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Analysis of phosphorus retention variations in constructed wetlands receiving variable loads from arable land
Linköping University, Department of Physics, Chemistry and Biology, Ecology . Linköping University, The Institute of Technology. (Wetland Ecology)
2011 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

Seven wetlands, constructed on agricultural land in the south of Sweden, were investigated with respect to phosphorus (P) retention. The overall aim was to increase the understanding of P retention and find possible explanations for the variations in retention that have been observed in previous studies. This was done by i) investigating P retention in wetlands receiving various water and P loads, ii) investigating the effect of variations in water flow on P transport, iii) comparing how well retention estimates based on water quality data agreed with measurements of the amount of P accumulated in the sediment.

Results showed that P retention was positive in all wetlands, but it was variable (1–58 kg ha-1 yr-1) and months with negative retention were observed in nearly all wetlands. Such  monthly negative retention coincided with i) high flow periods, when particulate P was either flushed straight through the wetlands or resuspended from the bottoms, and ii) warm low flow periods, in which case dissolved P was probably released from wetland sediments due to anoxic conditions.

The results from the two methods for estimating P retention differed. Based on water quality data, the total P load during four years was 65 kg ha-1 and the mean P retention 2.8 kg ha-1 yr-1, or 17% of the total P load. In contrast, the amount of P accumulated in the inlet zone alone amounted to 78% of the P load, and the P content in the upper sediment of the whole wetland area exceeded the P load with a factor four. This discrepancy showed the need to add studies of sediment accumulation to inflow-outflow estimates for an improved understanding of wetland P retention.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press , 2011. , 28 p.
Series
Linköping Studies in Science and Technology. Thesis, ISSN 0280-7971 ; 1482
National Category
Natural Sciences
Identifiers
URN: urn:nbn:se:liu:diva-67893Local ID: LIU-TEK-LIC-2011:21ISBN: 978-91-7393-168-7OAI: oai:DiVA.org:liu-67893DiVA: diva2:414122
Presentation
2011-05-25, Schrödinger, E324, Fysikhuset, Campus Valla, Linköpings universitet, Linköping, 10:15 (English)
Opponent
Supervisors
Available from: 2011-05-10 Created: 2011-05-02 Last updated: 2011-05-10Bibliographically approved
List of papers
1. Phosphorus load variations and retention in non-point source wetlands in southern Sweden
Open this publication in new window or tab >>Phosphorus load variations and retention in non-point source wetlands in southern Sweden
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(English)Manuscript (preprint) (Other academic)
Abstract [en]

Data from seven constructed wetlands receiving runoff from agricultural catchments in the south of Sweden were investigated with respect to phosphorus (P) retention. The seven wetlands differed in size (0.22-2 ha), design, land use and catchment characteristics. The hydraulic load varied between 7 and 725 m yr-1, which reflect the different geographical and hydrological conditions. The overall aim of this study was to increase the understanding of how water flow and inflow P concentration varations affect the P retention in constructed wetlands receiving runoff from arable land. Water flow was measured continuously, and time or flow proportional water samples were taken. Grab samples were taken during high flow periods and also to supplement the automatic water sampling. P retention varied between wetlands, from 1 to 58 kg ha-1 yr-1, and was correlated to the P load (R2=0.9, p<0.05). P retention in the wetlands varied strongly between years, and negative retention was recorded for some years and wetlands. When investigating monthly retention for each wetland, release of P corresponded to either high flow or possible anoxic conditions during low-flow periods in summer or during winter when ice covered the wetlands. Analyses of grab samples revealed a relationship between TP concentration and water flow for most wetlands. In some wetlands, P was transported mainly as particulate P (PP), but in other wetlands, soluble P was the dominating form in both inflow and outflow. Incoming concentrations varied greatly between wetlands (1-2000 μg l-1) which reflected the different catchment characteristics, e.g. land use, soil type and topography.

National Category
Ecology
Identifiers
urn:nbn:se:liu:diva-67877 (URN)
Available from: 2011-05-02 Created: 2011-05-02 Last updated: 2011-05-10Bibliographically approved
2. Efficiency of a constructed wetland for retention of sediment associated phosphorus
Open this publication in new window or tab >>Efficiency of a constructed wetland for retention of sediment associated phosphorus
2011 (English)In: Hydrobiologia, ISSN 0018-8158, E-ISSN 1573-5117, Vol. 674, no 1, 179-190 p.Article in journal (Refereed) Published
Abstract [en]

A constructed wetland (2.1 ha; 2% of catchment area) in southeast Sweden, in a catchment with 35% arable land on clay soils, was investigated with respect to phosphorus (P) retention, focusing on particulate P (PP) and sediment accretion. The aims were to i) estimate P retention and identify the dominating retention processes; ii) investigate how well estimates of P retention based on inflow-outflow measurements compared with the amount of P accumulated in the sediment. In- and outflow of P was measured during four years with continuous flow measurements and flow proportional weekly composite samples. P in the accumulated sediment was estimated based on core samples and analyzed using sequential fractionation. Total P load during four years was 65 kg/ha and intensive sampling events detected 69% as PP. Based on inflow-outflow estimates the mean P retention was 2.8 kg/ha/yr, or 17%, but the amount of P accumulated in the inlet zone  equated 78% of the TP load. This discrepancy showed the need to add studies of sediment accumulation to inflow-outflow estimates for an improved understanding of the P retention. The dominating P forms in the sediment were organic P (38%) and P associated with iron or aluminum (39%), i.e. potentially mobile forms. In areas colonized by Typha latifolia, the amount of P in the upper sediment layer (390 kg) was more than double the total P load of 136 kg. Cycling and release in those areas is a potential source of P that deserves further attention.

Place, publisher, year, edition, pages
Springer, 2011
Keyword
Constructed wetland, long-term retention, diffuse pollution, particulate phosphorus, sediment accretion, sediment phosphorus fractions
National Category
Ecology
Identifiers
urn:nbn:se:liu:diva-67880 (URN)10.1007/s10750-011-0728-y (DOI)000293163900013 ()
Note
The original publication is available at www.springerlink.com: Karin Johannesson, Jonas Andersson and Karin Sundblad-Tonderski, Efficiency of a constructed wetland for retention of sediment associated phosphorus, 2011, Hydrobiologia, (674), 1, 179-190. http://dx.doi.org/10.1007/s10750-011-0728-y Copyright: Springer Science Business Media http://www.springerlink.com/ Available from: 2011-05-02 Created: 2011-05-02 Last updated: 2015-04-16Bibliographically approved

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