Quantifying ecosystem service trade-offs: The case of an urban floodplain in Vienna, Austria

Journal of Environmental Management 111 (2012) 159e172

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Quantifying ecosystem service trade-offs: The case of an urban floodplain in Vienna, Austria Samai Sanon a, *, Thomas Hein b, c,1, Wim Douven a, 2, Peter Winkler b, c, 3 a

UNESCO-IHE Institute for Water Education, Westvest 7, PO Box 3015, 2611 AX Delft, The Netherlands University of Natural Resources and Life Sciences, BOKU Vienna, Institute of Hydrobiology and Aquatic Ecosystem Management, Gregor Mendel Straße 33, Max Emanuelstr. 17, A-1180 Vienna, Austria c WasserCluster Lunz GmbH, Inter-University Centre for Aquatic Ecosystem Research, Dr. Carl Kupelwieser Promenade 5, A-3293 Lunz am See, Austria b

a r t i c l e i n f o

a b s t r a c t

Article history: Received 23 September 2011 Received in revised form 5 June 2012 Accepted 13 June 2012 Available online

Wetland ecosystems provide multiple functions and services for the well-being of humans. In urban environments, planning and decision making about wetland restoration inevitably involves conflicting objectives, trade-offs, uncertainties and conflicting value judgments. This study applied trade-off and multi criteria decision analysis to analyze and quantify the explicit trade-offs between the stakeholder’s objectives related to management options for the restoration of an urban floodplain, the Lobau, in Vienna, Austria. The Lobau has been disconnected from the main channel of the Danube River through flood protection schemes 130 years ago that have reduced the hydraulic exchange processes. Urban expansion has also changed the adjacent areas and led to increased numbers of visitors, which hampers the maximum potential for ecosystem development and exerts additional pressure on the sensitive habitats in the national park area. The study showed that increased hydraulic connectivity would benefit several stakeholders that preferred the ecological development of the floodplain habitats. However, multiple uses including fishery, agriculture and recreation, exploring the maximum potential in line with national park regulations, were also possible under the increased hydraulic connectivity options. The largest trade-offs were quantified to be at 0.50 score between the ecological condition of the aquatic habitats and the drinking water production and 0.49 score between the ecological condition of the terrestrial habitats and the drinking water production. At this point, the drinking water production was traded-off with 0.40 score, while the ecological condition of the aquatic habitats and the ecological condition of the terrestrial habitats were traded off with 0.30 and 0.23 score, respectively. The majority of the stakeholders involved preferred the management options that increased the hydraulic connectivity compared with the current situation which was not preferred by any stakeholders. These findings highlight the need for targeted restoration measures. By that, it is recommended that additional measures to ensure reliable drinking water production should be developed, if the higher connectivity options would be implemented. In the next step it is recommended to include cost and flood risk criteria in the decision matrix for more specific developed measures. The research showed that pair-wise tradeoff figures provided a useful means to elaborate and quantify the real trade-offs. Finally, the research also showed that the use of multi criteria decision analyses should be based on a participatory approach, in which the process of arriving at the final ranking should be equal or more important than the outcome of the ranking itself. Ó 2012 Elsevier Ltd. All rights reserved.

Keywords: Wetland management Wetland ecosystem services Floodplain restoration Trade-off analysis Multi criteria decision analysis Lobau wetland

* Corresponding author. Tel.: þ47 47234328. E-mail addresses: [email protected] (S. Sanon), [email protected] (T. Hein), [email protected] (W. Douven), [email protected] (P. Winkler). 1 Tel.: þ43 7486 20060 40, þ43 1 47654 5229; fax: þ43 7486 2006020, þ43 1 47654 5217. 2 Integrated River Basin Management UNESCO-IHE Institute for Water Education Westvest 7, 2601 AX Delft, The Netherlands. Tel.: þ31 15 215 1886; fax: þ31 6 1383 4493. 3 Tel.: þ43 1 47654 5229; fax: þ43 1 47654 5217. 0301-4797/$ e see front matter Ó 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.jenvman.2012.06.008

1. Introduction Riparian zones, floodplains and river-marginal wetlands are key landscapes of strategic importance to human society (Acreman et al., 2007; Amezaga et al., 2002; Mitsch and Gosselink, 2000; Thoms, 2003; Tockner and Standford, 2002). They provide important ecosystem services such as climate regulation, nutrient cycling, retention of flood waters, infiltration and stabilization of groundwater levels for drinking water abstraction and recreational

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services in urbanized areas (Hoehn et al., 2003; MEA, 2005; TEEB, 2010). It is estimated that more than half of the original wetlands in the world have been lost due to anthropogenic modifications (Fraser and Keddy, 2005; Mitch, 2005) such as drainage for agricultural production (e.g. Kanyarukiga and Ngarambe, 1998; Walter and Shrubsole, 2003), construction of dams for hydropower, urbanization and increased pollution loads in general (Revenga et al., 2000). In Europe, the loss of natural riverine wetlands is estimated to be about 95% (Tockner and Standford, 2002). The remaining riverine wetlands are also altered by straightening and dredging of river channels for navigation purposes (Hesselink, 2002) and confined (Jungwirth et al., 2002) by flood protection measures such as construction of levees and embankments (Henry et al., 2002; Hey and Philippi, 2006; Mauchamp et al., 2002). The reduced floodplain dynamics has turned many riverine wetlands into static, shallow and lake-like systems (Schiemer et al., 2006; Hohensinner et al., 2008), with a reduced integrity of floodplain ecosystem functions (Hale and Adam, 2007; Simenstad et al., 2006; Weigelhofer et al., 2011). The degradation of floodplain ecosystem functions is particularly far progressed in urban settings. Faulkner (2004) and Groffman et al. (2003) indicate that the majority of urban floodplains have already been settled or converted into other ecosystem types, urban settlements, industrialized areas or arable land. The remaining aquatic habitats are often disconnected from the river or are severely altered by intense human uses (Grayson et al., 1999; Hein et al., 2006; Zedler and Kercher, 2005). This often leads to unbalanced floodplain conditions such as increased sedimentation and siltation processes and enhanced eutrophication processes caused by local diffuse and point pollution sources (Henry et al., 2002; Shields et al., 2008). Today, urban floodplains are also increasingly used for recreational activities (Anderson, 1995) like hiking, fishing and swimming. Although these latter activities create additional pressure on the sensitive floodplain ecosystems, they also raise the demand for protection and conservation of nature (Hein et al., 2006; Schaich, 2009). Therefore, the future demands for socio-economic activities and other societal uses, but at the same time, the importance of protecting these valuable floodplain areas, emphasizes the need for new management strategies (Hein et al., 2006; Hopfensberger et al., 2006; Orr et al., 2007; Tong et al., 2006). The development of such new management strategies can benefit from a multi criteria decision analysis (MCDA) approach due to the potential conflicts and trade-offs between different ecological, livelihood, water treatment and water supply functions. This approach is widely used to support the solution of multi objective decision making problems, where conflicts exist between different objectives (Tecle et al., 1998; Xevi and Khan, 2005). Multi criteria decision analysis aims at structuring the planning and decision making process (Mendoza and Martins, 2006). It provides a means to elaborate and quantify the explicit differences between the management objectives and hence can help in increasing the transparency of the decision-making process. Understanding the trade-off relationships between ecological, economic and social objectives is important in designing policies to manage or restore ecosystems (Cheung William and Sumaila, 2007; Reichert et al., 2005; Turner et al., 2000). Designing effective programs and policies to restore lost or degraded ecosystems also requires evaluation and prioritization of the management options (Prato, 2003). In addition, multi criteria decision analysis techniques allow the incorporation of stakeholders in decision making processes (Brown et al., 2001a; Linkov et al., 2004). The main aim of the research was to investigate the potential role of multi criteria decision analysis in wetland management, more specifically in the quantification of trade-offs between objectives of key stakeholders involved in wetland management.

The paper presents the results of an application of a multi criteria decision analysis to evaluate a set of management options for the Lobau floodplain, an urban floodplain along the Danube River in Vienna, Austria. For this purpose, a distance based algorithm was used to quantify and elaborate trade-offs between two conflicting objectives. The paper further explores what management options are the most preferred ones according to the preferences of stakeholders and, following that, also which option could theoretically offer the ‘best’ compromise between the group of stakeholders. The Mulino decision support tool called mDSS4 (Giupponi, 2007) was used to analyze the data. 2. Study area- the Lobau floodplain The Lobau is a 23 km2 floodplain formed by the discharge patterns of the Upper Danube River (Tritthart et al., 2011). The floodplain area is located on the left river bank of the Danube River at the eastern border of the Vienna City in Austria (Fig. 1). In its pristine condition, the Lobau area was one of the widest floodplains amongst the Austrian anabranching Danube River section, where braided river arms constituted the dominant floodplain habitats (Hohensinner et al., 2008). As part of improvements for navigation and flood protection, the Danube River was straightened and embanked substantially between 1870 and 1880, which changed the morphological character of this river section from an anabranching situation to a single channel system (Zornig et al., 2006). Since then, the former dynamic floodplain has been disconnected from the Danube River channel and changed floodplain development primarily due to altered geomorphological dynamics (Hohensinner et al., 2008). At present, the hydrodynamics of the Lobau is characterized as a groundwater-fed and back-flooded lake system with long periods of low to negligible flow (Janauer and Strausz, 2007). The reduced hydraulic connectivity has resulted in sediment accumulation and a reduction of water levels at the floodplain scale and subsequently enhanced the terrestrialization processes (Weigelhofer et al., 2011). Subsequently, the habitat distribution and vegetation cover has also changed (Hein et al., 2007) which together with prevailing sedimentation and eutrophication processes has resulted in a gradual decrease of size and quality of the aquatic habitats (Kirschner et al., 2001). The recent urban expansion of Vienna into the north-eastern part of the Lobau has turned the upper part of the Lobau (Fig. 1) into a highly urbanized floodplain, contributed to the degradation of the natural floodplain (Hohensinner et al., 2004; Schiemer et al., 1999). Urban development has also led to an increase in the number of visitors to the Lobau, which adds further pressure on sensitive habitats and species in the floodplain. Nevertheless, the Lobau still contains a high aquatic, semi-aquatic and terrestrial biodiversity (Reckendorfer et al., 1998; Baart et al., 2010). In 1996, this floodplain area was designated as national park area and the ecosystem management target was to rehabilitate the hydrological connectivity approaching pre-regulation conditions again (Schiemer et al., 1999). Hohensinner et al. (2008) show that without sound management practices, most aquatic and semi-aquatic habitats of the Lobau floodplain are expected to change further and the floodplain will soon become a primarily terrestrial ecosystem with major implications for its rich aquatic and amphibic biodiversity (Hein et al., 2006). However, restoring the natural floodplain conditions by increasing the surface connectivity between the Lobau and the river channel, might impose adverse effects on the potential groundwater abstraction and limit other societal utilizations (Hein et al., 2008). Currently, the main uses of the Lobau area include recreation, groundwater abstraction for drinking water production, ecosystem development through

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Fig. 1. Implementation of the hydraulic options (Hein et al., unpublished report). Delineation of the Lobau into three sub-areas including the Upper Lobau (UL), the Lower Lobau (LL) and the Vorland Strip (VL). The Dotation point is the point that receives water input from the two inlets (UL1 and UL2) located in the Upper Lobau. Main features of the hydraulic options are summarized in Table 2.

rehabilitation of functional processes and conservation of floodplain habitats and sport fishery (Hein et al., 2006). 3. Method and data 3.1. Multi criteria decision analysis 3.1.1. General approach The decision analysis implemented in this study was based on a multi criteria decision analysis (MCDA) framework. The iterative process of MCDA typically consists of the following steps: defining objectives, selecting set of criteria to measure the objectives, specifying the alternatives, transforming the criterion scales into commensurable units, pre-evaluating of the evaluation matrix, assigning weights to the criteria that reflect decision maker’s preferences, selecting and applying mathematical algorithms for ranking alternatives, performing a sensitivity analysis and choosing or recommending alternatives (Howard, 1991; Keeney, 1992). The objective of the MCDA in this study was to evaluate and quantify the explicit trade-offs between key ecosystem services related to the objectives of the stakeholders of the Lobau. Traditional MCDA often deals with only the implicit trade-offs in the form of weights expressed by the stakeholders involved (e.g. Brown et al., 2001b; Van Huylenbroeck, 1998). In this study, the purpose of the trade-off analysis was to make the trade-offs between the stakeholder’s objectives explicit by giving it a numerical value and hence enhance transparency. Integration of trade-off analysis in a general multi criteria decision strategy is addressed in Grierson (2008). The next two paragraphs will elaborate the MCDA methodology applied to quantify the tradeoffs and to rank the management options.

3.1.2. Quantification of trade-offs Standardized criteria scores were used to construct pair-wise trade-off figures in which the Pareto ecosystem front between the two criteria is formed by the non-dominated options between the two conflicting criteria (Van Huylenbroeck, 1998). A management option is non-dominated, if there are no other options in the decision space that score better for one criterion at least, and also which scores at least as well as all options for the other criteria (Lee et al., 1996). The sub-optimal (or the dominated) options do not inherit trade-offs (by this definition) as one objective can be improved without causing loss in the other (Cheung William and Sumaila, 2007; Lautenbach et al., 2010). Trade-offs between management criteria exist, if the optimum score of these criteria is achieved by different options in the decision space. Thus, the nondominated management options, that lay on the Pareto (ecosystem) front, form the curve of the trade-offs between the two criteria evaluated (see solid line in Fig. 2) (Tappeta et al., 2000). The trade-off between the two management criteria in this study was quantified by calculating the shortest distance from a theoretical ideal solution (in which both criteria score equals 1) to the nondominated option(s) that provided this shortest distance (see dashed line in Fig. 2). The approach of measuring the closest distance(s) to reference point(s) to rank the management options according to these distances was suggested by Wierzbicki in 1980 (Deb et al., 2006; Wo zniak, 2007). 3.1.3. Ranking of management options The ranking of the selected management options according to the preferences of the decision makers was based on two decision rules: the Simple Additive Weighting (SAW) and the Technique for Order Preference by Similarity to Ideal Solution (TOPSIS) (Giupponi,

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Fig. 2. Theoretical trade-off figure based on normalized criteria scores ranging from 0 to 1. The trade-off curve between the two criteria is formed by the non-dominated options that forms the ecosystem front.

2007). SAW uses the additive aggregation of the criteria outcomes and is a commonly used decision rule in single dimensional decision making problems because of its simplicity (Pohekar and Ramachandran, 2003). TOPSIS is a popular compromise decision rule and defines the most preferred option as the one that is closest to the ideal positive option but at the same time also furthest away from the ideal negative option (Giupponi, 2007). The two decision rules were applied to check the robustness of their ranking results. Then, the Borda group compromise decision rule was applied to compromise the individual rankings obtained by the SAW and TOPSIS decision rules. To support this process, the Mulino Decision Support tool (mDSS4) was used (Giupponi, 2007). The mathematical algorithms of the standardization technique and decision rules applied in this study are beyond the scope of this paper. 3.2. Data The quantification of the trade-offs between the stakeholder’s objectives related to key ecosystem services of the Lobau floodplain required various data sets. Data regarding the stakeholder groups and their interests in the Lobau floodplain was collected by the EU FP7 WETwin project (van Ingen et al., unpublished report). Data on management options, management criteria and decision maker’s preferences were collected by the Optima Lobau project in collaboration with the main stakeholders of the Lobau floodplain (Hein et al., unpublished report). 3.2.1. Stakeholder groups and their interests Stakeholder groups of the Lobau floodplain can be identified at different spatial scales including the local, wetland, municipal, national, provincial and international scales. The interests of the main stakeholder groups differed between these scales (Table 1). Ecosystem services like fishery, hunting, agriculture and recreation were of interest to the adjacent municipalities at the local scale but also to the Associations for Hunting and Fishing of Vienna and Lower Austria and to the Chamber of Commerce of Vienna and Lower Austria at the provincial scale. The conservation of nature was of interest to the stakeholder groups at the wetland, municipal, national, provincial and international scale. The stakeholder groups that preferred a combination of interests were typically from government. This difference was especially visible at the national scale in which the interest of the Environmental NGO was primary nature conservation, while the interests of governmental organizations, including the Federal Ministry for Environment and the Federal Ministry for Traffic, were both nature conservation and flood protection (Table 1).

3.2.2. Management options The management responses analyzed in this study aimed at a more active use of the floodplain for flood attenuation by increasing the hydraulic connectivity with the Danube river channel and hence stimulating the development of aquatic habitats and enhance geomorphic dynamics (Fig. 3). The stakeholders involved in the Optima Lobau project rejected hydraulic options that would increase the flood risk, and also expressed that costs of management options should not be a matter of concern in the first assessment. Given these boundary conditions, 4 hydraulic options ranging from complete disconnection downstream (Fig. 1) to fullreconnection with the Danube River channel upstream (Table 2) were developed. The main features of these 4 hydraulic options including the Current Status option are summarized in Table 2. The hydraulic connectivity with the Danube River channel and the openings are coded according to the option’s position in the Upper Lobau (UL) and the Lower Lobau (LL). The locations of the main features presented in Table 2 are shown in Fig. 1. In the current situation (Current Status option), water from the Danube channel can enter the Lower Lobau during high water levels through a small opening (Schönauer Schlitz) in the main levee located at the downstream end and flows out in case of receding water levels (Fig. 1). Groundwater exchange with the main river channel also contributes to water supply of floodplain waters (Janauer and Strausz, 2007). In the current situation, surface water input is allowed at a rate of 0.5 m3 s1 (Table 2) through a controlled opening (UL1) in the Upper Lobau (Fig. 1). The Disconnection option closes off the downstream opening point (Schönauer Schlitz) and further isolates the Lobau from the Danube river channel (Table 2). In this option, the hydraulic connectivity is mainly driven by the existing controlled opening at the Upper Lobau (UL1) with a maximum rate of 1.5 m3 s1 (Table 2). The Enhanced connectivity option increases the inflow from the existing controlled two openings at the Upper Lobau (UL1 and UL2) to a rate of 5 m3 s1 each. Thus, the Dotation point, that receives the input water from the two controlled points in the Upper Lobau area, equals 10 m3 s1 (Table 2). This hydraulic option does not increase the hydraulic connectivity of the Lower Lobau area and the backflow flooding point (Schönauer Schlitz) remains open. The Partial Reconnection option increases the water input in the Lower Lobau (LL2) at a rate of 20 m3 s1 during low water discharge (LW) in the Danube river channel and at a rate of 125 m3 s1 during mean water discharge (MW). This additional water input will create a new side arm in the Lower Lobau area (LL2). Therefore, it is necessary to enlarge the outflow area (Fig. 1) by removal of embankments in the Lower Lobau and also enlarge the downstream

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Table 1 Main stakeholder groups of the Lobau and their interests (van Ingen et al., unpublished report). Scale

Stakeholder groups

Main stakeholders of the Lobau Local Adjacent Municipalities Wetland Municipal

National

Provincial

International

National Park Authority (National Park GmbH) Governmental Administration units for:  Water Management Authority of Vienna,  Forestry,  Drinking Water, and  Nature Protection Nature Conservation NGOs (WWF, Bird Life) Federal Ministry for Environment and Federal Ministry for Traffic Governments of Vienna and Lower Austria, Governmental Administration unit for Environment and Water Management, Governmental Administration unit for Spatial Planning Associations for Hunting and Fishing of Vienna and Lower Austria, Chamber of Commerce of Vienna and Lower Austria (members of the National Park Advisory Board) Advocacy for the Environment of Vienna and Lower Austria International Commission for the Protection of the Danube River

Type

Interest

Civil Society

Fishery, recreational, flood protection and health issues (related to abundance of mosquitoes) Nature conservation, national park, research and education

Public Sector Regulator, Research and Education Governance Structure, Donor/Funder

Flood protection, nature conservation, drinking water supply and recreation

NGO Governance Structure, Donor/Funder and Advisory Governance Structure, and Donor/Funder

Nature conservation Nature conservation, flood protection and water ways

Civil Society/NGO and Advisory

Hunting, fishing, agriculture

Governance Structure

Legal questions regarding nature conservation

Governance Structure

Harmonize all interests and ecosystem protection

opening (Table 2) to flush out the input water. The rationale for the creation of a new side arm is to compensate for the loss of aquatic habitats and, at the same time, to preserve the developed highly endangered lentic habitats in the upper part of the Lobau. Under this hydraulic option, the hydraulic connectivity of the Upper Lobau with the Danube river channel is only driven by the controlled inflow point (UL1) at a rate of 1.5 m3 s1. In the Full Reconnection option, the inflow rate from the existing controlled opening (UL1) and the second one (UL2) in the Upper Lobau increase to a rate of 5 m3 s1 each, leading to a total of 10 m3 s1 for the Dotation point (Table 2). Reactivation of four former side arms through four water input points (LL1eLL4) to allow uncontrolled water input are re-established in the Lower

Flood protection, nature conservation, drinking water supply, sanitation, recreation

Lobau (Fig. 4). The different inflow rates, at the four input points, are dependent on the riverine discharge and the local elevation of the side-arms starting at low flow (Table 2). The substantial water input makes it necessary to enlarge the outflow point at the downstream end by partial removal of the flood protection dyke in the Lower Lobau (Fig. 1). 3.2.3. Future use-scenarios In addition to these hydraulic options, five future use-scenarios were identified, each having one dominant utilization of the Lobau floodplain (Hein et al., unpublished report): ecological development (ECO), drinking water production (DRINK), recreation (REC), agriculture (AGRI), and fishery (FISH). The five future use-scenarios

Fig. 3. Preferences of the representatives of the nine stakeholder groups (Hein et al., unpublished report). The weights were obtained by dividing the actual allocated points to the total of five points.

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Table 2 Main features of the 4 hydraulic options including the current status (Hein et al., unpublished report). LW ¼ low water discharge in the Danube river channel, MW ¼ mean water discharge in the Danube river channel. UL ¼ Upper Lobau, LL ¼ Lower Lobau. The locations of the water input areas UL1, UL2, LL1, LL2, LL3 and LL4 are shown in Fig. 1. The Dotation point is the point that receives water input from the upstream area through the two inlets (UL1 and UL2) located in the Upper Lobau area. Implementation of the hydraulic options

Water input Upper Lobau

Lower Lobau

UL1

UL2

Dotation point

LL1

LL2

LL3

LL4

Current status Disconnection

0.5 m3s1 1.5 m3s1

e e

0.5 m3s1 1.5 m3s1

e e

e e

e e

e e

Enhanced connectivity Partial reconnection

5 m3s1 1.5 m3s1

5 m3s1

10 m3s1 1.5 m3s1

e e

e e

e e

Full reconnection

5 m3s1

5 m3s1

10 m3s1

e 20 m3s1 (LW) 125 m3s1 (MW) 15 m3s1 (LW) 100 m3s1 (MW)

20 m3s1 (MW)

20 m3s1 (MW)

15 m3s1 (LW) 100 m3s1 (MW)

were developed in line with the regulations and the management plan of the National Park Authority (National Park Donau-Auen, 2004). The purpose of the scenarios was to assess the impact of maximizing one single utilization, but within the maximum limits set by the regulations of the National Park Authority. Generally this implied that in each dominating use-scenario, the areas for other uses were reduced. In the fishery scenario, a baseline study was used to estimate the maximum fishing activities based on the fishing licenses (Hadwiger et al., 1995). In the agriculture usescenario, all classified farmable areas in the Lobau, as defined by the National Park Authority, were assumed to be cultivated. In the recreation use-scenario, a maximum use frequency was estimated based on the expected population growth in the next 20 years in the vicinity of the Lobau. In the drinking water production usescenario, the maximum values were estimated based on the existing water rights (permits). In all other use-scenarios only the mean values of the last year’s water production were used and the other uses were only allowed outside the sensitive areas (of influence) for drinking water production, defined by the modeled area around each well of a groundwater residence time of 60 days. In the

Schönauer Schlitz - the back flow flooding point

Outflow area

Open Closed (during floods) Open Open

Open Closed

Open

Enlarged

Open Enlarged

ecological development use-scenario, all other uses including agriculture, fishery and recreational activities were kept at a minimum. The total number of management options identified for this study comprised of 21 management options (4 hydraulic options times 5 use scenarios, plus the Current Status). In the results section, a management option is referred to as a combination of the hydraulic option and the use-scenario. For example the disconnection hydraulic option and the ecological development usescenario is referred to as ‘Discon_ECO’. 3.2.4. Management criteria and indicators Through predictive hydrological, ecological and socio-economic models in addition to qualitative expert judgments, a total of 76 impact indicators were identified and assessed for each management option. A more detailed description of the models and the individual indicators can be found in Hein et al. (2006) and Hein et al. (unpublished report). The model structure for the hydrological and ecological models can be found in Weigelhofer et al. (2006) and Baart et al. (2010) for the aquatic vegetation. The model framework

Fig. 4. Impact on the ecological condition of the terrestrial habitats, ecological condition of the aquatic habitats and potential drinking water production. The x-axis represents the increasing hydraulic connectivity and the current status is marked by the yellow bar. The main hydraulic options are also listed in the x-axis. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)

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consisted of a digital terrain model for each management option, a spatial explicit (cell size 10  10 m) coupled hydrodynamic model assessing daily surface and ground water levels and flow conditions for each cell and combining these results with spatial explicit hydro-ecological models using hydrological parameters such as e.g. days of connectivity, water levels in floodplain water bodies as input to assess key ecological properties. Historical analyses of the hydrogeomorphic conditions were used to define the preregulation conditions and assess hydromorphologic indicators such as distribution of floodplain water body types, mean depth at specific riverine discharges (Hohensinner et al., 2008). A statistical approach based on long term data series (minimum of 4 years of available data) was used in the hydro-ecological models (Baart et al., 2010; Hein et al. unpublished report, Mayer, 2007). To analyze and quantify the trade-offs, indicators for each management criterion were selected and aggregated (Table 3). Selection and aggregation of individual indicators was carried out for the indicators with the same value function (minimize or maximize) until the best possible discrimination between the management options were achieved. The value functions used to standardize the selected and aggregated indicators were related to the objectives of the stakeholders. The benefit-type value function was used to normalize those impacts stakeholders were expected to maximize, while the cost-type value function was used to normalize those impacts stakeholders were expected to minimize (Giupponi, 2007). 3.2.5. Stakeholders preferences Data about preferences on management criteria was collected by consulting nine stakeholders representing each of the abovementioned stakeholders groups (Table 1). These representatives were asked to indicate their preferences on the management criteria by allocating a total of five points (Hein et al., unpublished report) (Fig. 3). In this study, we assume their preferences to be representative for each stakeholder group. The most important criterion for the Governmental unit for Environment and Water Management was drinking water production. The ecological condition of the aquatic habitats, the ecological condition of the terrestrial habitats and recreation were of moderate importance, but less than drinking water production. The Water Management Authority valued the ecological condition of the aquatic habitats as most important compared to recreation, ecological condition of terrestrial habitats and drinking water production. The Spatial Planning Administration valued the ecological condition of the

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aquatic habitats, the ecological condition of the terrestrial habitats and drinking water production as equally important. The Nature Protection Administration valued the ecological condition of the terrestrial habitats higher than the ecological condition of the aquatic habitats, while the National Park Authority and the International Commission valued the ecological condition of the aquatic habitats and the ecological condition of the terrestrial habitats as equally important. The representative of the Local Village valued fishery higher than any other criteria. 4. Results The results chapter is divided into three parts. The first part evaluates the impacts of the 21 management options including the current status on the management criteria presented in Table 3. The second part elaborates and quantifies the major trade-offs between management criteria by using trade-off figures. The third part ranks the management options according to the preferences of the nine stakeholder groups (Fig. 3) as obtained by the two decision rules. The identification of the best compromised option will be included in this last part. 4.1. Impacts on the management criteria The results show that increased hydraulic connectivity, through surface water exchange with the main channel of the river, increased the available aquatic area and improved the ecological condition of the aquatic habitats in general and further enhanced the ecological condition of the terrestrial habitats. The latter effect is linked to increasing exposure of terrestrial areas to more frequent flood inundation that enables development of typical floodplain vegetation. The enhanced hydraulic option showed no improvement of the ecological condition of the terrestrial habitats at the floodplain scale (Fig. 4). Therefore, the Full Reconnection option, that rehabilitates the surface water connection between the entire Lobau and the main river channel, maximized the ecological condition of the aquatic water bodies, the potential areas for fishing activities and the ecological condition of the terrestrial habitats at the floodplain scale (Figs. 4 and 5). Fostering the hydrological dynamics also increased the available areas for fishing (Fig. 5). On the other hand, increased hydraulic connectivity seemed to reduce the potential for drinking water production (Fig. 4). This is explained by the reduction of the groundwater residence time due increased surface water influence. The Disconnection hydraulic

Table 3 Management criteria and selected and aggregated indicators (Hein et al., unpublished report). The delineation of the Lobau floodplain into three sub-systems including Upper Lobau, Lower Lobau and Vorland is shown in Fig. 1. Management criteria

Selected and aggregated indicators

Stakeholder objective/value function

Ecological condition of the aquatic habitats

Sum of suitable habitats for selected species and other indicators for the ecological condition of the water bodies including; available phytoplankton biomass in the connected water bodies, area of Ranunculus fluitans, values for hydrophytes, values for all macrophytes, species number of macrophytes, percentage of shallow areas (<0.5 m water depth at summer mean water), area of connected water bodies at mean water and size of water bodies with a mean Chlorophyll-a content > 25 mg l1 during the vegetation period Lengths of hiking trails, public footpaths, visitor tracks, and bicycle paths (all in Upper Lobau and Lower Lobau) Total area of fishing waters in hectare for the whole Lobau floodplain Sum of area with cereal, vegetable and potatoes in the whole Lobau Sum of inundated areas at annual high water in Upper Lobau, Lower Lobau and Vorland Area, areas of helophytes in Upper Lobau, Lower Lobau and Vorland, species richness, dynamic vegetation elements and degree of naturality of floodplain vegetation Sum of days of Danube surface water influence on the 5 drinking water wells and the production days in one well suspended due to flood water input

Benefit value function- to be maximized

Potential recreation Potential fishery Potential agriculture Ecological condition of the terrestrial habitats

Potential drinking water production

Benefit value function- to be maximized Benefit value function to be maximized Benefit value function to be maximized Benefit value function- to be maximized

Cost value function to be minimized

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Fig. 5. Impact on the agriculture, fishery and recreation. The x-axis represents the increasing hydraulic connectivity and the current status is marked by the yellow bar. The main hydraulic options are also listed in the x-axis. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)

option and the Current Status maximized the potential drinking water production. The Disconnection option also maximized the potential agriculture and potential recreation (Figs. 4 and 5). However, the Disconnection option minimized the ecological development (of the aquatic and terrestrial habits) and also the potential areas for fishing at the floodplain scale. The Full Reconnection option did not result in any significant impacts on the potential agriculture and the potential recreation criteria (Fig. 5). The results indicate that the Disconnection option might lead to larger conflicts between the management criteria as the increased hydraulic options did not result in any significant impacts on potential agriculture and recreation. Therefore, increased hydraulic connectivity seems to reduce the potential conflicts as the Current Status option only maximized the drinking water production. Based on these results, it is reasonable to expect a substantial tradeoff between the management criteria that scored high under the Full Reconnection option (like the ecological condition of the aquatic habitats, the ecological condition of the terrestrial habitats and the potential fishery) and the potential drinking water production criterion (Figs. 4 and 5). Important interactions between the management options and the five use-scenarios were also apparent. For instance, the

ecological development (ECO) use-scenario had a negative impact on potential fishery, potential agriculture and potential recreation in each hydraulic option, as the area for other uses was limited (Figs. 4 and 5). On the other hand, the recreation (REC) use-scenario reduced for each hydraulic option the maximum potential for the development of aquatic habitats (Fig. 4), maximum potential for fishery (FISH) and maximum potential for agriculture (AGRI) (Fig. 5), which can be due to the fact that their areal extensions were reduced. The recreation use-scenario (REC) also reduced the maximum potential for the development of terrestrial habitats in each hydraulic option (Fig. 4). The drinking water (DRINK) usescenario reduced the maximum potential for drinking water production in each hydraulic option due to the increased groundwater abstraction rates and thus, a limited availability during different periods compared to the current situation. 4.2. Quantification of the major trade-offs In this section, we elaborat and quantify the trade-offs between management criteria resulting from the previous section by using trade-off curves. We will focus on the three major trade-offs resulting from the previous section: between drinking water and

Fig. 6. Trade-off between ecological condition of the aquatic habitats (y-axis) and potential drinking water production (x-axis). The management option (s) that provided the shortest distance to the theoretical solution is shown in bold.

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Fig. 7. Trade-off between ecological condition of the terrestrial habitats (y-axis) and potential drinking water production (x-axis). The management option (s) that provided the shortest distance to the theoretical solution is shown in bold.

aquatic ecology, drinking water and terrestrial ecology, and drinking water and fishery. The trade-off curve between the ecological condition of aquatic habitats and drinking water production (Fig. 6) showed a negative linear relationship between the two criteria. The Pareto front between the two criteria was formed by the Ecological Development (ECO) use-scenario in each hydraulic option except the Current Status. This is caused by the positive impact the ecological development (ECO) use-scenario will have on the ecology of the aquatic habitats in each hydraulic option as compared to other usescenarios. In this curve, the Partial Reconnection option with dominant Ecological Development (ECO) was located at the point that provided the shortest distance to the theoretical ideal solution (Fig. 6). The distance from this location to the ideal solution point, is 0.50. At this location in the figure, the ecological condition of the aquatic habitats is traded off with a 0.30 score and the drinking water production with a 0.40 score (Fig. 6). The trade-off curve between the ecological condition of terrestrial habitats and potential drinking water production was formed by the Current Status, Partial Reconnection and Full Reconnection options (Fig. 7). Their hydraulic gradients and the expected benefits are apparent as 4 clusters on the trade-off figure. The Pareto front between the two criteria shows that the Partial Reconnection option for the use-scenarios Ecological Development (ECO), Agriculture (AGRI) and Fishery (FISH), provided the point with the shortest distance to the theoretical ideal solution which maximizes both criteria (Fig. 7). This can be explained by the negative impact

the drinking water production (DRINK) use-scenario had on potential drinking water production in each hydraulic option. At this location in the figure, the potential drinking water production is traded off with a 0.4 score, while the ecological condition of the terrestrial habitats with a 0.23 score. Therefore, the trade-off between the two criteria is quantified at 0.46 (Fig. 7). The trade-off curve between fishery and drinking water production was formed by the Agriculture (AGRI) and Fishery (FISH) use-scenarios in each hydraulic option except the Current Status (Fig. 8). This result can be explained by the negative impact the recreation (REC) use-scenario had on potential fishery and the negative impact the drinking water (DRINK) use-scenario had on potential drinking water production in each hydraulic option. The ecological development (ECO) use-scenario reduced the potential fishery because other societal utilizations were kept at a minimum (except from drinking water production). In this Pareto front, the Enhanced Connectivity option with the Agriculture (AGRI) and Fishery (FISH) use-scenarios provided the shortest distance to the ideal solution. At this location in the figure, the potential fishery is traded off with a 0.3 score and the potential drinking water production with a 0.02 score (Fig. 8). Subsequently, the trade-off between the two criteria is quantified at 0.3 (Fig. 8). In summary, the largest trade-offs were between ecological development (of the aquatic and terrestrial habitat) and the potential drinking water production. The two trade-off curves show a strong negative and almost linear relationship between the

Fig. 8. Trade-off between potential fishery (y-axis) and potential drinking water (x-axis). The management option (s) that provided the shortest distance to the theoretical solution is shown in bold.

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conflicting criteria indicating a maximum trade-off at the two hydraulic extremes; Isolation and Full Reconnection. 4.3. Ranking of management options This section presents the individual rankings (Table 4) of the 21 management options according to the preferences of nine representatives of the stakeholder groups involved as presented in section 3.2. The results of the Simple Additive Weighting (SAW) decision rule show that six of nine stakeholder groups preferred one of the use-scenario options of the Full Reconnection option (Table 4). These six stakeholder groups included International Commission for River Protection, Local Village, Environmental NGO, Water Management Authority of Vienna, National Park Authority and Nature Protection Administration. These were also the stakeholder groups that valued the ecological condition of the aquatic habitats, the ecological condition of the terrestrial habitats and the potential fishery higher than any other criteria (Fig. 3). The representative for the Governmental unit for Water and Environment and the Spatial Planning Administration both valued the ecological conditions of the floodplain (i.e. terrestrial and aquatic) and the drinking water production equally high (Fig. 3). This is in line with the outcomes of SAW rankings showing that the Partial Reconnection option with the fishery (FISH) use-scenario was the most preferred option for both. For the Drinking Water Administration, who valued the drinking water production criterion higher than any other criteria, the SAW rankings resulted in the reduced hydraulic connectivity options as their most preferred option. The Disconnection option with the agriculture (AGRI) usescenario was the most preferred option for the Drinking Water Administration, because they more clearly assigned a moderate importance to the potential agriculture criteria (Fig. 3).

The results of the Technique for Order Preference by Similarity to Ideal Solution (TOPSIS) rankings show that four out of the nine stakeholder groups including the Local Village, Environmental NGO, National Park Authority and Nature Protection Administration, preferred one of the use-scenario options of the Full Reconnection option (Table 4). The Environmental NGO, National Park Authority and Nature Protection Administration valued the management criteria, which scored maximum under the Full Reconnection option (Figs. 4 and 5), highest (Fig. 3). Surprisingly, TOPSIS also resulted in the Full Reconnection as the most preferred hydraulic option for the Local Village as well (Table 4). This stakeholder group indicated the potential fishery criterion (which was maximized under the Full Reconnection hydraulic option) as the highest, but also placed a moderate importance on the potential drinking water criterion (which scored minimum under the Full Reconnection option) (Fig. 4). For the International Commission for River Protection, Spatial Planning Administration, Governmental unit for Environment and Water Management, Drinking Water Administration and the Water Management Authority of Vienna, which also indicated the importance of the potential drinking water criterion, the TOPSIS suggested the lower hydraulic options as their most preferred option (Table 4). The Enhanced hydraulic option with the recreation (REC) use-scenario was the most preferred option for the Spatial Planning Administration and Governmental unit for Environment and Water, and the Disconnection option with the agriculture (AGRI) use-scenario for the Drinking Water Administration. The Partial Reconnection option with ecological development (ECO) was the most preferred hydraulic option for the International Commission and the Partial Reconnection with the fishery (FISH) use-scenario for the Water Management Authority of Vienna. The difference is explained by the fact that the International Commission for River Protection and the Water Management Authority of Vienna gave less importance

Table 4 Ranking of the management options according to the preferences of the stakeholders. Results were obtained by the mDSS4 software (Giupponi, 2007). The preferences of the nine stakeholder groups are shown in Fig. 3. The management options are arranged according to their increasing hydraulic connectivity.

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to the potential drinking water (DRINK) criterion compared to the Spatial Planning Administration, Governmental unit for Environment and Water and the Drinking Water Administration (Fig. 3). Based on the SAW rankings, the Borda group compromise decision rule resulted in the Full Reconnection with dominant drinking water production as the best compromised option for all nine stakeholder groups. This hydraulic option was the best compromised option and identified as the most preferred option by the majority of the involved stakeholders (Table 4). The implementation of this hydraulic option, however, is associated with increased vulnerability for drinking water production and presumable higher costs. This will require additional measures to secure a reliable drinking water production and limitation of other uses within the sensitive areas for groundwater abstraction as defined by the zone of 60 days of groundwater residence time. The Borda group compromise rule resulted in the Partial Reconnection option with dominant fishery as the best compromised management option for all nine stakeholder groups. This hydraulic option was also the option that provided the shortest distance to the theoretical ideal solution in the two largest tradeoffs between ecological development and drinking water production (Figs. 6 and 7). The Partial Reconnection with dominant fishery (FISH) was the second best compromised option when compromising the SAW rankings. The Current Status and the Disconnection options scored lowest in each round of Borda rankings, which suggests it will be difficult to achieve a compromise around the options that reduces the hydraulic connectivity as compared to the current state. 5. Discussion and conclusions The aim of this study was to apply a trade-off analysis approach in an MCDA framework, to analyze and quantify the trade-offs between the objectives of the stakeholders related to key ecosystem services of the Lobau floodplain. A number of options related to changing hydraulic connectivity and future use-scenarios were assessed and ranked according to the preferences of the management sectors involved. Based on this application we tried to get more insights in the use of this approach in wetland management. The impact evaluation suggested that an increase in hydraulic connectivity improved the ecological condition of the aquatic habitats and increased the potential fishing waters in general (Figs. 4 and 5). The increase in hydraulic connectivity also improved the ecological conditions of the terrestrial habitats (Fig. 4), because increased inundation area and duration during the annual flooding benefits the ecological conditions of the natural floodplain vegetation in the terrestrial habitats (Rood et al., 2005). However, some currently established aquatic habitats characterized by permanent lentic conditions would decrease in aerial extent under the options that increased the hydraulic connectivity, as these habitats are shifted to frequently flowing waters. Thus, also suitable areas for species indicating these habitat types would be reduced (Reckendorfer et al., 2006). Such variations between the selected and aggregated indicators are important to consider when interpreting the results of the subsequent trade-off analysis (Jollands et al., 2003; Wanyama and Far, 2005). Therefore, the general conclusion should rather be that an increase in water input (by means of options that enhanced and partially reconnected the Lobau with the main river channel) was necessary to establish a dynamic exchange in order to conserve existing habitat qualities and to develop new water bodies in the floodplain. However, a full re-connection of all floodplain water bodies with the Danube river channel without gaining new areas with more lentic type water bodies might impose adverse impacts on the establishment of

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communities closely associated to these lentic habitat conditions (Baart et al., 2010). Another point to discuss is the clustering of the management options as shown in trade-off Figs. 6e8. This clustering can be explained by the fact that the predictive models could not sufficiently distinguish between all the use-scenarios in each hydraulic option. Either the models should be tuned in to be more sensitive to the individual use-scenarios or the management options should be revised to be more distinguishable from each other. A third possibility would be to include flood protection and cost criteria in the final decision matrix. This inclusion would also make the criteria space more exhaustive in terms of covering all stakeholder objectives (Table 1). But this could also have changed the preferences of the stakeholders which, in turn, would have affected the rankings of the management options and subsequently the best compromised option (Baker et al., 2001; Giove et al., 2009; Yoe, 2002). Thus, further research, in collaboration with the stakeholders, could be based on these findings, but with inclusion of flood risk and cost criteria. This would also increase the potential use of trade-off figures in a planning process; in particular, the steps to elaborate the explicit trade-offs (Dietrich et al., 2007; Kelly et al., 1996; Kollat and Reed, 2007; Lotov et al., 2005), quantification of the trade-offs and the identification of the option(s) that provides the shortest distance to the ideal solution. The use of the pair-wise trade-off figures to analyze the potential trade-offs and the quantification of the trade-offs provided a useful means to graphically elaborate the real trade-offs and not the assumed ones. The use of pair-wise trade-off figures also revealed the optimal solution space between the pair of objectives (Lu and van Ittersum, 2003). However, the obvious limitation of pair-wise trade-off figures is the fact that only two criteria can be evaluated simultaneously (Chen et al., 2008). Also, the use of Pareto trade-off figures to screen out the management options that were dominated across all criteria in a multi criteria decision space was not as straightforward as immediately thought. As demonstrated by the trade-off figures, the same management options were either dominated or non-dominated depending on the two criteria evaluated. Dominance is also rarely seen in planning and management of water and environmental resources (Dodgson et al., 2009; Yoe, 2002). An alternative approach to screen out management options in a multi criteria decision space could include the development of constraints on the management criteria (Chen et al., 2008; Yoe, 2002). The application of threshold values to limit the decision space to a smaller set of feasible management options prior to ranking and selection could even be a necessity, as the obvious limitations of multi criteria decision support tools in general are the number of management options and criteria they can compute. Another useful approach to limit the decision space is to apply multi criteria decision rules that require definition of threshold values e.g. the Preference Ranking Organization Method for Enrichment Evaluation (PROMETHEE) and the Elimination and Choice Translating Reality (ELECTRE) (Chen et al., 2008). The difference between the two selected decision rules became apparent in the rankings of the management options (Table 4). In the Simple Additive Weighting (SAW) rankings, six of nine stakeholders preferred the Full Reconnection hydraulic option, because the poor performance in the potential drinking water criterion was fully compensated with a good performance in the two ecological criteria and the potential fishery criterion. On the contrary, the Technique for Order Preference by Similarity to Ideal Solution (TOPSIS) suggested only four of the involved stakeholders preferred the Full Reconnection option, while the remaining five preferred the Disconnection, Enhanced and Partial Reconnection options (Table 4). This is explained by the fact that the TOPSIS calculates the most preferred option as the option that is closest to the ideal

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positive solution, but also as the option that is furthest away from the ideal negative solution. Thus, the TOPSIS only suggested the Full Reconnection option as the most preferred option for the Local Village, Environmental NGO, National Park Authority and Nature Protection Administration, who clearly placed highest importance on the management criteria that scored high under increased hydraulic connectivity (Fig. 4). The differences in the two rankings also suggests that the result of an MCDA not only depends on the standardization technique and calculation of weights, but also on the choice of decision rules used to aggregate the criteria scores (Malczewski, 2004). Therefore, it can be more appropriate to use the structure of a multi criteria decision analysis to guide the decision making process rather than making a decision based on the mathematical results (Kiker et al., 2005). The use of multi criteria decision support tool to assist the tradeoff analysis improved our understanding of how decision makers’ preferences, based on different decision rules, affect the rankings of the management options. Obviously, it also increases the possibility to evaluate the performances of a larger decision and criteria space more efficiently (Pearson and Shim, 1995; Shim et al., 2002). The advantage becomes more pronounced especially when many decision makers are being considered as illustrated in our case study. Multi criteria decision support tool also makes it easier for planners and decision makers to make use of decision rules that otherwise would be hard to apprehend mathematically. The next step would need to be the application of this multi criteria decision support in a real participatory planning process to see its role in support of wetland decision making processes. It is expected to increase the stakeholder’s understanding of how their preferences affect the floodplain system and how, in turn, that affects other decision maker’s preferences. We realize the approach is rather a technical approach (Kakoyannis et al., 2001; Sheppard and Meitner, 2005) assuming a stepwise planning process. However, involvement of the stakeholders in the selection and aggregation of indicators used in the trade-off analysis could increase the validity of the findings (De Steiguer et al., 2003; Gregory, 2002; Sheppard and Meitner, 2005). We also realize that the use of multi criteria decision support tool in a planning and decision making process might not influence the real decision making as there are other factors, e.g. economic and political factors, that will influence the real decision making process as well. However, we think it can play an important role in the preparation of a participatory decision making process by acting as an innovative tool to increase the transparency of gains and losses of different strategies. Hence, the efficiency of the learning process of complex decision making problems for both planners and decision makers can be positively affected. In conclusion, this research suggests that increased hydraulic connectivity would benefit the management sectors which preferred the ecological development of the floodplain habitats. However, multiple uses including fishery, agriculture and recreation in line with the national park regulations were also achievable under increased hydraulic surface water connectivity. Further, it was found that the majority of the involved management sectors preferred the higher connectivity options as compared to the Current Status option, which was not preferred by any management sectors. Interestingly the Current Status option was also not preferred by the Drinking Water Administration, which clearly preferred the Disconnection option. Therefore, the rankings of the management options also highlighted the potential conflict between the ecological development and the drinking water production. Because of that, it became obvious that, if the higher connectivity options were to be realized for ecological improvements, then additional measures to secure reliable drinking water production should be developed and incorporated in the

implementation. This also emphasizes the need to include cost (and also flood risk) criteria in the decision matrix. The research showed that pair-wise Pareto trade-off figures provided a useful means to elaborate and quantify the real trade-offs between wetland functions. The distance based algorithms applied here can also be used to quantify more than two dimensional trade-offs. Finally, the research showed that the use of multi criteria decision analyses should be based on a participatory approach, in which the process of arriving at the final ranking should be equal or more important than the outcome of the ranking itself. The next step could be the use of the method in a wetland decision making process, in which the stakeholders have to choose between wetland management options.

Acknowledgements This work was based on the Optima Lobau research project (funded by the Austrian Ministry of Science (ProVision 133-113), the Federal Ministry of Agriculture, Forestry, Environment and Water Management, the Federal Ministry of Transport, Innovation and Technology, Municipal Authorities of Vienna, the provincial government of Lower Austria and the National Park-Authority). Also, research leading to these results received funding from the WETwin project implemented under the European Union Seventh Framework Program (FP7/2007e2013) under grant agreement n [212300].

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