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Constructed wetlands - nature's kidneys or cleaning machines?: An analysis of papers on the self-purifying capacity of constructed wetlands
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]

This paper focuses on the purifying capacity of wetlands constructed to treat wastewater. Fifty-nine scientific papers about such wetlands, published during the period 1992-1997, were assessed. The aims of the study were, first, to examine how constructed wetlands were described and, second, to analyse the concepts and metaphors related to wetland purifying capacity. In the papers studied, the wetlands were described in terms of self-purifying, biochemical cycles. Particular metaphors, such as "agent", make it possible to convey a specific concept of a wetland's role in wastewater purification. However, the characteristics of self-purification were depicted in three very different ways in different papers. In some cases they were described as simple, stable and effective. In others they were described as complex, dynamic and very variable. Finally, they were sometimes paradoxically described as a combination of the two, for example, as simple and complex, stable and dynamic or effective and with variable efficiency. Thus, there was a conflict in the papers between the idealised view of the intrinsic purifying power of the wetlands and the actual results of purification. The paradox of wetlands being both simple and complex can be explained by the different explanations of the process of purification, as well as by the ambiguous relationship between humans and wetlands.

Keyword [en]
constructed wetland, purifying capacity, description, concept, metaphor, cycles
National Category
Social Sciences Interdisciplinary
URN: urn:nbn:se:liu:diva-79122OAI: diva2:538349
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.
Linköping Studies in Arts and Science, ISSN 0282-9800 ; 253
växthuseffekter, vattenrening, miljöaspekter
National Category
Social Sciences Interdisciplinary
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)
Available from: 2009-10-09 Created: 2009-10-09 Last updated: 2014-08-29Bibliographically approved

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Johansson, Elisabeth
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