Ecological risk assessment of wetland ecosystems using Multi Criteria Decision Making and Geographic Information System

Ecological Indicators 41 (2014) 133–144

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Ecological risk assessment of wetland ecosystems using Multi Criteria Decision Making and Geographic Information System B. Malekmohammadi ∗ , L. Rahimi Blouchi Graduate Faculty of Environment, University of Tehran, P.O. Box 14155-6135, Tehran, Iran

a r t i c l e

i n f o

Article history: Received 18 October 2013 Received in revised form 25 January 2014 Accepted 29 January 2014 Keywords: Ecological risk assessment (ERA) Risk factor Risk zoning Risk management Iran – Shadegan Wetland

a b s t r a c t Nowadays, wetlands are at risk from a wide range of stress factors. Practical application of wetland ecological risk assessment will result in a better understanding of how physical, chemical, and biological stressors impinge on wetlands and will provide a framework for prudent wetland management. An important aspect of wetland management is to identify ecological risks affecting the area and to develop a wetland-zoning map based on those risks. This study uses a process of ecological risk assessment (ERA) to identify stress factors and responses within the framework of an ecosystem-based approach. All potential environmental factors, physical, chemical and biological need to be examined in context. This study aims to present a systematic methodology for risk assessment and zoning of wetland ecosystems. Initially, the most important risks threatening wetlands are identified in an ecosystem-based approach. Endpoint assessments are defined according to values and functions of the wetland and the ecological risks associated with these endpoints are identified. In the characteristics step, risks are analyzed according to severity, probability and a range of consequences. A Multi Criteria Decision Making (MCDM) method is used to prioritize these risks on the basis of experts’ opinions. Geographic Information System (GIS) is used to develop a zoning map with a combination of risk layers according to importance. Finally, management strategies are proposed to deal with the risks. The proposed methodology was applied to Shadegan International Wetland, located in southwestern Iran. This wetland is in the Montero list and is currently threatened by various risks. According to the results, high-ranking potential risks and areas with different levels of risk and management strategies were proposed for this wetland. © 2014 Elsevier Ltd. All rights reserved.

1. Introduction Wetlands are one of the three major types of ecosystem on the Earth; they are formed through the interaction of land and water systems and provide an irreplaceable ecological service as an ecosystem for human society (Zedler and Kercher, 2005; Kim et al., 2011). Wetland ecosystems have an important role in maintaining biological diversity, they are also important for biochemical transformation, storage, production of living plants and animals and for decomposition of organic materials (USEPA, 2002; Clarkson et al., 2003). Wetlands have been exposed to a range of stress-causing alterations from activities such as dredging and filling operations, hydrologic modifications, pollutant runoff, eutrophication, impoundment, and fragmentation by roads and ditches (Klemas, 2011). These activities cause disruption to the ecological balance of animal and biotic reservoirs in wetlands (Ramsar Convention Secretariat, 2004).

∗ Corresponding author. Tel.: +98 21 61113185; fax: +98 2166407719. E-mail address: [email protected] (B. Malekmohammadi). 1470-160X/$ – see front matter © 2014 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.ecolind.2014.01.038

The spread of urbanization and industrialization has escalated wetland degradation in many parts of the world, in both developing and developed countries (Tiner, 1984; Holland et al., 1995; Dahl, 2000; Ralph, 2003; Zedler and Kercher, 2005). Previous studies of wetland protection focused mainly on the functioning of constructed wetlands, ecological water demands and vegetation development (Spieles, 2005; Chen et al., 2009; Cui et al., 2009). For different kinds of wetlands, changing environmental flow is an important risk factor that needs to be considered when undertaking ecological restoration and management of water resources of basins (Yang and Mao, 2011). Agricultural use and industrial production, pesticide residues, contamination of wetlands from chemicals outlets, change in natural habitats, over exploitation of natural resources, have caused potential risks to the wetland ecosystems. There is a need for tools to assess the ecological condition of wetlands for a range of purposes, including Environmental Impact Assessments (EIA), ecological reserve determinations and the planning and monitoring of wetland management and rehabilitation outcomes (Kotze et al., 2012). Recently, ecological risk assessment (ERA) has applied several tools for modeling. Ecological modeling has been used in other fields such as water quality modeling (Chau, 2007; Wu

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and Chau, 2006; Muttil and Chau, 2006). ERA evaluates the likelihood of potential adverse effects on ecosystems as a result of exposure to one or more stress factors (USEPA, 1992). Currently, ecosystem-oriented models of ERA have proved efficient in evaluating structural and functional responses within a variety of ecosystems to enable better environmental management (Christian et al., 2009; Chen et al., 2010, 2011). Applications of ERA include assessments that range from screening-level (qualitative) to detailed (quantitative) or a combination of both (i.e. tiered ERA); predictive to retrospective in temporal scale; local to global in spatial scale; and single threat to multiple threats (USEPA, 1998; Burgman, 2005). ERA involves examining an area’s environmental conditions by means of environmental risk assessment analyses that consider various aspects of the hazards as well as the vulnerability and specific environmental values of the studied area under (Heller, 2006). ERA of wetlands involves estimating potential hazards or threats posed by stressors (chemical, physical, or biological) to biotic and/or abiotic components of the wetland. This assessment forms the information base that drives important environmental management decisions on a local, national, and international levels worldwide. Practical application of this tool will result in a better understanding of how physical, chemical, and biological stressors impinge on wetlands and will provide a framework for prudent wetland management. An important aspect of wetland management is to identify ecological risks affecting the area and to develop a wetland-zoning map based on those risks. Wetlands can be viewed as complex temporal and spatial mosaics of habitats with distinct structural and functional characteristics. Because of the unique characteristics of wetlands the key stressors and receptors in the wetlands under study should be clearly identified and, if necessary, prioritized in order to guide the risk assessment process. Risk characterization requires an understanding of the major external and internal factors regulating the operational conditions of a wetland. Furthermore, an ecosystem-based approach involves determining links between these factors and identifying the way in which stress factors affect the wetland. Lemly (1997) examined the ERA of wetlands as a managerial tool. The study developed an ecosystem-based approach toward risk assessment in freshwater wetlands. Suter (2000) presented an argument for developing generic assessment endpoints in ERA that measured the ecological characteristics essential for protection against risks by quantification, measurement and modeling. Kellett et al. (2005) provided an analysis of ERA workshops for wetlands of the Lower Burdekin, and recommended strategies for the execution of ERA for irrigation planning and assessment. Hanson et al. (2008) evaluated ecological functions of the wetlands. This project demonstrated that assessment of wetland functions provides key information for wetland environmental assessment. Wang and Cheng (2011) applied ERA in zoning of the Baiyangdian Basin in China. Using Geographic Information System (GIS) and Remote Sensing (RS) technology, a region-wide environmental risk visualization was produced that enhanced the effectiveness of environmental risk management. Zhang and Huang (2011) employed a GIS-based multi-criteria method to evaluate potential nitrogen loss at the basin level, and applied the model to the Huai River Basin. The results helped to examine the complex responses of wetland systems to changes in land use under different socio-economic circumstances. A review of previous ERA studies reveals that the most recent studies have used structural features and functions of wetlands as valuable and important ecological features. Chen et al. (2013) reviewed state-of-the-art models that were developed for ERA and presented a system-oriented perspective for holistic risk evaluation and management. They concluded that assessing ecological risk with system-based models at different levels of organization

in a combined way, presents an evolutionary step for application of risk evaluation in environmental management. This study presents a systematic methodology in an ERA for wetland ecosystems to identify stresses and responses. The method used in this study applies all physical, chemical and biological stress factors affecting the environment in a semi-quantitative risk assessment approach. For this purpose, the most important environmental risks are identified. In the characteristics step, risks are analyzed according to severity, probability and range of consequence. These indicators are then used to determine scope and extent of each risk. The determinations of proposed measures to be applied in environmental control were made from gathering experts’ opinions. Analytical Hierarchy Process (AHP) is used to prioritize risks. A zoning map of risks threatening the wetland is developed using GIS. This map identifies wetland parts according to level of risk to achieve optimum planning with an ecosystem-based approach. Finally, management strategies are proposed to deal with these risks. The methodology has been subsequently applied to Shadegan International Wetland, located in the southwest of Iran. This wetland is in the Montero list and is now threatened by various factors. 2. Methodology A framework was developed for assessing the ecological risks for wetland areas using a semi-quantitative approach. Semiquantitative methods are used to describe the relative risk scale. For example, risks can be classified into categories like “very low” “low”, “moderate”, “high” and “very high”. In a semi-quantitative approach, different scales are used to characterize the likelihood of adverse events and their consequences. Analyzed probabilities and their consequences do not require accurate mathematical data (Radu, 2009). In semi-quantitative methods, risk indicators and values are determined according to information on real available data as well as using judgments made by experts. Fig. 1 presents a structural illustration of the methodology applied to wetland ecological risk assessment. This structure was formed with a combination of risk assessment technique, the AHP method and the GIS tool. The method was according to the following steps: Step 1: Identification of ecological endpoints and ecological risks associated with these endpoints. In order to set the ecological endpoints, according to the International Conversation Nature and Natural Resources (IUCN) booklet (Dugan, 1990), the most important wetland values and functions and the main related endpoints are identified. Assessment endpoints are the functions and associated values that need to be protected, enhanced, or created through risk management (Lemly, 1997). The focus of ecological endpoint assessment is to determine ecological endpoints that are threatened (Pastorok et al., 2002). Step 2: Risk characterization step. In this step risks are analyzed according to severity, probability and consequence. A risk index is calculated by analyzing severity, exposure and probability (SEP) in a semi-quantitative approach with Eq. (1). Risk = Probability of the risk × range of consequences of risk × severity of the risk

(1)

In Tables 1–4, severity, probability, range of consequences and range of risks are classified from very low to very high with scoring according to that taken from a review of related literature, engineering judgments and information gathered from brainstorming sessions with

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Fig. 1. Framework of the methodology in the wetland ecological risk assessment.

Table 1 Classification and scoring of the severity in the wetland ecological risk assessment.

Table 2 Classifying range of the consequences in the wetland ecological risk assessment.

Expected consequence

Scores range

Class

Wetland exposed area (portion of total area)

Class

Destroying the integrity and existence (5) Changes in the hydrological balance and regime (4) Disruption of the biological balances (3) Changes in physical and chemical parameters (2) Disruption of the biogeochemical cycles (1)

15–13

Very high (5)

12–10

High (4)

All of the wetland and the surrounding ecosystems Three quarter (¾) Half (½) One quarter (¼) Less than one quarter (¼)

Very high (5) High (4) Moderate (3) Low (2) Very low (1)

9–7

Moderate (3)

6–4

Low (2)

<4

Very low (1)

a group of experts. The determined environmental risks are given a score for severity by applying an assessment of consequences of each potential risk. Expected consequences are identified through assessment of the ecological endpoints. In Table 1, classification and scoring of the severity of wetland risks are developed by cumulative impact assessment of consequences in the wetland. Summation of numbers in the first column is equal to 15. Classes of severity are ranked from very high (5) to very low (1) and each class is assigned a score up to 15. Scores evaluating the consequences of each risk are performed by identifying the wetland area exposed to the risk. In Table 2, classification range of consequences of risks is done according to the wetland areas that are affected by the risks. The probability of a wetland ecological risk is classified according to probability of the expected consequence (Table 3). By applying Eq. (1), amounts are given

Table 3 Classifying of the probability in the wetland ecological risk assessment. Expected probability

The likelihood of the consequence

Class

Certain (risks occur continuously) Common (risks occur usually) Possible (risks may occur from existing risks) Likely, but are low

Very likely

Very high (5)

Greater than 50%

High (4)

Equal to 50%

Moderate (3)

Unlikely under normal conditions Impossible or remote under normal conditions

Low (2)

Likely, but are very low

Very low (1)

as an evaluation of each risk. Table 4 presents the range, classification and description of risks. Step 3: After identifying risks, they are prioritized on the basis of their importance. This can be done according to the classification of severity, probability and consequences of the risk. These criteria should be valued in risk

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Table 4 Classification and description of the risks in the wetland ecological risk assessment. Risk range

Classification

Description

125–101 100–76 75–51

Very high High Moderate

Unacceptable Unacceptable Acceptance with conditional control Acceptable Negligible

50–26 <26

Low Very low

assessment according to degree of importance and influence. Multi-criteria Decision Making (MCDM) is used to prioritize risks and effective indicators to estimate risk levels. MCDM were applied in different EIA and ERA studies such as Zhao et al. (2006) and Zhang et al. (2009). MCDM is a class of decision-making methodology based on the premise of assisting a decision-maker through the decision process via explicit formalized models (Figueria et al., 2005). Belton and Stewart (2002) and Kiker et al. (2005) presented a review of the available literature and provide some recommendations for applying different MCDM techniques. These include the AHP, ELimination and Choice Expressing the REality (ELECTRE), Multi Attribute Utility Theory (MAUT), Preference Ranking Organization METHod for Enrichment Evaluation (PROMETHEE), and various combinations of these methods. AHP is a theory of measurement through pairwise comparisons that relies on the judgments’ of experts to derive

priority scales (Saaty, 2008). In this study, AHP is utilized. A hierarchical structure of a target is used to find important weights for each wetland ecological risk. Pair-wise comparison matrixes in AHP are used to weight the indexes and options of the risks based on experts’ opinions. Risk prioritizing has been used to make proposals for corrective action to reduce risks. It should be noted that other methods such as ELECTRE, MAUT, PROMETHEE can also be applied in ERA for wetlands. Each of them has their advantages and disadvantages as evident from a series of regular debates in prominent journals. The advantages of AHP over other multi-criteria methods, as often cited by its proponents, are its flexibility, intuitive appeal to the decision-makers or experts, and its ability to check the inconsistencies in judgments (Saaty, 2000). AHP helps to elicit the complex judgments of different experts in a common platform. It also ensures accuracy in the sense that it has an inbuilt method to check the inconsistency of judgments. This ensures that the judgments are provided only with sufficient care and the error due to negligence is thus minimized (Ramanathan, 2001). Step 4: All risk factors must be spatially modeled, they need to appear on the map as points, lines, polygons or raster models. Man-made landscape features such as agricultural and urbanized areas, tourism zones and hotels, roads, industrial areas, also surrogate indicators such as population density can be included as human impacts and these are determined by experts and used as risk factors. The combination

Fig. 2. Location and specification of the Shadegan Wetland and related basin in Iran.

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of risk elements and their assigned risk parameters may vary for each habitat in order to account for the different ways in which human activities impact on biodiversity in each realm (McPherson. et al, 2008). Wetland zoning is used as a management strategy done to identify areas with highranking risk. GIS evaluates the ecological risks of human activities and natural disasters, which are the main factors that contribute to change on wetland ecological indexes. Using the GIS tool, the zoned wetland risk map is developed. Information layers are required for the main risk factors. These layers are overlaid according to the weights obtained from AHP. Weights are assigned to the layers using the Raster Calculator in Spatial Analyst functions and weighted linear combination (WLC) is used to overlay the weights. WLC is one of the most widely used methods of MultiCriteria Evaluation (MCE) for analysis of land suitability. It involves standardization of suitability maps, assigning weights of relative importance to the maps, and combining weights and standardized suitability maps to obtain an overall suitability score (Malczewski, 2004). WLC analysis was based on Eq. (2). S=



Wi Xi

(2)

where S is the zoning map of the wetland, Wi is the weight of layer i obtained from AHP, and Xi is the standard raster layer i. According to the zoning map, area zones with different levels of risk are determined. Step 5: Finally, risk management strategies will be provided for high-risk zones. The most effective risk management strategies are presented within wetland basin, because wetlands are associated and interacted with upstream and downstream processes. 3. Study area (Shadegan International Wetland, Iran) Shadegan International Wetland is located in southwestern Iran, in Khuzestan Province, between 48◦ 20 –49◦ 20 E longitude and 30◦ 50 –31◦ 00 N latitude. Fig. 2 shows the geographical location and specification of the study area. The cities of Ahwaz, Abadan, Mahshahr and Shadegan are the main population centers around the wetland. This wetland is located in the Jarahi River Delta with very flat land and low-gradient plains’ topography. The Jarahi basin is located in southwestern Iran and southern parts of the Zagros Mountain Range. The basin area is about 24,310 km2 . The Shadegan Wetland is about 537,731 ha, of which almost 61% is protected as a Wildlife Refuge (Environmental Protection Agency of Iran, 2010). This natural wetland has important hydrological, biological and ecological significance in terms of maintaining normal functions of the basin and coastal system. There are more than 100,000 water bird species with five of the world’s rare species of bird in this wetland. The unique diversity of this wetland includes plant and animal species specific to freshwater, brakish and saltwater environments. Specifications of different parts of the Shadegan Wetland are given in Table 5 (Pandam Consulting Engineers, 2002; Shadegan City Department of Environment, 2010). As can be seen in Fig. 2 and Table 5, the Shadegan Wetland consists of three distinct parts: (1) A freshwater zone, which is located in the upper part of the wetland. This area is fed by the Jarahi River and has lush vegetation cover. (2) A tidal zone, which is located in the southern part of the wetland (downstream of the Abadan-Mahshahr highway). The area is influenced by the tides of the Persian Gulf and involves multiple waterways (estuaries). Upstream freshwater is mixed with downstream saltwater as freshwater passes through the land.

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Table 5 Different regions of the Shadegan Wetland (Pandam Consulting Engineers, 2002). Shadegan Wetland zones

Freshwater Tidal Coastal (Mosa estuary) Other and marginal lands Total

Total

Wildlife Refuge

Area (ha)

Percent

Area (ha)

120,378 222,252 115,978

22.4 41.3 21.6

75,310 252,455 –

23 77 –

79,123

14.7

–

–

327,765

100

537,731

100

Percent

(3) The coastal zone or saltwater wetland, which includes the Persian Gulf coastline to at the water depth of 6 m. The Mosa estuary and several small islands are also in this area. Wetland vegetation is a vital characteristic of such an environment, it is important in terms of sustainability of the ecological and economic values of the wetland. The Shadegan Wetland, in addition to its global value was granted status as Wildlife Refuge by the Iran Department of Environment. Table 5 presents freshwater and tidal zones of the Wildlife Refuge areas in the wetland. The most significant human activities affecting the Shadegan Wetland are those of dam construction and irrigation projects in the Jarahi catchment, oil and gas platforms, industrial projects, infrastructure projects, exploitation of wetland resources and tourism. Recently, human activities such as water pollution, indiscriminate exploitation of biological products of the wetland, drought and change in natural habitats have directly or indirectly affected the wetland functions (Rahimi Blouchi, 2012). This wetland is in the Montero list and is now threatened by several risks. Despite its unique values, this wetland is now far removed from Table 6 Assessment of ecosystem functions and values of Shadegan Wetland (Behan Dam Consulting Engineers, 2010, according to IUCN booklet, Dugan, 1990). Function

Values

Statues of values in Shadegan Wetlanda

Hydrologic flux and storage

Groundwater recharge Groundwater discharge Flood control and protection Water supply

  䊉 

Biological productivity

Food storage Forest resource Wildlife resources Aquatic Forage resources Agricultural resources Historical and cultural resources

    䊉 䊉 

Biogeochemical cycling and storage

Stabilize the shoreline/erosion control Sediment control/toxic materials Protection from storm/wind break Wastewater treatment Water quality



Biodiversity Tourism/recreation Preservation of flora and fauna (refuge) Threatened, rare, and endangered species

 䊉 

Community/wildlife habitat (ecological)

 䊉  



a () absent or exceptional, (䊉) present, () common and important value of wetland.

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Table 7 Characteristics of the risk factors in Shadegan Wetland. Risk factor

Harmful potential effects

Receivers

Range of consequences

Drought/low water occurrence

- Reduction in productivity and survival of the wetland - Reduction of hydrological stability

- All organisms in the soil and aquatic life - Humans dependent to wetland

All of the wetland and the surrounding ecosystems

High temperature and high evaporation

- Increase of chemical and biological functions’ rates - Reduction in species richness

All organisms in aquatic life

Freshwater zone

Salinity of wetland water

- Reduces denitrification, biological uptake and photosynthesis - Diminishes species richness

All organisms in the soil and aquatic life

- Freshwater zone - Tidal zones in the south of Abadan – Mahshahr road

Sedimentation and filling

- Depresses biological uptake, processing and photosynthesis - Diminishes species richness - Reduces groundwater recharge - Changes in sediment particle size

All organisms in the soil and aquatic life

Freshwater zone (sediment entrance from the northern rivers)

Over exploitation of natural resources

- Increases erosion potential - Establishment of invasive species - Reduces the interception, condensation, evaporation and surface roughness - Reduces sediment stabilization

Organisms dependent to natural resources

- Freshwater zone (The vicinity villages) - Northeastern Wildlife Refuge

Entrance of agricultural and livestock wastewater

- Short-term: increases productivity - Long-term: encourages invasive species, decreases species - Reduces diversity and production - Enhances adsorption of some chemicals - Eutrophication

- All organisms in the soil and aquatic life - Humans dependent to wetland

Freshwater zone (from northern part)

- All organisms in the soil and aquatic life - Humans dependent to wetland

Freshwater and tidal zones (from industries on the north and northwest)

Entrance of rural and urban waste water

- Diminishes habitat suitability - Reduces photo-oxidation and increases denitrification rate

- All organisms in the soil and aquatic life - Humans dependent to wetland

Freshwater and tidal zones (from central and southwest)

Oil pollution

- Biological magnification - Soil pollution and contamination of groundwater

- All organisms in the soil and aquatic life - Humans dependent to wetland

- Northern boundary of the Wildlife Refuge - A part of tidal zone in southern

Change in flow regime

- Reduces in water inflow - Reduces in water flow purification

- All organisms in the soil and aquatic life - Humans dependent to wetland

Freshwater zone

Change in natural habitats

- Reduces groundwater recharge - Increases evapotranspiration - Increases concentration of inorganic

All organisms in the soil and aquatic life in wetland

All of the wetland and the surrounding ecosystems

Road construction

- Reduces biodiversity - Disturbing hydrological flows - Reduces the water quality - Habitat loss

All organisms in the soil and aquatic life in wetland

- Northern part - North of the Wildlife Refuge

Entrance of industrial wastewater

its natural condition. This study aimed to identify and manage the most stress inducing risks that threaten the wetland and to maintain its ecological balance and to protect the study area. 4. Results and discussion Prior to modeling an ERA, it is important to identify previously developed information for the wetland under consideration in the study. Information from aerial photographs, historical maps and

land-use documents are useful for gaining an understanding of the history and status of an area. It is also important to gain an understanding of the hydrologic and geologic forces affecting a wetland. Understanding a wetland’s function and determining its values is an important part of ERA for wetlands. These function–value relationships provide an important conceptual framework that can formulate the operation’s goals and objectives. Application of ERA methodology on the Shadegan Wetland firstly used important values and functions of Shadegan Wetland to determine endpoints. Assessment of the Shadegan Wetland in

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Table 8 Results of calculation of the risks in the Shadegan Wetland. Risk factor

Severity

Range of consequence

Probability

Risk level

Importance weight in AHP

Weighted risk

Risk ranking number

Drought/low water occurrence High temperatures and high evaporation Salinity of wetland water Sedimentation and filling Over exploitation of natural resources Entrance of agricultural and livestock wastewater Entrance of industrial wastewater Entrance of rural and urban waste water Oil pollution Change in flow regime Change in natural habitats Road construction

4 2 4 5 4 4 4 4 4 4 4 4

5 2 3 2 3 3 4 4 3 5 5 3

3 5 5 4 5 5 5 5 5 4 4 5

60 20 60 40 60 60 80 80 60 80 80 60

0.064 0.090 0.061 0.056 0.098 0.072 0.087 0.082 0.089 0.099 0.12 0.082

3.84 1.8 3.66 2.24 5.88 4.32 6.96 6.56 5.34 7.92 9.6 4.92

9 12 10 11 5 8 3 4 6 2 1 7

terms of its ecosystem functions and values was done according to the method cited in the IUCN booklet by Behan Dam Consulting Engineers (Behan Dam Consulting Engineers, 2010). The booklet includes field studies and information on environmental characteristics of the wetland and this information was used to complete the IUCN checklist for values of the Shadegan Wetland. Results of this assessment are presented in Table 6. Then, the most important ecological endpoints were identified according to these values and functions. All of the parameters (hydrological and ecological) that were considered critical to long-term sustainability of the wetland were considered as possible ecological endpoints. Biogeochemical processes such as hydrological regime, primary productivity (food web stability), biodiversity (abundance, species richness), sensitive and natural habitats, integrity and existence of wetland, were determined as the most important endpoints. Risks and stressors imposed on Shadegan Wetland were identified in accordance with the ecological endpoints and shown in Table 7. This table describes harmful potential effects, receivers and the range of consequences for each risk factor. The most important consequences of determined by evaluation of risk factors were identified as destroying the integrity and existence of the wetland, changes in its hydrological balance and regime, biological imbalance, changes in physical and chemical parameters and disruption of biogeochemical cycles of the wetland. The risk factors threatening Shadegan Wetland were analyzed according to step 2 of the methodology and are presented in Table 8. The information shown in Table 7 was used to calculate severity,

probability and to determine the range of consequences for each risk from the step that evaluated risk analysis. According to the severity index, drought (low water occurrence), sedimentation and over exploitation of plant resources of the wetland were evaluated as having the greatest level of risk (very high). Also, factors of high temperatures and high evaporation were evaluated as having the lowest level of the risk. According to the consequence index, drought, change in flow regime and change in the natural habitat were evaluated as having the greatest amount of risk (very high). In addition, factors of high temperatures and high evaporation, gradual sedimentation and filling and over exploitation of plant resources of the wetland were evaluated as having the lowest level of risk (low). According to the probability index, almost all of the stressors have continuous impact and as such are associated with a very high level of risk. Table 8 shows calculations of risk level based on Eq. (1). Results of risk calculation for each of the risk factors show that almost all of the risks were evaluated as having high and medium level risk. Table 8 shows the industrial wastewater outlets, rural and urban waste-water outlets, and changes in natural habitats that were had the maximum degree of risk. Also, the lowest amounts of the risk were calculated for factors of high temperatures and high evaporation. Results of sensitivity analysis on the risk assessment values in Table 8 show the evaluations for elimination of the criteria ‘range of consequence’, ‘probability’, and ‘severity’ that contribute to a change in risk level of about 31.4, 22.4, 26 and risk ranking numbers of about 91%, 41.7%, 8%, respectively. These evaluations show the importance of considering these three criteria, especially that of

Fig. 3. Hierarchical structure of ecological risk assessment of Shadegan Wetland.

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Fig. 4. Risk zoning layers for risk factors in Shadegan Wetland. (a) High temperatures and high evaporation, (b) salinity, (c) over exploitation of biological resources, (d) water pollution, and (e) change in natural habitat

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Table 9 Percentages of categories in each layer in the ecological risk zoning of Shadegan Wetland. Category of risk

Very high High Moderate Low Very low

Risk factor High temperatures and high evaporation

Salinity of wetland water

Over exploitation of natural resources

Water pollution

Change in natural habitats

Final zoning map

10.07 7.67 6.37 5.48 70.41

6.9 5.9 6.22 4.25 76.7

5.54 1.05 2.25 17.02 86.44

12 15 33 30 10

16.59 8.81 5.87 7.82 60.91

10.4 11.56 14.88 44.09 19.07

‘range of consequence’ in wetland ecological risk assessment. Also, variation evaluations for these three criteria show changes of up to 27% but evaluations for risk level and risk ranking number are stable. These evaluations demonstrate an acceptable level of stability in calculations of risk values in the proposed methodology for wetland ecological risk assessment. Sensitivity analysis on importance of weights, based on average weights, shows that risk ranking number is dependent on about 33.3% in terms of importance weights. A hierarchical structure of the ecological risks, according to the indexes of the risks (severity, range of consequences and probability) is shown in Fig. 3. Information on experts’ opinions was used to weight the criteria and alternatives of the risks through Pairwise Comparison according to the hierarchical structure. In this study, national experts were selected from different organizations in the region. There was a lack of communication and understanding between the wetland community and those doing

the risk assessment in the study region. It is essential that those individuals that contribute to process of wetland ecological risk assessment have a common understanding of some basic principles from both disciplines. Thus, access to experts with scientific knowledge of the area was difficult in this particular case study. In total, contributions from the opinions 15 experts were considered and confirmed by the AHP Consistency Ratio. Five environmentalists, five water resources experts, and five agricultural experts were used in brainstorming session and to answer a questionnaire. Expert Choice software (www.expertchoice.com) was used for calculations of AHP weights. Final weights of AHP for the risk factors are presented in Table 8. Risk factors were prioritized by multiplying risk level and importance weight of each risk. Rankings of risks are shown in the last column of Table 8, and represent the priority of each risk factor, for the wetland. Based on these priorities, change in natural habitat factor was high ranking factors and sedimentation and filling factor was low ranking factors.

Fig. 5. Ecological risk zoning map for Shadegan Wetland.

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Table 10 Management strategies (control measures) for reducing effects of risk factors in Shadegan Wetland. Risk factor

Risk level

Affected zone

Management strategies (control measures)

Category

Rating

Change in natural habitats

High

1

All of the wetland and surrounding ecosystems

- Developing a legal regional binding guideline to prevent land use changes - Avoid or minimize wetland disturbance by applying wetland setback regulation

Change in flow regime

High

2

Freshwater zone

- Allocating the minimum of water rights - Restricting unauthorized exploitation of the rivers, especially in drought periods - Implementation of integrated water resources management at the Jarahi basin

Entrance of industrial wastewater

High

3

Freshwater and tidal zones

- Industrial wastewater treatment - Continuous monitoring of wetland water quality and applying water quality standards

Entrance of rural and urban wastewater

High

4

Freshwater and tidal zones

- Keeping the canebrakes in the entrance

Over exploitation of natural resources

Medium

5

Freshwater zone and Northeastern of Wildlife Refuge

- Identifying the capacity of grazing and harvesting of hays and straws - Establishing buffer strips for arable lands - Developing wetland operation guidelines

Oil pollution

Medium

6

Northern boundary of the Wildlife Refuge and a part of tidal zone

- Insulating the oil transfer pipes

Road construction

Medium

7

North part of wetland and north of the Wildlife Refuge

- Constructing culverts - Maintaining the wetland habitat corridors

Entrance of agricultural and livestock wastewater

Medium

8

Freshwater zone

- Controlling the time and amount of using agricultural materials

Drought/low water occurrence

Medium

9

All of the wetland and surrounding ecosystems

- Designing a drought monitoring network in the Jarahi Basin

Salinity of wetland water

Medium

10

Freshwater and tidal zones

- Usage of halophyte plants - Transfer of agro-industrial complexes of saline drainage water to Persian Gulf (at 6 m depth of sea)

Table 8 shows changes in natural habitats, changes in upstream flow regimes (such as dam building in the catchment of Jarahi), industrial wastewater outlets, rural and urban wastewater outlets, over exploitation of natural resources of the wetland, oil pollution, agricultural and livestock wastewater outlets, road construction in and around the wetland, and drought occurrence in recent years were determined as the main risks threatening the Shadegan Wetland respectively. Based on the importance of risk factors and available information, five layers were selected for consideration in wetland ecological risk zoning. Change in natural habitat, water pollution (by wastewater outlets), over exploitation of biological resources, salinity of wetland water, and high temperature and high evaporation are the layers that were developed in ecological risk zoning. Wetland risk-zoning layers were produced using spatial analyst tools in Arc-GIS 9.3 software (Environmental Systems Research Institute ESRI, 2008). Each layer was reviewed, classified and ranked according to the degree of threat that was considered for each in relation to the habitat or species in question. Data in the past 10 years were used for developing the layers. These layers are presented in Fig. 4 and explained according to the following:

(1) High temperature and high evaporation (Fig. 4a): due to high temperature, the greatest influence was on the shallow parts of the wetland. To produce this layer, water depth in the freshwater zone was used as an index. Water depth in different parts of the wetland varied from a few centimeters to about 3 m. Zoning of the wetland was done with regards to the adverse effects of high temperature on wetland flora and fauna. Shallow parts were determined as having a high level of risk and the deep parts with lower levels. (2) Salinity of wetland water (Fig. 4b): This map was produced from data on electrical conductivity of wetland water in the freshwater zone. Electrical conductivity changed at different parts of the wetland water ranging from 1.4 to 21 dS/m. Those parts with high salinity were considered as high risk and vice versa. (3) Over exploitation of natural resources (Fig. 4c): the likely extent of impact of the over exploitation are considered as zoning criteria. The buffer extension in GIS software was used to produce this map. The influence of distance for direct and indirect impacts was considered at 50 and 2000 m, respectively. In locations that had been over exploited, distance of the buffer zone increased from the centers of points, lines or polygons. Areas

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with risk level ranked as very high and high were those of freshwater wetland in the vicinity of villages due to road access roads in those areas. (4) Water pollution (Fig. 4d): Data on source pollution and entrance points to the wetland were used to develop this layer. The main sources of water pollution were those of upstream irrigation development projects, the sugar cane industry in the northern part of wetland, petrochemical activity in Mahshahr, shipping, carbon and steel industries in Ahvaz, Maroon desalination, wastewater from surrounding cities and villages in the east area of freshwater wetland and burst pipes that leaked oil into the wetland. Wastewater outlets from agricultural and livestock farms, industrial, rural and urban areas, and oil pollution were considered in this layer. Due to lack of data on amounts of pollution concentrations in the wetland, sources of pollution and their relative entrance points; these values were rated according to experts’ opinions, judgments of engineers and information collected from field studies. Industrial pollution, rural and urban pollution, oil pollution, agricultural and livestock pollution and other pollutions were rated as very high, high, moderate, low, and very low, respectively. The Spatial Analyst interpolation was used in GIS software to produce this layer. The Spatial Analyst interpolation was used in GIS software to produce this layer. (5) Change in natural habitat (Fig. 4e): This layer was prepared from a map of existing land-use in the wetland. Zoning was done according to the influence distance of change in land-use. The influence distance was determined as the spatial extent or footprint of change in the natural habitat on the wetland and represents the maximum distance at which a feature has a negative impact on the wetland. For example, adverse effects of roads within the wetland’s ecological range were considered to have a range of impact extending to 1000 m (Forman et al., 2003). The influence distances for direct and indirect impacts were considered as 200 and 1000 m, respectively. The buffer extension was used in GIS software to produce this map. The zones that were evaluated as having very high and high levels of risk were in areas disturbed by human activities.

Percentage of categories in each layer that were used for ecological risk zoning of the Shadegan Wetland are given in Table 9. Based on Step 4 of the methodology, by applying importance weights from Table 8, the final ecological risk-zoning map of the Shadegan Wetland was produced and is shown in Fig. 5. As can be seen in this figure, the area that was evaluated with the least risk was that of the southern wetland in the saltwater area, probably because it was a pristine environment inaccessible to humans. Evaluations determined the area most at risk was the northern area of the wetland, a freshwater area with access roads that facilitated of human access to the wetland. This map enables decision makers and environmental planners to regulate human activities in and around the wetland. Results of sensitivity analysis on the final risk-zoning map show that classification of the final risk-zoning map did not change with variation of important weights of up to 30% change, on these weights. These results show acceptable stability in classification of risk-zoning layers. In addition, the final risk-zoning map was sensitive to the elimination of each layer and more sensitivity was observed for elimination of the layer representing over exploitation. Based on the results of risk analysis and the ecological risk-zoning map, strategies to manage and reduce the ecological risks of Shadegan Wetland are abstracted in Table 10. The proposed management strategies for the wetland were determined by the above-mentioned ecosystem-based approach. In Table 10, risk factors were ordered according to the ranking number of each risk

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from Table 8. Zones relating to each risk factor are described with regards to the risk-zone maps.

5. Conclusions Development projects such as road construction, thermal power plants, transmission lines, oil and petrochemicals and factories threaten the life of wetlands. In order to protect and manage wetlands in a sustainable way, it is necessary to reduce ecological risks that impact on the wetlands. The best approach toward applying ERA in wetland studies is ecosystem-based management. In this study, an ecosystem-based approach was considered to present a methodology for identifying and characterizing risks and to develop management strategies. Experts’ opinions were used to prioritize risks according to the AHP. A zoning map of the risks that threaten the wetland was developed using GIS. Risk zoning is an important measure in environmental risk management. It involves dividing an area into sub-areas according to general risk characteristics. Identifying the similarities and differences of risk factors between sub-areas by making comparisons between sub-areas can help to determine the most appropriate environmental risk management policies. The GIS that was used in this article constitutes a powerful tool for decision-makers in conservation to establish preferences, which need to identify human activities in terms of spatial interactions and other factors that influence the health and viability of critical habitats and key species in a wetland. ERA can provide a description of the actual situation of ecological, health status or risks that threaten wetlands. The presented methodology can be redeveloped to apply to different types of wetlands to identify and manage the risks. This method focuses on identification of wetland endpoints and conservation of values associated with these endpoints. This target is obtained by identification of hazards/threats to values of the wetland endpoints. Results of this study for Shadegan Wetland reveal that the stressors inflicted on the environment of this wetland causes adverse effects on characteristics of the wetland. Alteration in natural habitats, changes in the water balance of wetland, water pollution, over exploitation of biological resources, and drought are the main stressors of this wetland. All of these factors are interrelated and due to the complexity of wetland ecosystems, it is difficult to separate the effects and consequences of these factors. For Shadegan Wetland, management strategies are suggested on the basis of the results of this research. Preventing change in wetland land-use, providing sufficient water for the wetland, ensuring water quality of the wetland, protecting biodiversity, sustainable use of wetland resources, increasing awareness of wetland values and threats, and promoting public participation are the main goals of the proposed strategies. Most threats in the study area were found to be in the northern region and in areas of freshwater that be attributed to the existence of access roads in such areas that facilitate increased human access to the wetland. The lowest risk zone was identified in the southern part of the wetland in a saltwater region that is a pristine environment inaccessible to humans. The key stressors and receptors in a wetland under consideration must be clearly identified in order to make properly targeted risk assessment and to provide useful data. However it is very difficult to assess and determine the threshold of permitted reserves of these resources and to identify stress factors in those wetlands, in which potential reserves of biological components do not have any scientific data or documentation. Further development of the proposed methodology can focus on risk assessment of wetland functions to manage the activities that reduce capacity of the wetland ecosystem. Assessment of wetland functions through standard quantitative risk assessment can be used to restore wetlands and

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