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Greenhouse gas emission from tropical reservoirs: Spatial and temporal dynamics
Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology. (Limnology, Department of Ecology and Gene)ORCID iD: 0000-0002-3609-5107
2019 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The emission of methane (CH4) and carbon dioxide (CO2) from reservoirs has been estimated to make up for about 1.3% of the global anthropogenic greenhouse gas emission. The impoundment of a river leads to the accumulation of sediment that is brought in from inflowing rivers, and the sediment organic matter is degraded to CH4 and CO2. CH4 is of particular concern as its global warming potential is 34 times stronger than that of CO2. In the tropics, high temperatures and high availability of fresh organic matter from high net primary production fuel CH4 and CO2 production. As the construction of hydropower plants is currently undergoing a boom, especially in the tropics, reservoir emission is probably bound to increase.

The emission of CH4 and CO2 from reservoir surfaces is, however, highly variable, which makes current estimates uncertain. This thesis is built on the hypothesis that the spatial and temporal variability of greenhouse gas emission in tropical reservoirs, particularly of CH4 ebullition (the emission via gas bubbles), is so large that the sampling strategy affects whole-system estimates of greenhouse gas emission.

This thesis shows that greenhouse gas emission from the four studied tropical reservoirs in Brazil varied greatly at different timescales – over 24 hours, between days and between seasons. Seasonal variability was identified as the most important temporal scale to be covered for CH4 ebullition inventories. In addition, the spatial variability of gas emission was large for all pathways. The variability of CH4 ebullition across space, for example, was estimated to be almost as large as its variability between seasons, and patterns of spatial variability in diffusive CH4 and CO2 emission differed between seasons. For both ebullition and diffusion, river inflow areas were prone to elevated greenhouse gas emission.

This thesis shows that for retrieving solid emission estimates, there is no alternative to time-consuming measurements in the field. Measurements should be repeated at least once during each hydrological season (i.e. falling and rising water level). The seasonal surveys should cover space at a high resolution, including areas with and without river inflows, and different water column depths. CH4 ebullition made up for 60–99% of the total CO2-equivalent emission from the whole water surface of the studied reservoirs, with the highest contribution in the most productive reservoir. The most variable greenhouse gas emission pathway is therefore the most important one to be measured at appropriate resolution, particularly in productive reservoirs.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2019. , p. 79
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1859
Keywords [en]
methane, carbon dioxide, climate, carbon cycle, lake, limnology, inland water
National Category
Environmental Sciences Climate Research Oceanography, Hydrology and Water Resources Geosciences, Multidisciplinary
Identifiers
URN: urn:nbn:se:uu:diva-393433ISBN: 978-91-513-0757-2 (print)OAI: oai:DiVA.org:uu-393433DiVA, id: diva2:1353264
Public defence
2019-11-08, Friessalen, Norbyvägen 18, Uppsala, 09:15 (English)
Opponent
Supervisors
Available from: 2019-10-18 Created: 2019-09-22 Last updated: 2019-11-12
List of papers
1. Deconstructing carbon emission pathways of a diel cycle from four tropical reservoirs
Open this publication in new window or tab >>Deconstructing carbon emission pathways of a diel cycle from four tropical reservoirs
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(English)In: Article in journal (Refereed) Submitted
National Category
Climate Research Environmental Sciences Oceanography, Hydrology and Water Resources Geosciences, Multidisciplinary
Identifiers
urn:nbn:se:uu:diva-393436 (URN)
Available from: 2019-09-22 Created: 2019-09-22 Last updated: 2019-09-30
2. Comparing methane ebullition variability across space and time in a Brazilian reservoir
Open this publication in new window or tab >>Comparing methane ebullition variability across space and time in a Brazilian reservoir
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(English)In: Article in journal (Other academic) Submitted
Keywords
CH4, carbon cycle, lake, biogeochemistry, spatial, temporal scale
National Category
Climate Research Environmental Sciences Geosciences, Multidisciplinary Oceanography, Hydrology and Water Resources
Research subject
Biology with specialization in Limnology
Identifiers
urn:nbn:se:uu:diva-393435 (URN)
Available from: 2019-09-22 Created: 2019-09-22 Last updated: 2019-09-30
3. Spatially Resolved Measurements of CO2 and CH4 Concentration and Gas-Exchange Velocity Highly Influence Carbon-Emission Estimates of Reservoirs
Open this publication in new window or tab >>Spatially Resolved Measurements of CO2 and CH4 Concentration and Gas-Exchange Velocity Highly Influence Carbon-Emission Estimates of Reservoirs
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2018 (English)In: Environmental Science and Technology, ISSN 0013-936X, E-ISSN 1520-5851, Vol. 52, no 2, p. 607-615Article in journal (Refereed) Published
Abstract [en]

The magnitude of diffusive carbon dioxide (CO2) and methane (CH4) emission from man-made reservoirs is uncertain because the spatial variability generally is not well-represented. Here, we examine the spatial variability and its drivers for partial pressure, gas-exchange velocity (k), and diffusive flux of CO2 and CH4 in three tropical reservoirs using spatially resolved measurements of both gas concentrations and k. We observed high spatial variability in CO2 and CH4 concentrations and flux within all three reservoirs, with river inflow areas generally displaying elevated CH4 concentrations. Conversely, areas close to the dam are generally characterized by low concentrations and are therefore not likely to be representative for the whole system. A large share (44–83%) of the within-reservoir variability of gas concentration was explained by dissolved oxygen, pH, chlorophyll, water depth, and within-reservoir location. High spatial variability in k was observed, and kCH4 was persistently higher (on average, 2.5 times more) than kCO2. Not accounting for the within-reservoir variability in concentrations and k may lead to up to 80% underestimation of whole-system diffusive emission of CO2 and CH4. Our findings provide valuable information on how to develop field-sampling strategies to reliably capture the spatial heterogeneity of diffusive carbon fluxes from reservoirs.

National Category
Ecology
Identifiers
urn:nbn:se:uu:diva-337400 (URN)10.1021/acs.est.7b05138 (DOI)000423012200025 ()29257874 (PubMedID)
Funder
EU, European Research Council, 336642
Available from: 2017-12-25 Created: 2017-12-25 Last updated: 2019-09-22Bibliographically approved
4. Upscaling spatially-resolved methane ebullition measurements in two contrasting tropical reservoirs
Open this publication in new window or tab >>Upscaling spatially-resolved methane ebullition measurements in two contrasting tropical reservoirs
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(English)Manuscript (preprint) (Other academic)
National Category
Environmental Sciences Climate Research Geosciences, Multidisciplinary Oceanography, Hydrology and Water Resources
Identifiers
urn:nbn:se:uu:diva-393434 (URN)
Available from: 2019-09-22 Created: 2019-09-22 Last updated: 2019-09-30
5. Spatial heterogeneity of diffusive CO2 and CH4 emission varies seasonally in four tropical reservoirs
Open this publication in new window or tab >>Spatial heterogeneity of diffusive CO2 and CH4 emission varies seasonally in four tropical reservoirs
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(English)In: Article in journal (Refereed) Submitted
National Category
Climate Research Environmental Sciences Geosciences, Multidisciplinary Oceanography, Hydrology and Water Resources
Identifiers
urn:nbn:se:uu:diva-393437 (URN)
Available from: 2019-09-22 Created: 2019-09-22 Last updated: 2019-09-30

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