MULTI-OBJECTIVE ENVIRONMENTAL MANAGEMENT IN CONSTRUCTED WETLANDS MICHELLE BENYAMINE1∗ , MATTIAS BÄCKSTRÖM1 and PER SANDÉN2 1 Man-Technology-Environment Research Centre, Örebro University, Örebro, Sweden; 2 Department of Thematic Studies, Campus Norrköping, Linköping University, Norrköping, Sweden (∗ author for correspondence, e-mail:
[email protected])
(Received 9 September 2002; accepted 24 December 2002)
Abstract. We examined multi-objective environmental management as applied to pursuing concurrent goals of water treatment, biodiversity and promotion of recreation in constructed wetlands. A case study of a wetland established to treat landfill leachate, increase biodiversity, and promote recreation was evaluated. The study showed that attempts to combine pollution management with activities promoting biodiversity or recreation are problematic in constructed wetlands. This could be because the typical single-objective focus of scientific research leads to contradictions when planning, implementing and assessing the multi-objective use of wetlands. In the specific case of wetland filters for landfill leachate treatment, biodiversity, and recreation, there is a need for further research that meet practical needs to secure positive outcomes. Keywords: biodiversity, recreation, theoretical disputes, water treatment, wetlands
1. Introduction Multi-objective environmental management is increasingly used in regional environmental planning. Activities designed to reduce pollution or attract tourists at the same time as preserving diversity can make environmental conservation economically justified. A convenient example is the case of constructed wetlands developed primarily for on-site water treatment, while increased biodiversity and recreation are promoted as additional effects. Wetlands are commonly regarded as key ecosystems for preserving species diversity of, for example fish, amphibians, aquatic invertebrates, and birds. Awareness that over 60% of the world’s wetlands disappeared in the 20th century (Innis et al., 2000), has focused scientific attention on the conservation of existing and creation of new wetlands. Wetland ecosystems have also proven to be effective for the on-site management of municipal and agricultural wastewater. In wetland environments, soil micro-organisms can oxidise organic matter and nitrify and denitrify nitrogen compounds. The main mechanism for metal removal is precipitation and adsorption in the oxidised wetland sediments (Martin and Moshiri, 1994). Constructed wetlands have been studied for the treatment of industrial wastewater in the form of landfill leachate, pulp and paper wastewater, mine drainage, petroleum refinery wastewater, and wastewater from electroplating industries and textile proEnvironmental Monitoring and Assessment 90: 171–185, 2004. © 2004 Kluwer Academic Publishers. Printed in the Netherlands.
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duction (Kadlec and Knight, 1996). The use of constructed wetlands for landfill leachate treatment is still in the development stage, and knowledge concerning the dynamics and long-term operation of such systems is preliminary (Haarstad and Maehlum, 1999; Kadlec and Knight, 1996; Yallop and O’Connell, 2000). However, compared to high-cost and labour-intensive conventional purification systems, inexpensive and easily constructed on-site wetlands have come to be regarded as a successful alternative in treating landfill leachate (Barr and Robinson, 1999; Dobberteen and Nickerson, 1991; Staubitz et al., 1989). The often valuable land occupied by former landfill sites in rural locations requires cost-effective and sound after-use strategies. With increasing public emphasis on environmental protection and control, the restoration of landfill sites is regarded as an opportunity for authorities to concentrate on nature conservation and ecological diversity. Landfill sites restored with an abundance of wild-flowers, shrubs, and trees, in turn attract insects, amphibians, birds, and mammals, and contribute to the visual amenity of the area. Besides being a relatively inexpensive and easily constructed habitat, it is claimed that such sites encourage public support for environmental conservation by promoting recreational values (Simmons, 1999). The aim of the current study is to explore the possibility of uniting several environmental goals in a single management operation. A case study is used to illustrate the advantages and disadvantages of such an approach. The study examines a 30 yr old landfill site in the municipality of Örebro in central Sweden. Its primary goal of establishing a wetland system for protecting ecological values – thereby creating recreational possibilities – has been combined with that of landfill leachate treatment.
2. Site description Since the level of Lake Hjälmaren was lowered in the 1880s (Claesson and Klingnéus, 1999) its western shores have been the backyard of the municipality of Örebro. For over 50 yr the area was used as a municipal waste dump, oil port, industrial area, and military training camp, although in recent decades these activities have ceased. Growing interest in restoring the area closer to its condition a century ago led the municipality of Örebro to launch a wetland management project in 1992. The goal of the project was to create a wetland landscape from natural meadow beaches and constructed wetlands that cover 500 ha. The current study examines the component of the project that involves the dump-site (Figure 1). The limited availability of background information and data restricted the scope of the analysis. The landfill site studied is located 5 km east of central Örebro on the western shores of Lake Hjälmaren. Between 1967 and 1978, this site was used as a dump for municipal waste (Adolfsson etal., 1972). The site covers 32 ha, and waste was deposited in five hills, having a total area of 28 ha and a volume of 1 million
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Figure 1. Rynningeviken, municipality of Örebro, old landfill area, showing the landfill hills, ditches, containment pond, constructed wetlands, plots for collection of surface water samples (Y1, Y2) and groundwater sampling sites (G1, G2, G3, G4).
m3 (Tekniska Förvaltningen, 1998; Tekniska Förvaltningen, 1999). Although the landfill site received oil residues and chemical wastes in its first years of operation (Rydén, 1972), the deposited material now mainly comprises domestic waste and treated sewage sludge (Adolfsson et al., 1972). Some industrial waste was also deposited, consisting mainly of debris from the extensive construction in the late 1960s and early 1970s (Larsson, 1999). The entire landfill area consists of two main dumping sites: an eastern one, closer to the lake, used between 1968 and 1973; and a western one used from 1973 to 1978 (Adolfsson et al., 1972). An inner ditch around and between the deposit hills directs the landfill leachate to a containment pond (Tekniska Förvaltningen, 1998), while an outer ditch was built to prevent leachate from contaminating surrounding areas (Fagerlind, 1993).
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Embankments between the landfill deposit and the lake and between the outer and inner ditches are designed to protect surrounding water from the leachate (Fagerlind, 1993). The entire landfill site lies on young granite bedrock overlaid with loose clay and with a thick peat layer closest to the surface (Fagerlind, 1993). The clay layer varies between 0 and 7 m in thickness (Tekniska Förvaltningen, 1994), and the thinness of the clay layer in some areas implies a risk of leachate infiltration into the groundwater (Fagerlind, 1993). The area has a typical cool temperate continental climate with an annual mean air temperature of + 5.7 ◦ C and annual precipitation of 614 mm (SMHI, 1999).
3. Material and Methods The municipality of Örebro kindly supplied all available geological, chemical and biological data gathered from the area. Interviews with a key person involved in project management complemented these written reports and documents. The documents used in the analysis can be divided into five categories: 1) official municipal government documents pertaining both to the design and to management actions; 2) consultants’ reports on various aspects of area management; 3) technical reports on monitoring the leachate from the waste deposit; 4) protocols from the chemical analysis of water samples; and 5) records on the diversity of birds in the vicinity of the landfill area. The first category comprises one main official document, which justifies the decision to declare the area a nature reserve (Örebro Kommun, 1995), and unofficial reports complementing this document. Two consultants’ reports were prepared. The first was made by the Geological Survey of Sweden (SGU), and concerns the impact of the deposit on surface- and groundwater (Fagerlind, 1993). The second was made by Golder Associates AB, and describes the design parameters for constructing wetland filters for leachate treatment (Golder Associates AB, 1994). Four technical reports present monitoring assessments of water quality throughout the wetland, in the ditches surrounding the deposit, and of the groundwater. These documents are annual reports, made by municipal officials for submission to the Swedish Environmental Protection Agency (Tekniska Förvaltningen, 1998; Tekniska Förvaltningen, 1999; Tekniska Förvaltningen, 2000; Tekniska Förvaltningen, 2001). These reports also include design descriptions and management activities of the constructed wetland system. Water samples were sent for chemical analysis to KM lab in Linköping until 1997; from 1998, AnalyCen in Göteborg has done the analysis. The analytical data from 1995 to 1998 are used in this study to assess the effectiveness of the wetland system.
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The species and number of breeding pairs and nests of birds in the area in the vicinity of the landfill have been recorded annually since 1983 (Rosenberg in interview 1999; Sandgren, 2000; Sandgren, 2001). The written source material was complemented with interviews with a key actor in the project, Mats Rosenberg. He was employed by the municipality of Örebro as project initiator and leader, and was interviewed twice in 1999, on March 12 and October 22.
4. Project Goals and Implementation The three goals of the project are to create an attractive recreational area, increase biodiversity, and manage the pollution in the area. The objectives of the project can be found in the plan for the nature reserve (Örebro Kommun, 1995), which comprised the basis for declaring the area a nature reserve. This document states the overall objective of the entire project to be as follows: ‘to create varied green space with great natural and recreational values close to the centre of Örebro’ (translated from Örebro Kommun, 1995). This formulation of the objective greatly emphasises the recreational and aesthetic aspects of the project. Management of leachate is not mentioned and the biodiversity objective seems subordinate to recreation. The overall objective is broken down into specific goals and management activities for the area. Specific goals are phrased as visions, and the vision for the landfill site and the constructed wetlands is described as: ‘Well-grazed pasture and marshes with optimal conditions for resting and nesting wetland birds which depend on mowed and grazed wet meadows. Along the northern edge, are shallow-margined leachate ponds suitable for batrachians and other fauna. . . Beautiful rolling heath grazed by sheep, with isolated trees and scattered groups of bushes, and some small marshy areas in the depressions. The whole area should be easily accessible by visitors’ (translated from Örebro Kommun, 1995). This description paints a vivid and colorful picture of the intended landscape; aesthetic values are prominent, and the articulated biodiversity goals focus on wetland birds. Amphibians are also mentioned but are not given the same emphasis. Management of the leachate water is merely noted in passing when describing the position of the treatment wetlands. No other quantified goals or plans for evaluating the project are set forth in the official municipal documents. Rosenberg did, however, articulate specific pollutionmanagement goals in the March 12, 1999 interview. He stated that the landfill should not affect surrounding surface- and groundwater, and that water-quality standards should correspond to the requirements of surrounding ecosystems. The consultant’s report describing the design of the wetland filters (Golder Associates AB, 1994) supplies figures for the expected reduction of certain pollutants as water passing through the wetland. The report projects a 30% reduction of nitrogen in the wetland (two tons annually), and further that leachate be fully
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cleansed of suspended substances through sedimentation and filtration. It was also projected that less than 10% of the original content of organic compounds in the leachate would escape the final wetland pond, and that the iron content would be reduced by up to 50% through sedimentation in the ponds and the sedge zone (Golder Associates AB, 1994). As the wetland filters were constructed according to the design specifications contained in the report, it is fair to assume that the municipality accepted the stated levels of pollution reduction. The documents supply no information on when and how to cut and harvest the vegetation. Implementation has followed the plans of the project (Rosenberg in interview, 1999). The deposits have been covered with excavated clay material and currently have a vegetation cover consisting mainly of grass with isolated trees and bushes. Sheep and cattle graze the entire area. Roads lead visitors into the area and a shelter for visitors has been built on top of the deposit. A couple of bird-watching towers have been constructed, and several paths leading into the meadows were built to facilitate bird watching. Ditches were present around and within the dumpsite even before project initiation, and leachate was pumped from the containment pond to the municipal wastewater treatment plant. Wetland filters have now been constructed according to the consultant’s suggestions (Golder Associates AB, 1994). Today all landfill leachate is pumped from the containment pond to the first wetland pond (Figure 1). The water passes through three constructed wetland ponds having open water surfaces and using local peat as substrate material. The total water volume of the ponds is approximately 6 500 m3 and the maximum depth is 1.5 m. The dimensions of the ponds are 120 × 40 m, 160 × 40 m, and 80 × 40 m (Tekniska Förvaltningen, 1999), and the theoretical retention time is estimated to be 20 days (Golder Associates AB, 1994). The first pond has sparse vegetation with reeds (Typha latifolia) growing only on its margins. Vegetation in the second pond is growing more even in the entire wetland pond, with Typha latifolia and Alisma plantago-aquatica. The last pond is almost completely covered with vegetation, including Typha latifolia, Alsima, Juncus Conglomeratus, Juncus effesus, Juncus alpinoarticulatus, Potamogeton alpinus, and Phragmites australis. 5. Assessment 5.1. R ECREATION Only limited information is available that can be used in assessing achievement of the recreation objective. Rosenberg reported in interview (1999) that the number of cars in the reserve has been counted on occasions, and it was estimated that approximately 10,000 people visited the area annually. No other quantitative or qualitative information has been found that could be used in assessing the achievement of the recreation objective.
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TABLE I Number of bird species and breeding couples in the meadows south of the wetland Year
1995
1996
1997
1998
1999
2000
Number of breeding couples Number of species
23 7
20 7
218 9
523 10
425 10
511 6
TABLE II Number of bird species and colonies on the landfill Year
1993
1994
1995
1996
1997
1998
1999
2000
Number of colonies Number of species
44 20
45 23
36 20
34 21
35 20
35 16
44 21
74 24
5.2. B IODIVERSITY Data useful in evaluating biodiversity is limited to bird inventories. The focus on birds has historical reasons: in 1910 the area was discovered to be particularly rich in bird life, and has since been a popular area for bird watching (Rosenberg, 1998). No inventory has been found for vegetation, for amphibians, or any other fauna. Thus, bird diversity seems to be the primary focus of the biodiversity objective. Bird inventories have been performed annually since 1985 in the meadows south of the constructed wetlands and on the landfill (Sandgren, 2000; Sandgren, 2001). Table I presents the number of breeding bird species and breeding couples observed in the meadows south of the wetlands from 1995 to 2000, and Table II shows the number of breeding birds and colonies observed on the landfill from 1993 to 2000. The large increase in number of breeding couples from 1996 to 1997 (Table I) is accounted for by the growth of the black-headed gull (Larusridibundus) population on the shore meadows from one and zero couples in 1995 and 1996, to 200 in 1997, 500 in 1998, and 400 couples in 1999 (Sandgren, 2000). When the landfill hills were being covered in 1996–1998, the number of colonies was at its lowest (Table II); however, in 1999 the number returned to its 1993 level. In 2000, the population of ground-breeding birds, such as the blue-headed wagtail (Motacilla flava) and lark (Alauda arvensis), increased three- and two-fold, respectively; and by preserving a large stand of reeds near the lake the reed warbler (Acrocephalus arundinaceus) and sedge warbler population (Acrocephalus schoenobaenus) nearly doubled (Sandgren, 2001).
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5.3. P OLLUTION MANAGEMENT Plenty of data is available concerning pollution management. A monitoring program, originally designed by the technical authority of the municipality with guidance from SGU, has been in operation since 1995. The aim of this program is to control the efficiency of the constructed wetland system and the impact of the landfill on surrounding areas. Samples of in- and out-flow leachate are collected six times a year, and surface water from the outer ditches is collected at two sites, three times a year (Figure 1). Groundwater is collected from four wells, twice a year (Figure 1). Data pertaining to groundwater and water from the ditches is available dating back to 1992. The volume of incoming leachate to the ponds from the pumps is estimated from the pump runtime, pump capacity being estimated once a year (Tekniska Förvaltningen, 1998; Tekniska Förvaltningen, 1999). To calculate the water balance, the outflow from the third pond was to be estimated once a week, according to the monitoring program (Tekniska Förvaltningen, 1999); however, no outflow was observed most weeks during the first years of the program. Runoff was only estimated five times in 1997 (Tekniska Förvaltningen, 1998) and eleven times in 1998 (Tekniska Förvaltningen, 1999). Due to these problems, it was decided in 1999 that no further estimates of outflow runoff would be made; instead, outflow is assumed to equal inflow (Tekniska Förvaltningen, 2000; Tekniska Förvaltningen, 2001). Absence of outflow has also resulted in missing water chemistry data, and in 1997 only two samples were collected at the outlet (Tekniska Förvaltningen, 1998). Together with SGU, the municipality chose the variables and required detection limits for the program, and in all, 25 variables have been analysed. The SGU report (Fagerlind, 1993) paid particular attention to the risk of dispersion of lead, cadmium, nitrogen, and phosphorus. Golder Associates (Golder Associates AB, 1994) focused on the concentration of nitrogen, suspended substances, organic compounds, and iron. Table III summarises the median concentrations at the inlet and outlet of the wetland ponds, based on a selection of variables from the chemical analysis made by KM lab in Linköping and AnalyCen in Göteborg. The selection of variables is based on the statements of expected reduction in the wetland filters (Golder Associates AB, 1994) and major hazards identified by SGU (Fagerlind, 1993). Despite the fact that organic compounds were included during planning (Golder Associates AB, 1994), these are not measured and, thus, cannot be evaluated. All other variables with a significant change in concentration are also presented. The difference in concentrations is statistically significant for total nitrogen, ammonium, suspended substances, iron, potassium, magnesium, and chloride. For all these variables, concentrations found at the outlet are lower than at the inlet. To compare these differences with the expected reduction mentioned in the consultant’s report (Golder Associates AB, 1994), the differences in concentration
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TABLE III Median concentrations at the inlet and outlet of the wetland ponds, p-value (Mann-Whitney), difference in concentration between the sample sites (Hodges-Lehmann estimator), with 95% confidence limits (CL). Number of samples is 20 for the inlet and 12 for the outlet Variable
Inlet
Outlet
p-value
Total nitrogen (mg l−1 ) 69 25 < 0.001b −1 58 22 < 0.001b Ammonium (mg l ) 2.25 2.35 0.74 Nitrate (mg l−1 ) −1 11 0.04b Suspended substances (mg l ) 22 −1 4.55 1.7 0.019b Iron (mg l ) −1 820 780 0.53 Phosphorous (µg l ) 0.25 < 0.1 0.17 Cadmium (µg l−1 ) −1 2 < 1 0.18 Lead (µg l ) 8.5 6 0.17 Chromium (µg l−1 ) 6.5 5.5 0.47 Coppera (µg l−1 ) −1 83 59 0.026b Potassium (mg l ) −1 35 28 0.005b Magnesium (mg l ) −1 174 120 0.005b Chloride (mg l )
Difference Upper CL Lower CL –40 –34 – 0.27 – 8.4 – 2.3 10 – 0.1 0 – 3 – 1 –25 – 9.4 –64
– 66 – 52 – 2.6 – 27 – 6.4 – 29 – 0.3 – 2 – 20 – 7 – 42 – 23 –116
–22 –18 1.3 0 – 0.5 57 0 0 2 2 – 2 – 3 –20
a Only data from 1998 is used due to change in detection limit (n = 6 for both sites). b Statistically significant at the 5% level.
were recalculated so as to yield percentage values. The total nitrogen values were found to differ by almost 60%, while the inlet and outlet values for suspended substances and iron differed by 40% and 50%, respectively. The expected reduction stated in the consultant’s report was, however, expressed in terms of amounts, and thus cannot be compared with the reported concentration values without thorough knowledge of the water flow. If we accept the municipality’s assumption that the wetland outflow equals the inflow from the containment pond, the expected reduction has been achieved for nitrogen and iron but not for suspended substances. This assumption, however, leads to some serious problems. According to the data, the chloride level is also being reduced by almost 40%, but at current levels of chloride there are no known processes that can reduce the amount of chloride in the wetlands. The most probable explanation for the lower outlet concentrations is instead dilution. As outflow was non-existent at several sampling occasions, there is an over-representation of data from periods with relatively high water-flow – an event that normally results in decreased concentrations due to rainwater dilution. If we assume chloride to be conservative and that the diluting water has a negligible chloride concentration, the reduction of nitrogen, suspended substances, and iron will all be lower. An estimate for nitrogen reduction based on this new assumption produces a reduction of only approximately 40%.
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Figure 2. Box plot of chloride concentrations in the four wells. Wells 1 and 2 are located west of the deposit, while wells 3 and 4 are located to the east; N = 7.
Other interesting variables from a pollution perspective, such as chromium, copper, phosphorous, lead, and cadmium, show no tendency towards reduction in the wetland filters. According to The Swedish Environmental Protection Agency (Naturvårdsverket, 1999) concentrations of these metals are moderately high, but at current levels any adverse effect on the recipient water body is unlikely. However, negative impact on the fauna in the wetland filter cannot be excluded. Evaluation of the groundwater data indicates leakage from the deposit (Figure 2). The observed concentration of chloride can only be explained by leakage from the deposit, since the site is far from the sea and no chloride minerals exist in the area. The highest concentrations are found in wells 3 and 4, located east and downstream of the deposit towards the lake (Figure 1). Data from these wells also show several other variables to be at elevated levels: ammonium concentration is between 1 and 2 mg l−1 – extremely high for groundwater – while potassium, magnesium, and manganese concentrations also are higher at these wells compared to the two wells on the western side of the deposit. Since project start no improvement has been found in the groundwater quality. In some cases, there are even signs of deteriorating quality: data indicates that zinc concentrations are increasing while pH is decreasing.
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Thus, in general, the pollution management objectives have not been completely achieved, as the pollution reduction in the wetland filter appears not to have reached expected values. Most problematic are the incomplete records at the outlet of the wetland filter. Inspection of the site revealed leakage from the outlet, and this will produce errors in flow estimates and problems when samples are collected.
6. Multi-Objective Management Three major issues are identified in the current case that could constitute problems in this multi-objective project. The first is the hydrology of wetlands, as required hydrological conditions are different depending on whether water treatment or biodiversity is the objective. Second, the chemical composition of the leachate is a problem, as it influences both treatment results and wetland biodiversity. Finally, biodiversity is an issue as water treatment often benefits from single species macrovegetation (Barr and Robinson, 1999; Maeluem, 1995), which of course limits the plant biodiversity and possibly also the faunal diversity (Creighton et al., 1997; Galatowitsch et al., 1999). Treatment efficiency of wetland filters depends on that the major pollutant load coinciding with high biological activity in the wetland. In northern humid climates special attention must be paid to seasonal hydrological fluctuations, as the largest volumes often occur during periods of low microbial activity (Staubitz et al., 1989). In the current case, technical consideration seems to have dominated the design of the wetland system as a containment pond is used to damp peak flows to meet the estimated theoretical retention time, calculated at 20 days (Golder Associates AB, 1994). However, the pond as well as the whole wetland filter is too small to even out the seasonal fluctuations, and the resulting drying-out and floodings of the area leads to missing or biased data. Moreover, considering the statements that the flow of contaminated water should be controlled according to biological activity, the design does not correspond to the seasonal effects on treatment efficiency. On the other hand, in view of integrating ecological functions in constructed wetlands, the water flow should be regulated according to wildlife goals (Kadlec and Knight, 1996). Attention should be paid to seasonal variations of water depth, length and/or timing of flood inundation, flow velocity, and water source (Gilvear and Bradley, 2000). In other words, when the aim is to promote biodiversity, the seasonal variation in hydrology should be kept as close as possible to the natural variation. However, no attempts to mimic natural hydrological conditions have been considered in the wetland construction reports in order to promote biodiversity in this case. The seasonal fluctuations affecting the wetland system is a setback if considering the original construction proposal aimed to treat the leachate. The biodiversity objective has obviously been neglected when planning for the construction of the wetland system despite the fact that the biodiversity – which the recreation goal depends on – was one of the main objectives of the
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area. Concurrently, treatment efficiency also diminishes due to the disregards of the biological aspects of the wetlands. Nowhere in the documentation of the project are there any considerations on possible adverse effects of the chemical composition of the leachate passing through the wetlands on the biological activity. Not only is it questionable whether the typically high concentrations of organic compounds and metals in landfill leachate can coexist with a functioning ecosystem, but the chemical composition of the leachate also differs greatly from one landfill to another (Kadlec and Knight, 1996; Staubitz et al., 1989). This requires investigations of the composition and effects of the leachate in each particular case. The problem increases as the treatment objective should coincide with biodiversity. The volume and composition of the chemical contents of wetlands receiving landfill leachate is claimed to affect amphibians and other sensitive species which are easily disturbed by alterations in the environment (Horne and Dunson, 1995; Mensing et al., 1998). However, in this particular case there are no other data on biological activity in and around the wetlands beside the observations of the bird species diversity. Thus, it is difficult to evaluate the treatment effects on the biodiversity objective. Moreover, the lack of data on biological organisms also reduces evaluation of the biota-dependent treatment efficiency. Regarding the assessment of the biodiversity objective, this is primarily discussed from the perspective of bird species diversity, even if amphibians and vegetation are mentioned in the documents describing the project goals. Moreover, vegetation is expected to be self-colonizing and no suggestions about vegetation management besides grassing are found. However, the quality and quantity of vegetation is of considerable importance in achieving treatment efficiency. Fast invading and dominant vegetation species, such as Phragmites australis and Typha latifolia, are assessed to be advantageous for the oxygenation of the sediment and as a habitat for the degrading micro-organisms (Maeluem, 1995; Martin and Johnson, 1995). This condition even agree with the biodiversity objective as wetland faunal diversity is argued to stay high in wetlands constructed for water treatment with a low plant diversity (Kadlec and Knight, 1996; Zedler, 2000). In contrast, there are also studies showing that species optimal for water treatment replace a diversity of plant species, which in turn decrease resting, feeding, and breeding areas and invertebrate resources for migratory waterfowl (Creighton et al., 1997; Galatowitsch et al., 1999). Again, the biological aspects are obviously ignored in the construction of the wetland system; the biological organisms concerning both the treatment- and the biodiversity objective are not considered in the documentary. The case study illustrates the point that even if the project is presented as multiobjective; the objectives seem to be ranked hierarchically. Recreation is interpreted as the overarching goal, which itself validates the lesser biodiversity goal: high biodiversity effectively increases the recreational value of the area. Pollution management, on the other hand, has a lower priority in the official documents. Many of the management activities pertaining pollution treatment are legally regulated and specified, which might explain why they are glossed over in the documents.
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Pollution prevention measures must be implemented and the municipality has a limited choice of measures. For the other two objectives the community has much more leeway. A reason for the current formulation of the objectives could be that it is easier for a project to gain acceptance if it produces immediate benefits for the public. Several scientific studies highlight the possibility in combing treatment wetlands with vital recreation areas for birdwatchers and nature -lovers (Gearheart and Higley, 1993; Kadlec and Knight, 1996). Such uses of wetlands are regarded as important in building public support for the protection and enhancement of existing natural and constructed wetlands (Kadlec and Knight, 1996; Simmons, 1999). In this light, the problems with building and operating multi-objective constructed wetlands are subordinate to the fact that, to be approved, environmental protection must benefit the public, economically and socially. The major part of the project focuses on increasing bird diversity in the area. However, the leachate water treatment was designed primarily from an engineering perspective, where the biodiversity implications of the wetland filters have a low priority. Failure of wetland projects, according to Young (1996), often stems from the absence of integrating technical, chemical, biological, hydrological etc., knowledge as to wetlands: if engineers are responsible, biological aspects will be ignored and if biologists plan and implement wetland projects, engineering and hydrological aspects are overlooked. A number of constructed wetlands have succeeded when targeted to a single, specific function such as wastewater treatment or increased wildlife. But when it comes to multi-objective environmental management in constructed wetlands, the scientific experience is small and successful realization of such projects is doubtful. In society, economic prerequisites guide many environment-related projects. Single objectives, such as the improvement of hydrological balances in particular areas have, for example, proven to be inadequate economic motivation for establishing new wetlands in Sweden. Thus, apart from increasing water quality, diversity and recreational benefits are promoted as secondary objectives that can justify the implementation of wetland construction projects (Naturvårdsverket, 2001). However, in this case scientific results and recommendations seem inconsistent with practical needs. The typical single-objective focus of scientific research leads to contradictions when planning, implementing, and assessing the multi-objective use of wetlands. Practitioners and scientists are apparently working separately, increasing the barriers between various segments of society. Carley and Cristie (1992) claim that inflation of scientific authority is the problem, in particular when dealing with human - environmental interactions. Instead, higher integration is necessary to bring together scientific knowledge and practical applications.
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7. Concluding Remark The overarching question whether multi-objective environmental management can be successful could not be answered. Lack of clearly defined goals, inadequate monitoring, and lack of consideration as to how the objectives effect one another is the reason to this failure. These problems are particularly severe when insufficiently studied methods are used on a local or regional scale. Further research is needed that meet practical needs to secure positive outcomes.
Acknowledgements This work is part of a larger project dealing with theoretical disputes, funded by The Knowledge Foundation and The Swedish Research Council for Environment, Agricultural Sciences, and Spatial Planning (Swedish Council for Forestry and Agriculture Research, SJFR and Swedish Council for Building Research, BFR). Dr. Anders Düker and the municipality of Örebro, especially Magnus Fridolfsson, Katrin Larsson and Mats Rosenberg, are gratefully acknowledged for important input and discussion, and for reviewing earlier versions of this manuscript.
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