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Nitrogen removal in treatment wetlands: Factors influencing spatial and temporal variations
Linköping University, Department of Physics, Chemistry and Biology, Ecology . Linköping University, The Institute of Technology.
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 [en]
Wetlands, denitrification, macrophytes, nitrogen, nitrification, model, treatment wetlands, potential denitrification
National Category
Biological Sciences
Identifiers
URN: urn:nbn:se:liu:diva-7564ISBN: 91-85523-12-7 (print)OAI: oai:DiVA.org:liu-7564DiVA: diva2:22580
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
List of papers
1. Modelling nitrogen transformations in free water surface wastewater treatment wetlands in Sweden
Open this publication in new window or tab >>Modelling nitrogen transformations in free water surface wastewater treatment wetlands in Sweden
2001 (English)In: Water Science and Technology, ISSN 0273-1223, Vol. 44, no 11-12, 237-244 p.Article in journal (Refereed) Published
Abstract [en]

The purpose of this study was to describe and compare the fate of nitrogen (N) in two Swedish wastewater treatment wetlands in the cities of Oxelösund and Hässleholm. Specifically, we wanted to see if a fairly simple model, developed with regard to common data availability, could satisfactorily describe the concentration dynamics at the outlet from the wetlands. A first-order area-based model, with two alternative expressions for temperature dependence, was set up to describe three major processes: ammonification, nitrification and denitrification. The N concentration dynamics at the outlet of the Oxelösund wetland was not satisfactorily described, R2(NH4+-N)=0.33 and R2(NO3--N)=0.10, while the modelled concentrations corresponded quite well with measured concentrations in the Hässleholm wetland, R2(NH4+-N)=0.83 and R2(NO3--N)=0.58. The NO3--N concentrations, in both wetlands, could be slightly better described when introducing a temperature coefficient as an additional free parameter. The explained variances reported above were achieved when the model was calibrated individually for the two wetlands, when the resulting (optimised) reaction rate coefficients for each of the three processes were quite different between the two wetlands. To improve model performance, the rate equations may have to be changed to include factors in addition to concentration and temperature, such as dissolved oxygen and hydraulic efficiency. It may also be important to include other processes, such as plant uptake/decay and ammonia volatilisation.

National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-14075 (URN)
Available from: 2006-10-09 Created: 2006-10-09
2. Potential nitrification and denitrification on different surfaces in a constructed treatment wetland
Open this publication in new window or tab >>Potential nitrification and denitrification on different surfaces in a constructed treatment wetland
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2004 (English)In: Journal of environmental quality, ISSN 0047-2425, Vol. 32, no 6, 2414-2420 p.Article in journal (Refereed) Published
Abstract [en]

Improved understanding of the importance of different surfaces in supporting attached nitrifying and denitrifying bacteria is essential if we are to optimize the N removal capacity of treatment wetlands. The aim of this study was therefore to examine the nitrifying and denitrifying capacity of different surfaces in a constructed treatment wetland and to assess the relative importance of these surfaces for overall N removal in the wetland. Intact sediment cores, old pine and spruce twigs, shoots of Eurasian watermilfoil (Myriophyllum spicatum L.), and filamentous macro-algae were collected in July and November 1999 in two basins of the wetland system. One of the basins had been constructed on land that contained lots of wood debris, particularly twigs of coniferous trees. Potential nitrification was measured using the isotope-dilution technique, and potential denitrification was determined using the acetylene-inhibition technique in laboratory microcosm incubations. Nitrification rates were highest on the twigs. These rates were three and 100 times higher than in the sediment and on Eurasian watermilfoil, respectively. Potential denitrification rates were highest in the sediment. These rates were three times higher than on the twigs and 40 times higher than on Eurasian watermilfoil. The distribution of denitrifying bacteria was most likely due to the availability of organic material, with higher denitrification rates in the sediment than on surfaces in the water column. Our results indicate that denitrification, and particularly nitrification, in treatment wetlands could be significantly increased by addition of surfaces such as twigs.

National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-14076 (URN)
Available from: 2006-10-09 Created: 2006-10-09 Last updated: 2009-05-22
3. Potential denitrification in wetland sediments with different plant species detritus
Open this publication in new window or tab >>Potential denitrification in wetland sediments with different plant species detritus
2005 (English)In: Ecological engineering, ISSN 0925-8574, Vol. 25, no 2, 183-190 p.Article in journal (Refereed) Published
Abstract [en]

The effect of detritus originating from different plant species on denitrifying capacity was investigated in a Swedish wastewater treatment wetland. Intact sediment cores containing sediment with a detritus layer were collected from wetland basins dominated by Typha latifolia, Phragmites australis, or Elodea canadensis in November 2000 and potential denitrification was measured using the acetylene-inhibition method.

The cores from stands of E. canadensis showed more than three times higher denitrification capacity than the cores of the other plants. Bacterial abundance per unit dry weight was both highest and lowest in the detritus of P. australis, whereas the C/N ratio was lower in the cores of E. canadensis. This suggests that the submerged plant provided more organic material of high quality to support heterotrophic organisms. It is also possible that the surfaces of E. canadensis offered more or more suitable surfaces for bacterial growth and thereby increased the bacterial population.

It is apparent that denitrifying bacteria were more favored by E. canadensis detritus than by detritus from the emergent plant species at the time of sampling. Since the turnover of plant detritus varies considerably among species, the seasonal variation in denitrification capacity is likely to be quite different for different plants.

Keyword
Constructed wetland; Potential denitrification; Detritus; Macrophytes; Cold climate
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-14077 (URN)10.1016/j.ecoleng.2005.04.013 (DOI)
Available from: 2006-10-09 Created: 2006-10-09
4. Seasonal denitrification potential in wetland sediments with organic matter from different plant species
Open this publication in new window or tab >>Seasonal denitrification potential in wetland sediments with organic matter from different plant species
2007 (English)In: Water, Air and Soil Pollution, ISSN 0049-6979, E-ISSN 1573-2932, Vol. 183, no 1-4, 25-35 p.Article in journal (Refereed) Published
Abstract [en]

Vegetation both physically and biochemically influences denitrification in wetlands. Litter from various plant species supplies various amounts and qualities of organic carbon to denitrifying bacteria, and may thus affect denitrification capacity. We explore whether there is seasonal variation in the denitrification potential in stands of Glyceria maxima, Phragmites australis, Typha latifolia, and Potamogeton pectinatus (the stands differed in terms of which species was predominant). Experiments and measurements investigated whether denitrification potential was related to organic matter and its availability to denitrifying bacteria, suitability for bacterial growth, and amount in the wetland. Availability of organic material, as measured in the slurries, was highest in the G. maxima and P. pectinatus samples, with the highest availability in May and August. However, when the samples were closer to wetland conditions, i.e., intact sediment cores containing litter and organic sediment, the denitrifying capacity was highest in the cores from G. maxima stands, but lowest in P. pectinatus cores. In addition, the denitrification potential of the intact cores was highest in November. Differences in denitrification capacity between the slurries and intact sediment cores, considering the organic material of the plant species and the seasonal pattern, were attributed to differences in the amount of plant litter generated.

Keyword
denitrification, potential denitrification, wetlands, macrophytes, litter, organic material, organic matter, sediment, intact core
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-14078 (URN)10.1007/s11270-007-9352-x (DOI)
Available from: 2006-10-09 Created: 2006-10-09 Last updated: 2017-12-13
5. Effects of vegetation and hydraulic load on seasonal nitrate removal in treatment wetlands
Open this publication in new window or tab >>Effects of vegetation and hydraulic load on seasonal nitrate removal in treatment wetlands
Show others...
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.

Keyword
Hydraulic load, Removal rate coefficient, Season, Vegetation, Wetland nitrate removal
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-18951 (URN)10.1016/j.ecoleng.2009.01.001 (DOI)
Available from: 2009-06-06 Created: 2009-06-05 Last updated: 2011-01-10

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