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avai lab le at www.sc iencedi rec t .com

journa l homepage: www.e lsev ier .com/ locate /eco leng

ditorial

ollution control by wetlands

r t i c l e i n f o

eywords:

onstructed wetlands

eavy metals

itrogen removal

rganic pollutants

harmaceuticals

hosphorus retention

a b s t r a c t

The 2nd International Symposium on Wetland Pollutant Dynamics and Control (WETPOL

2007), organised by the Department of Geography of the University of Tartu (Estonia) in co-

operation with partners from the Estonian University of Life Sciences (Tartu, Estonia), Ghent

University (Belgium), and the UNESCO-IHE (Delft, The Netherlands), was held 16–20 Septem-

ber 2007, in Tartu, Estonia. At this meeting, 140 oral presentations (including 9 keynote

speeches) and 70 posters by representatives from 38 countries were presented. About half

of the presentations considered purification processes in both semi-natural and constructed

etland modelling

etland restorationwetlands. The editorial paper highlights trends in studying the cycling of nitrogen, phos-

phorus, carbon, heavy metals, and organic pollutants in wetlands, but also in the modelling

of pollutant removal and the functioning of plants in the wetland environment. It also

describes the WETPOL 2007 meeting, which served as the source of the selected papers,

and briefly explains the main aspects of these papers.

. Introduction

mong the values of wetlands and the ecosystem ser-ices they provide (Costanza et al., 1997), water qualitymprovement and the control of pollutant transport are the

ost important regulatory functions (Mitsch and Gosselink,000, 2007; Blackwell et al., 2002; Zedler and Kercher, 2005;erhoeven et al., 2006).

People have used wetlands for pollution control for cen-uries (Mitsch and Jørgensen, 1989, 2004), although thecientifically based use of wetlands for wastewater treat-ent in constructed wetlands began in the 1950s and 1960sith investigations by Prof. K. Seidel and Prof. R. Kickuth inermany (Seidel, 1966; Kickuth, 1970, 1984). Constructed treat-ent wetlands are defined as engineered wetlands that utilize

atural processes involving wetland vegetation, soil, and theirssociated microbial assemblages to assist, at least partially,n treating wastewater or other polluted water sources (Kadlecnd Knight, 1996). The number of constructed treatmentetlands receiving wastewater from municipal, industrial,

gricultural, and storm water sources has increased to more

han 20,000 across the world (Vymazal and Kröpfelová, 2008).f planned properly, these treatment wetlands offer oppor-unities to regain some of the natural functions of wetlandsnd offset some of the significant losses in the wetland area.

The success is based on the combination of differently loadedand organized smaller wetland cells, which have the ability toguarantee proper oxic and/or anoxic conditions and outflowquality. With appropriate siting, design, pretreatment, moni-toring, operation and maintenance, these manmade systemscan often emulate natural wetlands by providing integratedecological functions within the watershed and landscape(Kadlec and Knight, 1996; Mitsch and Gosselink, 2007).

A brief analysis using publications indexed by the Instituteof Science Information (ISI) Web of Science (WoS) from 1980to July 2008 shows that the number of papers on constructedwetlands has been increasing up to 194 per year, reachingthe total number of 1894 papers over that period (Fig. 1). Inthis study, the following combinations of keywords occurredin the title, keywords and abstract of papers that have beenused: “constructed wetland(s)”, “pollution control” and wet-land(s), and purification and wetland(s). About 95% of all ofthe publications contained the term “constructed wetlands”.The majority of the publications in this field were published intwo journals: Water Science and Technology and Ecological Engi-neering. The average share of Ecological Engineering was 15%,

varying from 0 to 23% (Fig. 1).

This special issue covers a wide spectrum on pollution con-trol by wetlands from various aspects of constructed wetlands’performance to the cycling of heavy metals in wetlands.

154 e c o l o g i c a l e n g i n e e r i n g 3 5 ( 2 0 0 9 ) 153–158

Fig. 1 – Pattern of scientific publications on pollutioncontrol by wetlands in 1989–July 2008. All the journals

Table 1 – Invited plenary lectures at the 2ndInternational Symposium on Wetland PollutantDynamics and Control (WETPOL 2007) held 16–20September 2007 in Tartu, Estonia.

Ülo Mander, University of Tartu and Tiina Nõges, EstonianUniversity of Life Sciences: “Wetlands and lakes in Estonia”

Robert H. Kadlec, University of Michigan, USA: “Comparison offree water and horizontal subsurface wetlands to treat nutrientsand pollutants”

Chris Freeman, University of Wales, UK: “Molecular and microbialadvances in wetland research”

William J. Mitsch, Ohio State University, USA: “Restoration ofcoastal and riverine wetlands”

Jerome O. Nriagu, University of Michigan, USA: “Heavy metals inwetlands”

Chris Craft, Indiana University, USA: “Tidal marshes and climatechange”

Hans Brix, University of Århus, Denmark and Tom Headley, NewZealand Water and Wastes Association: “The role ofmacrophyte-derived organic carbon for denitrification intreatment wetlands”

Nancy B. Dise, Manchester Metropolitan University, UK:“Atmospheric deposition, microbial cascades and ecosystemresponses”

Jos T.A. Verhoeven and Merel B. Soons, Utrecht University, TheNetherlands: “Wetland restoration for biodiversity or

indexed by the ISI Web of Science (WoS) areconsidered.

2. The 2nd International WETPOL 2007Symposium in Tartu, Estonia

The 2nd International Symposium on Wetland PollutantDynamics and Control (WETPOL 2007), organised by theDepartment of Geography of the University of Tartu (Estonia)in co-operation with partners from the Estonian Universityof Life Sciences (Tartu, Estonia), Ghent University (Belgium),and the UNESCO-IHE (Delft, The Netherlands), was held 16–20September 2007 in Tartu, Estonia. The main objective of thisworkshop was to provide participants with new and innova-tive methods for wetland research and wastewater treatmentthat will help reduce pollution from several pollutionsources.

The WETPOL 2007 symposium was a follow-up to the firstWETPOL meeting held in September 2005 in Ghent, Belgium,considering similar process-based topics on pollutant dynam-ics in various types of wetlands. The removal and fate ofpollutants in natural and constructed wetlands for pollutioncontrol and wetland restoration aspects were the other maintopics of the symposium.

The main conference topics were:

• nitrogen, phosphorus and carbon cycling in wetlands;• heavy metals in wetlands;• organic pollutants in wetlands;• attenuation of faecal microbial contaminants in wetlands;• redox-sensitive processes;• molecular/microbial advances in wetland research;• functioning of plants in the wetland environment;• assessment and evaluation of ecological effects;• modelling of pollutant removal;• model-based design and operation;• site-specific and generic risk assessment of pollutants;• wetlands’ role in catchment management;• wetland hydrology.

One hundred forty oral presentations and 70 posters werepresented during this symposium. Nine keynote speakersfrom the USA, UK, Denmark, the Netherlands and Esto-

environmental quality: Landscape considerations”

nia highlighted the most important results of and problemsin wetland research and restoration (Table 1). Contribu-tions to this symposium represent 38 countries. In additionto European presentations, contributions from Australia,Brazil, Canada, China, Colombia, India, Japan, Korea, Mex-ico, New Zealand, Tanzania, Taiwan, Thailand, Turkey andthe United States were included. The size of the WETPOL2007 symposium was about the same as the first WETPOLsymposium (ca. 165 participants from 40 countries) in Bel-gium.

Based on the papers presented at the symposium,three special issues of the journal Ecological Engineer-ing will be published in 2009: Molecular and MicrobialAdvances in Wetland Research (guest editor Dr. Karin Ton-derski), Wetland Restoration (guest editor Dr. Jos Verho-even), and on Pollution Control by Wetlands (this specialissue).

During the symposium, three field trips were made: (1)to Lake Võrtsjärv and its catchment, (2) to the Endla NatureReserve (with visits to the Männikjärve raised bog; Fig. 2a), theVooremaa drumlin landscape, and Lake Peipsi (Fig. 2b), and (3)to the South-East Estonian landscapes. During technical fieldtrips, the participants became acquainted with the problemsof the use and sustainable management and protection of wet-lands in various conditions. In addition, a post-symposiumexcursion to several protected wetland ecosystems in westernEstonia was organized from 21 to 22 September: the Kure-soo raised bog (the largest bog complex in Estonia; Fig. 2c)in Soomaa National Park, the Nigula raised bog in the Nigula

Nature Reserve, and reedbeds, coastal meadows and flood-plain meadows in Matsalu National Park. Also, the largestrestored wooded meadow of Nedrema (Pärnu County) wasvisited.

e c o l o g i c a l e n g i n e e r i n g 3 5 ( 2 0 0 9 ) 153–158 155

Fig. 2 – Sites of technical field trips and the post-symposium tour of the WETPOL 2007 symposium in Estonia. (a) TheMännikjärve raised bog in the Endla Nature Reserve; left: wooden path across the bog pools and beds; right: Dr. Leon Lamers(Nijmegen University, The Netherlands) sampling Sphagnum moss for methanotroph analyses; (b) Lake Peipsi: participantslistening to the story of the lake’s development in the Holocene; (c) the raised bog of Kuresoo. Photos by Margit Kõiv.

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156 e c o l o g i c a l e n g i n e e

3. This special issue

This special issue consists of 19 selected papers presented atthe 2nd International WETPOL 2007 Symposium held from 16to 20 September 2007 in Tartu, Estonia.

The main topics of this special issue concentrate on:(1) the efficiency and modelling of purification processesin constructed wetlands in different climate zones, designparameters and various flow regimes; (2) the role of aquaticmacrophytes in purification processes and wetlands’ services;(3) heavy metal cycling in natural and constructed wetlands;and (4) restoration of wetland ecosystems.

Kadlec (2009) presents a comparative overview of the per-formance of the two prevalent types of treatment wetlands– free water surface (FWS) and horizontal subsurface flow(HSSF) wetlands – using data from several hundred con-structed and semi-natural wetlands for wastewater treatmentfrom North America and several European countries. Thestudy shows that FWSs are more efficient in mineralizingorganic matter (BOD) and removing total suspended solids(TSS), NH4–N, total N and phosphorus. HSSFs are more effec-tive for tertiary BOD levels, NO3–N and pathogens. There isno significant difference when these two systems are com-pared in terms of areal basis and space saving. However, incold climates, HSSF systems are less cold sensitive, and easierto insulate for winter operation. In general, from the economicpoint of view HSSF wetlands did not show a significant advan-tage.

In each individual study, the performance efficiency ofFSWs and HSSFs may differ from general relationships(Kadlec, 2009), as shown for total N removal in pilot-scalebatch-operated HSSF systems in the paper by Van de Moortelet al. (2009). Nevertheless, the removal of P can be hamperedby reducing conditions occurring in both wetland systems.

Austin and Nivala (2009) analysed the energy requirementsfor nitrification in subsurface flow constructed wetlands andfound that engineered wetlands that use mechanical powerinputs by pumping air or water to nitrify wastewater showthe highest performance, and are preferable even in com-parison to two aeration-effective wetland systems—tidal flowand pulse-fed vertical subsurface flow (VSSF) wetlands. Engi-neered HSSFs are, however, more expensive than “traditional”constructed wetlands (see also Kadlec and Wallace, 2008).

Põldvere et al. (2009) show in their pilot-scale studies thatthe batch-operated wetland systems and the recirculation rateof 200% in hybrid constructed wetlands guarantee optimalaeration and the highest performance of BOD and total Nreduction.

The importance of filter material choice for phosphorusremoval efficiency in constructed wetlands is considered byKõiv et al. (2009). In their pilot-scale studies, the authors havefound that well mineralized peat efficiently removes nitro-gen and phosphorus from both preliminarily treated landfillleachate and municipal wastewater. However, the experi-ments demonstrated that the phosphorus removal efficiency

in VSSF peat filters begins to decrease after 6 months of oper-ation.

The role of macrophytes in constructed wetlands has beenstudied in several papers, but the results are somewhat con-

3 5 ( 2 0 0 9 ) 153–158

tradictory. Some works do not find any preferences of plants inpurification processes (Maehlum and Stålnacke, 1999; Mitschet al., 2005), while other studies found that the role of plantsis almost positive (Brix, 1997; Gottschall et al., 2007; Manderet al., 2008). Several papers in this special issue consider therelevance of various plant species on purification processes.Zhou et al. (2009) have not found total N removal efficien-cies in vertical flow columns planted with rice (Oryza sativa)to exceed 90%, whereas N assimilated by the rice plants inthe flooded column accounted for 60% of total input N, whilethat in the non-flooded column was only 36%. Interestingly,the authors found that an anammox process may occur inanaerobic deeper zones of columns.

Maltais-Landry et al. (2009) found that mesocosms plantedwith common reed (Phragmites australis) and broadleaf cattail(Typha latifolia) emitted less CH4 than unplanted beds. In con-trast, N2O emission was higher from planted beds. However,the general suggestion of this study is that planted systems,especially when artificially aerated, have the best overall per-formances in that they lead to a reduction of the flux ofgreenhouse gases and promote nitrogen removal from wet-land ecosystems.

Experiments carried out by Wang et al. (2009) with threecommon helophyte species – P. australis, T. latifolia and yellowflag (Iris pseudacorus) – in vertical flow mesocosms loaded withhighly concentrated sludge from a food industry companydemonstrated that planted mesocosms were more efficientthan unplanted mesoscosms, showing the efficiency of TSSand COD removal efficiency to be >98% and total Kjeldahlnitrogen (TKN) removal to be >87%. Mesocosms planted with P.australis and T. latifolia performed better in TKN removal thanthose planted with I. pseudacorus.

In their study on VSSF wetlands treating high-strengthwastewater in tropical conditions, Kantawanichkul et al. (2009)did not find any significant difference in mass removal rates ofCOD, TKN, and total P in mesocosms planted with T. angustifo-lia and Cyperus involucratus and unplanted beds. However, thenumber of Nitrosomonas was two to three orders of magnitudehigher in planted systems than in unplanted systems. Theauthors also point out the importance of the correct designand loading regime of constructed wetlands.

Two papers in this special issue illustrate additional ben-efits from using treatment wetlands. Konnerup et al. (2009)demonstrate that ornamental plants such as Canna spp. andHeliconia spp. can be effectively used in constructed wet-lands for domestic wastewater treatment in tropical countries.The use of ornamental species can increase the aestheticappearance and hence the public acceptance of wastewatertreatment wetland systems. Maddison et al. (2009) demon-strate that the biomass of cattail (T. latifolia) harvested fromwastewater treatment wetlands in boreal conditions is a valu-able insulation material in ecological construction, whereasthe fibre from spadixes mixed with clay gives elasticity to clayplasters. Due to the varying biomass in the long-term perspec-tive (0.36–1.76 kg DW m−2 in autumn and 0.33–1.38 kg DW m−2

in winter), the stabile production of cattail biomass is compli-

cated and needs further investigation. On the other hand, theharvesting of above-ground biomass in winter does not guar-antee effective removal of N and P from the wetland system,because most of the nutrients are in below-ground biomass.

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Three papers consider modelling approaches to under-tanding treatment wetlands. Giraldi et al. (2009) used anriginal plug-flow model and tracer tests to analyse hydro-ynamics in a VSSF pilot plant, whereas Ascuntar-Rios et al.

2009) examined the model dynamics of flow patterns in a full-cale HSSF tropical treatment wetlands. Toscano et al. (2009)odelled both hydraulic behavior and the elimination process

f organic matter, nitrogen, and phosphorus in an HSSF pilot-cale treatment wetland system and obtained a good match ofeasured data in the area of water flow, tracer experiments,

nd pollutant removal processes.Dordio et al. (2009) evaluate the sorption capacity of light

xpanded clay aggregates (LECA) in subsurface flow (SSF)onstructed wetlands to remove mixtures of ibuprofen, car-amazepine and clofibric acid in water and wastewater, andound high removal efficiencies for two of these pharmaceu-icals, with a less satisfactory performance for clofibric acid.owever, the results of this innovative study are a first step in

he process of selecting an appropriate combination of mate-ials to be used in SSF constructed wetlands.

Three papers describe heavy metal cycling in variousetland ecosystems. Vymazal et al. (2009) analyze the con-

entration of 19 trace elements in the biomass of commoneed plants growing in four HSSF constructed wetlands treat-ng municipal wastewater. They found that concentrationsf all of the monitored elements in both above-ground andelow ground plant tissues were similar to those found in nat-ral stands. Du Laing et al. (2009) analyse the factors affectingetal concentrations in reed plants of intertidal marshes in

he Scheldt estuary in Belgium and found that metal mobil-ty and thus plant availability were higher in sediments withower clay or organic matter content. Likewise, sandy sedi-

ents are expected to be susceptible to occasional oxidationf sulphides, which leads to increased metal availability andigher salinity promotes uptake of Cu, Cr, and Zn. Rinklebe etl. (2009) demonstrate a successful optimization of a simpleeld method for the determination of mercury volatilizationrom soils in the floodplain area.

In the final paper, Huang et al. (2009) provide an examplef the ecological restoration design of a stream and wetlandomplex on a college campus in Ohio, which covers measuresrom riparian vegetation restoration to the creation of newetland ecosystems.

cknowledgements

e acknowledge the financial assistance of the Department ofesearch and Institutional Development of the University ofartu and the Doctoral School of Ecology and Environmentalciences of the University of Tartu, Estonia. Special thanks goo Ms. Margit Kõiv, Ms. Christina Vohla, Mr. Martin Maddison,r. Alar Noorvee, Mr. Elar Põldvere, Mr. Kristjan Karabelnik,r. Kaido Soosaar and Mr. Reimo Alas, Ph.D. students of theepartment of Geography of the University of Tartu, for tech-ical help in organizing the WETPOL 2007 conference. Prof.õnu Oja and Dr. Tiit Hang from the Institute of Ecology and

arth Sciences of the University of Tartu helped guide theechnical excursions, and Mr. Alexander Harding proofreadelected manuscripts. Ruthmarie Mitsch edited several of theaper proofs and the editorial.

3 5 ( 2 0 0 9 ) 153–158 157

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Ülo Mander ∗

Department of Geography, Institute of Ecology and Earth Sciences,University of Tartu, 46 Vanemuise St., Tartu 51014, Estonia

William J. MitschWilma H. Schiermeier Olentangy River Wetland Research Park,

The Ohio State University, 352 W. Doridge St.,Columbus, OH 43202, USA

∗ Corresponding author.E-mail address: mander@ut.ee (Ü. Mander)

5 September 2008

0925-8574/$ – see front matter© 2008 Elsevier B.V. All rights reserved.

doi:10.1016/j.ecoleng.2008.10.005