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Predicting Methane Formation Rates of Freshwater Sediments in Different Biogeographic Regions
Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.ORCID iD: 0000-0001-7262-8911
Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics.
Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics.
Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.ORCID iD: 0000-0002-3251-7974
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2024 (English)In: Journal of Geophysical Research - Biogeosciences, ISSN 2169-8953, E-ISSN 2169-8961, Vol. 129, no 1, article id e2023JG007463Article in journal (Refereed) Published
Abstract [en]

Freshwater lakes and reservoirs cover a small fraction of the Earth, however their emission of the greenhouse gas methane (CH4) from the sediment to the atmosphere is disproportionately high. Currently, there is still a limited understanding of the links between sediment characteristics and CH4 formation. Earlier studies have indicated that sediment age and nitrogen content are related to sediment CH4 formation rates, but it is uncertain such relationships are valid across gradients of sediment characteristics. We therefore measured potential CH4 formation rates in multiple layers of sediment sampled from nine lakes situated in the temperate, boreal and alpine biogeographic regions of Sweden, thus differing in productivity, catchment and climate properties. Potential CH4 formation varied over 3 orders of magnitude, and was broadly related to the quantity and reactivity of organic matter, and generally decreased with sediment depth. Sediment age and total nitrogen content were found to be the key controlling factors of potential CH4 formation rates, together explaining 62% of its variability. Moreover, the model developed from the Swedish lake sediment data was able to successfully predict the potential CH4 formation rates in reservoirs situated in different biogeographic regions of Brazil (R2 = 0.62). Therefore, potential CH4 formation rates in sediments of highly contrasting lakes and reservoirs, from Amazonia to alpine tundra, could be accurately predicted using one common model (RMSE = 1.6 in ln-units). Our model provides a valuable tool to improve estimates of CH4 emission from lakes and reservoirs, and illustrates the fundamental regulation of microbial CH4 formation by organic matter characteristics.

Abstract [en]

Lakes and reservoirs are important emitters of methane, a strong greenhouse gas, to the atmosphere. Methane is produced in absence of oxygen by specific microbes that degrade the organic matter in the sediment. Currently, it is still uncertain which specific sediment properties control the production of methane, and if such properties are the same across lakes and reservoirs located in different ecosystem. To test this, we collected sediment cores from several lakes across different ecosystems in Sweden, and we measured potential methane formation rates. Methane formation rates varied greatly among lakes and was related to the quality and quantity of organic matter in the sediment. From this experiment, we calculated an empirical model that can predict methane formation rates as a function of sediment age and nitrogen content. Moreover, we found that our model could well predict potential methane formation rates in tropical reservoirs. In conclusion, sediment age and nitrogen content are universal controlling factors of methane formation rates across lakes and reservoirs in different ecosystems, from tropics to arctic tundra. Our findings provide a valuable tool to improve estimates of methane emission from lakes and reservoirs and illustrates how sediment characteristics play a crucial role in regulating methane formation rates.

Place, publisher, year, edition, pages
American Geophysical Union (AGU), 2024. Vol. 129, no 1, article id e2023JG007463
Keywords [en]
carbon cycle, methane, lakes, sediment age, nitrogen
National Category
Environmental Sciences Ecology
Identifiers
URN: urn:nbn:se:uu:diva-522266DOI: 10.1029/2023JG007463ISI: 001146869400001OAI: oai:DiVA.org:uu-522266DiVA, id: diva2:1834684
Funder
Swedish Research Council, 2017-04405Olsson-Borghs stiftelseAvailable from: 2024-02-05 Created: 2024-02-05 Last updated: 2024-04-05Bibliographically approved
In thesis
1. Understanding and predicting methane formation and bubble emission from lakes
Open this publication in new window or tab >>Understanding and predicting methane formation and bubble emission from lakes
2024 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The role of lakes and reservoirs as significant emitters of the potent greenhouse gas methane (CH4) to the atmosphere is well established, but several uncertainties remain particularly due to knowledge gaps in the relationship between CH4 dynamics and sediment characteristics, which limit our capabilities to provide robust estimates of CH4 fluxes from lakes. 

In my thesis, I investigated CH4 formation and CH4 bubble emissions (ebullition) in lakes, with a particular focus on sediment characteristics that control these processes, using different approaches such as laboratory experiments, field surveys and process-based modelling.

Sediment incubation experiments have revealed that CH4 formation rates can be predicted based on the age and total nitrogen content of the sediment. This relationship holds true across a wide range of sediment types found in various climates, ranging from alpine tundra to tropical regions, and can be effectively estimated by a common empirical model. Additionally, the supply and the quality of organic matter play a crucial role in determining the extent of CH4 formation in the sediment. Moreover, frequent additions of organic matter to surface sediment enhance the speed of CH4 formation rates. Importantly, the relationship between organic matter supply, its quality and frequency of addition with CH4 formation rates can be predicted with a logistic model. 

Field surveys conducted in a small eutrophic lake revealed that the spatial variability in CH4 ebullition is regulated by site-specific sediment characteristics: high CH4 ebullition rates were observed in areas characterized by elevated organic matter density in surface sediment and temporary sediment deposition, although no correlation was found with sediment accumulation rates.

The use of a 1D model to simulate CH4 fluxes from a lake demonstrated its ability to simulate fairly well the whole-lake average CH4 ebullition fluxes observed in the field, despite experiencing some interannual variability in model performance. However, when dividing the lake into smaller sections to simulate the observed longitudinal spatial variability in CH4 ebullition, the model systematically overestimated the fluxes. 

Overall, this thesis highlights the critical role of sediment characteristics and sedimentation regime on regulating the CH4 formation and ebullition fluxes, providing advancements in understanding CH4 dynamics in lakes.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2024. p. 55
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 2390
Keywords
methane, carbon cycle, lakes, sediment, modelling, limnology
National Category
Ecology Environmental Sciences Geochemistry
Research subject
Biology with specialization in Limnology
Identifiers
urn:nbn:se:uu:diva-526222 (URN)978-91-513-2100-4 (ISBN)
Public defence
2024-05-30, Ekmansalen, Evolutionary Biology Centre, Norbyvägen 14, Uppsala, 09:30 (English)
Opponent
Supervisors
Available from: 2024-05-03 Created: 2024-04-05 Last updated: 2024-05-03

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Moras, SimoneGrasset, CharlotteSobek, Sebastian

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