100-year time horizon (GWP100). CO2 emissions, primarily from tropical river systems, contribute approximately three-quarters of this total, while CH4, largely from lakes and reservoirs, accounts for most of the remainder. Notably, boreal and Arctic lakes are important emitters due to their large total area, while nutrient-rich lakes and reservoirs with warmer temperatures in the mid to low latitudes exhibit the highest per-area CH4 emission rates. Contributions from N2O emissions are relatively minor.
About one third of CH4 emissions and about three quarters of N2O emissions from global inland waters can be attributed to anthropogenic perturbations, primarily through eutrophication. For inland water CO2 emissions, quantification of the anthropogenic component is more complex. Empirical and modelling studies suggest that global greening also increases terrestrial carbon deliveries to inland waters, and through that, emissions of CO2 from inland waters. Moreover, changes in streamflow are an uncertain, but very important driver. Most dramatic increases are expected for inland water CH4 and N2O emissions, which are projected to strongly increase in response to global warming, while changes in nutrient loads from agricultural runoff may offset or enhance that trend.
References
Lauerwald et al. 2023a, GBC, https://doi.org/10.1029/2022GB007657
Lauerwald et al. 2023b, GBC, https://doi.org/10.1029/2022GB007658
How to cite: Lauerwald, R., Bastviken, D., Battin, T., Ciais, P., Tian, H., Allen, G. H., Abril, G., Catalan, N., Deemer, B. R., del Giorgio, P., Marzadri, A., Prairie, Y., Tank, S., Zhuang, Q., Ran, L., Canadell, J., and Regnier, P.: Global Inland Water Greenhouse Gas Emissions: Patterns, Trends, and Anthropogenic Drivers, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-13764, https://doi.org/10.5194/egusphere-egu25-13764, 2025.
As droughts become more frequent, understanding their impact on diel CO2 variations in river ecosystems—particularly at sub-daily scales—becomes increasingly crucial. To explore diel CO2 fluctuations and carbon dynamics at fine temporal scales, we deployed in situ sensors to monitor CO2 concentrations in two rivers in Germany during both non-drought and drought summers, aiming to quantify how drought affects sub-daily CO2 dynamics.
Our results show that summer drought significantly amplifies diel CO2 amplitude, with increases of 62% in the stream and 24% in the river under drought conditions. However, daily mean CO2 concentrations did not differ significantly between drought and non-drought summers. Shallower water depths are the main cause of the amplified diel CO2 fluctuations, which reduce gas exchange and ecosystem respiration. Specifically, a 43% decrease in water depth in the stream and 44% in the river resulted in 13% and 25% reductions in gas exchange, respectively, and a corresponding 26% and 57% decline in ecosystem respiration.
These findings suggest that diel CO2 amplitude is more sensitive to changes in water depth than to the increased radiation and temperature associated with drought. Our study highlights the vulnerability of shallow rivers to drought and underscores the importance of high-frequency CO2 monitoring to capture sub-daily variations more accurately. As droughts become more frequent, single daily measurements may become highly uncertain, making high-frequency monitoring essential for improving CO2 emission estimates.
How to cite: Leng, P., Rode, M., and Koschorreck, M.: Summer droughts amplify the diel CO2 variations in temperate rivers, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-7678, https://doi.org/10.5194/egusphere-egu25-7678, 2025.
Rewetting of previously drained wetlands in the forested landscape is suggested as an efficient Nature Based Solution to combat multiple environmental challenges e.g. to protect biodiversity, improve water resilience, and reduce greenhouse gas emissions. In parallel with this human induced re-creation of wet areas there are also non-human activities i.e. damming by beavers, that that could have a similar water retaining function. However, the consequence of these different water retaining actions on carbon exported via runoff is often ignored in climate benefit and water quality assessments. Here we explored the effect of rewetting and beaver dams on total organic carbon (TOC), carbon dioxide (CO2) and methane (CH4) in runoff by comparing data collected in a coordinated sampling campaign across hemiboreal Sweden. In total, runoff from 68 sites were sampled across five site types including rewetted sites (n=15), beaver dams (n=14) and pristine wetlands (11). To assess the effect of rewetting and beaver dams, runoff samples was also collected in drained wetlands (n=15) and at sites without beaver dams (n=14), both used as reference sites.
It was evident that rewetted sites stood out and displayed higher runoff TOC and CO2 concentrations (on average 2-fold higher) than observed in all other site types. In contrast, no difference in TOC or CO2 concentrations was observed among the remaining four site types. Rewetted sites also showed the highest CH4 concentrations, 5-fold higher than observed in pristine and reference (drained wetlands and sites without beaver dams) sites. However, CH4 concentrations in rewetted sites were not statistically different than observed in beaver dams. Collectively, this suggest that rewetting cause elevated runoff concentrations of all major carbon forms compared to both drained and pristine wetlands. In addition, beaver dams were identified as potential hotspots for CH4 formation despite not showing any elevated runoff concentrations of the other carbon forms. We attribute the effect of rewetting on runoff carbon to an enhanced connectivity to carbon-rich terrestrial sources, but also to enhanced metabolic production under anoxic conditions, as rewetted sites showed lower oxygen in runoff than all other site types. We further speculate that the elevated CH4 in beaver dams could be linked to another type of organic substrate, as beaver dams are not necessarily located in areas with peat-rich soils. The findings from the current study suggest that rewetting of drained wetlands has implications for both climate and downstream water quality, and that those implications might differ compared to effects from non-human inundation (i.e. beaver dams).
How to cite: Wallin, M., Wang, M., Ecke, F., and Eklöf, K.: Inundation of forested landscapes by human induced rewetting and beaver dams – effects on dissolved carbon and greenhouse gases in runoff , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-9862, https://doi.org/10.5194/egusphere-egu25-9862, 2025.
Estuaries play a crucial role in the global nitrous oxide (N2O) budget, but significant uncertainties remain in estimating their emissions due to anthropogenic impacts, particularly wastewater discharge. Using advanced high-resolution, real-time measurements, this study reveals that the Pearl River Estuary is a substantial N2O emission source, estimated at 1.05 Gg yr-1 (range: 0.92-1.23 Gg yr-1) with pronounced spatial heterogeneity. Wastewater discharge significantly enhances emissions by introducing abundant nutrients, altering carbon-to-nitrogen stoichiometry, and stimulating biochemical processes. A meta-analysis further demonstrates that nitrogen inputs from wastewater widely increase N2O emissions in global estuaries, though emission factors are considerably lower than IPCC estimates due to biological saturation. These findings highlight the need for refined emission factor estimates through comprehensive bottom-up studies to better understand estuarine contributions to the global N2O budget.
How to cite: Dong, Y., Cheng, X., Wang, S., Xiao, S., and Wang, C.: Significant spatial heterogeneity and distinct determinants of N2O emission in Pearl River Estuary, China, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-5790, https://doi.org/10.5194/egusphere-egu25-5790, 2025.
Agricultural ditches have been identified as emission hotspots of the three main atmospheric greenhouse gases (GHGs) i.e., carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O). However, due to lack of representative GHG emission data from these small waterbodies, their contribution to the total GHG emissions from the agricultural sector are reported as highly uncertain. In this study the aim was to 1) quantify the magnitude of GHG emissions and understand their spatiotemporal dynamics in agricultural ditches, and 2) identify gas specific controls that regulate those dynamics.
In our two-year field study, dissolved concentrations and fluxes of CO2, CH4 and N2O were measured in ditches, as well as concentrations in groundwater, of a clay soil dominated agricultural catchment located in central Sweden. Sampling was carried out biweekly during the growing season (April–November). Additional sampling for water chemistry and runoff was made to aid assessment of GHG controls. Local floating chamber-based GHG fluxes were further scaled for the entire ditch network for representative catchment scale emission estimates.
The results showed that both dissolved GHG concentrations and their respective fluxes were highly variable in space and time. In general, higher GHG concentrations and fluxes were observed during the summer and after rain events, but patterns were gas and site-specific. Across all sites, N2O concentrations were positively related to dissolved inorganic nitrogen (DIN), and CO2 to total organic carbon (TOC), whereas patterns for CH4 were more unpredictable. Groundwater data also revealed highly variable gas-specific patterns over time. While groundwater N2O concentrations was on average close to concentrations observed in the ditch, CO2 was 5-fold and CH4 1000-fold higher in groundwater indicating a gas-variable terrestrial source contribution to observed ditch emissions. Our study identified ditches as significant but also highly variable sources of CO2, CH4 and N2O emissions to the atmosphere. This further highlights the need for appropriate sampling and scaling designs that can capture these high spatiotemporal dynamics to provide representative catchment-based emission estimates.
How to cite: Aziz, K., Audet, J., Conroy, H., Geranmayeh, P., Kyllmar, K., Peacock, M., Sobek, S., and Wallin, M.: Spatiotemporal dynamics and controls of greenhouse gas emissions in agricultural ditches, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-17014, https://doi.org/10.5194/egusphere-egu25-17014, 2025.
Greenhouse gas production in riverine sediments is extensively influenced by the aerobic and anaerobic breakdown of organic matter and the processes of nitrification and denitrification. These processes are further enhanced by nitrogen-rich organic substrates in the sediments, which produce potent GHGs such as Methane (CH4) and Nitrous Oxide (N2O). While extensive research has been conducted on terrestrial ecosystems, little attention is given to estimating GHG emissions from riverine sediments. In this context, an incubation study was conducted to estimate the emissions of CH4 and N2O from sediment samples collected from the Ganga River at three locations representing varied environmental conditions: the urban area, city outskirts, and an agricultural area. Samples were taken during the winter (wet season) and summer (dry season) to assess seasonal emission variations. The study observed a wide range in the daily production of CH4, varying from 0.51 μg g-1d-1 to 3.82 μg g-1d-1 across the sampling sites (S1, S2, and S3). The highest CH4 production was observed during the summer (March) season at the urban periphery (S1), indicating that warmer temperatures and increasing microbial activities during the dry season may enhance CH4 emissions. Similarly, the daily N2O production ranged from 1721.37 μg g-1d-1 to 2024.57 μg g-1d-1, with the highest N2O emissions occurring at S3 during the summer season. N2O production is driven primarily by the microbial reduction of nitrates in anoxic conditions, and higher nitrogen inputs from fertilizers at the agricultural site likely amplify denitrification, leading to elevated N2O emissions. Moreover, the significant positive correlation of CH4 production with Total Organic Carbon (TOC), C/N ratio and Electrical Conductivity (EC), while N2O with EC, pH, and Water Temperature (TW) confirms the crucial role of environmental variables in GHG emissions. These findings highlighted the substantial role of riverine sediments as sources of GHG emissions, which are often understated in national/global GHG inventories. Riverine sediments, particularly in regions influenced by human activities, are significant in the global carbon budget. The study emphasizes incorporating riverine sediments in future GHG emission models and inventories, especially in the context of climate change mitigation strategies. In addition, more comprehensive studies are required to understand the GHG dynamic in these environments and their impact on global climate change.
How to cite: Upadhyay, P., Verma, J. P., Prajapati, S. K., and Kumar, A.: Estimation of Greenhouse Gas Emissions from Ganga River Sediment, India, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-920, https://doi.org/10.5194/egusphere-egu25-920, 2025.
Groundwater-fed springs are crucial for human well-being in sub-Saharan Africa but are unsustainably managed, with a 2.3% annual population growth rate and 50% of the population relying on groundwater. Over-abstraction and contamination from land-use changes persist, impacting biogeochemical processes and greenhouse gas (GHG) emissions. However, the extent and effects of this contamination are understudied and not included in GHG budgets for tropical systems. Analyzing spring water quality provides valuable insights into subsurface processes and their effect on GHG emissions. This study, investigated the impact of land use changes on GHG emissions from 10 springs in diverse land uses (Agricultural and Mixed Forest-Agricultural) within a tropical highland ecosystem in Taita Hills, Kenya, from April 2023 to February 2024. Gas samples (CO2, CH4, and N2O) were collected using the headspace equilibrium technique. Gas concentrations, fluxes, and transfer velocities were calculated and compared between the land uses. Additionally, in-situ measurements (pH, Electrical Conductivity, Dissolved Oxygen, stream velocity, and discharge) and laboratory analyses (NO3-N, NH4-N, DOC, TDN) determined the underlying biogeochemical conditions relevant to GHG emissions. The results indicated significantly higher average CO2 flux from the agricultural-impacted springs compared to the mixed forest-agricultural springs (mean ± SE = 2722.7 ± 248.1 mg CO2-C m-2 h-1 and mean ± SE = 2098.5 ± 75 mg CO2-C m-2 h-1 respectively; p < 0.05). This was due to the significantly higher negative correlation with DO, pH and DOC, and positive correlation with stream velocity which may be attributed to microbial respiration and decomposition in the system. CH4 was significantly higher in the mixed forest-agricultural springs compared to the agricultural springs (mean ± SE = 8.9 ± 1.2 mg CH4-C m-2 h-1 and mean ± SE = 4.7 ± 0.8 mg CH4-C m-2 h-1 respectively; p < 0.05). This was mainly due to the higher negative correlation with DO and positive correlation with DOC and NH4-N which was only evident in the mixed forest-agricultural attributed to methanogenesis in these springs. N2O was significantly higher in the agricultural springs with one order of magnitude higher than mixed forest-agricultural (mean ± SE = 3.6 ± 0.5 mg N2O-N m-2 h-1 and mean ± SE = 0.3 ± 0.05 mg N2O-N m-2 h-1 respectively; p < 0.05). N2O was mainly driven by high positive correlations with NO3-N, DO and stream velocity. Correlations inferred nitrification was the main controlling process in the mixed forest-agricultural springs while denitrification was the major process in the agricultural springs due to the negative correlation with DO. The results indicate that increased fertilizer use increased NO3-N thus an increase in GHG emissions. Understanding the various controlling processes at different land use points of the springs is crucial for better management. Our study suggests that water quality significantly influences biogeochemical processes and GHG emissions, such as high NO3-N leading to N2O-N. We also recommend that practicing mixed forest-agricultural could help manage CO2 and N2O emissions. Further analysis incorporating seasonal variations is underway to better understand the GHG hot moments.
How to cite: Gubamwoyo, S., Gettel, G., Mwanake, R., Kisha, D., and Hein, T.: Biogeochemical dynamics and greenhouse gas emissions from groundwater-fed springs in a tropical highland system, Taita Hills, East Africa, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-8529, https://doi.org/10.5194/egusphere-egu25-8529, 2025.
According to recent data-driven upscaling, emissions from rivers in the Arctic-boreal region offset between half to all of the wetland carbon dioxide (CO2) sink, and release substantial amounts of methane (CH4) despite their much smaller surface area. However, observational data in natural riverine ecosystems in this region remain scarce, and carbon emission estimates show large uncertainties.
In order to estimate the carbon budget of a natural river, we determined chamber-derived water-air fluxes and surface partial pressures of CO2 and CH4 on four transects along the Fennoscandian river Teno. In addition, hydrochemical parameters were measured. CO2 fluxes were low and ranged from -0.1 to 0.9 µmol m-2 s-1 without significant spatial differences. CH4 fluxes were highest in an area of shallow water and pronounced benthic vegetation, but overall showed small emissions (0.02 to 13.66 nmol m-2 s-1). Partial pressures of CO2 and CH4 were mostly in equilibrium with the atmosphere, and pCH4 was only slightly elevated where highest CH4 fluxes were found.
On each transect, the carbon fluxes were driven by different local factors including dissolved oxygen saturation, water temperature, pH and turbidity. Therefore, knowledge about heterogeneous patterns across landscapes is important to understand spatial variability of riverine biogeochemistry and enhance process understanding. Results from this study can be used to benchmark Earth System and process-based models, and to evaluate the impact of disturbances on river carbon dynamics.
How to cite: Vogt, J., Ala-Könni, J., Mammarella, I., Mendoza-Lera, C., Pumpanen, J., Palacin-Lizarbe, C., Saarela, T., Hashmi, W., Zhang-Turpeinen, H., Kinnunen, N., Ojala, A., Rinne, J., and Göckede, M.: Equilibrium unveiled: Carbon fluxes of a natural Fennoscandian river, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-9701, https://doi.org/10.5194/egusphere-egu25-9701, 2025.
Mountain streams are hot spots for the exchange of gases such as oxygen or carbon dioxide with the atmosphere. Air-water gas exchange is accelerated by air bubbles entrained in turbulent flow and depends on bubble concentration and size. Yet, our understanding of gas exchange mechanisms and our ability to upscale gas fluxes is hampered by a severe lack of data on bubble size distributions in streams. Here, we measured bubble size distributions in 16 step-pool systems across six stream reaches in two mountain ranges (Dolomites, Italy; Vosges, France), combining Acoustic Bubble Spectrometry and ambient underwater sound recording. Bubble size distributions in our study streams were similar to those reported previously for ocean breaking waves: bubble concentrations decreased with bubble size following a power-law scaling, with a power exponent generally ranging from -2/3 to -10/3, increasing with bubble size, and varying both within and among step-pool systems. Total bubble concentrations exhibited a bilinear power law relationship with turbulent kinetic energy dissipation rates estimated from Acoustic Doppler Velocimetry, suggesting distinct bubble formation regimes under low and high turbulence. Bubble concentrations generally decreased with distance from steps, but invisible microbubbles still exhibited significant concentrations several meters downstream from steps where no visible macrobubbles were recorded. Our findings provide novel scaling laws for bubble size distributions, offering insights into the different gas exchange regimes observed in mountain streams. Additionally, they underscore the potential of bubble-mediated gas exchange even under absence of visible bubbles, highlighting the complexities involved in upscaling gas exchange mechanisms in such environments.
How to cite: Klaus, M., Durighetto, N., Chatton, E., Peruzzo, P., and Botter, G.: Bubble size distributions in mountain streams, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-16016, https://doi.org/10.5194/egusphere-egu25-16016, 2025.
Accurate estimation of carbon gas (CO2 and CH4) emissions from lakes is crucial for understanding the global carbon budget. Carbon gas emissions have been considered greatest in small lakes, however, this conclusion may be biased due to limited samples of diverse lake types and sizes. Remote sensing would allow detailed mapping of regional emissions but has hitherto not been developed. Here, we demonstrate the high accuracy, continuity, and large-scale observation capabilities of optical satellite data in mapping CO2 and CH4 dynamics. Using this innovative approach, we investigated 113 meso-eutrophic lakes in eastern China and estimated diffusive carbon gas fluxes. Our findings indicate that eutrophication tends to shift small productive lakes from being CO2 sources to sinks. However, the sampled lakes acted zonally as carbon sources due to significant CO2 emissions from larger lakes. Furthermore, CH4 emissions offset CO2 uptake, accounting for 56% of the total annual carbon efflux (in CO2-equivalents). We found that large lakes (>100 km2, comprising 23% of the total abundance) dominated the carbon emissions (92% of total efflux) due to their larger surface area and less eutrophication. Moreover, eutrophication affected the relationship between lake size and carbon emissions. Neglecting these effects may result in significant overestimation of CO2 emissions (by one order of magnitude) and underestimation of CH4 emissions (by three times). This study highlights the remarkable potential of satellite-based observations in addressing biases in lake carbon emission estimation. It emphasizes the necessity of incorporating large lakes to enhance global-scale carbon upscaling estimates.
How to cite: Duan, H., Xiao, Q., Qi, T., and Luo, J.: Eutrophication reshaped the dependence of carbon emission on lake size: More attention to global upscaling, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-9105, https://doi.org/10.5194/egusphere-egu25-9105, 2025.
Inland waters, including small lakes and ponds, play a major role in the global carbon cycle. While they typically act as organic carbon sinks, they also emit the greenhouse gases (GHGs) carbon dioxide (CO2) and methane (CH4) to the atmosphere. Nonetheless, small inland waters, defined as those with a surface area (SA) of less than 5 hectares (further referred as “ponds”), are often excluded from large-scale CO2 and CH4 budgets. To help overcome this gap, we reviewed available global datasets on inland waters and selected G1WBM, GLCF GIW, GSW, and OSM, because these datasets provide sufficient information on ponds to assess their global distribution. We further compiled a dataset of CO2 and CH4 emissions plus water chemistry data from 950 ponds worldwide from existing literature and databases. Next, we applied a Monte Carlo analysis to the estimated surface areas and CO2 and CH4 emission ranges of ponds. The results suggest that ponds with SA < 1 ha emit 0.25–0.42 Pg C yr-1, and those of 1–5 ha emit 0.18–0.45 Pg C yr-1, accounting for up to 14 and 17%, respectively, of the total carbon gas emissions from all-sized lakes and ponds worldwide. Our estimates thus further highlight the potentially disproportionate, yet poorly constrained, importance of ponds in global GHG budgets. In addition to water chemistry data, we also extracted global gridded hydrometeorological and socio-economic data matched to each HydroBASIN-delineated basin of the 950 lakes. Using Random Forest regression (RFR) models, we found that pond water pH and watershed urbanization were the most important predictors of the CO2 emissions, while electrical conductivity (EC), SA, and pond depth were the most important variables for the CH4 emissions. The RFR modeling revealed that ponds in urban areas typically exhibit elevated pH levels, probably due to the ubiquitous use of cement-based construction materials. High pH levels, in turn, suppress CO2 emissions by retaining dissolved inorganic carbon under the form of aqueous bicarbonate (HCO3-). The role of non-sulfate-derived EC in modulating the CH4 emissions is attributed to the effect of salinity on the mixing intensity and the associated impact on water column oxygenation. Overall, our findings confirm the significant role of ponds in global carbon cycling. At the same time, they suggest that site-specific characteristics, including land use and water chemistry, can induce considerable variability in GHG emissions from ponds.
How to cite: Radosavljevic, J., Shahvaran, A. R., Rezanezhad, F., Passeport, E., Slowinski, S., and Van Cappellen, P.: The Global Importance of CO2 and CH4 Emissions from Ponds: A Large-Scale Data Perspective, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-13596, https://doi.org/10.5194/egusphere-egu25-13596, 2025.
Fresh waters are known to be significant, but highly uncertain, sources of greenhouse gas (GHG) emissions to the atmosphere. In particular, lakes and ponds have been identified as hotspots of methane (CH4) emissions, with large variation across systems. One reason for this variability in estimates of emissions may be a mismatch between the scale of observation (often monthly) and how variable emissions are over relatively short timescales. Whilst studies have highlighted the importance of nutrient concentration, primary production and temperature in shaping fluxes of GHG, it is increasingly clear that physical limnology in small and shallow lakes may play a significant role. Recent research has highlighted the prevalence of temporary thermal stratification in lakes previously classified as non-stratifying lakes, i.e. smaller shallow lakes and ponds. Here we present high frequency measurements from automatic flushing chambers and a novel CH4 sensor measuring dissolved concentrations to quantify diffusive and ebullitive emissions of CH4 along with diffusive fluxes of carbon dioxide (CO2) from an 11 hectare lake, with a maximum depth of 5 m. We compare these emissions with patterns of thermal stratification, that featured partial and full mixing events, over a three-month period from mid-June to late September. This shows that diffusive emissions of both CH4 and CO2 are shaped primarily by partial and full mixing events between the GHG-rich hypolimnetic waters and the lower concentrations in the surface waters and by full mixing events. Whereas ebullition is largely a function of the extent of the duration of anoxia in the bottom waters, with large releases triggered by atmospheric pressure changes. The results show that the variable emissions found in syntheses of spatial data from multiple lakes can be found within this single lake over time. Thus, the high variability in emissions reported across lakes may be the result of infrequent sampling of temporally highly dynamic systems, rather than the systems having such variable emissions.
How to cite: Davidson, T. A., Bucak, T., Levi, E., Ladwig, R., Jørgensen, C. J., Søndergaard, M., and Christensen, J. R.: Temporary thermal stratification and mixing drive variation in CO2 and CH4 dynamics in a shallow lake, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-15534, https://doi.org/10.5194/egusphere-egu25-15534, 2025.
Lacustrine littoral zones are generally considered as carbon (C) sources towards the atmosphere because oxygen availability in sediments and dissolved organic matter stimulate bacterial respiration and carbon dioxide (CO2) emissions. On the contrary, pelagic zones can promote methane (CH4) emissions linked to anoxic conditions in sediments. These processes can be disrupted by aquatic primary production or by CH4 oxidation. In the context of climate change and anthropogenic water withdrawals, long-lasting droughts will significantly increase the exposure to the air of lake littoral zones, that likely accelerating the organic matter decomposition and C emissions. In this study, we assess net ecosystem uptake and emission from C fluxes at the scale of two natural shallow lakes (SW of France) related to hydroperiod. CO2 and CH4 fluxes were measured seasonally by terrestrial and floating chambers in the littoral zone on soils exposed to the air under different conditions (presence or absence of vegetation, sands or organic sediments, degree of water saturation) and in the pelagic zone according to the depth. Our results reveal significant variations in C fluxes along the littoral wet-dry continuum, that underlying the relevance of considering the lacustrine littoral zone for obtaining comprehensive carbon budgets, especially within climate changing scenarios.
How to cite: Mayen, J., Bartoli, M., Benelli, S., Bertrin, V., Lecchini, B., Jan, Q., and Ribaudo, C.: Carbon fluxes under the littoral wet-dry continuum of natural shallow lakes, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-2515, https://doi.org/10.5194/egusphere-egu25-2515, 2025.
China’s lakes are globally significant and have experienced widespread changes, however, how they shift their roles in CO2 emissions over time remains elusive due to a shortage of time series data. We took advantage of two national lakes surveys to calculate the CO2 partial pressure (pCO2) and quantify the CO2 emissions during two time periods (1988-1992 and 2007-2010). Lakes across China have shifted from a substantial CO2 source (2.748 Tg C yr-1) to a minor sink (-0.408 Tg C yr-1), advocated by the fact that pCO2 was halved from 709 μatm to 332 μatm. This shift was predominantly caused by increased primary production in eutrophic lakes, decreased external loadings in organic carbon-rich lakes, and expanded water volume in endorheic lakes. This nationwide CO2 source-sink transition highlighted the roles of multiple mechanisms in altering CO2 flux in lakes, calling for a comprehensive investigation of multiple environmental changes in assessing CO2 dynamics.
How to cite: Xiao, Q., Luo, J., Qi, T., and Duan, H.: China’s lakes shifted from a CO2 source to a sink over two decades, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-8448, https://doi.org/10.5194/egusphere-egu25-8448, 2025.
Eutrophic lakes are considered as an important source of methane (CH4) to the atmosphere. However, the prediction for CH4 emission from lakes with different trophic states under warming is still enigmatic. Here, we found temperature dependence of diffusive methane emissions was lower in phytoplankton-dominated zone than that in macrophyte-dominated zone in two typical shallow lakes. Furthermore, an investigation on twenty lakes from the middle and lower reaches of Yangtze River showed that diffusive CH4 flux was significantly higher in summer than that in winter, with the ecosystem-level Q10 ranged from 0.77 to 3.94 and significantly decreased with increasing phytoplankton. This indicates that eutrophication reduces temperature dependence of diffusive methane emissions in freshwater lakes. When the view extends to diffusive CH4 emission in global lakes, the estimation regarding temperature dependence as a constant in the past overestimated global methane release for 2.3%-30% under warming for 1-2 °C. This weak positive feedback of CH4 emission suggests that climate warming may have a lesser exacerbating effect on atmospheric CH4 concentrations than predicted.
How to cite: Li, B.: Eutrophication reduces temperature dependence of diffusive methane emissions in freshwater lakes, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-5579, https://doi.org/10.5194/egusphere-egu25-5579, 2025.
Greenhouse gas (GHG) emissions from freshwater ecosystems contribute significantly to global carbon budgets. However, these emissions remain poorly constrained due to limited high-frequency measurements. In this study, we tested a low-cost, high-frequency GHG measurement system in a long-running mesocosm experiment in Lemming, Denmark, over a seven-month period, focusing on CO₂ and CH₄ fluxes. We propose a methodology for calculating diffusive CH₄ fluxes using high-frequency sensor data and tested the effects of sampling interval upscaling of emissions by conducting theoretical experiments.
Our findings reveal substantial temporal variability in GHG emissions, particularly for CH₄, with ebullitive fluxes dominating with high daily variation. Pronounced diurnal fluctuations were observed for CO₂ and diffusive CH₄ fluxes, while ebullitive CH₄ emissions showed no clear diurnal pattern. Our results show that relying solely on daytime measurements leads to a significant underestimation of overall CO₂ fluxes, whereas daytime measurements of diffusive CH₄ fluxes significantly overestimate the total flux.
The results of the theoretical sampling interval experiments emphasize that infrequent sampling can introduce substantial uncertainty and lead to an underestimation of total emissions, particularly for ebullitive CH₄ fluxes. Simulated experiments demonstrated that increasing the sampling interval from daily to monthly markedly increased uncertainty, whereas weekly sampling intervals better captured overall GHG flux patterns and reduced the uncertainty compared to less frequent sampling.
Our results highlight the importance of high-frequency GHG measurements in capturing both diurnal and seasonal variations, improving the accuracy of flux estimates, and reducing uncertainties in upscaling emissions to broader scale. Therefore, we emphasize the critical importance of optimizing sampling intervals and incorporating diurnal cycle measurements to enhance the accuracy and reliability of upscaled GHG measurements. Further development and application of low-cost, high-frequency sensor systems are critical to enhance the temporal and spatial coverage of freshwater GHG emissions and support future research in mitigating climate impacts from freshwater ecosystems.
How to cite: Bucak, T., Levi, E. E., Ladwig, R., and Davidson, T. A.: How Important is Sampling Frequency? Exploring Temporal Dynamics of GHG Emissions Using Low-Cost Sensors in Lake Mesocosms , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-12836, https://doi.org/10.5194/egusphere-egu25-12836, 2025.
Lakes are significant sources of the greenhouse gas methane (CH₄) to the atmosphere, with littoral zones recognized as hotspots for CH₄ emissions. However, the specific pathways driving the enrichment of CH₄ in the littoral zones of lakes remain poorly understood, contributing to uncertainties in global lake CH₄ budgets. To address this gap, our study investigates the role of littoral sediments as the main source of dissolved CH₄ in lakes and the drivers behind the high yet variable CH₄ concentrations in the water column along the different seasons. We specifically focus on the impact of temperature fluctuations on methanogenic rates in sediments over different seasons.
The CH₄ dynamics in lake sediments exhibit significant spatial variability driven by differences in sediment properties. In this study, we aimed to explain the seasonal variability of dissolved CH₄ concentrations in the water column by linking them to sediment fluxes, which are driven by methanogenic activity within the sediments. To achieve this, we conducted seasonal field campaigns in Lake Constance, Germany, during 2024 and complemented them with data obtained ten years ago. We measured sediment-to-water CH₄ fluxes, dissolved CH₄ concentrations in water and sediments, and potential methanogenesis rates under varying temperature conditions in sediment cores from diverse littoral sites. Stable isotope analysis of CH₄ and CO₂ provided further insights into the origin and fate of methane from the sediments into the water column.
Our findings reveal that CH₄ cycling varies spatially across sites and among seasons, as expected, yet long-term trends remain relatively stable over several years despite short-term seasonal fluctuations. Methanogenic rates represent a good proxy for explaining the spatial heterogeneity of CH₄ dynamics in the littoral zone and remain as the main source of littoral dissolved CH4. These results highlight the importance of site-specific and seasonal variations in regulating CH₄ cycling in Lake Constance, providing valuable insights into the drivers of CH₄ dynamics in lake littoral zones.
How to cite: Kiefel, K. J., Sepulveda Jauregui, A., Peeters, F., Ropella, L. L., Hofmann, H., and Martinez Cruz, K.: Methanogenic Rates in Sediments Explain Long-Term Trends on Spatial and Seasonal Variation of CH4 Cycling in the Littoral Zone of Lake Constance, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-2719, https://doi.org/10.5194/egusphere-egu25-2719, 2025.
Aquaculture in floating cages has rapidly expanded in African lakes, driven by economic development and the need to increase fish production. However, this development has raised concerns about environmental impacts, including potential alterations of the benthic processes that could contribute to increased greenhouse gas emissions from cage culture sites which have not been measured so far. This study examined methane concentrations and fluxes from tilapia cage farming in Lakes Muhazi and Kivu, currently some of the major sites for cage aquaculture development in African lakes. In Lake Kivu, methane fluxes (FCH4-C) varied between 0 - 45.6 mg/m2/h in sites with cages, and 0 - 5.1 mg/m2/h in sites without cages. In Lake Muhazi, the FCH4-C varied between 0 - 67.6 mg/m2/h in sites with cages, and 0 - 7.7 mg/m2/h in sites without cages. Methane fluxes generally were higher in the shallow Lake Muhazi than in the deep Lake Kivu. Cage farms in bays exhibited higher fluxes than the cages located on open water. These findings suggest a contribution of cage aquaculture to methane fluxes in lakes, especially in shallow and enclosed areas. Understanding the dynamics of methane fluxes in response to aquaculture practices is essential for developing strategies for sustainable aquaculture that balance fish production in cages with environmental conservation.
How to cite: Tuyisenge, J., van Dam, A., Irvine, K., and Gettel, G.: Response of methane gas fluxes to cage aquaculture in African lakes-Kivu and Muhazi, Rwanda, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-17543, https://doi.org/10.5194/egusphere-egu25-17543, 2025.
Lakes play a significant role in the global carbon cycle by transforming, burying, emitting, and transporting carbon from terrestrial ecosystems to the ocean. Carbon is emitted primarily as carbon dioxide (CO₂) and methane (CH₄), both potent greenhouse gases (GHGs), but it can be difficult to determine whether lakes are net sources or sinks of those GHGs. Alpine lakes, which are sentinel systems experiencing rapid and severe climate change-related impacts, are especially challenging. Anthropogenic activities such as fishing or intensive pasture might additionally impact their C balance forcing them into net C sources to the atmosphere. Restoring those lakes might lead not just to recover their threatened biodiversity, but also their GHG balance, constituting a great mitigation strategy. Here we aim to test the potential of ongoing restoration efforts based on the recuperation of biodiversity for reducing C gas emissions in alpine lakes.
To do so, we focused on two alpine lakes in the Pyrenees, as representative examples of broader trends in mountain lake ecosystems. Lake Tres Estanys de Baix (TEB) has been suffering a eutrophication process due to the introduction of invasive fish species in the past. Conversely, Naorte has undergone ecological restoration, with the near-total removal of invasive fish through two European LIFE projects. In 2023, sensor-equipped platforms were installed in both lakes to continuously gather data on weather, oxygen (O₂), and CO₂ at depths of 2 and 8 meters. To obtain additional information on nutrients and carbon concentrations and the quality of dissolved organic matter (DOM), weekly manual samples were taken. The restored lake, Naorte, demonstrated remarkable recovery, with significantly improved water clarity and reduced emissions of CO₂ and CH₄ compared to the impacted lake, TEB. In TEB, DOM was more colored, and concentrations of dissolved organic carbon and nitrogen were higher. This lake also exhibited signs of nutrient imbalance, with lower levels of inorganic nitrogen species, further showing a disrupted metabolism. The carbon gas balance based on coupled O2 and CO2 measurements, revealed a striking contrast: TEB functioned as a net carbon source, actively emitting GHGs, whereas Naorte acted as a net carbon sink, sequestering more carbon than it released. These findings validate our initial hypothesis that removing invasive species can restore alpine lake’s natural ability to act as carbon sinks by significantly reducing its GHGs emissions.
Beyond in-lake measurements, atmospheric CO₂ sensors were deployed in the surrounding basins to capture broader carbon dynamics. The data collected was made available online in real-time allowing for immediate access and integration into educational resources, bringing the project’s findings directly to local communities. Approximately 300 students and teachers from rural schools in the Pyrenees participated in an outreach program, engaging with the data and exploring its implications. This initiative highlighted the transformative potential of ecological restoration not only to mitigate greenhouse gas emissions but also to recover mountain ecosystems. By involving young minds in understanding and addressing these environmental challenges, we aim to inspire a new generation to contribute to a sustainable and resilient socio-ecological future.
How to cite: Catalán, N., Pastor, A., Comas, A., Olid, C., Burgada, N., Gandois, L., Ventura, M., Buchaca, T., Gacia, E., and Lupon, A.: Mitigation through restoration: reducing carbon gas emissions in alpine lakes, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-12503, https://doi.org/10.5194/egusphere-egu25-12503, 2025.
Saline lakes are experiencing significant changes in salinity and organic matter content due to climate change. However, the specific impacts of these environmental changes on the production processes of nitrous oxide (N₂O)—particularly nitrification and denitrification—in saline lake sediments are still poorly understood, leading to significant uncertainty in current estimates of greenhouse gas (GHG) emission from these ecosystems. To address this gap, the present study used the isotope pair labelling technique to quantitatively assess the effects of climate-induced changes in environmental variables such as salinity and organic matter and their combined influence on N₂O production rates and production pathways from lake surface sediments. The results showed that saline lake sediments act as hotspots for N₂O production, with nitrification making a significant, although previously underestimated, contribution to the total N₂O flux; Salinity was found to limit N₂O production through both nitrifying and denitrifying processes in lake sediments, although dissolved organic carbon (DOC) in the sediment could mitigate the limitation caused by salt. In low-salinity lakes (salinity < 35 g/L), N₂O production, which mainly comes from denitrification, was significantly suppressed by salinity increase due to the increased sensitivity of denitrifying microbes to salinity change. Conversely, in high-salinity lakes (salinity > 35 g/L), where salinity stress remained pronounced, an increase in DOC appeared to play a crucial role in increasing N₂O production by triggering both denitrification and heterotrophic nitrification processes. Consequently, future investigations on GHG emissions from lakes should prioritize the evolving environmental dynamics driven by climate change and provide new insights and a solid scientific basis for predicting and managing future changes in these critical ecosystems.
Key words: N₂O production pathways, saline lakes, climate change, salinity, dissolved organic carbon.
How to cite: Sun, X. and Wang, B.: Antagonistic effect of changing salinity and dissolved organic carbon on N₂O production via different pathways in saline lakes, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-14939, https://doi.org/10.5194/egusphere-egu25-14939, 2025.
Methane is transported from wetlands by a variety of physical processes through a variety of pathways: ebullition (the formation of bubbles that rise to the surface), flushing (advection by pore water flowing into streams), and diffusion (both into plant roots and out through the surface). We have formulated a theory that couples ebullition, diffusion, and flushing, and predicts how the competition between these processes leads to different porewater concentrations of dissolved gases and their isotopes. We apply the theory to explain why ebullition creates much higher concentrations of carbon dioxide and much different ratios of carbon-13 in both methane and carbon dioxide and then we use these results to explain the oberserved differences in carbon dioxide and methane concentrations and their isotope ratios between northern and southern wetlands. Implications of the theory also include: (1) Carbon isotope ratios in methane and carbon dioxide depend not only on the fractionation factor in methanogenesis but also on the magnitude of ebullition relative to advection. (2) Counterintuitively, higher methane concentrations in pore water occur at lower rates of methanogenesis, for all else held constant. (3) Pore water gas concentrations can be used to infer historical rates of ebullition.
How to cite: Harvey, C. F. and Hoyt, A.: Methane fluxes from wetlands: Competition between Ebullition, Advection, and Diffusion, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-13995, https://doi.org/10.5194/egusphere-egu25-13995, 2025.
We intoduce the development of a new wetland-focused version of the Energy’s Exascale Earth System Model (E3SM) Land-surface Model (ELM). The updated version, ELM-Wet, activates a separate wet-landunit for simulation of wetlands. This Wet-landunit handles multiple eco-hydrological functional type patches. We introduced wetland-specific hydrology through prescribing site-level (whole wetland) constraints on surface water elevation and including a patch-level characteristic maximal inundation depth that enables resolving different sustained inundation depth for different patches, and if data exists, prescribing inundation depth at the site and patch levels. We modified the calculation of methane transport through palnt aerenchyma based on observed conductance for different vegetation types. We use BOA, a new Bayesian Optimization toolpack, to parameterize the processes controlling CO2 and CH4 fluxes in the wetland landunit. Site-level simulations of a coastal freshwater wetland in Louisiana (US-LA2) were performed with the updated model. Eddy covariance observations of CO2 and CH4 fluxes from 2012-2013 were used to train the model. Flux data from 2021 were used for validation. Patch-specific chamber flux observations and observations of CH4 concentration profiles in the soil porewater from 2021 were used for evaluation of the model performance in terms of soil concentration profiles at the patch level. Our results show that ELM-Wet with BOA optimization was able torepresent inter-daily and seasonal CO2 and CH4 fluxes and concentration dynamics across the wetland’s eco-hydrological patches.
How to cite: Bohrer, G., Yazbeck, T., Missik, J., Villa, J., Scyphers, M., Bordelon, R., Taj, D., Shchehlov, O., Ju, Y., Wrighton, K., Ward, E., Zhu, Q., Oh, H., Sulman, B., and Riley, W.: ELM-Wet: A new wet-landunit patch-level approach for modeling carbon and methane fluxes from wetlands, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-1353, https://doi.org/10.5194/egusphere-egu25-1353, 2025.
Treatment wetlands are recognized as multifunctional ecosystems capable of treating agricultural runoffs. Yet, while their nutrient removal efficiency can be high, it also comes with elevated emissions of greenhouse gases (GHGs), most importantly methane (CH4). Dense vegetation and availability of nutrients can make these water treatment systems into landscape-scale CH4 hotspots. Therefore, wetland management practices need to be developed to sustain nutrient removal efficiency while also reducing GHG emissions. Typha-dominated wetlands can modulate microbial processes and plant-mediated fluxes of CH4. However, understanding these emission patterns requires capturing seasonal trends and diurnal fluctuations. This study investigated CH4 flux variations and environmental parameters in a Typha-constructed wetland treating agricultural runoff from late spring (May 2024) to the end of the growing season (October 2024). The closed chambers (both opaque and transparent) were used with a LI-7810 trace gas analyzer (LICOR Biosciences). Biweekly measurements of CH4 and CO2 fluxes were made at five vegetated sampling spots and five non-vegetated sampling spots. During each sampling occasion, other parameters such as water temperature, pH, dissolved oxygen, oxidation-reduction potential, turbidity, conductivity, leaf area index (LAI), and water depth were measured using portable devices. To examine diurnal variability, three intensive 24-hour sampling campaigns were conducted on June 15, July 22, and August 18. During each of these campaigns, GHG fluxes, and the environmental parameters were measured hourly. The results showed that CH4 fluxes varied considerably across the five vegetated sampling points over the study period, ranging from 105 μg CH4-C m⁻² h⁻¹ to over 30,000 μg CH4-C m⁻² h⁻¹ while the non-vegetated sampling points peaked above 50,000 μg CH4-C m⁻² h⁻¹. However, a distinct diurnal pattern for CO2 and CH4 was observed. CO2 uptake peaked around mid-day, reaching above -700 CO2-C m-2 h-1driven primarily by photosynthetic activity influenced by photosynthetically active radiation (PAR), while CH4 fluxes varied with peak fluxes reaching above 10,000 μg CH4-C m⁻² h⁻¹ observed mostly in the evening (e.g., 4–5 pm and 6–7 pm), clearly driven by elevated temperature. Our studies show how plant growth, microbial activity, and environmental factors interact to regulate greenhouse gas fluxes in treatment wetlands. Understanding seasonal and daily variations is important for monitoring greenhouse gas fluxes and improving wetland management practices.
How to cite: Okiti, I., Tamm, I., Yildiz, K., Sarjas, J., Saarepuu, K. M., Pindus, M., and Kasak, K.: Seasonal and diurnal dynamics of methane fluxes in Typha-dominated wetland treating diffuse agricultural pollution, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-15113, https://doi.org/10.5194/egusphere-egu25-15113, 2025.
Measuring reliable greenhouse gases (GHGs) fluxes at the interface between water bodies and the atmosphere in inland waters is crucial in the context of climate change but remains highly challenging. GHG fluxes can be measured directly in-situ with chambers placed at the water-atmosphere interface and connected to portable gas analysers providing high-frequency timeseries of GHGs partial pressures inside the chamber. Fluxes are usually assumed constant over the time of incubation, but varying GHG sources and changing environmental conditions and/or ebullition from the sediment produce non-linear patterns and breakpoints in the timeseries, not mentioning the possibility for poor manipulation of the device, disturbance of the sampling site by the operator, or malfunctioning sensors. Accordingly, it is common procedure to visualize and select part of the measurements manually for each incubation before proceeding with fluxes computation. In the ongoing Horizon Europe project RESTORE4Cs, we have performed CO2 and CH4 chamber measurements in 36 different sites located in 6 major coastal wetlands across Europe, including intertidal saltmarshes and seagrass beds, freshwater and brackish ponds and marshes, and coastal lagoons. Between October 2023 and August 2024, we have gathered a database of 822 floating chamber incubations, collected by multiple operators and with 3 different gas analysers.
Here we focus on the data processing part and assess to what extent we need expert evaluation of the time series to produce reliable flux estimates. We have developed an automated data processing script able to compute fluxes estimates for all incubations. Timeseries are fitted with both a linear and non-linear models. The script identifies potential bubbling in CH4 measurements and estimates the diffusive versus ebullitive components based on the statistical characteristics of the first derivative of pCH4. All incubations were manually inspected by 16 members of our team, all experts in GHG chamber measurements with various levels of experience. About half of these timeseries were inspected independently by at least 3 experts, enabling to compare if and why experts disagree.
For both CO2 and CH4, non-linear fitting performed better than linear models for 69% incubations, indicating a substantial number of non-linear patterns in the dataset; however, the difference between the two models was less than 10% for 86% of the incubations. The ebullition pathway was the dominant CH4 flux in less than 10% of the incubations. Experts disagreed substantially on the data selection in 34% of the incubations, which produced uncertainties in flux estimates larger than 10% of the inter-expert flux average. The highest discrepancies were related to suspicious or non-linear features in the time series. To avoid subjectivity and ensure robustness and repeatability of flux estimates, we present guidelines on how CO2 and CH4 incubation time series should be processed, regardless of whether they are processed automatically or after an expert manual inspection.
How to cite: Minaudo, C., Attermeyer, K., Cabrera Brufau , M., Camacho Santamans, A., Camacho, A., Cazacu, C., Constantin Giuca, R., Misteli, B., Montes Perez, J., Morant, D., Obrador, B., Oliveira, B., Petkuvienė , J., Picazo, A., Rochera, C., and von Schiller, D.: Automated versus expert processing of in situ CO2 and CH4 chamber measurements in complex and heterogeneous aquatic ecosystems , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-17722, https://doi.org/10.5194/egusphere-egu25-17722, 2025.
Methane (CH4), even though orders of magnitude less abundant than carbon dioxide (CO2) in the atmosphere, is today recognized as one of the most powerful greenhouse gases, being an even stronger absorber of Earth’s emitted thermal infrared radiation than CO2. Atmospheric CH4 concentrations are now more than 2.6 times above estimated pre-industrial equilibrium levels and such an increase is largely the result of anthropogenic emissions related to human activities. In order to verify potential emission reductions linked to the adoption of effective climate change mitigation strategies, a precise quantification of the global CH4 budget is actually needed. According to the most recent modelling, these calculations are still subject to considerable uncertainties, the most important of which is due to the potential ocean natural emissions. In particular, the global marine CH4 flux appears to be mainly driven by shallow marine coastal environments (depth <50 m), where gas released from the seafloor could escape to the atmosphere before oxidation. However, due to limited and sparse data, there are large uncertainties in quantifying the actual contribution of coastal areas to atmospheric CH4.
The MEFISTO project, combining classical physical, chemical, and molecular methods with innovative hydroacoustic approaches, aims to help close this knowledge gap by investigating the forcings favouring or preventing the release of CH4 in the atmosphere from two Italian shallow coastal areas: a seepage zone located off the Marano and Grado lagoon (Gulf of Trieste, Northern Adriatic Sea - NAd), characterised by the intermittent release of microbial gases, and the persistently degassing hydrothermal vent area off the Panarea Island (Aeolian Archipelago, Southern Tyrrhenian Sea). Preliminary data collected during seasonal sampling campaigns revealed large differences in terms of gas composition and flux intensity between the two study sites. In particular, very low gas fluxes (1.1 x 10-4 L/h) were detected in the NAd site, where seafloor depth varies between 14 and 21 meters below sea level (mbsl) and seeping gases are mainly composed of CH4. Conversely, remarkably variable fluxes, ranging from 1.0 x 10-1 to 2.2 x 103 L/h, were observed in the Panarea site, where seafloor depth varies between 8 and 21 mbsl but leaking gases have an extremely high CO2 content (about 98%). Our preliminary results suggest that neither the microbial nor the hydrothermal CH4 is released into the atmosphere in the respective study areas. Low CH4 fluxes combined with high hydrostatic loads and temperature seems to act as controlling factors in both sites, while tides appear to play a key role in particular in the NAd site. However, as methanotrophic bacteria can act as "methane filters" along the water column, ongoing metagenomic analyses on different environmental matrices will help us to assess the presence of these microorganisms, providing useful information about their role in regulating the CH4 fluxes. This in turn will help to achieve the MEFISTO project’s goal of elucidating the complex interplay between physical and biological forcings that favour or prevent the release of CH4 into the atmosphere from such environments.
How to cite: Bazzaro, M., Caruso, C. G., De Vittor, C., De Rosa, G., Esposito, V., Graziano, M., Fonti, V., Iacuzzo, F., Laudicella, V. A., Longo, M., Morici, S., and Lazzaro, G.: Hydrothermal versus microbial methane degassing pathways: case studies from two Italian shallow coastal systems, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-10882, https://doi.org/10.5194/egusphere-egu25-10882, 2025.
Shallow coastal waters play a crucial role in the global carbon cycle through the sea-air exchange of greenhouse gases such as carbon dioxide (CO2) and methane (CH4). These regions are hotspots for both sequestration and emission of these gases; however, their contributions to global and regional budgets remain poorly quantified. Understanding the spatial and temporal variability of CO2 and CH4 exchange in coastal waters is essential for refining our knowledge of the climate system, especially as these systems face increasing anthropogenic pressures that may significantly alter their gas dynamics. Here, we present findings on CO2 and CH4 fluxes from seven shallow (<6 m) sampling locations in the Stockholm archipelago, Baltic Sea. These locations represent four distinct habitat groups – macroalgae on pebbles/bedrock, sand, macrophyte communities, and reed beds – and were monitored across a full annual cycle using the floating chamber method. In the summer months, most habitats acted as CO2 sinks, with the highest uptake recorded in the pebbles/bedrock habitat in July (-937 ± 161 mg m-2 d-1). During autumn and winter, however, all habitats shifted to CO2 emission, peaking in the reed beds in October with an efflux of 1757 ± 328 mg m-2 d-1. Annually, five of the seven locations exhibited net CO2 emissions. Further, all habitats were year-round sources of CH4, with average monthly diffusive emissions ranging from 0.1 ± 0.01 mg m-2 d-1 to 26 ± 1.5 mg m-2 d-1. The fluxes generally followed a seasonal pattern, with higher emissions in summer and lower emissions in winter. Ebullition fluxes were observed in all habitats except the pebbles/bedrock, with monthly fluxes reaching up to 249 mg m-2 d-1 and contributing between 20 and 98% of the total annual CH4 flux in the locations where it occurred. Upscaling the CO2 and CH4 fluxes over waters < 6 m in the Stockholm archipelago (680 km2) rendered CO2-equivalent fluxes for a 100-year timescale ranging between -0.04 and 0.3 Tg CO2-eq yr-1, where 80% of the uncertainty from flux variability could be attributed to CH4. These findings suggest that CH4 plays a much larger role in the sea-air exchange of carbon-based greenhouse gases than previously estimated in northern, temperate coastal waters.
How to cite: Bisander, T., Prytherch, J., and Brüchert, V.: Mapping of carbon dioxide and methane sea-air fluxes in coastal, shallow waters of the Stockholm archipelago, Baltic Sea, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-8378, https://doi.org/10.5194/egusphere-egu25-8378, 2025.
Seagrass meadows are critical components of coastal ecosystems, playing a significant role in the global carbon cycle. These "Blue Carbon Ecosystems" (BCEs) are highly effective natural carbon sinks because they are highly productive, trap allochthonous carbon, and can store sequestered carbon for centuries to millennia in the sediment. Hence, they contribute to the long-term removal of atmospheric CO2 and prevent the remineralization of buried carbon via methanogenesis, thereby supporting climate regulation. This study evaluates the recovery of ecosystem services, specifically greenhouse gas (GHG) flux regulation, in a Zostera marina seagrass meadow that has undergone phased restoration since 2015.
By assessing the fluxes of methane (CH4) and carbon dioxide (CO2) across different restoration stages using a LICOR 7810 and an incubator chamber, we explore how the meadow's GHG emissions and carbon sequestration capacity change over time as the ecosystem recovers. Our findings show that, after 9 years of restoration, CH4 emissions decreased by 1.11-fold and CO2 net sequestration increased by 1.23-fold compared to the eroded meadow. While CO2 fluxes in the older restored meadow are 1.33 times higher than those in the original meadow, CH4 fluxes are 3 times higher, indicating a greater challenge in restoring ecosystem services related to methane flux. Despite this, GHG fluxes, especially methane emissions, decrease over time, suggesting that restored meadows are gradually recovering their capacity as carbon sinks. This study highlights the potential of phased restoration to enhance carbon sequestration and support long-term climate mitigation efforts.
How to cite: Máñez-Crespo, J., Marbà, N., Ferias-Rodríguez, Á., Infantes, E., and Hendriks, I.: Evaluating the Recovery of Ecosystem Services in a Restored Seagrass Meadow: Greenhouse Gas Fluxes and Climate Mitigation Potential , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-21913, https://doi.org/10.5194/egusphere-egu25-21913, 2025.
Posters on site: Wed, 30 Apr, 16:15–18:00 | Hall X1
Due to complexity, inland water carbon (C) cycling processes have a significant impact on the C source-sink status of terrestrial ecosystems over short-term (days, months, and years), long-term (decades, centuries, and millennia), and geological timescales. This has a determining effect on the C source-sink stability status of inland waterbodies. In such waterbodies, stable C source-sink processes primarily include terrestrial biosphere production, lithospheric organic carbon (OC) oxidization, rock weathering, and riverine C transport. Conversely, metabolic C processes have an unstable effect on the C source-sink status of inland waterbodies. Moreover, these inland water processes may cause significant C sink underestimations, which relevant studies have largely ignored. A new means to account for this “missing C” in inland waterbodies is an in-depth understanding of the metabolic C processes and associated driving effects of biological regulation mechanisms on the C source-sink status. This new approach can help us to more accurately quantify the global ecosystem C budget. The purpose of this study is threefold: (i) to clarify metabolic C processes and associated biological regulation mechanisms in inland waterbodies; (ii) to systematically analyze C cycling processes and associated C source-sink effects in inland waterbodies; (iii) to reveal driving mechanisms of metabolic C processes on C source-sink stability in inland waterbodies. This will allow us to gain a better understanding into how to more accurately calibrate C source-sink functions globally. It will also provide an in-depth understanding of the role that terrestrial ecosystems play in C neutralization under global climate change.
How to cite: Gao, Y., Wang, M., and Sun, K.: Metabolic inland water carbon cycling processes and associated biological regulation mechanisms that drive shifts in unstable carbon sources and sinks, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-1989, https://doi.org/10.5194/egusphere-egu25-1989, 2025.
Catchment land-use has multiple impacts on streams affecting water quality, organic matter quantity and microbial community structure and function, which are key drivers of biogeochemical cycling and greenhouse gas fluxes. While previous studies have examined effects of land-use on stream greenhouse gas emissions, few have considered these together with microbial community structure and function or the connectivity between streams, their sediments and nearby riparian zones. Here, we examined microbial communities, dissolved organic carbon quantity and quality, and nutrient concentrations as drivers of greenhouse gas fluxes in headwater streams. We investigated potential greenhouse gas fluxes from streambed sediments and adjacent riparian zone sediments, as well as in-situ, surface water greenhouse gas concentrations, in 16 headwater streams across a land use gradient (categorised by percent agriculture, residential, industrial, and human development) in Massachusetts, USA. We found that riparian and streambed sediments at paired locations had different responses to land-use and that different greenhouse gases had different responses to land-use diversity. This work underscores the importance of combining microbial and biogeochemical measurements, especially in highly connected and complex systems that experience human-driven impacts across scales, to further understanding of whole corridor greenhouse gas fluxes.
How to cite: Comer-Warner, S., Wollheim, W., and Bulseco, A.: Drivers of stream-microbial cycling and greenhouse gas dynamics across a land-use gradient, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-7104, https://doi.org/10.5194/egusphere-egu25-7104, 2025.
Rivers are important sources of the carbon dioxide (CO2) released into the atmosphere; however, research on CO2 fluxes from riverine headwater regions is sparse, particularly from rivers from in the Tibetan Plateau (TP) region, which has large glaciers and permafrost. We conducted a three-year (2020–2022) observational study of CO2 fluxes from the riverine headwater region of the Qilian Mountains (QLMs) to determine diurnal and seasonal CO2 variations and fluxes. Our results revealed that the annual average CO2 emission was 0.45 (0.03–1.60) kg m–2 yr–1, with the highest fluxes observed in winter [0.87 (0.08–2.67) μmol m–2 s–1], which was approximately three times higher than fluxes in other seasons. Glacier meltwater altered the diurnal pattern of riverine CO2 fluxes by diluting CO2 and dissolved inorganic carbon. Meanwhile, CO2 release from rivers in the permafrost region was dictated by river order, with a linear decrease as river order increased. Considering diurnal and seasonal variations, the total CO2 fluxes from the headwater regions of the QLMs were approximately 39.57 (30.04–50.21) Gg C yr–1, representing 76% of the pre-calibration fluxes. This study provides essential insights into CO2 release from headwaters, which have substantial implications for understanding CO2 outgassing.
How to cite: Shang, X.: Riverine Carbon Dioxide Release in the Headwater Region of the Qilian Mountains, Northern China, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-1795, https://doi.org/10.5194/egusphere-egu25-1795, 2025.
Methane (CH4) emissions from permafrost catchments represent a critical component of climate feedback mechanisms. Therefore, understanding spatiotemporal dynamics and drivers of CH4 emissions from rapidly changing permafrost regions is critical for improving our understanding of these changes. However, flux calculations must rely on methods which precisely and flexibly account for non-linear gas concentration increases when using a floating chamber system. Exponential concentration increase, convex increases, and/or step changes from ebullition occur frequently in CH4 concentrations collected using floating chambers. This study introduces a flexible alternative to the available methods for isolating non-linear concentration increases by using the results of gradient boosting models and general additive models to calculate flux via an interactive algorithm. We used the algorithm to calculate CH4 fluxes for 707 floating chamber measurements collected from a surface water in a permafrost catchment between May and August and over two field seasons on Disko Island, Greenland. Resulting flux calculations were visualized as heatmaps overlaid on an orthomosaic of the catchment area, revealing significant spatial and temporal patterns in CH4 emission hotspots. Approximately 94% of CH4 emissions were attributed to diffusive processes while the remaining 6% were attributed to processes resulting from ebullition. Because ebullitive events were statistically unpredictable, we report here on diffusive CH4 emissions, which had a median of 0.0002 mg/m2/s-1 and showed seasonal variability, ranging between -0.0001 and 0.02 mg/m2/s-1, with highest emissions occurring during the thaw period and in the height of growing season. The highest uptake levels were outliers detected atop snow in 2024, but overall, there was not significant uptake across surface water. Streams connected to the lake emitted significantly higher rates of CH4 throughout the season as compared to the surface of the lake. Gradient boosting machine results suggest emission hotspots were partially dependent on shifting environmental conditions where fluxes during the thaw season were controlled by variability in rainfall, wind direction, increasing air and soil temperatures, and high soil moisture content in the active layer (i.e., increasing surface water levels). Climatological and hydrogeological controls progressively gave way to biogeochemical controls as the system began to warm, oxidize, and utilize the 24-hour Arctic sunlight and the accumulated dissolved organic matter from the thaw period. Overall, this study provides insight into the seasonal dynamics shaping CH4 emissions in a dynamic permafrost catchment.
How to cite: Thayne, M., Kemper, K., Wille, C., and Sachs, T.: Decoding Spatiotemporal Methane Emissions in Permafrost Catchments: A Machine Learning Approach, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-8709, https://doi.org/10.5194/egusphere-egu25-8709, 2025.
Agricultural ditches are pervasive in agricultural areas and are potential greenhouse gas (GHG) hotspots, since they directly receive abundant nutrients from neighboring farmlands. However, few studies measure GHG concentrations or fluxes in this particular waterbody, likely resulting in underestimations of GHG emissions from agricultural regions. Here we conducted seasonal field studies to investigate the GHG concentrations and fluxes from agricultural ditch systems in the North China Plain. The results showed that almost all the ditches were large GHG sources, and their concentration were higher than that in the rivers connecting to the ditch systems. Nutrient input was the primary driver stimulating GHG production and emissions, resulting in GHG concentrations and fluxes increasing from rivers to collector ditches as the ditch systems approached farmlands and potentially received more nutrients. Overall, this study demonstrated that agricultural ditches were hotspots of GHG emissions, and future GHG estimations should incorporate this ubiquitous but underrepresented waterbody.
How to cite: Yan, Z. and Ge, Z.: Greenhouse Gas Emissions from Agricultural Ditches in the North China Plain, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-1516, https://doi.org/10.5194/egusphere-egu25-1516, 2025.
Advancing our understanding on physical and biogeochemical processes controlling turbulent exchange of energy, carbon dioxide (CO2), methane (CH4) and other trace gases across lacustrine systems is crucial in order to improve climate and weather forecast models. Lakes are capable of processing large amounts of organic carbon of terrestrial origin, and their importance in landscape carbon cycle and climate change issues is well recognized. Nevertheless, the amount of CO2 and CH4 released into the atmosphere is still uncertain.
Here, we investigate the temporal dynamics of CO2 and CH4 exchange using eleven years (for CO2) and three years (for CH4) of eddy covariance flux measurements over the Lake Kuivajärvi, a small boreal lake in southern Finland.
The lake ecosystem acted mostly as a net CO2 source (0.42±1.56 mmol m-2 s-1) throughout the ice-free periods and had a relatively high interannual variability when compared to the surrounding forests and wetlands. On average, the lake is a net source of CH4 (0.63±2.44 nmol m-2 s-1), but the measured annual emissions are lower than for CO2, revealing thatmost of the CH4 produced at the lake bottom is oxidized in the water column. Carbon dioxide and methane emissions are largely affected by the weather forcing through the effects of wind shear and nocturnal water cooling, which deepens the mixed layer and enhances gas exchange at the air-water interface.
How to cite: Mammarella, I., Ala-Könni, J., Fregona, M., Heiskanen, J., Kohonen, K.-M., Laasonen, A., Li, X., MacIntyre, S., Ojala, A., Vähä, A., and Vesala, T.: Long term flux measurements of carbon dioxide and methane over a small boreal lake using eddy covariance technique, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-10179, https://doi.org/10.5194/egusphere-egu25-10179, 2025.
Aquatic vegetation (AV), as vital primary producers and carbon sinks in lakes, is crucial for lake ecosystem health, with submerged aquatic vegetation (SAV) and floating/emergent aquatic vegetation (FEAV) representing distinct states. However, global dynamics of SAV and FEAV are poorly understood due to data scarcity. We developed an innovative AV mapping algorithm using 1.4 million Landsat images from 1989 to 2021, creating a global database of 5587 lakes. On average, AV covers 108,186 km2 globally (FEAV: 15.8%, SAV: 13.1%). Over two decades, SAV decreased by 30.4% while FEAV increased by 15.6%, indicating a significant net loss of AV. This shift suggests a move towards shaded and turbid conditions, driven primarily by human-induced eutrophication until the early 2010s, with global warming likely playing a role thereafter. These trends signal deteriorating lake health globally.
How to cite: Luo, J., Xu, Y., Xiao, Q., Zhang, C., and Duan, H.: Satellite remote sensing reveals rapid loss of submerged aquatic vegetation in global lakes, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-9431, https://doi.org/10.5194/egusphere-egu25-9431, 2025.
Methane (CH4) and nitrous oxide (N2O) are potent greenhouse gases (GHGs) and are involved in ozone depletion. They are the second and third most significant GHGs contributing to climate change, with global warming potentials approximately 25 times and 300 times greater than CO2. The contribution of freshwater lakes to CH4 and N2O emissions remains debatable. Oxygen-rich subsurface waters are recognized as hotspots of metalimnetic CH4 flux, while oxygen-driven diffusion in deep water columns is expected to enhance hypolimnetic N2O production in deep freshwater lakes. Therefore, understanding the seasonal dynamics of water-column CH4 and N2O in freshwater ecosystems is crucial for predicting their impact on future climate projections. Traditionally, both GHG gases have been thought to be primarily produced in sediments, with higher emissions occurring during the mixing events. However, the seasonal dynamics and characteristics of both water-column gases, including production in the water column which may contribute to atmospheric emissions, are often overlooked. Here, we hypothesize that both metalimnetic CH4 and hypolimnetic N2O might be present and emitted from deep lakes year-round. We will present our preliminary measurements of seasonal variations in CH4 and N2O concentrations in the deep Swiss alpine Lake Geneva. They relied on laser spectrometric probes called SubOcean, allowing in-situ and real-time observations of CH4 and N2O along the water column, with a remarkable depth resolution.
How to cite: Khatun, S., Grilli, R., Lavanchy, S. M., Jézéquel, D., Schubert, C. J., Perga, M.-E., and Chappellaz, J.: Insights into seasonal dynamics of metalimnetic methane and hypolimnetic nitrous oxide in a deep Swiss alpine lake , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-15932, https://doi.org/10.5194/egusphere-egu25-15932, 2025.
Climate warming is stronger in the northern high latitudes than the global average, making ecosystems in the region prone to change with future warming. Approximately 50% of all lakes are located north of 60°N, and lake area is projected to increase from permafrost thaw and meltwater from glaciers, making lakes increasingly important parts of the terrestrial ecosystem carbon budget. We currently lack a process understanding of variations in CO2 and CH4 fluxes from high latitude lakes. Lakes are also a source of biogenic volatile organic compounds (BVOCs), and these reactive compounds influence atmospheric oxidation and contribute to aerosol formation. However, to the best of our knowledge, almost no flux measurements of BVOCs have been conducted on lakes and no measurements have been conducted in high latitude lakes, leaving this area largely unexplored but with growing interest due to expanding lake areas in this pristine environment.
This field study aims to quantify the magnitude, composition and variation in emission of CO2, CH4 and BVOCs from two small thermokarst lakes at different ages and a riverine lake, all located in subarctic Sweden. Data was collected during a two-week campaign in July-August 2024. For each site, we measured CO2, CH4 and BVOCs fluxes using floating chambers, analyzed chemical and physical properties of water samples and collected environmental variables. The lakes had different DOC, NO3- and PO43- concentrations as well as pH, despite being located less than one km from each other. The riverine lake is neutral while both thermokarst lakes are acidic. DOC ranged from mean 61.91 mg L-1 in the younger thermokarst lake to 20.93 mg L-1 in the vegetation-colonized thermokarst lake and 6.67 mg L-1 in the riverine lake.
All three lakes had distinguished emission magnitudes of BVOCs. The colonized thermokarst lake showed larger isoprene and hydrocarbon emissions than the other two lakes. Overall, the lake BVOC emissions are of similar or higher magnitude than the surrounding terrestrial ecosystem emissions found in other studies. We found that the younger thermokarst lake had the highest emissions of CH4. For CO2, the riverine lake and the colonized lake are small sinks of CO2 while the younger thermokarst lake is a source. We observed large hourly variation in CO2 and CH4 emissions in the three lakes with no clear diel pattern. This could be because of a temporal lag effect between production and consumption in the water and sampling at the surface, as well as relatively stable water temperatures over the diel cycle. Additionally, for the colonized thermokarst lake, photosynthesis was limited because the high vegetation density blocked light from entering the water around the non-see-through chamber.
This study provides quantitative information about emissions of three climate-relevant gases from different high latitude lakes in the growing season. The pioneering sampling of BVOC emissions from lakes paves the way for further exploring reactive volatiles from freshwater systems. Understanding the processes behind these flux variations allows for a more holistic representation of high latitude ecosystems by including diverse freshwater ecosystems, e.g. in regional ecosystem model simulations.
How to cite: Roos Friis, I., Seestern Christoffersen, K., Rinnan, R., Stage Sø, J., Egebjerg Ravn, L., and Tang, J.: CH4, CO2 and BVOC emissions from three subarctic lakes in Northern Sweden with different chemical properties, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-9172, https://doi.org/10.5194/egusphere-egu25-9172, 2025.
Dams play a critical role in water management and hydropower across Europe, yet the greenhouse gas (GHG) emissions from these reservoirs remain largely understudied, particularly in Germany. While hydropower is often considered a clean energy source, reservoirs can play a significant role in global carbon cycling and the global GHG budget, acting as both sources and sinks of carbon dioxide (CO₂) and methane (CH₄), depending on their ecological and management conditions. In this study, we measured CO₂ and CH₄ fluxes from the Rur Reservoir, located in the Eifel district of western Germany, in a catchment area characterized by a mix of agricultural and forested land. Land use practices in the area influence water quality, nutrient levels, and greenhouse gas emissions, particularly through organic matter input. Using floating chambers, we conducted weekly measurements during the summer and autumn and biweekly measurements in winter, starting in August 2024.
CO₂ fluxes displayed a distinct seasonal pattern, with the reservoir acting as a sink during summer (negative fluxes) before transitioning to a source in autumn, peaking mid-fall (~2600 mg CO₂ m⁻² d⁻¹). Fluxes declined to near-zero levels in early winter, with a transient spike (~6000 mg CO₂ m⁻² d⁻¹) in late November. Throughout the study period, the reservoir consistently emitted methane (CH₄), with fluxes ranging from 1 to 3 mg CH₄ m⁻² d⁻¹ with a slight peak observed mid-fall. CH₄ emissions were significantly higher in the pelagic zone compared to the dam and shoreline areas, whereas CO₂ fluxes showed no discernible spatial pattern across these zones. CO₂ fluxes were strongly correlated with water temperature (r =-0.82, p < 0.01), highlighting the sensitivity of emissions to thermal conditions.
These findings underscore the dynamic nature of GHG emissions in reservoirs and emphasize the importance of considering both seasonal and spatial variability to accurately quantify their contribution to regional and global carbon budgets.
How to cite: Iddris, N. A.-A., Tyystjärvi, V., Halbig, M., Janzen, J., Bonazza, M., Jahanbakhsi, F., Esters, L. T., and Meijide, A.: Seasonal and spatial dynamics of carbon dioxide and methane fluxes from a reservoir in Western Germany, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-18312, https://doi.org/10.5194/egusphere-egu25-18312, 2025.
Cities are at the heart of global anthropogenic greenhouse gas (GHG) emissions, with rivers embedded in urban landscapes as a potentially large yet uncharacterized GHG source. Urban rivers emit GHGs due to excess carbon and nitrogen inputs from urban environments and their watersheds. Here relying on a compiled urban river GHG dataset and robust modelling, we estimated that globally urban rivers emitted annually 1.1, 42.3 and 0.021 Tg CH4, CO2 and N2O, totalling 78.1 ± 3.5 Tg CO2-equivalent (CO2-eq) emissions. Predicted GHG emissions were nearly twofold those from non-urban rivers (~815 versus 414 mmol CO2-eq m−2 d−1) and similar to scope-1 urban emissions in intensity (1,058 mmol CO2-eq m−2 d−1), with particularly higher CH4 and N2O emissions linked to widespread eutrophication and altered carbon and nutrient cycling in urban rivers. Globally, the emissions varied with national income levels with the highest emissions happening in lower–middle-income countries where river pollution control is deficient. These findings highlight the importance of pollution controls in mitigating urban river GHG emissions and ensuring urban sustainability.
How to cite: Xu, W. and Xia, X.: Globally elevated greenhouse gas emissions from polluted urban rivers, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-3208, https://doi.org/10.5194/egusphere-egu25-3208, 2025.
Understanding the biological processes of natural ecosystems is integral to predict their responses to anthropogenic climate change and increasingly extreme climate events. Our ability to quantify net primary production (NPP) is key to better understand community food web structure and carbon sequestration. Traditional ex situ and discrete laboratory experiments, using Winkler incubation methods, provide limitations when accounting for the complex biological processes that occur in aquatic ecosystems. Current in situ chamber approaches are limited in their physical scope. Previous experiments have measured primary productivity in flora using benthic enclosures, as well as spatially discrete geochemical changes in the water columns by using either the Eulerian or Lagrangian fluid motion models. This work shows a non-invasive two-chambered mesocosm, coupled with an equilibrator and a weather station, to accurately calculate levels of net primary production, gross primary productivity (GPP) and total respiration (R) in aquatic communities. Equilibrator data allowed us to calculate daily changes in pCO2, and their correlation with NPP, GPP, and R. A three-day deployment measured r trends that were consistent with expected diurnal natural cycles, demonstrating that our novel mesocosm is a reliable non-invasive method to measure NPP, GPP, and R in aquatic ecosystems. This tool also may provide a standardized approach to quantify marine community productivity and it can be deployed for longer periods of time to understand the trends between NPP and anthropogenic climate change. This study is part of a larger effort to explore how climate change is impacting net community production.
How to cite: Burckin, D. and Telesca, L.: How does climate change impact aquatic net community production? - A novel mesocosm, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-1226, https://doi.org/10.5194/egusphere-egu25-1226, 2025.
Methylotrophic methanogenesis was recently recognized as a key process in driving cryptic methane cycling within sulfate-reducing sediments. In this study, we conducted biogeochemical analyses of methanogenic substrates, activity, and communities in two sediment cores (4−5 m) from the East China Sea, to constrain the dynamics and control of methylotrophic methanogenesis in coastal sediments. We detected micromolar concentrations of methane in the presence of sulfate and high methane concentrations (up to 4.2 mM) below the sulfate-methane transition zone (SMTZ, ~150-170 cm). The stable isotope composition of methane was strongly depleted (−77 to −91‰), indicating the biological production. Methanogenic substrates including H2/CO2, acetate, and methylated compounds were detected in the porewaters and/or sediments. Radiotracer experiments indicated methane production from various substrates, and the presence of sulfate did not inhibit methanogenesis at either site. At the coastal site with the dominance of marine organic matter (TOC: 0.4%; C/N ratio: ~6; δ13C-TOC: −22‰), methane was primarily produced from hydrogenotrophic methanogenesis, consistent with the progressive enrichment of 13C in dissolved inorganic carbon with depth below the SMTZ. However, methylotrophic methanogenesis from methanol and trimethylamine contributed significantly to methane production (up to 30.2%) at the estuarine site (TOC: 0.5%; C/N ratio: 7.4, δ13C-TOC: −23‰) with elevated terrestrial organic matter input, also reflected from the predominance of long chain odd carbon n-alkanes. These findings suggested that organic carbon source and composition, instead of sulfate, control methanogenic activity, providing evidence that high terrestrial organic inputs could significantly enhance methylotrophic methanogenesis in coastal sediments.
How to cite: Liu, Q., Wu, B., Wang, F., and Zhuang, G.-C.: Control and contribution of methylotrophic methanogenesis to methane production in coastal sediments, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-7903, https://doi.org/10.5194/egusphere-egu25-7903, 2025.
Marine nutrient cycling, particularly of carbon (C), nitrogen (N), phosphorus (P), and silicon (Si), is intricately linked to phytoplankton metabolism, with the Redfield ratio (106:16:1, extended to 15–20 for Si) traditionally serving as a benchmark for nutrient stoichiometry. However, tropical coastal ecosystems experience significant spatial and temporal heterogeneity due to anthropogenic activities, geographic variability, and seasonal shifts, exacerbating imbalances in carbon and nutrient dynamics.
Blue-carbon ecosystems, as a "natural solution," offer the potential to mitigate eutrophication and acidification. These highly productive systems can transform CO₂ sources into carbon sinks, contributing to carbon neutrality and improving coastal ecosystem resilience. Xiaohai Lagoon, the largest lagoon in Hainan, China, represents a successful case study of blue-carbon restoration. Over three years of comprehensive restoration measures, including large-scale seagrass and seaweed planting, the lagoon achieved Class I water quality through substantial government investment.
Using high-resolution field surveys and real-time water quality monitoring, this study demonstrates how blue-carbon ecosystems dynamically regulate lagoon health through in situ metabolism. During the rainy season (October–December), blue-carbon species rapidly absorbed excess nutrients from land sources, and by November, shifted nutrient dynamics from nitrogen (N) limitation to phosphorus (P) limitation. This transformation converted the lagoon from a CO₂ emission source to a CO₂ sink through photosynthesis. During this process, the combined CO₂ equivalents of three typical greenhouse gases—CO₂, CH₄ (methane), and N₂O (nitrous oxide)—turned negative, −617 g CO₂e m⁻² annually under mean conditions and up to −1,800 g CO₂e m⁻² annually under optimal conditions, underscoring the substantial role of blue-carbon systems in mitigating climate change. In addition, dissolved oxygen (DO) levels increased (107%–136%), and acidification was alleviated (pH 8.41 ± 0.14). However, the decomposition of organic matter from declining blue-carbon species disrupted stoichiometry and caused water quality to deteriorate again, underscoring the critical need for sustained ecological governance.
Our findings highlight the pivotal role of blue-carbon restoration in regulating offshore nutrient stoichiometry, mitigating greenhouse gas fluxes, and enhancing coastal ecosystem health. Scaling these results to 10 Hainan lagoons reveals a mitigation potential of ~310,000–500,000 tons CO₂e annually. These insights provide a scientific foundation for advancing Hainan’s ecological civilization pilot zone and offer practical strategies for global coastal management and achieving carbon neutrality.
How to cite: Quan, X., Zhuang, Y., Wang, Y., Fu, C., Huang, Y., Xiao, S., Wang, S., Mi, H., Yang, H., Chen, B., Li, F., Xu, M., Wang, L., Chang, Y., Li, X., Du, C., Liu, J., Tan, E., Su, J., and Kao, S.: Dynamic Regulation of Nutrient Stoichiometry and Greenhouse Gas Mitigation through Blue-Carbon Restoration in Xiaohai Lagoon, Hainan—China's Largest Tropical Lagoon , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-6281, https://doi.org/10.5194/egusphere-egu25-6281, 2025.
Methane is commercially exploited at continental margins (worldwide/globally) from drilled wells. Typically, these are sealed with concrete once exploitation becomes commercially unprofitable. However, such wells may leak methane to the overlying water column and potentially to the atmosphere. Tailored towards the shallow water depth of the Dutch EEZ (Exclusive Economic Zone) of the North Sea, we developed four ship-based methods to detect methane in the water column or to measure methane emissions from the sea surface to the atmosphere.
1. Online measurements of methane in the water column. Water from a few meters above the seabed was pumped up via a weighted hose (“SLURF”) and the concentration and composition of gases in the water (CH4, C2H6, N2O, CO2 and CO) were measured with a laser spectrometer.
2. Floating chamber to quantify the flux of CH4 coming from the water phase into the atmosphere. Trace gases in the sampled air from a custom build floating chamber for offshore measurements were transported in a closed loop to the same laser spectrometer as the water phase measurements for concentration measurements. A known amount of a tracer gas was added to the return line with a controlled flow to estimate fluxes.
3. Gradient measurements. A 3D sonic anemometer and a frame equipped with three inlets positioned at three heights above sea level were mounted at the ship’s portside. Gradient measurements for determining gas emissions were conducted by using a valve system that alternated between the inlets, allowing to measure CH4, CO2 and CO at each height with a gas analyzer for 5 min intervals.
4. Plume measurements. The multibeam (MBES) was used to detect the bubble plumes and to detect the exact location where the bubble plume exit the water (exit point). Fluxes of bubble plumes from the water column to the atmosphere were then assessed by sailing downwind of the bubble plumes with the gradient system facing towards the exit point upwind. Emission rates were then determined by using a Gaussian plume model.
In this presentation, we will show preliminary data sets collected with these methods showing that bubble plumes rising from the seabed can be indicated next to dissolved methane and we will provide estimates of methane fluxes from individual bubble plumes into the atmosphere.
How to cite: Velzeboer, I., Hensen, A., van den Bulk, P., van Mansom, H., de Bruin, G., de Haas, H., Delre, A., de Stigter, H., Wilpshaar, M., Niemann, H., and Reichart, G.-J.: Ship-based methodologies to investigate methane emissions from abandoned wells and natural sources: a case study from the Dutch North Sea, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-8267, https://doi.org/10.5194/egusphere-egu25-8267, 2025.
The ocean accounts for ~20 to 30% of global nitrous oxide (N2O) emissions, with coastal upwelling systems estimated to contribute disproportionately to the sea-air flux of this potent greenhouse gas. To resolve the mechanisms of and controls on N2O production in coastal upwelling systems, we measured the concentration and nitrogen and oxygen isotopic composition of N2O (δ15N-N2O and δ18O-N2O) along a cross-shelf transect in the Southern Benguela Upwelling System. At the shelf bottom, N2O concentrations increased from the outer shelf towards the shore (11 to 32 nM) inversely to dissolved oxygen (182 ± 17 to <1 μM) and in concert with the remineralization tracers, Apparent Oxygen Utilization (AOU; 108 ± 21 to 221 ± 33 μM) and Nitrogen (N)-deficit (up to 20.4 μM). These observations suggest that both nitrification and denitrification may be involved in N2O production on the SBUS shelf. The δ15N-N2O confirms both processes as potential N2O sources on the shelf, with high δ18O-N2O values (≤ 57.2‰) specifically implicating the sediments as the primary N2O source to the water column. Isotopic changes across the shelf delineate three discrete domains, each with distinct N2O sources. Sedimentary nitrification dominates N2O production on the midshelf, while coupled nitrification-denitrification or direct denitrification explains N2O production on the inner-shelf. At the shallow inner-shelf, where oxygen concentrations are depleted, both water column and sedimentary denitrification account for the production and partial consumption of N2O. This study uncovers the disproportionate contribution of sedimentary N cycling to N2O production on the SBUS shelf.
How to cite: Wallschuss, S., Granger, J., Bourbonnais, A., Flynn, R., Burger, J., Pillay, K., and Fawcett, S.: The role of sediments in modulating nitrous oxide production in the Southern Benguela Upwelling System: insights from stable isotopic tracers, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-343, https://doi.org/10.5194/egusphere-egu25-343, 2025.
Posters virtual: Wed, 30 Apr, 14:00–15:45 | vPoster spot A
EGU25-4681 | ECS | Posters virtual | VPS4
Keystone taxa drive the synchronous production of methane and refractory dissolved organic matter in inland watersWed, 30 Apr, 14:00–15:45 (CEST) | vPA.23
Inland waters are an important source of greenhouse gas methane (CH4). The production of CH4 is influenced by various factors, including the concentration of dissolved organic matter (DOM), redox conditions, and the composition of microbial communities, with clear spatiotemporal heterogeneity in inland waters. Refractory DOM (RDOM) can resist rapid biodegradation and preserve up to thousands of years; therefore, it is important for assessing the natural carbon sequestration potential of aquatic ecosystems. As a critical part of carbon biogeochemical processes in inland waters, the production of CH4 and RDOM depends on the microbial successive processing of organic carbon. However, it is unclear yet the link of these two processes and the underlying microbial regulation mechanisms. Therefore, a large-scale survey was conducted in China’s inland waters, with the measurement of CH4 concentrations, DOM chemical composition, microbial community composition, and relative environmental parameters mainly by chromatographic, optical, mass spectrometric, and high-throughput sequencing analyses, to clarify the abovementioned questions. Here, we found a synchronous production of CH4 and RDOM linked by microbial consortia in inland waters. The increasing microbial cooperation driven by the keystone taxa (mainly Fluviicola and Polynucleobacter) could promote the transformation of labile DOM into RDOM and meanwhile benefit methanogenic microbial communities to produce CH4. This process was also influenced by environmental factors such as total nitrogen and dissolved oxygen concentrations. Future studies need to combine more field investigations and laboratory control experiments to fully understand these complex processes. This study deepened the understanding of microbial-driven carbon transformation and highlighted the role of microbial keystone taxa in these processes, providing some useful references for the future laboratory control experiments (e.g., the selection of microbial species). Considering that CH4 emission and RDOM production are closely related to the carbon source-sink relationship, this finding will help to more accurately evaluate the budget in inland aquatic ecosystems.
How to cite: Shi, X., Li, W., Wang, B., Yang, M., and Liu, C.-Q.: Keystone taxa drive the synchronous production of methane and refractory dissolved organic matter in inland waters, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-4681, https://doi.org/10.5194/egusphere-egu25-4681, 2025.
EGU25-2079 | ECS | Posters virtual | VPS4
Responses of greenhouse gases production to land-use change and the underlying microbial mechanisms in mangrove wetlandsWed, 30 Apr, 14:00–15:45 (CEST) | vPA.33
Tidal wetland reclamation could profoundly alter ecological function and ecosystem service provision, but its impacts on sediment microbial communities and functions remain poorly understood. We investigated spatial and seasonal patterns of greenhouse gases (GHGs) production response to land-use changes in mangrove wetlands and unraveled the underlying mechanisms by integrating environmental parameters and microbial communities. Land-use changes substantially reduced microbial community richness and diversity and shaped their composition. Converting mangrove to drier orchard and vegetable field reduced sediment organic matter, carbon GHGs production rates, and microbial network complexity and stability, while increased N2O production rates. Converting mangrove to chronically flooded aquaculture pond increased sediment CH4 production rates, but reduced N2O and CO2 production rates. Although increasing anthropogenic disturbance in aquaculture pond have reduced microbial community richness and diversity compared to native mangrove wetland, they have increased complexity of species associations resulting in a more complex and stable network. Microbial community richness and network complexity and stability were strongly related to CH4 and N2O production rates, but not significantly associated with CO2 production rates, suggesting microbial community richness, network complexity and stability are better predictors of the specialized soil/sediment functions CH4 and N2O production). Therefore, preserving microbial “interaction” could be important to mitigate the negative effects of microbial community richness and diversity loss caused by human activities. Furthermore, as the residual bait accumulation is a severe issue in aquaculture activities, we especially focused on the influence of bait input at time scale through a 90-day incubation experiment, aiming to observe temporal variations of physicochemical properties, sediment microbial community, and GHGs production in response to different amounts of bait input. The results showed that dissolved oxygen of overlying water was profoundly decreased owing to bait input, while dissolved organic carbon of overlying water and several sediment properties (e.g., organic matter, sulfide, and ammonium) varied in reverse patterns. Meanwhile, bait input strongly altered microbial compositions from aerobic, slow-growing, and oligotrophic to anaerobic, fast-growing, and copiotrophic. Moreover, both GHGs production and global warming potential were enhanced by bait input, implying that aquaculture ecosystem is an important hotspot for global GHGs emission. Overall, bait input triggered quick responses of physicochemical properties, sediment microbial community, and GHGs production, followed by long-term resilience of the ecosystem. Future research should comprehensively consider microbial diversity, species composition and interaction strength, functions, and environmental conditions to accurately predict soil/sediment functioning and emphasize the necessity of sustainable assessment and effective management.
How to cite: Lin, G. and Lin, X.: Responses of greenhouse gases production to land-use change and the underlying microbial mechanisms in mangrove wetlands, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-2079, https://doi.org/10.5194/egusphere-egu25-2079, 2025.
