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Spatial Variability in Greenhouse Gas Production in Sediments of a Tropical Reservoir
Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
2015 (English)Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesisAlternative title
Rumslig variation i produktion av växthusgaser i sediment hos ett tropiskt vattenmagasin (Swedish)
Abstract [en]

The objective was to study the spatial variability of organic matter degradation in the sediments of a tropical reservoir to answer the hypothesis that degradation is significantly higher in river inflow areas than in other parts of the reservoir.

Sediment cores were collected from twelve sites in the nutrient poor drinking water reservoir Chapéu d’Uvas in Minas Gerais, Brazil. The sediments were analysed for CH4 concentrations in the pore water, degradation rates (in incubation experiments), and for the sediment properties: water content, carbon content and C/N-ratio.

The sediment properties: water content, carbon content and C/N-ratio were found to show higher values in non-inflow areas compared to inflow areas of the reservoir, and lowest in the main inflow river. This indicates other sources of sedimentary organic matter than the inflow rivers, and such sources could be erosion and/or landslides from the surrounding area. Also the CH4 concentration in the pore water was highest in the non-inflow areas, and lowest in the main inflow area. The oxic degradation rates from the sediment core incubation experiment on the other hand showed the highest mineralization rates in the main inflow area of the reservoir and lowest in the non- inflow bays, this is supporting the hypothesis.

Altogether the superficial aerobic degradation is highest in the inflow area while the methanogenic degradation in the deeper sediment layers is not highest in the inflow area. This implies that the organic load from the inflows is sufficient to supply the superficial degradation but not the degradation in the deeper layers of the sediment, which is fuelled by loads of organic matter from other sources, such as erosion. Other contributing explanations could be that the inflow pattern varies over time, so that the classification of the sites is not accurate for longer timescales.

Abstract [sv]

Målsättningen var att studera den rumsliga variationen av nedbrytningen av organiskt material i sediment hos en tropisk reservoar för att besvara hypotesen att nedbrytningen är signifikant högre i inflödesområden än i andra delar av reservoaren.

Sedimentprover har tagits vid tolv olika provplatser i den näringsfattiga dricksvattenreservoaren Chapéu d’Uvas i delstaten Minas Gerais, Brasilien. Sedimentproverna analyserades för CH4 koncentration i porvatten, nedbrytningshastighet (genom inkuberingsexperiment), och sedimentegenskaperna: vatteninnehåll, kolhalt och kol/kväve-kvot.

Sedimentegenskaperna visade på lägst halt organiskt material och minst andel terrestert material i huvudinflödet och högst i vikar utan inflöden. Detta indikerar att det förekommer materialtransport även till vikar utan inflöden vilket skulle kunna bero på erosion och/eller jordskred. Även metankoncentrationen i porvattnet visade sig vara högst i vikar utan inflöden och allra lägst vid huvudinflödet till reservoaren. Däremot visade inkuberingsexperimenten att mineraliseringen av kol i de ytliga sedimentlagren, i enlighet med hypotesen, var högst i huvudinflödet, lägre i inflödesvikarna men allra lägst i vikarna som saknade inflöden.

Sammantaget visar resultaten att den ytliga aeroba nedbrytningen var högst i huvudinflödena och lägst i vikar utan inflöden medan en omvänd tendens kunde observeras den metanogena nedbrytningen i de djupare sedimentlagren. Detta indikerar att tillförseln av organiskt material från inflödena är tillräcklig för att stimulera den aeroba ytliga nedbrytningen, medan den anaeroba nedbrytningen i de djupare sedimentlagren inte påverkas av detta. Förklaringen till detta kan vara att organiskt material inte bara tillförs reservoaren genom inflödena utan även genom jordskred och/eller erosion.

Place, publisher, year, edition, pages
2015. , 43 p.
UPTEC W, ISSN 1401-5765 ; 15054
Keyword [en]
CH4 production, C/N-ratio, water content, carbon mineralisation, tropical reservoir, greenhouse gas emission
National Category
Ecology Earth and Related Environmental Sciences Engineering and Technology
URN: urn:nbn:se:uu:diva-269586OAI: oai:DiVA.org:uu-269586DiVA: diva2:885110
Educational program
Master Programme in Environmental and Water Engineering
ERC Starting Grant 336642-HYDROCARB: "Towards a new understanding of carbon processing in freshwaters: methane emission hot spots and carbon burial in tropical reservoirs” led by Sebastian Sobek (Department of Ecology and Genetics, Limnology, UU).
Available from: 2016-01-21 Created: 2015-12-17 Last updated: 2016-01-21Bibliographically approved

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