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Efficiency of a constructed wetland for retention of sediment associated phosphorus
Linköping University, Department of Physics, Chemistry and Biology, Ecology . Linköping University, The Institute of Technology. (Wetland Ecology)
WRS Uppsala AB, Sweden.
Linköping University, Department of Physics, Chemistry and Biology, Ecology . Linköping University, The Institute of Technology.
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. Vol. 674, no 1, 179-190 p.
Keyword [en]
Constructed wetland, long-term retention, diffuse pollution, particulate phosphorus, sediment accretion, sediment phosphorus fractions
National Category
Ecology
Identifiers
URN: urn:nbn:se:liu:diva-67880DOI: 10.1007/s10750-011-0728-yISI: 000293163900013OAI: oai:DiVA.org:liu-67880DiVA: diva2:413995
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
In thesis
1. Analysis of phosphorus retention variations in constructed wetlands receiving variable loads from arable land
Open this publication in new window or tab >>Analysis of phosphorus retention variations in constructed wetlands receiving variable loads from arable land
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:nbn:se:liu:diva-67893 (URN)LIU-TEK-LIC-2011:21 (Local ID)978-91-7393-168-7 (ISBN)LIU-TEK-LIC-2011:21 (Archive number)LIU-TEK-LIC-2011:21 (OAI)
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
2. Particulate phosphorus accumulation and net retention in constructed wetlands receiving agricultural runoff: Critical analysis of factors affecting retention estimates
Open this publication in new window or tab >>Particulate phosphorus accumulation and net retention in constructed wetlands receiving agricultural runoff: Critical analysis of factors affecting retention estimates
2015 (English)Doctoral thesis, comprehensive summary (Other academic)
Alternative title[sv]
Ansamling och fastläggning av partikelbunden fosfor i anlagda våtmarker på jordbruksmark : Faktorer som påverkar retentionsskattningar
Abstract [sv]

Övergödning är ett allvarligt miljöproblem, som bland annat orsakar omfattande blomningar av alger och blågrönbakterier. I söt- och brackvatten är fosfor ofta det mest begränsande näringsämnet för dessa organismer, varför en minskning av fosfortillförseln är nödvändig för att nå förbättringar. I Sverige beräknas jordbruket bidra med 44 % av fosforbelastningen till Egentliga Östersjön, och olika åtgärder för att minska fosforförlusterna från jordbruksmark tillämpas runtom i Sverige.

Våtmarker anläggs ofta för att fånga näringsämnen och partiklar från jordbruksmark innan de läcker ut i vattendrag och slutligen i Östersjön. Tidigare utvärderingar av anlagda våtmarker i Sverige har visat på en varierande och relativt låg fastläggning av fosfor. Osäkerheten kring dessa utvärderingar är dock ganska hög, och bottnar i kunskapsluckor både vad gäller processer för fastläggning och transport av fosfor från mindre jordbruksområden. I denna avhandling utreds därför hur anlagda våtmarker fungerar som fällor för jordpartiklar och partikelbunden fosfor i områden med höga fosforförluster.

Sju anlagda våtmarker i jordbruksområden med mycket lerjordar studerades, och mängden fosfor och partiklar som fastlades på botten varierade mycket mellan olika våtmarker (13-108 ton partiklar/ha/yr och 11-175 kg fosfor/ha/yr). De faktorer i området uppströms som var kopplade till fosforfastläggning var lutningen i området, markens lerhalt och innehåll av växttillgänglig fosfor samt områdets djurtäthet.

Resultat från fyra våtmarker visade på en hög resuspension (partiklar från botten virvlas tillbaka upp i vattnet), men en del av de uppvirvlade partiklarna kom troligtvis från erosion från våtmarkernas sidor och inte från det material som fastlades på botten. Man såg även indikationer på resuspension från vattenprover tagna i utloppet av en annan våtmark. Där var partikelbunden fosfor klart dominerande, vilket kan ha varit en konsekvens av resuspension från botten.

Variationerna av fosforkoncentrationer vid in- och utlopp i sju anlagda våtmarker studerades, för att kritiskt kunna granska tidigare retentionsskattningar. Det var stora variationer i sambanden mellan vattenflöde och fosforkoncentrationer mellan de olika våtmarkerna. De faktorer som påverkade sambandet mellan flöde och koncentration var 1) om det var varm eller kall årstid (d v s sommar eller vinter), 2) om det var högt eller lågt vattenflöde, samt 3) om inflödet bestod av ett dräneringsrör eller ett öppet dike/åfåra. I våtmarker med öppet dike som inflöde var flödes-koncentrationssambandet av totalfosfor negativt vid låga flöden och positivt vid höga flöden. De olika sambanden visar hur viktig sättet att provta vatten är, då inkommande mängd fosfor både kan över- och underskattas om man inte är medveten om sådana variationer. Vid automatisk provtagning styrd av flödesmätningen sker detta ofta i utloppet, men eftersom vattnet har en viss uppehållstid i våtmarken (speciellt sommartid) kan retentionsberäkningen påverkas av att all provtagningen styrs av flödet i utloppet.    

För att identifiera vilka områden som bidrar med mest näring och partiklar valdes ett stort område dominerat av jordbruksmark ut – för att undersöka hur man skulle kunna bedöma var anlagda våtmarker skulle kunna göra mest nytta. Området delades in i tio mindre områden, och vattenprover samlades in från diken och åfåror. Resultaten visade på stora skillnader i fosfordynamik mellan olika delområden med olika jordtyper, trots att de hade liknande markanvändning. Det fanns ofta en koppling mellan höga fosforkoncentrationer i vattnet och en hög andel lerjordar i området. För partiklar fanns det en tendens till samband mellan höga koncentrationer och hög andel vinterbar mark. En anlagd våtmark skulle antagligen ha högst effekt om den placerades nedströms områden som är känsliga för erosion – områden med hög andel lerjordar eller med hög andel vinterbar mark.

Abstract [en]

Eutrophication is one of the more serious current environmental problems, causing algal blooms and anoxic bottoms. In fresh and brackish water, phosphorus (P) is often the most limiting nutrient, and various mitigating strategies are used to reduce the load of P to sensitive recipients. In the agricultural sector, this includes both on-field measures (e.g. managing P inputs) and measures at the field edge (e.g. buffer zones and constructed wetlands). Previous evaluations of constructed wetlands (CWs) in Sweden have indicated a variable and relatively low P retention. However, the uncertainties in the estimates are large, and related to an incomplete knowledge about both retention processes and factors determining the P load from agricultural land. Hence, the overall aim of this thesis was to investigate possible reasons for the variation in wetland P retention estimates, and to assess the P retention in wetlands located in agricultural areas where losses are expected to be high.

When comparing seven CWs located downstream small catchments with predominantly arable land, the particle and P net accumulation varied considerably (13-108 t particles ha-1 yr-1 and 11-175 kg P ha-1 yr-1, respectively). Catchment factors that were statistically correlated with accumulation of particles and P in the CWs were the slope of the arable land, the P content of the top soil, the animal density (expressed as livestock units per arable land) and the percentage clay in the topsoils.

In four of the wetlands, resuspension was studied using sediment traps and plates. The results showed that up to 87 % of the settled material was resuspended, and indicated that erosion of the wetland sides and bottom probably contributed a substantial part of the trapped particles.

In order to critically evaluate existing retention data from earlier investigations, the temporal dynamics of P concentrations and P retention in seven CWs were evaluated. The relationships between water flow and concentration (from grab sampling) varied, and depended on the season (warm or cold period of the year), water flow (high or low) and the inlet type (drainage pipe or open ditch). In CWs that received water through an open ditch, flow-concentration relationships were negative during low flow periods but positive during high flow periods. These differences in flow-concentration relationship have implications for water sampling, since P loads can be both over- and underestimated with grab or automatic sampling guided by clock-time. Also composite automatic sampling, regulated from the water flow at the outlet, can lead to errors in transport calculations since the same ‘water parcel’ is not measured at in and out (difference depending on how long the water retention time is in the CW). This may have an effect on estimates of P retention in both past, present and future investigations of constructed wetlands.

Finally, a synoptic sampling approach with ten sampling points was used in an agriculturally dominated catchment area (160 km2) to identify differences in nutrient transport dynamics and areas with the highest losses. Spatial differences in P concentrations were strongly correlated with some of the catchment factors, for instance with soil type, and particle concentrations were weakly correlated to agricultural practices associated with bare soils during winter. This supports the practice to focus P mitigation measures – such as constructed wetlands – to erosion sensitive areas.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2015. 49 p.
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1648
Keyword
Phosphorus retention, constructed wetlands, agriculture, sampling strategy
National Category
Biological Sciences
Identifiers
urn:nbn:se:liu:diva-117116 (URN)10.3384/diss.diva-117116 (DOI)978-91-7519-107-2 (print) (ISBN)
Public defence
2015-05-29, Planck, Fysikhuset, Campus Valla, Linköping, 10:00 (English)
Opponent
Supervisors
Available from: 2015-04-16 Created: 2015-04-16 Last updated: 2015-05-19Bibliographically approved

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