Mathematical modelling of methane-induced transitions in aquatic ecosystems.

Methane is a potent greenhouse gas that significantly contributes to global warming, yet it often receives less attention than carbon dioxide. While anthropogenic sources of methane are well-documented, natural sources, especially marine environments, remain less understood, introducing uncertainties into the global methane budget. Coastal waters on the inner continental shelf, despite covering a small fraction of the global ocean, are major contributors to marine methane emissions due to their high productivity and the presence of cold seeps. These shallow ecosystems often exhibit elevated methane concentrations, with their close seafloor-atmosphere proximity limiting the effectiveness of methane-oxidizing bacteria (methanotrophs) to fully mitigate emissions. Dynamic factors such as ocean currents, tidal fluctuations, seasonal variations, and land runoff further influence microbial activity and the efficiency of the "microbial methane filter." This thesis investigates the relationship between coastal waters and atmospheric methane levels, focusing on how environmental factors affect microbial methane oxidation. To address limitations of prior studies, this research incorporates high-frequency measurements across diverse coastal regions, including the Doggerbank seep area, the Dutch Wadden Sea, and Arctic seep areas north of Svalbard. Complementary laboratory experiments simulated future climate scenarios to evaluate methanotroph resilience to environmental changes in temperature, salinity, and methane concentration. In the Doggerbank seep area, tides and seasonal stratification strongly influenced methane release. Falling tides triggered methane emissions and increased methanotroph activity, while fully mixed autumn conditions reduced microbial efficiency, leading to higher atmospheric methane release. In the Wadden Sea, warmer seasons showed elevated methane concentrations and oxidation rates but also increased atmospheric emissions. Even in colder seasons, methane supersaturation persisted, with wind and tidal currents transporting methane to the North Sea. These findings emphasize the interplay of seasonal, tidal, and environmental dynamics in shaping methane fluxes. In Arctic regions, studies revealed that bottom waters in seep systems north of Svalbard contained higher methane concentrations and supported diverse methanotrophic communities. Hydrological connectivity, driven by the West Spitsbergen Current, influenced community similarities between sites. While methanotrophs rapidly responded to elevated methane levels, their capacity to fully oxidize methane was constrained by water currents, underscoring the role of physical transport in methane dispersal. Laboratory experiments highlighted the adaptability of methanotrophs to varying methane levels and environmental conditions, with shifts in methane availability significantly impacting microbial community composition. Functional redundancy within these communities suggested their capacity to adapt to high-methane scenarios in a changing ocean. This research advances understanding of methane dynamics in coastal waters, demonstrating how environmental factors govern the microbial methane filter's efficiency. Insights from this work are crucial for predicting methane emissions under future climate conditions and contribute to broader efforts to mitigate greenhouse gas emissions.

The COVID-19 pandemic has significantly influenced various aspects of society, including environmental factors such as methane emissions. This study investigates the changes in methane concentrations in Seoul, South Korea, from 2019 to 2023, using TROPOMI satellite data and rigorous statistical analyses. The normality of the sample data is first assessed using the Shapiro-Wilk (S-W) and Kolmogorov-Smirnov (K-S) tests, indicating that the data can be considered to come from a normal distribution. The S-W test demonstrated superior discriminative power (highest statistical power: 0.8668) compared to the K-S test (highest statistical power: 0.4002), confirming the validity of parametric tests for our data. The S-W test shows better discriminative power than the K-S test in terms of sensitivity to departures from normality, particularly for small sample sizes. Based on this confirmation, parametric tests such as analysis of variance (ANOVA) and post-hoc tests (Bonferroni correction, Tukey’s HSD, Scheffe’s method) are employed to identify significant differences in methane levels across different years. The ANOVA results show a statistically significant difference in methane concentrations across years (p-value: 2.02times 10^{-13}, F-value: 26.572). Post-hoc analyses reveal no significant difference in methane concentrations between 2019 and 2020 (p-values: Bonferroni - 0.1045, Tukey’s HSD - 0.397, Scheffe’s - 0.1045), and no significant difference between 2020 and 2021 (p-values: Bonferroni - 0.917, Tukey’s HSD - 0.840, Scheffe’s - 0.917). However, a significant increase in methane levels is observed from 2022 to 2023 (p-values: Bonferroni - 0.0001, Tukey’s HSD - 0.0002, Scheffe’s - 0.0001), correlating with the “new normal” policy implemented in South Korea starting in November 2021 and effectively from the beginning of 2022. This suggests that changes in industrial activities and transportation patterns due to the “new normal” have contributed to higher methane emissions. Student’s t-test and Welch’s t-test were used to validate the ANOVA results. Permutation tests showed no significant difference between 2019 and 2020 (test statistic: -0.0096, p-values: 0.1191 for Student’s and 0.1156 for Welch’s). However, a significant difference was found between 2022 and 2023 (test statistic: -0.0172, p-value: 0.0001), confirming ANOVA results that indicated increased methane levels post-pandemic. This study provides a robust quantitative assessment of the pandemic’s impact on methane levels and sets a methodological statistical approach for future research in the environmental research community.Supplementary InformationThe online version contains supplementary material available at 10.1038/s41598-024-72843-9.

This study investigated the effects of supplementing 40 g lauric acid (C12) kg(-1) dry matter (DM) in feed on methane emissions from early-lactating dairy cows and the associated effects on methane, nitrous oxide and ammonia release from the manure during storage. Stearic acid (C18), a fatty acid without assumed methane-suppressing potential in the digestive tract of ruminants, was added at 40 g kg(-1) DM to a control diet. The complete feed consisted of forage and concentrate in a ratio of 1.5:1 (DM basis). The manure was stored for 14 weeks either as complete slurry or, separately, as urine-rich slurry and farmyard manure representing two common storage systems. Methane release of the cows, as measured in respiratory chambers, was lower with C12 by about 20%, but this was mostly resulting from a reduced feed intake and, partly, from a lower rate of fibre digestion. As milk yield declined less than feed intake, methane emission per kg of milk was significantly lower with C12 (11.4 g) than with C18 (14.0 g). Faeces of C12-fed cows had a higher proportion of undigested fibre and accordingly methane release from their manure was higher compared with the manure obtained from the C18-fed cows. Overall, manure-derived methane accounted for 8.2% and 15.4% of total methane after 7 and 14 weeks of storage, respectively. The evolution of methane widely differed between manure types and dietary treatments, with a retarded onset of release in complete slurry particularly in the C12 treatment. Emissions of nitrous oxide were lower in the manures from the C12 treatment. This partially compensated for the higher methane release from the C12 manure with respect to the greenhouse gas potential. The total greenhouse gas potential (cow and manure together) accounted for 8.7 and 10.5 kg equivalents of CO2 cow(-1) d(-1) with C12 and C18, respectively. At unaffected urine-N proportion ammonia and total nitrogen losses from stored manure were lower with C12 than with C18 corresponding to the differences in feed and nitrogen intake. The present results suggest that manure storage significantly contributes to total methane emission from dairy husbandry, and that the identification of effective dietary mitigation strategies has to consider both the digestive tract of the animals and the corresponding manure.

Methane emissions along biomethane and biogas supply chains are underestimated

This project produced detailed data on the processes that affect methane and nitrous oxide emissions from rice agriculture and their inter-relationships. It defines the shifting roles and potential future of these gases in causing global warming and the benefits and tradeoffs of reducing emissions. The major results include: 1). Mechanisms and Processes Leading to Methane Emissions are Delineated. Our experiments have tested the standard model of methane emissions from rice fields and found new results on the processes that control the flux. A mathematical mass balance model was used to unravel the production, oxidation and transport of methane from rice. The results suggested that when large amounts of organic matter are applied, the additional flux that is observed is due to both greater production and reduced oxidation of methane. 2). Methane Emissions From China Have Been Decreasing Over the Last Two Decades. We have calculated that methane emissions from rice fields have been falling in recent decades. This decrease is particularly large in China. While some of this is due to reduced area of rice agriculture, the bigger effect is from the reduction in the emission factor which is the annual amount of methane emitted per hectare of rice. The two most important changes that cause this decreasing emission from China are the reduced use of organic amendments which have been replaced by commercial nitrogen fertilizers, and the increased practice of intermittent flooding as greater demands are placed on water resources. 3). Global Methane Emissions Have Been Constant For More Than 20 Years. While the concentrations of methane in the atmosphere have been leveling off in recent years, our studies show that this is caused by a near constant total global source of methane for the last 20 years or more. This is probably because as some anthropogenic sources have increased, others, such as the rice agriculture source, have fallen. Changes in natural emissions appear small. 4). Nitrous Oxide Emissions From Rice Fields Increase as Methane Emissions Drop. Inundated conditions favor anaerobic methane production with high emission rates and de-nitrification resulting in modest nitrous oxide emissions. Under drier conditions such as intermittent flooding, methane emissions fall and nitrous oxide emissions increase. Increased nitrogen fertilizer use increases nitrous oxide emissions and is usually accompanied by reduced organic matter applications which decreases methane emissions. These mechanisms cause a generally inverse relationship between methane and nitrous oxide emissions. Reduction of methane from rice agriculture to control global warming comes with tradeoffs with increased nitrous oxide emissions. 5). High Spatial Resolution Maps of Emissions Produced. Maps of methane and nitrous oxide emissions at a resolution of 5 min × 5 min have been produced based on the composite results of this research. These maps are necessary for both scientific and policy uses.

The study investigates the influence of atmospheric pressure fluctuations on methane emissions in a decommissioned coal mine in Poland (SRK S.A., KWK “Krupiński”). Continuous measurements of methane concentrations and atmospheric pressure were analyzed to identify periods of dynamic pressure drops, which were then correlated with recorded methane levels. Strong linear relationships were observed, with correlation coefficients ranging from 0.88 to 0.97 and determination coefficients exceeding 0.85, indicating that pressure changes are a primary factor influencing methane release. Individual regression models for each identified case showed the lowest mean absolute errors compared to generalized models, highlighting the impact of atypical cases on predictive performance. Key findings align with previous studies, confirming that both the magnitude and the gradient of pressure decline directly affect the rate and scale of methane release and that threshold effects may limit further concentration increases despite continued pressure drops. The results suggest the potential to develop a predictive model linking atmospheric pressure variations to methane emissions, which could support forecasting of methane capture in decommissioned mines or ventilation methane levels in active mines. Understanding these mechanisms is crucial for both occupational safety and for effective methane emission reduction strategies in the mining sector.

Methane release is considered to be from human activities, Arctic Ocean, and the terrestrial regions such as wetland, lakes, geological seeps in the Arctic although glaciers have not been considered a source of methane emissions. A large amount of methane has been observed at the terminus of large glaciers and ice sheet, associated with methane-saturated meltwater runoff. We observed several glaciers in Alaska and found methane emissions from the runoff water of the small mountain glaciers.The observation periods, which was the beginning of the ablation season for the glacier, were June 12-14, 2022, and June 3-9, 2023. We measured methane and CO2 concentrations in ambient air over the water with a portable gas analyzer G4301 (Picarro, Inc.). Dissolved methane concentrations in runoff water were measured using the method of Morishita et al. (2015).The maximum methane concentration in the ambient air near the runoff water was higher than the background level, and the concentration decreased as the gas analyzer moved away from the tunnel. The dissolved methane concentration in runoff water was saturated. These results suggest that the high concentration methane observed in the ambient air near the glacier terminus was released from the runoff water saturated by methane underneath of the glaciers. This study was supported by ArCSII project (JPMXD1420318865).

<p>Changing environmental conditions have significantly altered the phenology, spatial distribution, and abundances of species in terrestrial and freshwater ecosystems. Recent work has shown that such changes may alter the strengths of interactions between species and may jumble structural patterns in networks of trophic, mutualistic and/or other interactions that are crucial for biodiversity. ‘Blue’ (aquatic) and ‘green’ (terrestrial) ecosystems are closely interlinked through biogeochemical cycles and species that inhabit both ecosystems. When the effects of abiotic drivers of global environmental change, such as a change in temperature, precipitation, or land use, are different for lakes and their surrounding watersheds, a blue-green phenological mismatch may therefore occur. In particular, because such changes in seasonal patterns may cascade down food webs. <br>Remote sensing provides spatially and temporally dense information on biochemical properties of the Earth surface, including biomass and primary production indicators for both aquatic and terrestrial ecosystems. Deriving phenology metrics for these indicators is routine practice for terrestrial vegetation, and several case studies demonstrate the feasibility of analogous metrics for lakes and inland seas. In this study, we used remote sensing data to extract phenology metrics (e.g. start of the growing season) for 4264 lakes distributed across a wide range of biomes from daily chlorophyll estimates and vegetation indices spanning a time-period of 15-20 years. We investigate whether changes in the phenology of lake phytoplankton and the surrounding terrestrial vegetation have occurred during this period, and how the phenology in either ecosystem type is synchronized.<br>Analysis are underway, but preliminary results suggest contrasting results across different biomes as well as substantial differences in the way in which the phenology of primary producers in lakes and on their surrounding watersheds has changed within these biomes.</p>

Impact of climate change and anthropogenic activities on aquatic ecosystem – A review

Methane production, transport and emission in a floodplain lake in central Amazonia were investigated by isotopic studies and gas exchange measurements. Samples of sediment free gas were depleted in δ13CCH4, δ13DCH4,and δ13CCO2 values. The isotopic composition of the sediment free methane clearly demonstrated a methane production by methyl fermentation. This finding was strengthened by the coexisting δ13CCO2 and δ13CCO2 values in the sediment free gas. The flux rates of methane ebullition and diffusion were measured during a complete annual cycle using the static chamber method. Significant differences were observed in the release of methane from individual vegetation types, i.e., phytoplankton, floating grass mats, and flooded forest. Each vegetation type showed a distinct seasonal pattern. The highest ebullition rates (mean value, 69 mg CH4 m−2d−1) were recorded in the flooded forest, covering the higher areas of the floodplains with a long subaerial period. Significantly lower averages of the gas bubble flux were recorded in the permanently aquatic areas of the lake (mean value, 29 mg CH4 m−2d−1) and in the intermediate area with floating grass mats (mean value, 23 mg CH44 m−2d−1. Ebullition was the predominant mechanism for the methane transport from the varzea sediment into the atmosphere with maximum values of up to 200 mg CH4 m−2d−1. The diffusive flux remained below 29 mg CH4 m−2d−1 at all sites throughout the entire annual cycle. The variation of the ebullutive flux was found to determine the spatial and temporal variation of the total methane flux in the varzea. We estimate that ebullition accounts for 80% of the total methane emission from the varzea.

Book Review| October 01, 2004 Ecology of Humic Substances in Freshwaters ANN-KRISTIN BERGSTRÖM ANN-KRISTIN BERGSTRÖM 1Department of Ecology and Environmental Sciences, Umeå University, Umeå SWEDEN Search for other works by this author on: GSW Google Scholar PALAIOS (2004) 19 (5): 520–521. https://doi.org/10.1669/0883-1351(2004)019<0520:BR>2.0.CO;2 Article history first online: 03 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Twitter LinkedIn Tools Icon Tools Get Permissions Search Site Citation ANN-KRISTIN BERGSTRÖM; Ecology of Humic Substances in Freshwaters. PALAIOS 2004;; 19 (5): 520–521. doi: https://doi.org/10.1669/0883-1351(2004)019<0520:BR>2.0.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyPALAIOS Search Advanced Search Christian E.W. Steinberg (Editor), 2003, Springer-Verlag, Berlin, Germany, 429 p. (Hardcover, US $109.00) ISBN: 3-540-43922-6. The Ecology of Humic Substances in Freshwaters is a comprehensive book describing how dead organic matter (i.e., humic substances—HS) affects abiotic and biotic processes in freshwaters. The editor and author, Christian E. W. Steinberg, writes in the Introduction that “the link of ecology and dead may look like a strange alliance, since most limnological studies involve living organisms, and their interaction with the surrounding environment”, and, consequently, not the opposite. However, after reading the book, the link between ecology and dead organic matter seems very... You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Climate change can impact ecosystems by reshaping the dynamics of resource exploitation for predators and their prey. Alterations of these pathways could be especially intense in ecosystems characterized by a simple trophic structure and rapid warming trends, such as in the Arctic. However, quantifying the multiple direct and indirect pathways through which climate change is likely to alter trophic interactions and their relative strength remains a challenge. Here, we aim to identify direct and indirect causal mechanisms driven by climate affecting predator-prey interactions of species sharing a tundra food web. We based our study on relationships between one Arctic predator (Arctic fox) and its two main prey - lemmings (preferred prey) and snow geese (alternate prey) - which are exposed to variable local and regional climatic factors across years. We used a combination of models mapping multiple causal links among key variables derived from a long-term dataset (21years). We obtained several possible scenarios linking regional climate factors (Arctic oscillations) and local temperature and precipitation to the breeding of species. Our results suggest that both regional and local climate factors have direct and indirect impacts on the breeding of foxes and geese. Local climate showed a positive causal link with goose nesting success, while both regional and local climate displayed contrasted effects on the proportion of fox breeding. We found no impact of climate on lemming abundance. We observed positive relationships between lemming, fox and goose reproduction highlighting numerical and functional responses of fox to the variability of lemming abundance. Our study measures causal links and strength of interactions in a food web, quantifying both numerical response of a predator and apparent interactions between its two main prey. These results improve our understanding of the complex effects of climate on predator-prey interactions and our capacity to anticipate food web response to ongoing climate change.

Recent analyses of ice core methane concentrations suggested that methane emissions from wetlands were the primary driver for prehistoric changes in atmospheric methane. However, these interpretations conflict as to the location of wetlands, magnitude of emissions, and the environmental controls on methane oxidation. The flux of other reactive trace gases to the atmosphere also controls apparent atmospheric methane concentrations because these compounds compete for the hydroxyl radical (OH), which is the primary atmospheric sink for methane. In a series of linked biosphere‐atmosphere chemistry‐climate modeling experiments, we simulate the methane and biogenic volatile organic compound emissions from the terrestrial biosphere from the Last Glacial Maximum (LGM) to the present. Using a state‐of‐the‐art chemistry‐climate model, we simulate the atmospheric concentrations of methane, OH, and other reactive trace gas species. Over the past 21,000 years, methane emissions from wetlands increased slightly to the end of the Pleistocene but then decreased again, reaching levels at the preindustrial Holocene that were similar to the LGM. Global wetland area decreased by 14% from LGM to the preindustrial time. Emissions of biogenic volatile organic compounds (BVOCs), however, nearly doubled over the same period of time. Atmospheric OH burdens and methane concentrations were affected by this major change in BVOC emissions, with methane lifetimes increasing by more than 2 years from LGM to the present. We simulate a change in methane concentration of ∼385 ppb, accounting for 88% of the ∼440 ppb increase in methane concentrations observed in ice cores. Thus glacial‐interglacial changes in atmospheric methane concentrations would have been modulated by BVOC emissions. In addition, the increase in atmospheric methane concentrations since the mid‐Holocene is partly caused in our results by the increases in anthropogenic methane emissions over this period. While the interplay between BVOC and wetland methane emissions since the LGM cannot explain the entire record of ice core methane concentrations, consideration of BVOC source dynamics is central to understanding ice core methane. Rapid changes in atmospheric methane concentrations, also observed in ice cores, require further study.

This study investigates the role of surface waves and the associated disturbance of littoral sediments for the release and later distribution of dissolved methane in lakes. Surface wave field, wave‐induced currents, acoustic backscatter strength, and the concentration and distribution of dissolved methane were measured simultaneously in Lake Constance, Germany. The data indicate that surface waves enhance the release of dissolved methane in the shallow littoral zone via burst‐like releases of methane during the passage of wave groups. The amount of released methane depends on the surface wave field and the water temperature that controls the methane production in the sediments. The dissolved methane concentrations in the shallow littoral zone were always higher than concentrations in the deep water and open water, while methane concentrations in the epilimnion were typically higher than methane concentrations in the metalimnion and upper hypolimnion. The relatively high epilimnetic methane concentrations in the pelagial can be explained by lateral transport of methane from the littoral zone to the pelagic zone. Littoral zones can thus be an important source of methane in lakes. Methane released by surface waves from littoral sediments may cause elevated near‐surface methane concentrations in large areas that enhance the flux of methane at the air‐water interface and, thus, the overall methane emissions from lakes to the atmosphere.

Aquatic ecosystems are significant methane (CH4) emitters, potentially surpassing direct anthropogenic sources. Despite the advantages of satellite monitoring, its application for assessing methane content over freshwater bodies is not commonly encountered in scientific publications. Therefore, this study aims to assess methane levels in the atmosphere in and around the temperate reservoir area (Kuibyshev Reservoir, Russia) using Sentinel-5P/TROPOMI remote sensing data. The spatial distribution of CH4 content across the study area was heterogeneous and exhibited a latitudinal dependence, with concentrations decreasing from south to north. Seasonal variability in methane levels is observed, with the lowest values in spring and the highest in autumn. The average CH4 concentration over the period 2019–2023 was 1860±13 ppb. Additionally, a consistent trend of increasing annual methane background levels has been observed (up to 1878±11 ppb in 2023). Differences in methane levels are noted across different land cover types, with higher values typically observed above anthropogenically transformed landscapes, while minimal ones are found over extensive forested areas and the waters of the Kuibyshev Reservoir.