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Diurnal variation of methane and nitrous oxide fluxes from a constructed wetland with emergent macrophytes
Linköping University, The Tema Institute, Department of Water and Environmental Studies. Linköping University, Faculty of Arts and Sciences.
Linköping University, The Tema Institute, Department of Water and Environmental Studies. Linköping University, Faculty of Arts and Sciences.
(English)Manuscript (preprint) (Other academic)
Abstract [en]

In order to obtain valid integrated estimates of annual fluxes of gases like methane and nitrous oxide using daytime measurements, it is essential to know their diurnal variations. Therefore, this study was done to supplement measurements of the daytime emission of these two gases from a constructed wetland in southern Sweden. The wetlandconcerned is a pilot scale system of ponds designed to reduce nitrogen levels in the wastewater from a neighbouring sewage treatment plant before it is released into a nearby river. Measurements were made during three occasions spread over the I998 and I999 growth seasons in order to cover young, mature and early senescent phases of the plants present (Typha latifolia L. and Lemna minor L.). Care was taken to capture the morning peaks in gaseous emissions (if present) that have been reported to occur sometimes. The rates of methane emission showed minor diurnal variations, which correlated with fluctuations in carbon dioxide assimilation rates together with wind speed (R2 = 0.55), supporting the hypothesis that pressurised ventilation of plants is involved in the fluxes. Only once was any indication of a morning peak in the methane emissions observed. Nitrous oxide emissions were also correlated with the wind speed (R2 =o.8o), so nitrous oxide was likely transported in the same manner. A conceptual model is presented, accounting for the effects of several importantvariables, such as production, consumption and different gaseous transport mechanisms,that explains the small diurnal variations observed in the methane emissions. The emission rates of the two gases rarely followed the same pattern, and sometimes even had reversed trends. The relatively small diurnal variations could be largely ignored, because of the much larger variations in daytime rates observed over the seasons due to a range of other factors.

National Category
Social Sciences Interdisciplinary
Identifiers
URN: urn:nbn:se:liu:diva-79119OAI: oai:DiVA.org:liu-79119DiVA: diva2:538341
Available from: 2012-06-29 Created: 2012-06-29 Last updated: 2012-06-29Bibliographically approved
In thesis
1. Constructed Wetlands and Deconstructed Discourses: Greenhouse gas fluxes and discourses on purifying capacities
Open this publication in new window or tab >>Constructed Wetlands and Deconstructed Discourses: Greenhouse gas fluxes and discourses on purifying capacities
2002 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis is a study within the sciences ofconstructed wetlands. It has two sections. Section one is a natural scienrific study ofgas fluxes from construcred wetlands and section two is an analysis ofhow natural sciences describe constructed wetlands.

The aim of section one was to determine methane and nitrous oxide fluxes between the atmosphere and constructed wetlands. The result from these gas flux studies showed that methane fluxes ranged between -375 and 1739 mg m-2 day1, whereas the nitrous oxide fluxes ranged from consumption at -350 to emissions at 1791 Jlg m-2 h-1. The annual inregrated methane fluxes were 87 mg m-2 day1, whereas the inregrated nitrous oxide fluxes resulred in an overall average of 126 µg N2O m-2 h-1. There were large temporal and spatial variations in gas fluxes but no differences between night and day. The methane rates were lower than the average rate, 225 mg m-2 day1, found at a constructed pilot scale wetland treating dairy wastewater in New Zealand (Tanner, 1997), but the cited measuremenrs were only taken during one monrh in mid-summer. The average and range of methane flux values in my study also showed that the methane emission rates were of the same magnitude as those observed from natural wetlands with similar vegetational composition. The nitrous oxide emissions observed in the Nykvarn study were ca. three to ten times higher than in previous studies of constructed wetlands treating wastewater, whereas the nitrous oxide consumption rate was approximately 80 times higher. The nitrous oxide fluxes were 3 to 180 times higher compared to other wetland systems. Emission factors were calculated according to the methods presenred by the Inrergovernmenral Panel of Climate Change (IPCC). The calculated nitrous oxide emission factors from Nykvarn were always lower (0.02 to 0.27%) compared to the default factor provided by the IPCC (0.75%).

The aim of section two was to analyse descriptions on purifying capacities in constructed wetlands in selected scienrific articles. This was made with help of a discourse analysis, which can be explained as a study of communication. The results from this analysis showed that the wetlands were described in terms of self-purifying, biochemical cycles. The cycle concept is used in all three discourses (case I to 3) but it is comprehended differently. In case I the cycling processes are treated as inrrinsic and unproblematic in relation to purification. In case 2, the purifying cycles are treated as dynamic, complex and problematic, but humans could influence them and develop their inrrinsic ability. In case 3 th~ cycling processes became a tool, allowing us to grasp, handle, act upon and influence the wetlands. In the thesis these differences are discussed with respecr to scienrific ideals including language in general and metaphors and concepts in parricular as weil as to the ambiguous relationship between humans and wetlands. Finally, the thesis conrain a reflection on the studies discussed in section I and II. The reflection aims at developing new paths for of gas flux investigations (with biosemiotic perspectives) in research fields related to constructed wetlands.

Place, publisher, year, edition, pages
Linköping: Linköpings universitet, 2002. 106 p.
Series
Linköping Studies in Arts and Science, ISSN 0282-9800 ; 253
Keyword
växthuseffekter, vattenrening, miljöaspekter
National Category
Social Sciences Interdisciplinary
Identifiers
urn:nbn:se:liu:diva-29577 (URN)14953 (Local ID)91-7373-321-0 (ISBN)14953 (Archive number)14953 (OAI)
Public defence
2002-04-26, Elysion, Hus T, Campus VAlla, Linköpings universitet, Linköping, 10:15 (English)
Supervisors
Available from: 2009-10-09 Created: 2009-10-09 Last updated: 2014-08-29Bibliographically approved

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Johansson, ElisabethSvensson, Bo

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