Ecosystem services of wetlands: pathfinder for a new paradigm

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Ecosystem services of wetlands: pathfinder for a newparadigmEdward Maltby a & Mike C. Acreman ba School of Environmental Science, University of Liverpool, Liverpool, UKb Centre for Ecology and Hydrology, Crowmarsh Gifford, Wallingford, OX10 8BB, UKPublished online: 16 Dec 2011.

To cite this article: Edward Maltby & Mike C. Acreman (2011): Ecosystem services of wetlands: pathfinder for a newparadigm, Hydrological Sciences Journal, 56:8, 1341-1359

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1341Hydrological Sciences Journal Journal des Sciences Hydrologiques, 56(8) 2011Special issue: Ecosystem Services of Wetlands

Ecosystem services of wetlands: pathfinder for a new paradigm

Edward Maltby1 and Mike C. Acreman2

1School of Environmental Science, University of Liverpool, Liverpool, UK2Centre for Ecology and Hydrology, Crowmarsh Gifford, Wallingford, OX10 8BB, UK

Received 3 May 2011; accepted 3 October 2011; open for discussion until 1 June 2012

Co-editors D. Koutsoyiannis and Z.W. Kundzewicz

CitationMaltby, E. and Acreman, M.C., 2011. Ecosystem services of wetlands: pathfinder for a new paradigm. Hydrological SciencesJournal, 56 (8), 13411359.

Abstract Ecosystem services are natural assets produced by the environment and utilized by humans such asclean air, water, food and materials and contribute to social and cultural well-being. This concept, arguably,has been developed further in wetlands than any other ecosystem. Wetlands were historically important in pro-ducing the extensive coal deposits of the Carboniferous period; key steps in human development took place incommunities occupying the wetland margins of rivers, lakes and the sea; and wetlands play a key role in thehydrological cycle influencing floods and river droughts. In this paper we examine three pillars that support thewetland research agenda: hydrology, wetland origins and development, and linkages to society. We investigatethese through an overview of the evolution of wetland science and assessment of the wide range of topics relat-ing to ecosystem services covered in this Special Issue. We explain the seminal change in how modern societyvalues the benefits of natural ecosystems and highlight the pathfinder role that wetland research has played in theparadigm shift.

Key words wetlands; ecosystem services; hydrological functions; paradigm shift

Services cosystmiques des zones humides: claireur pour un nouveau paradigmeRsum Les services cosystmiques sont des biens naturels produits par lenvironnement et utiliss par leshumains, comme lair pur, leau, la nourriture et les matriaux, et contribuent au bien-tre social et culturel.Ce concept a sans doute t davantage dvelopp dans les zones humides que dans tout autre cosystme. Leszones humides ont t historiquement importantes dans la production des normes gisements de charbon de lapriode carbonifre; des tapes cls dans le dveloppement humain ont eu lieu dans des communauts qui occu-paient les marges humides des rivires, des lacs et de la mer, et les zones humides jouent un rle cl dans le cyclehydrologique en influenant les crues et les tiages des rivires. Dans cet article, nous examinons trois piliersqui soutiennent la recherche sur les zones humides: lhydrologie, les origines et le dveloppement des milieuxhumides, et les liens avec la socit. Nous les tudions travers un passage en revue de lvolution de la sciencedes zones humides et une valuation de la vaste gamme de sujets lis aux services cosystmiques abords dansce numro spcial. Nous expliquons le changement fondamental dans la faon dont la socit moderne value lesbnfices des cosystmes naturels, et soulignons le rle pionnier que la recherche sur les zones humides a joudans ce changement de paradigme.

Mots clefs zones humides; services cosystmiques; fonctions hydrologiques; changement de paradigme

INTRODUCTION

Ecosystem services are natural assets (Barbier 2011)produced by the environment and utilized by humans,such as clean air, water, food and materials. They con-tribute to social and cultural well-being (Fischer et al.2009) and have high economic value (Barbier et al.1997, Emerton and Bos 2004, Turner et al. 2008).They have been broadly classified as provisioning,regulating, cultural and supporting (Fig. 1, MEA2005). This concept has much earlier origins in

the context of wetland research where it has beenembedded in the ideas of ecosystem functioning andresulting human values (Maltby 1986). Managementof land and water has focused on enhancing someecosystem services, such as food production, butthis has been often at the expense of degradation ofother services, such as those described as regulat-ing, e.g. pollutant removal to improve water quality.This Special Issue of Hydrological Sciences Journalinvestigates the ecosystem services provided by wet-lands, with particular emphasis on the trade-off of

ISSN 0262-6667 print/ISSN 2150-3435 online 2011 IAHS Presshttp://dx.doi.org/10.1080/02626667.2011.631014http://www.tandfonline.com

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1342 Edward Maltby and Mike C. Acreman

Ecosystem services

Provisioning Cultural

Food AestheticFreshwater EducationalWood RecreationalFuel

Supporting Regulating

Nutrient cycling ClimateSoil formation FloodsPrimary production Water

Well-being

Social relations Health

Social cohesion StrengthMutual respect Well-beingAbility to help Recreational

Basic material Freedom of choice

Livelihoods Opportunity toNutrition achieve individualShelter vales

Fig. 1 Ecosystem services and well-being (after MEA 2005).

individual services as these systems have been manip-ulated either purposely or unintentionally.

In this paper, we examine three pillars that sup-port the wetland research agenda and which are inves-tigated through the wide range of topics covered inthis Special Issue: hydrology, wetland origins anddevelopment, and linkages to society. We illustratesome of the more intriguing relationships with humandevelopment and document significant changes intheir perception resulting in a fundamental alterationin their appreciation, use and management over time.This has mirrored a seminal shift in how modernsociety values the benefits of natural ecosystems andhighlights the pathfinder role that wetland researchhas played in the paradigm shift (Fig. 2).

The dominance of water, at least periodically,is the defining feature of wetlands (Acreman andJos 2000). The variation in hydrological regimes,largely determining their structure, processes and

Fig. 2 Wetlands at the centre of concerns of society (afterMaltby 2009a).

functioning, results in a wide range of wetlandecosystem types (Maltby 1986, Mitsch and Gosselink2002, Maltby 2009b). The major types are marshes,swamps and mires (bogs and fens), each demon-strating considerable diversity within the generic cat-egory, depending on water quality, dominant veg-etation, topography, soils or sediment, and climate(Gore et al. 1983). Distinct landscapes, such asfloodplains, deltas, peatlands, estuaries and coastalmargins, also support a wide variety of wetlandtypes, which often carry distinctive geographicalnames such as billabong (ox-bow), carr (wet wood-land), rhos or culm grassland (wet grassland) anddambo (headwater depressions). There is frequentambiguity among the scientific community as towhat exactly constitutes wetland, especially in rela-tion to the inclusion or not of rivers and lakes.Wetlands are the only ecosystem type to have adedicated international conventionThe Conventionon Wetlands of International Importance, called theRamsar Convention, after the city in Iran where itwas signed in 1971. This has adopted the most inclu-sive of definitions: areas of marsh, fen, peatlandor water, whether natural or artificial, permanent ortemporary, with water that is static or flowing, fresh,brackish or salt, including areas of marine water, thedepth of which at low tide does not exceed six metres(Davis 1993). Coral reefs and caves are also nowincluded specifically within the definition under theConvention.

Whatever the conflicts of opinion, there are atleast three features of wetlands that singly or togethercan be considered diagnostic:

1. the predominant presence and dynamics of watereither at or above the surface or within the root-zone;

2. unique soil or sediment conditions that differfrom adjacent non-wetland (terrestrial or fullyaquatic) areas; and

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Ecosystem services of wetlands: pathfinder for a new paradigm 1343

3. vegetation (and generally animals) specificallyadapted to permanently or seasonally wet condi-tions (see Maltby 2009b for details).

Yet, because the effects of hydrological pro-cesses and resulting functions extend well beyond thewetland boundary, there are also significant interac-tions with, and influences on, the wider landscapesof which they are part. The need for connectivityof hydrological processes between different elementsof the landscape is especially important in the case offisheries, as demonstrated by riverlake interactionsin Tanzania (Hamerlynck et al. 2011, this issue).

Wetlands have been estimated to cover some6% of the worlds land surface (Maltby and Turner1983). This is probably about half of the extent thatexisted before human modifications during histori-cal times (Maltby 1986). Original estimates of wet-land area and loss were compiled through inventoriesand maps. More recently, satellite images have beenused (http://www.globwetland.org). However, the trueextent and loss remains unclear due to complex-ity of wetlands and natural variations. Wetland lossand degradation has proceeded at least in part dueto the poor understanding of their functioning andof their role in providing benefits to people throughdelivery and maintenance of ecosystem services. Thiscontrasts with their intimate link with human commu-nities in pre-historic times. Wetland loss has occurredeither through deliberate or simply inadvertent actionsresulting from decisions which have failed to takeaccount of their full worth (Maltby 1991).

The essential linkage to water supplies (Acremanand Miller 2006, McCartney and Acreman 2009) alsoplaces wetlands centrally in some of the most con-tentious and urgent issues governing the most appro-priate management of a resource for which there isintense competition and increasing uncertainty due toclimate change. Whilst wetland hydrology is a naturalscience, its relationship to the water cycle is highlyrelevant to wider societal concerns, such as issuesof alternative water resource allocation, water qualityand flood risk (Maltby 2009a).

SPECIAL PLACE IN EARTH HISTORY ANDHUMAN DEVELOPMENT

On a geological time scale, wetlands created animmense economic resource, but with potentially far-reaching unintended consequences for global climate,

as a result of the imbalance in the wetland ecosys-tem between carbon sequestration and decomposition(Maltby 2010). Within the prehistoric period, theyhave provided the resources which supported humancommunities, ranging from the possibility of stimulat-ing hominid evolutionary development to providingthe platform for the establishment of early civilisa-tions (Bell 2010). Wetland functioning in terms offood chain support, underpinned by the natural hydro-logical dynamics, was an essential ingredient to suchprogression.

Sieffermann (1988) described the modern-dayanalogues in Central Kalimantan of the tropical peat-swamps of 250 million years ago that produced theextensive coal deposits of the Carboniferous period.Continental shift and a different climate regimemoved these vast carbon stores into the higher lati-tudes of Europe and North America where they woulddrive the Industrial Revolution of the 19th century(Maltby 2009a). Thus, the fossil forms of carbonsequestration by ancient wetlands had an immenseimpact on both economic and social developmentthrough industrialisation and world trade patterns.Further than this they are also a major source ofthe sharp rise in CO2 emissions to the atmospherewith consequences for global warming. Such a rela-tionship is a strong reminder of the importance ofbiogeochemical coupling between wetlands and thelarger global system, and the importance of time, andrate of change, as considerations in environmentalmanagement (Maltby 2009a). In this case, the rateof conversion of the carbon store, which is ordersof magnitude faster than its accumulation by naturalwetland processes, is a cause of potential imbalancewith undesirable consequences (Roulett 2000). Themodern-day counterpart is the drainage or extrac-tion of peat resulting in oxidation to CO2 at ratesfar exceeding its fixation by peat-forming plant com-munities (Immirzi and Maltby 1992). Ironically, suchdegradation of peatlands in the modern era reducesthe possibility of these ecosystems providing a widerresource for future generations or in future geologi-cal time.

A key challenge is to recognize the potentialcomplexity of the wetland heritage in generatingbenefits at one time, but costs and potentially con-straints at another; wealth to some, but hardship, evenpoverty to others; and competitive advantage in oneplace, but disadvantages in another (Maltby 1991,2009a, 2009b).

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HUMAN EVOLUTION AND CULTURALDEVELOPMENT

Wetlands have played a significant role in the evo-lution of many species, contributing significantly tobiodiversity (Gopal 2009). Tourenq et al. (2011,this issue) illustrate the link between a uniquehydrological system and a unique biodiversity. It isalso possible that key steps in human developmenttook place in communities occupying the wetlandmargins of rivers, lakes and the sea. The aquatic apetheory suggests that the fatty acids derived from fishenabled brain capacity to expand to that characteristicof the modern human species (Morgan 1982).

For millennia, prehistoric communities bene-fited from the natural goods and services of thesemarginal wetlands, which were the sites of the ear-liest stages in the development of tool-producinghominids. Dolukhanov (1992) has ascribed the socio-economic development of prehistoric communities tothe adaptation to the riverine-lacustrine environmentby intensified foraging strategies. The intimate andhighly dependent relationship between humans andwetlands in Mesolithic and Neolithic Europe is clearfrom excavations of numerous post-glacial lake mar-gin settlements (Coles and Coles 1989). The StarrCarr house, recently excavated from the peat-infilled,former post-glacial Lake Pickering in North Yorkshirehas been dated at 8500 BC and is the oldest knowndwelling in the UK (Wainwright 2010). One aspectthat is unknown, however, is the extent to whichclose proximity to water brought with it discomfortand health problems arising from disease vectors orcontamination.

In developed countries, economic developmenthas led to major wetland loss and has meant thatpeople have apparently become less directly depen-dent on ecosystem services of wetlands over time.The main objectives for retention and managementof remaining wetlands are often related to recreationservices, and major funds have been dedicated torestoration and conservation, which is considered anaffordable choice. This contrasts with the developingworld, where many people still depend directly on thenatural resources of wetlands and their ecosystem ser-vices for their livelihoods, but are, conversely, muchmore likely to modify wetlands to try and improvetheir livelihoods. Wetlands are very much viewed asa development opportunity, such as through agricul-ture, and the idea of protectioneven to safeguardecosystem servicesis often viewed as a luxury

that cannot be afforded. Thus the value that humansocieties put on wetlands has changed over time.

Whilst dependency was the mainstay of pre-historic communities in Europe, early civilisationswere flourishing along the floodplains of major riverssuch as the Tigris-Euphrates, Indus, Ganges andNile (Solomon 2010). This was achieved throughhydrological modification using simple water controlstructures, which stored and diverted water, andimprovements in irrigation techniques. This led toless direct dependence on the variable natural annualflood pulse. It transformed the economy and reducedconsiderably the effort required to secure food.Harnessing and modification of the natural function-ing of floodplain wetlands created agricultural wealthand surpluses for trade. Maltby (2009a) reviews howsuch hydraulic civilisations led to a step change insocietal development and describes more fully as anexample the technological and cultural legacy in theMesopotamian wetlands, home of the Marsh Arabs.

As a result of periodic inundation, the flood-plains of the major rivers of Africa, including theSenegal, Niger, Nile and Zambezi, support wetlandecosystems of exceptional productivity, particularlyin comparison with the surrounding arid and semi-arid rangelands where the dry season is long andvery arid (Acreman 1996). For centuries, these flood-plains have played a central role in the rural econ-omy of the region, providing fertile agricultural landwhich supports a large human population. They pro-vide, uniquely, two sets of services associated withthe distinctive and characteristic alternation betweenaquatic and terrestrial ecosystem phases (Drijver andMarchand 1985). The flood waters provide a breedingground for large numbers of fish and bring essentialmoisture and nutrients to the soil. Water that soaksthrough the floodplain recharges the undergroundreservoirs, which supply water to wells beyond thefloodplain, as demonstrated for the Senegal valley(Hollis 1996). As the flood waters recede, arable cropsare grown, and some soil moisture persists to the dryseason providing essential grazing for migrant as wellas domestic herds. The floodplains also yield valuablesupplies of fish, timber, medicines and other products,and provide crucial habitats for wildlife, especiallymigratory birds (Acreman and Hollis 1996). Thuswetlands have been particularly crucial for supportinglivelihoods of rural poor, and Kumar et al. (2011, thisissue) provide a conceptual framework for manag-ing together the wetland ecosystem, poverty reductionand sustainable livelihoods.

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The benefits of wetlands were presumably fullyappreciated by earlier human cultures and certainlyby traditional users of wetlands (such as wildfowlers,reed-harvesters, fishermen). However, malaria wasendemic in many European countries and still is inmany tropical countries, which often encouraged theseasonal use of wetlands, when resources were mostplentiful, with permanent homes on higher, drier andmosquito-free ground. The benefit of wetlands wereeither ignored or dismissed as less significant bymore powerful sectoral interest groups, and conver-sion was justified by promoting wetlands as unhealthyand disease-ridden (Maltby 1986).

Drainage of the English Fens to create richfarmland (Darby 1983) and establishment of agricul-tural polders in The Netherlands, where previouslythere had been sea and coastal marsh (Idema et al.1998), were generally hailed as remarkable and desir-able engineering achievements. For centuries thedrainage of wetlands has been seen as a progressive,public-spirited endeavour, the very antithesis of van-dalism (Baldock 1984). Yet, there was often localoppositionfor example, the Fen Tigers, peoplewhose livelihoods were threatened by the ecologi-cal changes resulting from agricultural conversion.Facilitated by technological development and chang-ing economic circumstances, the transformation ofwetlands has led to the provision of other wetland ser-vices, such as food production from arable farmland,and non-services, such as residential or industrialuse. This has necessitated fundamental hydrologicalalteration which carries a risk if modification is insuf-ficient to deal with extreme events or the effects ofunanticipated climate change. In effect, it reducesresilience in the landscape. Further, the properties ofthe wetland that make them attractive in the first placefor alternative use may depend on maintenance of acertain hydrological regime. Without it, their valuemay decline or unanticipated consequences increase.The potential impact of drainage of organic soils onthe world carbon cycle was recognized more than30 years ago, primarily through research in Latvia(Glazacheva 1975), Estonia (Hommik and Madissoon(1975), Belorussia (Klueva 1975), and Sweden andFinland (Johansson and Seuna 1994), which demon-strated the significant alterations to the hydrologicalcycle of wetland drainage (Armentano 1980). Largeagricultural areas reclaimed in the past century, southof the Venice Lagoon, Italy, have experienced signifi-cant land subsidence due to oxidation of peat organicsoils (Gambolati et al. 2006). Such is the case, in the

UK, of the Fens, in which the fertile peat has rapidlydeclined due to oxidation in a non-waterlogged envi-ronment. The Holme Post shows a loss of 5 m ofpeat in the East Anglian fens since 1858 (Waltham2000). This exposes much less fertile inorganic sub-strates, requiring artificial fertilizer to support agri-culture, but increasing the risk of groundwater aswell as surface water contamination. The former reg-ulatory services of the wetland have declined andthe increase in provisioning services has persistedfor a finite time only before requiring significantexternal subsidies, resulting in growing costs frompollution.

Despite increasing recognition of the adverseconsequences, wetland alteration has continuedworldwide. Well publicized examples include theshrinkage of Lake Chad in Africa (Coe and Foley2001) and Central Asias Aral Sea (Roggieri 2009),desertification of the marshlands of southern Iraq(Maltby 1994, Partow 2001), drainage of the peat-lands of central Kalimantan (Morrogh-Bernard et al.2002), and eutrophication of the Florida Everglades(Kadlec 2009). Such wetland degradation is often anindicator of adverse change in the catchment supply-ing the wetland. The changes in ecosystem servicesthat occur as a result of drainage and alternative man-agement are illustrated for the Hula Wetlands, Israel(Cohen-Shacham et al. 2011, this issue). Stratfordet al. (2011, this issue) have developed a single toolfor assessing the vulnerability of wetland ecosystemservices to a range of such impacts.

RECOGNITION OFWETLAND VALUES

Initial scientific interest in wetlands focused rathernarrowly on their description, origins of formationand ecological relationships. Research emphasizedthe individuality of separately-defined ecosystems inthe landscape, such as bog versus fen or marsh ver-sus swamp, instead of recognizing the over-archingimportance of variation in the hydrological regimedetermining the range of wetland-forming conditions.Early studies were restricted to either their naturalscience or their part in the human economy (e.g.Good et al. 1978, Godwin 1981, Scudder and Conelly1985); the two were rarely linked. Maltby (2009a)summarized from earlier analyses of the literature fivefeatures that have broken down this dichotomy andwhich have resulted in a paradigm shift, with wet-lands assuming greater prominence on the scientificand political agenda in recent years:

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1. An increasing scientific research focus on wet-lands linked with the environment and conserva-tion movements.

2. Raised awareness of the socio-economic signif-icance of wetland functioning and delivery ofecosystem services.

3. Wider recognition of the far-reaching conse-quences of wetland degradation and loss, espe-cially in relation to climate change.

4. Opportunities for wetlands, particularly in thedeveloping world to deliver improvements in thewelfare and livelihoods of local people throughintegrated development and poverty alleviationinitiatives.

5. Progressive recognition of the potential or actualrole of wetlands within various policy frame-works, including specific legislative instrumentsto deliver the wider objectives of sustainabledevelopment.

Especially since the 1970s, there has been greateremphasis of wetlands generically as a rich naturalresource offering a wide range of goods and servicesthat stem from how they function in the landscape.In particular, research in the USA began to high-light the functions and values of wetlands (e.g.Horwitz 1978, Greeson and Clark 1980, Adamus andStockwell 1983, Tiner 1984, Sather and Smith 1984).Whilst leading to some confusion through this mix,and publishing lists initially that did not caution suf-ficiently that not all wetlands performed all functions(Maltby et al. 1996, Maltby 2009a), and that someperformed contrary functions (Bullock and Acreman2003), this emphasis underpinned a new policy direc-tion not only for the USA, but which would beinfluential globally.

Continuing to move beyond the individual site orecosystem type, the vital role of wetland habitats andtheir connectivity across national boundaries and con-tinents for conservation of populations of migratorybirds was the essential driver for the Convention onWetlands of International Importance Especially asWaterfowl Habitatknown by the initial title of theRamsar Convention. The rationale of protecting notjust individual wetlands, but whole networks, was amajor step forward in recognizing the need to safe-guard breeding, over-wintering, resting and feedingsites that made up often complex life cycles. Theundoubted success in raising the profile of wetlandsinternationally also attracted criticism from develop-ing nations, reluctant to join the Convention on thebasis that it failed their alternative priorities, such as

poverty alleviation, due to lack of economic devel-opment and burdens of debt. With sensitivity to theinherent bias towards the interests of richer nations,there was a dramatic change in the character ofthe Convention at the 1987 Conference of Partiesin Regina, Canada. This took the form of a revi-sion of the criteria for designation of a Wetland ofInternational Importance to reflect more the widerfunctional role of wetlands, and also the elaborationof the wise use requirement to put more emphasison the link to sustainable development (Maltby 1991,2009a). The wise use concept was particularly impor-tant for recognizing the value to local communitiesof exploiting wetland resources and services, pro-vided that this was sustainable and did not degradethe wetland. It also recognized the fact that many tra-ditional management practices shaped and enhancedthe character of wetlands, rather than wetlands beingin need of complete protection that excluded people.There is now a comprehensive conceptual frame-work for the wise use of wetlands and the mainte-nance of their ecological character (i.e. the struc-ture and inter-relationships between the biological,chemical, and physical components of the wetland,Ramsar Handbook 1). This complements the otherConvention volumes dealing with water management.Thus, whilst the bird lobby had succeeded fromthe 1960s in raising the profile of wetlands inter-nationally, it was the translation of their functionalimportance, contributing for example to flood con-trol, water quality and fisheries, that attracted thebroader international commitment. Since Regina, keynew members joining the Convention have includedBotswana, Brazil, Cameroon, Chad, China, Cuba,Congo, Tanzania, Zambia and Iraq; the total num-ber of contracting parties is now 160 and includes1923 sites covering more than 187 million hectares(Ramsar Secretariat 2011).

The transformation of emphasis at Regina wasfive years ahead of the Earth Summit in Rio in1992, which brought to global prominence the con-cept that natural ecosystems are vital for human life.Whilst this was already well known by earlier gen-erations, Rio succeeded in codifying the recognitionof the importance of nature. Manifest through theConvention on Biological Diversity (CBD), the bal-anced objectives of conservation, sustainable devel-opment and equitable sharing of the benefits ofgenetic resources were proposed to be realized bymeans of the ecosystem approach. The ecosystemapproach was adopted as the methodological frame-work for meeting the key objectives of this important

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global convention. Its definition under the CBD hasa clear hydrological component: . . . the integratedmanagement of land, water and living resourcesto achieve sustainable management in an equitableway. In parallel, water managers were develop-ing ideas of Integrated Water Resource Management(IWRMsee Global Water Partnership http://www.gwp.org/), and catchment managers the notion ofIntegrated River Basin management (IRBM), whichhave many fundamental concepts in common, such asworking at a landscape (normally river basin) scale,involving diverse scientific disciplines from engi-neering, through life and environmental sciences tosociology and economics, and ensuring participationof stakeholders from local communities to nationalgovernments and international bodies. Many devel-oping countries are endorsing IWRM approaches,and changing policies etc. to incorporate the princi-ples. However, few have the resources to implementthem well, and so, given the constraints they face,this generally reflects an aspiration rather than a real-istic approach to water resources management. TheEuropean Water Framework Directive incorporatesthis type of thinking, and de la Hera et al. (2011, thisissue) have developed a wetland typology to supportriver basin management plans for the implementationof the Directive. The cross-cutting features of wet-lands place them centrally in the implementation ofthe ecosystem approach and they feature prominentlyin case study examples worldwide (Smith and Maltby2003, Maltby 2006).

Explanation of the links from wetland ecosystemprocesses to functioning as part of a natural envi-ronment domain and, thence, through socio-culturaland economic networks to human values (Maltbyet al. 1994) established a rationale to underpin thescientific relationships between ecosystem structureand functioning and the delivery of ecosystem ser-vices. Hydrological processes and functioning are keydrivers of the many physical and biochemical inter-actions within ecosystems which in turn control theperformance of the services beneficial to humans.

The Millennium Ecosystem Assessment formal-ized the concept and definitions of ecosystem ser-vices, the recognition of which is a vital element inthe practical operationalisation of the EcosystemApproach. Acreman and Mountford (2009) pro-vide a link between processes, functions and ser-vices (Table 1) with examples from wetlands, whilstMaltby (2009b) developed an innovative methodolog-ical approach to predict the likelihood of particularwetland functions and resulting service delivery.

Table 1 Wetland processes, functions and services (afterAcreman and Mountford 2009).

Processes Functions Services

Denitrification andothertransformationsof nutrients inplant cells

Uptake from waterand use ofnutrients byplants

Improvement inwater qualitythrough reducednutrient

Downwardmovement ofwater by gravityfrom the wetlandinto underlyingstrata

Recharge ofaquifers

Augmentation ofgroundwaterresourcesavailable forhuman use

Movement of waterfrom riversduring high flowsto inundate afloodplainsurface, filldepressions andsaturate the soil

Flood water storage Reduction indownstreamflood risk

Production of peatfrom dead plantmaterial inanaerobicconditions

Carbon storage Reduction ingreenhouse gases

Vilardy et al. (2011, this issue) and Singh et al.(2011, this issue) provide examples of the linksbetween hydrology, ecosystem services and humanwell-being. Campos et al. (2011, this issue) foundthat there were no significant differences betweenswamps and marshes in their ability in water retentionand carbon sequestration. The provision of ecosys-tem services may depend on the particular ecologicalstate of the aquatic system, and Gomez-Baggethunet al. (2011, this issue) indicate how changes canoccur depending on the alternative stable states inDonana Marsh, Spain. Changes in state do not nec-essarily mean the complete destruction of a wetland.In certain circumstances, maintaining fixed ecologi-cal character may not be appropriate; this is a societalchoice.

Integrated catchment management involvesputting in place a series of linked actions thattogether deliver the goods and services requiredby mankind, including: land for farming, housingand industry; supplies of freshwater for public use,irrigation and power generation; protection fromfloods; and a healthy environment for recreation.River basin authorities are increasingly recognizingthe maintenance of natural resources and functionsof ecosystems, such as wetlands, as a key strategyfor sustainable development (UNEP/WI 1997). The

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Ramsar Convention provides guidance on integratingwetlands into river basin management (RamsarSecretariat 1999). Clear recognition of the importantlinks between the hydrological functioning of wet-lands and human well-being emerged from studiesof the Charles River watershed, Massachusetts, USA(Sather and Smith 1985, Doyle 1987) and the effectsof closure of the Aswan High Dam. The United StatesCorps of Engineers demonstrated the financial bene-fits of using natural wetlands for flood control in theCharles River catchment. This was further elaboratedfor Europe under the ECOFLOOD project (Blackwelland Maltby 2006). It was estimated that flood damagewould increase by at least US$ 3 million per yearif 40% of the wetland area were removed, rising toUS$ 17 million if all were lost. An annual valueof over US$ 1 million was placed on the retainedwetlands. It was financially advantageous to retainwetlands rather than build new engineering structuresto achieve flood control, and the Corps of Engineersfinished in 1984 the acquisition of the wetlandsat fair market value (Doyle 1987). The recent workby McCartney et al. (2011, this issue) has shown thatthe GaMampa wetland of South Africa has a valueof more than US$ 80 000, even though it comprisesless than 1% of its catchment. Lack of understandingof the economic value of the services provided bywetlands inevitably leads to poor policy decisions(Verma and Negandhi 2011, this issue).

Closure of the Aswan High Dam in 1965, andthe consequent alteration in hydrology, sedimentand nutrient dynamics, caused a dramatic declinein the sardine and shrimp fishery in the easternMediterranean causing the closure of canning facto-ries and substantial economic losses (El-Sayed andvan Dijken 1995). However, the dam was benefi-cial to the general economic development of Egyptand a new fishery (of a different type) has beencreated in Lake Nasser. This provides a good exam-ple of trade-off and distributional effects (i.e. whobenefits and who loses as a consequence of develop-ment. Despite the strength of evidence, Barbier (2011,this issue) contends that wetland services are nearlyalways underdeveloped and non-marketed. There isthus a particular need to make more explicit valu-ations to determine the trade-offs between convert-ing or exploiting wetlands and any resulting lossof services. Rouquette et al. (2011, this issue) dis-cuss this in relation to the switch in Western Europefrom floodplain management for agriculture to theprovision of wider services. A detailed analysis of

trade-offs in ecosystem services according to differ-ent management regimes has been carried out byAcreman et al. (2011, this issue) for the SomersetLevels and Moors, UK. It reveals both synergiesand conflicts that inevitably make decision-making inoptimal water management complex and subject todifferent stakeholder pressures and influence.

LINKS TO SUSTAINABLE DEVELOPMENT

Delivery of water to sustain wetland functioning is akey element in maintaining or enhancing the servicesfrom wetlands. Management for the long term isessential and may require institutional support, suchas through legal instruments (Sullivan and Fisher2011, this issue).

In many parts of Africa, water is the limit-ing resource and development options need to beconsidered in terms of the most beneficial use ofwater. Barbier et al. (1991) demonstrated that thenet economic benefits of ecosystem services (fishing,agriculture and fuel wood) from the Hadejia-Nguruwetlands in Nigeria were US$ 32 per 1000 m3 ofwater, whereas returns from crops grown on theKano River project (to which water upstream of thewetlands is now diverted) were only US$ 0.15 per1000 m3. Barbier and Thompson (1998) concludedthat the additional value of production from large-scale irrigation schemes does not replace the lostproduction attributable to the downstream wetlands.Furthermore this valuation did not include other ser-vices of the wetlands, such as groundwater recharge,biological diversity and cultural heritage. Rechargingof groundwater has long been recognized as an impor-tant function of wetlands and Hollis et al. (1993)concluded that recharge in the Hadejia and Jamaareriver basins of northern Nigeria occurs primarily dur-ing flood flows, since the floodplain provides a largesurface area and the river bed is often imperme-able. Changes in the recharge function result in wel-fare losses for wetland populations (Acharya 1998).Recently constructed dams have reduced the areainundated, but insufficient monitoring of groundwa-ter levels is being undertaken to assess the impact,at a time when development agencies are sponsoringagricultural development by pumping of water fromaquifers beneath the floodplain, which may not besustainable (Acreman 1996).

The maintenance of naturally flooded condi-tions may also be an essential requirement to avoidsevere environmental degradation. Such is the case

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in avoiding the oxidation of potential and acid sul-phate soil materials (PASS) resulting from drainageschemes, upstream river regulation or local engineer-ing works. Of particular significance is the MekongDelta, which contains an estimated 2 106 ha ofPASS. The drawdown of water associated with con-version of Melaleuca-dominated wetland forest torice paddy may increase acidity of surface watersto below pH 2.0 with serious implications for riceyields, fisheries and human health (Maltby 1996,2006, Safford et al. 2009). The annual flood pulsein the Tonle Sap wetland in Cambodia supports greatbiodiversity and major fisheries (Kimmu et al. 2006).Pioneering work by Ni (2000) has shown the multiplebenefits of the traditional Melaleuca wetland ecosys-tem and, more importantly, how re-establishment ofwetland hydrological flows in close association withrice paddy can counteract adverse levels of acidity,improve rice yields and enhance sustainability.

SOME KEY MILESTONES

During the past 40 years, there has been a series ofkey milestones in the evolution of wetland science andpolicies.

A dedicated international Convention

The Ramsar Convention has been highly adaptivesince its original adoption in 1971. It has movedsignificantly from its origins in the bird conserva-tion lobby to a much broader remit linked to thewider benefits of wetland conservation and manage-ment to people. A wetland qualifies for the designa-tion of international importance if it meets criteriarelated to functioning, such as hydrology, ecology andsupport of human as well as wildlife populations.Fulfilling wise use requires the understanding of thehydrological fundamentals which retain ecologicalcharacter and set the parameters for sustainable use.

Regulatory frameworks in North America andelsewhere

Wetland functions are given particular emphasisunder United States Federal Law through implemen-tation of the 404 Program authorized under section404 of the Clean Water Act (33 US Code 1344).Activity likely to impact on wetlands requires a per-mit and no permit will be granted which involvesalteration of wetlands identified as performing func-tions important to the public interest. The need to

assess wetlands in the context of the permitting pro-cess coupled with a no net wetland loss policyunderpins the development of functional assessmentmethodologies in the USA (Smith et al. 1995, Brinson1996, 2009). Canadian policy on wetlands has alsoemphasized an approach that highlights their func-tional importance. As early as 1991, the objectivewas to promote the conservation of Canadas wet-lands to sustain their ecological and socio-economicfunctions, now and in the future (Government ofCanada 1991). The policy goals are very much inline with the wise use requirements of the RamsarConvention and include maintenance of functions andvalues, as well as recognizing wetland functions inresource planning, management and economic deci-sion making (Maltby 2009a). It is noteworthy that theCanadian Policy model has been influential elsewherein framing a wetland policy, notably in the case ofUganda (Republic of Uganda 1995).

Further elaboration of the Functional Approachin Europe

A functional approach to wetland assessment isone that acknowledges that wetlands can performwork at a variety of scales in the landscape, whichmay result in significant direct and indirect bene-fits to people, wildlife and the environment (Maltby2009b). The development of a European methodolog-ical procedure for the assessment of wetland func-tions has paralleled that in the USA (Maltby et al.1994). The key differences from the USA contextare manifest at the detailed operational level, e.g.lack of a regulatory programme in Europe, with astrong element of human intervention through fre-quent direct wetland management, including formalconservation strategies in Europe and extreme geo-graphical diversity coupled with often small sizeof individual wetlands. A major interdisciplinaryresearch initiative resulted in the development ofFunction Assessment Procedures (FAPs), which alsoprovide insight into the delivery of ecosystem ser-vices (Maltby 2009b). The FAPs focus on rivermarginal and lake marginal wetlands and differ fromUS methodologies primarily through their scale ofapplication and link to an underlying empirical sci-ence base. The fundamental unit of assessment isthe hydro-geomorphic unit (HGMU) defined as anarea of homogeneous geomorphology, hydrologyand/or hydrogeology and under normal conditions,homogeneous soil/sediment (Maltby et al. 1998).Hydrological functions assessed include floodwater

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detention, groundwater recharge / discharge and sed-iment retention. Other functions assessed are biogeo-chemical and ecological. Full details are given byMaltby (2009b). One of the important implications ofthis approach is that it provides a means of assess-ing the many undesignated or non-formally protectedwetlands that often occur in association with farm-land or other land uses. These may play a pivotalrole in the delivery of important ecosystem servicesin some landscapes (Blackwell and Pilgrim 2011,this issue). In comparison, Okruszko et al. (2011,this issue) present an overview of ecosystem ser-vices of European protected wetlands and examinethe implications of hydrological alterations caused byfuture climate and socio-economic changes.

INNOVATIONS

Recent policy changes in some countries have recog-nized an unprecedented level of significance of wet-lands. Notable is the importance of major wetlands inAustralia identified through the Water Act (2007) andthe emerging plan of the Murray-Darling Basin(MDBA 2010). Some 18 significant wetlands arerecognized as environmental assets, which requireguaranteed water flows for maintenance. Historically,the necessary environmental flows have been defi-cient not least because of diversion to agricultural(primarily) irrigation use. The Australian Governmenthas embarked on a major programme of purchas-ing the irrigation licences from farmers willing tosell, and has also made funds available for improvedinfrastructure to make better use of water resources,in particular to achieve increased environmental flowsfor the major wetlands of the Basin. The guide tothe proposed Murray-Darling Basin Plan, however,has met with considerable opposition, especially fromrural communities, and resolution of the conflictingdemands is still awaited.

The recognition of the ecosystem services of wet-lands led to appreciation of their economic value(Barbier et al. 1997, Turner et al. 2008) and a pro-gressive willingness to pay to maintain them (Smithet al. 2006). For example, the Catskills and Delawareriver basins cover some 4000 km2 and provide 90%of the drinking water supply to New York Citys9 million residents. Historically, these catchmentshave supplied high-quality water, but, in the 1980s,concerns about pollution increased. In 1989, the USEnvironmental Protection Agency initiated a require-ment that all surface drinking water supplies had tobe treated by filtration, unless it could be demon-strated that existing treatment processes or natural

river basin services were sufficient to provide safewater. In 1992, the City of New York decided toinvest in protecting the river basin area rather thanbuild new water filtration facilities, which would havecost US$ 68 billion to build and US$ 300 mil-lion annually to operate (Smith et al. 2006). Thecosts of investing in basin management to main-tain and restore natural filtration are much lower.Investment of US$ 11.5 billion over 10 years wasfinanced by a 9% tax increase on New York Citywater bills; a new filtration plant would have requireda two-fold increase in water bills. The City has alsoprovided US$ 40 million in compensation to cover theadditional costs of dairy farmers and foresters whoadopted best management practices.

In many cases, ecological restoration has beenattempted to recover the benefits of wetland ecosys-tems. From the mid-1990s, the scale of the schemeswas greatly increased. The justification for theselandscape-scale restoration schemes was: (a) to safe-guard existing wetland fragments through creatingbuffer zones around them; (b) to achieve a criti-cal extent of wetland for species that require largeareas; (c) to link wetland fragments to allow dis-persal of species; (d) to achieve carbon sequestra-tion through vegetation growth and peat formation;and (e) to meet fundamentally the goals of theConvention on Biological Diversity at national scalesfor habitat restoration (Acreman and Mountford2009). In Europe, the first major schemes werein The Netherlands, e.g. Oostvaarders Plassen andLauwersmeer, both exceeding 5000 ha (Kampf 2000).Over the past two millennia, the Fenlands of east-ern England have changed from a natural wetland offens, swamp, carr and open water to an almost entirelypump-drained intensive arable landscape, such that,by 1900, only 0.1% of the original fen habitat resourcesurvived (Colston 2003). From the early 1990s, aWet Fens for the Future programme stimulated wet-land restoration. The largest scheme (37 000 ha)is the Great Fen Project; it incorporates remain-ing island wetlands at Holme and WoodwaltonNational Nature Reserves (Gerrard 2004) and inter-vening arable land. Restoration objectives focus onfunctional integrity and resistance to invasion bynew species (Hughes et al. 2005), which requiresan appropriate hydrological regime. Initial focus wastherefore on the feasibility of sufficient water avail-ability to meet the requirements of wetland plantcommunities (Wheeler et al. 2004) under currentand future climates and the potential for hydrolog-ical functions, such as flood water storage. Resultsof hydrological modelling (Mountford et al. 2002)

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showed that wetland restoration of the majority ofthe scheme area would require storage of around3 106 m3 of the winter excess water to meetsummer demand for 17 000 ha restoration one yearin two. Winter discharge from the Great Fen areaexceeded 3 106 m3 during 32 of the 38 years ofrecord available. However, it was estimated that stor-age of 8 106 m3 would be needed to cope underthe 2050 climate (with reduced summer rainfall) pre-dicted by the Hadley Centre HadCM2 model (UKClimate Impacts Programme 1998). Considerablesavings are anticipated as currently flood water ispumped mechanically from the area.

Restoration of the Mesopotamian marshes posesone of the worlds greatest hydrological and socio-political challenges. The historical snowmelt floodpulse of the Tigris and Euphrates rivers fed a wet-land area of some 25 000 km2 until the 1970s(Maltby 1994, Partow 2001). The range of marshlandtypes generated by variation in hydro-period providedvital services, not only to the unique Marsh Arab(Madan) culture, but also more widely (Table 2).Some 90% of the wetland area had been lost by2000, increasing to 93% by 2003, as a result ofupstream and in-country engineering works whichare well documented (Maltby 1994, Partow 2001).The loss of marsh ecosystems has raised concerns

Table 2 Importance of the Mesopotamian Marshlands(after Maltby 1994).

Unique human community supported by natural resourcesProductive traditional agricultureSustainable utilisation of wetland and adjacent landBuffalo and cattleFishing and birdsReeds and other plantsCultivationIntegrated transport

Habitat for important populations and speciesIntercontinental migrationRegional biodiversityRare and endemic speciesGlobally threatened birds, mammals, invertebratesCyprinid marsh species of high evolutionary significance

Linkage to GulfHydrological interface between catchment and marineecosystem; Discharge; Water quality (nutrients, salinity,contaminants); Sediment; Temperature continuum formovement of economically important fish/shrimp e.g. Metapenaeus affinis Pomphret Saboor

MicroclimateEnvironmental reconstructionPeat/sedimentary deposits

over depletion of important bird populations, extinc-tion of endemic rare animal and fish species . . .Increased frequency of dust storms and the effects onregional climate and loss of fish nursery grounds . . .which extend well beyond the boundaries of thefreshwater wetlands (Maltby 2005). Initially unco-ordinated, but subsequently government supported,re-flooding of the marshes started in 2003. In Spring2005, UNEP reported 50% recovery. Field surveyshave documented a surprising degree of biodiver-sity recovery (Richardson and Hussein 2006, Abed2007). It is not clear what will be the final extentof restored wetland. This is dependent inter aliaon the priority use of water resources upstream inIraq, as well as bilateral/ multilateral discussionswith neighbouring countries, especially Turkey andIran who are drawing down water which otherwisecould support restoration. Unfortunately, the abil-ity of restored marshes to generate a wide rangeof human benefits is not always realized let alonequantified (Maltby 2009a). Restoration must com-pete with other priorities of a fledgling govern-ment. Security, urban and agricultural water sup-ply, power generation, health and economic devel-opment all currently attract greater attention ofgovernment time.

STRENGTH OF THE SCIENTIFIC EVIDENCE

Whilst there have been considerable recent advancesin knowledge, there are still many commonly-heldviews about the functioning of wetlands and provisionof resulting services that do not necessarily have thesupport of a sufficiently robust evidence base. This isdue at least in part to the inherent variability of wet-land ecosystems and the limited scope of hydrologicalresearch. We have selected just a few examples toquestion the verifiable evidence against the anecdotalviewpoint which may be more prevalent.

Wetlands and floods

In many analyses of ecosystem services of wet-lands, their role in the hydrological cycle has beenhighlighted. Wetlands are often said to act like asponge, soaking-up water during wet periods andreleasing it during dry periods (e.g. Bucher et al.1993). The basic references on the hydrological func-tions of wetlands are summaries of studies collatedin the USA in the 1980s (Adamus and Stockwell1983, Bardecki 1984, Carter, 1986). These summarieshave been used by organizations, such as IUCNtheWorld Conservation Union (Dugan 1990), Wetlands

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Fig. 3 Observed flows on the River Cherwell (dashed line) compared with modelled flows removing floodplain storage byembanking the river (solid line) (after Acreman et al. 2003).

International (Davies and Claridge 1993) and theRamsar Convention on Wetlands of InternationalImportance (Davis 1993). In a literature review ofthe hydrological functions of wetlands, Bullock andAcreman (2003) found that most (23 of 28) studiesshow that floodplain wetlands reduce or delay floods,with examples from all regions of the world. Forexample, a modelling study of the River Cherwell inOxfordshire, UK (Acreman et al. 2003) showed thatseparation of floodplains from the river by embank-ments increases the peak flows downstream by up to150% (Fig. 3). Floodplain water storage is largely onthe surface; thus the wetland is not strictly acting likea sponge.

For wetlands to soak-up water internally withintheir soils, there would need to be some storagecapacity, i.e. the soil would need to be dry. Many wet-lands have a hydro-period that includes drier and wet-ter phases. Campos et al. (2011) show that forestedwetlands and marshes along the Gulf of Mexico take-up water from June to October, as water levels riseby up to 1.2 m. Whether this reduces floods dependson when flood-producing rainfall occurs; if a wet-land is already saturated, it offers no or limited floodstorage (Acreman et al. 2007). Indeed, areas of satu-rated soils in headwater areas are defined as runoffcontributing areas by hydro-geomorphologists (e.g.Hewlett and Hibbert 1967).This relationship formsthe basis of rainfallrunoff models used by hydrolo-gists, such as TOPMODEL (Beven and Kirkby 1979).Runoff from these areas tends to be overland andrunoff speed is faster across bare soils than thoughvegetation (Holden and Burt 2003). Runoff speedis also faster if water can travel through drains ornatural pipes in the soil. Thus, wetland restorationcan reduce floods downstream by re-vegetating bare

wetlands (Bonn et al. 2009), or blocking of grips,drainage ditches in peatland (Wilson et al. 2010).Because of this complex relationship between wetlandwater regimes and hydrology of the wider catchment,care must be taken when extrapolating findings fromone wetland study to produce generic guidance onwetland functions and services.

Wetlands and groundwater

Many wetlands exist because of underlying imperme-able layers that prevent vertical movement of water.However, other wetlands are hydrologically con-nected to underlying aquifers (Acreman and Miller2002). For example, the Azraq Oasis in Jordon(Fariz and Hatough-Bouran 1998) is fed by upwardmoving groundwater (discharge). In contrast, duringinundation of the floodplain wetlands of the SenegalRiver valley, water moves downwards to the under-lying aquifer (recharge) (Hollis 1996). Alteration ofcatchment hydrology, including abstractions from sur-face water and groundwater, impoundment or diver-sion of rivers and land-use change, can all have asignificant impact on wetlands and the functions theyperform. For example, the Las Tablas de Daimielwetland in Spain (Llamas 1989) was historicallygroundwater-fed, by water moving upwards from theunderlying aquifer. From 1972, irrigated agricultureexpanded rapidly with EU subsidies and throughintensive use of groundwater from 16 000 wells(Acreman 2001). During long periods of low rainfall,groundwater levels declined by 2030 m (Bromleyet al. 1996) stopping groundwater discharge andcausing degradation of the wetlands. Any water thatreached the wetland percolated downwards into thedepleted aquifer (Forns and Llamas 2001), reversing

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the function of the wetland to that of a groundwa-ter recharge site. Local farmers considered reducedevaporation (from a smaller wetland) and increasedrecharge as a beneficial change in ecosystem function,yielding more groundwater for abstraction.

Wetlands and water quality

There is a substantial literature relating to the roleof wetlands in the protection and/or enhancementof water quality (Maltby 2009b). For example, theNakivubo papyrus swamp in Uganda receives semi-treated sewage effluent and highly polluted stormwater from Kampala. During the passage of the efflu-ent through the wetland, sewage is absorbed and theconcentrations of pollutants are considerably reduced,such that water can be abstracted nearby for publicwater supply (IUCN 2003). This function has led totheir use as buffer zones, particularly in the preven-tion of contaminants from agriculture and sometimesurban or industrial sources reaching main streamsor lakes. The degree to which this service and theresulting purification of water occur depends not onlyon hydrology but also on size, location, vegetationand soil type (Leeds-Harrison et al. 1996, Dosskeyet al. 1997), as well as the nature of the sourceimpacts. Processes including denitrification, plantuptake, absorption and sediment retention enable theremoval or storage of nutrients, heavy metals bio-cides and sediment (Blackwell and Maltby 1998,Blackwell et al. 1999). Hydrological conditions con-trol these processes and the precise functioning ofthe wetland buffer (Maltby 2009b). Convention hasgenerally advocated the position of buffer zones asriparian strips alongside rivers and streams to coun-teract the contaminating effect of runoff (e.g. Cooper1990, Haycock and Burt 1993). Whilst such position-ing can be highly effective in removing pollutantsfrom diffuse sources such as shallow groundwateror sheet-flow runoff, they may be completely by-passed when hydrological flows are intercepted byditches or drains. This is particularly common in theEuropean agricultural landscape (Goudie 1986). Themost effective location of the wetland buffer mayactually be along the alignment of such ditches, anddownslope, generally at right angles to the river orstream course (Blackwell and Maltby 1998). In astudy site on the River Torridge, UK, it was found thatthe wetter overflow zones associated with drainageditches regularly removed more than 90% of thenitrate from adjacent agricultural land (Blackwell

1997). This emphasizes the importance of hydrologi-cal pathways in the landscape as a factor to determinethe most efficient pattern and management of wetlandbuffer zones.

Peatlands and carbon sequestration

Interest in the capacity of peatlands to help miti-gate climate change through carbon sequestration hasstimulated significant questions regarding the statusof current peat resources and the possibility of newformation (Immirzi and Maltby 1983, Maltby 2010).The answers are particularly relevant to the manage-ment of upland ecosystems in the UK. This is the casewith the potential benefits associated with the block-ing of ditches (grips) in the peat to help restore hydro-logical integrity previously disrupted by drainage. It isstill uncertain whether such management actions toincrease waterlogging are sufficient to reverse thecarbon balance in favour of increased storage. (e.g.Worral et al. 2003, Worral and Evans 2009). Otherfactors, such as burning and grazing, are important indetermining the stability of the existing carbon store.Of overriding importance, however, is whether thecurrent (or immediate future) climatic conditions aresufficient in combination with the local factors suchas topography, substrate conditions, vegetation, acid-ity and nutrient status to enable new peat formation.Despite considerable on-going research, there is stilluncertainty regarding the existence of the necessaryclimate template, at least in the UK, for the net accu-mulation of new peat. It does not detract, however,from the argument to maintain or restore hydrologi-cal conditions so as to minimize any further losses ofexisting carbon store in peatlands.

Trade-off

The issue of trade-off arises when wetlands aremodified from their natural state. This usuallyinvolves hydrological change. The management deci-sion then becomes influenced by policy prioritiesor particular stakeholder influence. Dilemmas areinevitable. An example highlighted as illustration inthe UK National Ecosystem Assessment (2011) isthat of using wetlands for water quality protection/improvement with resulting increase in generation ofnitrous oxide, a potent greenhouse gas. Based on thepossible implications of trade-offs, a compatibilitymatrix (Table 3) has been developed for particu-lar ecosystem services in upland peatland (Maltby2010). Acreman et al. (2011) examined trade-offs

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Table 3 Compatibility matrix for management of ecosystem services in upland peatlands (after Maltby 2010).

Affected ecosystem service Managed ecosystem service:

Carbonstorage/sequestration

Waterquality

Flood riskreduction

Crops/livestock/gameproduction

Habitat/species

Palaeo-environmentalinformation

Traditionalrecreation

Landscape(especiallywilderness)

Carbon storage/ sequestration + + b + + c +Water quality +a + d + + c +Flood risk reduction + + + + c +Crops/ livestock/ gameproduction

d d d d d d No effect +Habitat/ species + + + d + c +Palaeo-environmentalinformation

+ + + d + No effect +Traditional recreation d No effectLandscape (especiallywilderness)

+ + + d + No effect +

anot necessarily for colour; bstorage may be maintained depending on level of impact; ccertain low-impact amenity access may becompatible; dexcept game.

Maximise overall

benefits

Water retained in the reservoir

Income

Floodplain grazing

Flood recession agriculture

Floodplain fisheries

Floodplain products

Employment Flood dependent livelihoods

Domestic water supply

IndustryIrrigated

agricultureHydropower production

Extent, duration, frequency, timing of flood release

Available water resource in the

reservoir

Fig. 4 Trade-off considerations in making decisions about managed flood releases from reservoirs to conserve downstreamfloodplain wetlands (after Acreman and McCartney 2002).

in ecosystem services in the Somerset Levels andMoors, UK. Results show that high water levelsreduce carbon dioxide emission and increase birdhabitat and hay production, whilst lower water lev-els improve grazing quality, reduce floods and reduce

methane emissions. Management decisions on wet-lands are thus a trade-off of ecosystem servicesas demonstrated for flood releases from reservoirs(Fig. 4) to conserve downstream floodplain wetlands(Acreman and McCartney 2002).

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More evidence-based assessments for differentwetland types and locations will be necessary tostrengthen the basis for decision making regardingother use and management. Further development andtesting of the functional approach to assess the extentto which a wetland or part of a wetland can actu-ally deliver a particular individual, or combinationof service(s) will be a key step in strengthening theevidence box. It will be essential to link the natu-ral science evidence with outcomes expressed in bothsocial and economic terms, to enable fully informedsocietal decisions on the optimal (wisest) use ofwetland resources.

There are still many gaps in our technical under-standing, methodological techniques and locationalknowledge that need filling. Notably we will need tounderstand much more about the effects of land-usechange on wetland functioning, the interactionsamong ecosystem processes and the influence ofenvironment, especially climate change, on function-ing and service provision. There is still limited knowl-edge of the location and distribution of small wetlandsin the landscape, or of the amount of wetland requiredto support a specific quantity or quality of ecosystemservice.

INFLUENCING POLICY

Wetlands have played an important role in influ-encing government and international policy. Theseinclude those seeking subsidies to drain them or con-vert them to forest (e.g. UK incentives leading toplanting of blanket bogs of Caithness and Sutherland,Maltby 2010), as well as those seeking their protec-tion and sustainable management (e.g. EU environ-mental policy, Water Framework Directive, RamsarConvention).

The growing ecosystem service evidence base,outlined in a growing number of over-arching assess-ments, and further demonstrated in this Special Issue,provides a platform for an even stronger focus onthe potential importance of wetlands within the pol-icy mix. Yet, a major constraint lies in the fact thatthere is a wide range of services provided with amajor range in performance depending on wetlandtype and cutting across contrasting policy sectors.There are few countries with a distinct wetland policy.Europe is noteworthy in lacking a Wetlands Directiveeven though it has developed a holistic policy forwater through the Water Framework Directive (WFD)The WFD is lacking in its consideration of non-designated wetlands despite the fact that their man-agement in the landscape is highly relevant to many

of the measures required to deliver the ambitions ofthe Directive.

Two recent initiatives, one global, the othernational, can contribute to raising the profile of wet-lands and their hydrological management as a lynch-pin for a sustainable environment. The Economics ofEcosystems and Biodiversity (TEEB) project (Kumar2010) has demonstrated the real value of naturalcapital including wetlands. In the UK the NationalEcosystem Assessment (NEA, WCMC 2011) hasraised awareness of the services provided by specificpriority habitats such as wetlands and their connec-tions with human well-being. Such initiatives furtherreinforce the case for a more coherent approachto wetlands. Hydrology is key and the hydrologicalcycle links land and water across different landscapesand economic sectors. The inappropriate distributionof the costs and benefits associated with watermanagement can only be rectified by more holisticand integrated approaches to the natural environmentand socio-economic sectors.

THE WAY AHEAD

The rationale and strategy for wetland protectionand management has relied for a long time on thestrength and significance of the conservation (andespecially the bird) lobby. This will no doubt con-tinue to be important. However, in the face ofunprecedented increases in world food and othercommodity prices, the growing concern in meet-ing basic human needs, such as clean water, relieffrom poverty and safety from environmental haz-ards, there is need for a complimentary human-centric approach that takes account of aspects seenas more directly related to wider aspects of liveli-hoods and human well-being. Such a new paradigmwould attempt to couple the often contradictory pol-icy areas by focusing the hydrological managementand associated management of wetlands on outcomesrather than ecological or other typologies. Such out-comes could be structured around ecosystem ser-vices, e.g. cleaner water, reduced flooding, slowerclimate change, improved human health. Economicanalysis should be used to examine the efficiencyof spend/costs associated with wetland managementcompared with the expenditure across different sec-tors, not always working in the same direction. Thispaper has illustrated some historic examples wherethe cost of maintaining wetland hydrology was byfar the least expensive option in meeting a desiredoutcome.

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The successful implementation of a newapproach will require widespread buy-in from vestedinterests, especially farming communities. Innovativetools can assist in thisnotably payments for ecosys-tem services which can go a long way in rectifyingthe imbalances between costs and beneficiaries fromthose services (e.g. Kumar et al. 2011). A unifyingWetland Policy, complementing existing legislationswould go a long way in achieving greater coherenceto the complexity of different policies impacting onland and water management. It would move awayfrom the silo of protected areas alone to emphasizethe importance of the greater wetland resource whichexists outside formal designation. The designatediconic sites can still serve as the standard bearersof our vital natural environment, but the broaderview is likely to generate greater resonance amongstthe wider public and the political process that iswrestling with the enduring impact of the result ofglobal financial crisis.

Acknowledgements We would like to thankMatthew McCartney (IWMI) and an anonymousreviewer for their constructive comments.

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