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Effects of vegetation and hydraulic load on seasonal nitrate removal in treatment wetlands
Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
Halmstad University.
Halmstad University.
Halmstad University.
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2009 (English)In: ECOLOGICAL ENGINEERING, ISSN 0925-8574, Vol. 35, no 5, 946-952 p.Article in journal (Refereed) Published
Abstract [en]

Optimising nitrate removal and identifying critical factors for nitrate removal in wetlands is an important environmental task in the effort to achieve better surface water quality. In this study, eighteen free water surface wetlands with similar shape and size (22 m(2) each) received groundwater with a high nitrate-N concentration (about 11 mg l(-1)). The effects of two hydraulic loads, 0.13 m d(-1) and 0.39 m d(-1), and three vegetation types - emergent, submersed and freely developing vegetation - on the nitrate-N removal were investigated through mass inflow and outflow measurements. No significant difference in nitrate removal between the different hydraulic loads could be detected. Significantly higher area-specific nitrate removal and first-order area-based rate coefficients were found in the basins with emergent vegetation, with no difference between the basins with submersed and freely developing vegetation. The nitrate-N removal increased as the wetlands matured and the vegetation grew denser, emphasizing the role of dense emergent vegetation for nitrate removal at high nitrate concentrations.

Place, publisher, year, edition, pages
2009. Vol. 35, no 5, 946-952 p.
Keyword [en]
Hydraulic load, Removal rate coefficient, Season, Vegetation, Wetland nitrate removal
National Category
Natural Sciences
Identifiers
URN: urn:nbn:se:liu:diva-18951DOI: 10.1016/j.ecoleng.2009.01.001OAI: oai:DiVA.org:liu-18951DiVA: diva2:222139
Available from: 2009-06-06 Created: 2009-06-05 Last updated: 2011-01-10
In thesis
1. Nitrogen removal in treatment wetlands: Factors influencing spatial and temporal variations
Open this publication in new window or tab >>Nitrogen removal in treatment wetlands: Factors influencing spatial and temporal variations
2006 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Decreasing the nitrogen transport from land to surrounding seas is a major task throughout the world to limit eutrophication of the coastal areas. Several approaches are currently used, including the establishment of wetlands, to decrease the transport of nitrogen. Wetlands represent ecosystems where the nitrogen removal from water can be efficient given that they are appropriately designed. The aim of this thesis was to investigate and quantify the effect of critical factors that regulate the nitrogen removal in wetlands, and to develop better guidelines for wetland design. Studies were performed at different scales, from microcosms to full scale wetlands, and methods included modelling, mass balance calculations and process studies.

A first order rate model was used to simulate the nitrogen transformations in two large wetlands treating wastewater containing both ammonium and nitrate nitrogen. It was found that the dynamics of the main itrogen transformation processes could not be satisfactorily described using this approach. Large wetlands containing vegetation are complex ecosystems, and the process rates vary in both time and space. The great diversity of microenvironments favours different nitrogen processes, and large differences in potential nitrification and denitrification rates were found between different surface structures within a wetland. The results from microcosms measurements showed that the highest potential for nitrification was on surfaces in the water column, while the denitrification capacity was highest in the sediment.

For the sediment denitrification capacity, the plant community

composition was shown to be of major importance primarily by supplying litter serving as a carbon and energy source, and/or attachment surfaces, for denitrifying bacteria. Denitrification rates may be affected more than three fold by different types of litter and detritus in the sediments. Intact sediment cores from stands of the emergent plants Glyceria maxima and Typha latifolia had higher denitrification potential than sediment cores from stands of the submersed plant Potamogeton pectinatus. However, the quality of the organic material for the denitrifying bacteria was highest in G. maxima and P. pectinatus stands. All sediment cores from the wetland were limited by carbon, and the lower denitrification capacity of the submersed plant, P. pectinatus, was likely due to lower amounts of organic matter. However, in another wetland, intact cores from stands of the submersed plant Elodea canadensis had a higher denitrification capacity than the cores from stands of T. latifolia and Phragmites australis. This was possibly due to a larger biomass, and better quality, of the organic matter from that submersed specie, or to epiphytic biofilms on the living plants. Those microcosms studies showed that both the quality of the organic matter as a substrate for the microbial communities, and the amount of organic material produced were important for the denitrification capacity.

In pilot scale wetlands, the composition of the plant community was also a more important factor for high nitrate removal than the differences in hydraulic loads (equivalent of 1 or 3 d retention time), despite the cold climate. The greatest removal was found in wetlands with emergent vegetation dominated by P. australis and G. maxima, rather than in wetlands with submersed vegetation. In brief, the results presented in this thesis emphasize the importance of dense emergent vegetation for high annual nitrate removal in treatment wetlands.

Place, publisher, year, edition, pages
Institutionen för fysik, kemi och biologi, 2006
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1041
Keyword
Wetlands, denitrification, macrophytes, nitrogen, nitrification, model, treatment wetlands, potential denitrification
National Category
Biological Sciences
Identifiers
urn:nbn:se:liu:diva-7564 (URN)91-85523-12-7 (ISBN)
Public defence
2006-11-10, Planck, Fysikhuset, Campus Valla, Linköpings universitet, Linköping, 10:15 (English)
Opponent
Supervisors
Available from: 2006-10-09 Created: 2006-10-09 Last updated: 2009-06-10

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