Before Roman times, as much as a 25% of the British Isles is thought to have been covered by wetlands. But by the 1980s, wetlands covered only 5% of the UK landscape (Rackham, 1986). This decline is thought to have been caused primarily by the combined impacts of drainage, nutrient enrichment and urbanisation.
Recently, our awareness of the ecological importance of wetlands has grown, increasing interest in wetland creation and restoration (Odland, 1997). A wide range of initiatives are now in place to reverse this decline by creating and restoring wetland systems in both rural and urban environments in recognition of their physicochemical, socioeconomic and conservation benefits.
Ecologically valuable wetlands with potentially high species diversity can be created even in intensively used, secondary urban recreational areas, provided the water body and its surroundings are suitably designed (Gemmell and Connell, 1984; Stewart et al., 1998; McKinstry and Anderson, 2002). Brownfield land is increasingly recognised as having potential for engineered wetland-creation schemes. For example, gravel pits provide good opportunities for wetland creation or restoration due to their relative abundance, geographical location and low potential contamination risk (Merritt, 1994).
Wetlands in urban regions take on human-related values that they lack in non-urban areas, as they provide people with contact to nature, and opportunities for recreation, that are otherwise rare in the urban landscape (Ehrenfeld, 2000). So integrating wetlands into planned landscapes requires not only an understanding of wetland ecology and hydrology, but also an understanding of the human perceptions of natural environment and the importance of social factors.
Greenspace is an important part of complex urban ecosystems, and benefits urban communities environmentally, aesthetically, recreationally and economically (McPherson, 1992; Bolund and Hunhammar, 1999; Beer et al., 2003; Jackson, 2003; Li et al., 2005). Areas designated as urban greenspace within new projects must adhere to sound ecological principles (Sellers et al., 2006).
Ecosystems will develop best if located near, or adjacent to, an existing or remnant area of the same type, and smaller habitats are likely to be less resilient to disturbance (Zedler, 1997). It is important to consider scale and surrounding land use when engineering wetlands – a wetland that appears to be extensive at the local scale may be an isolated patch when evaluated at a regional scale (Whited, 2000). As engineered wetlands created on brownfield land are often located in urban areas, potential hydrological and ecological isolation is important. At the same time, careful management is needed to control the increased risk of colonisation by non-native invasive species from surrounding gardens and parks.
One complication in applying ecological principles to urban greenspace projects is the public’s preference for certain types of natural landscape – the preferred habitat type may not always support the richest wildlife structure or species diversity. For instance, people generally express more pleasure and enjoyment when shown scenes of open water with mown lawns along the banks that when shown natural open-water wetlands with tall vegetation around the margins. But the habitat and species diversity of a natural wetland are much higher than those of a less diverse, but visually pleasing pond (Tilton, 1995). A further problem with negative public perception is that the area may quickly become depreciated with litter, disrepair, crime and pollution, whatever the perceived benefits it may seem to offer (Pauleit, 2003).
Although landscape-level processes dominate wetland ecosystem development and sustainability, wetland creation and restoration decisions are typically made on a project-by-project basis (White and Fennessy, 2005). To reduce the effects of hydrological and ecological isolation, wetland creation and protection needs to be expanded beyond the immediate area in an effort to integrate wetland habitats into the wider landscape (Tilton, 1995). With careful planning, design, implementation and public education, wetland habitats can be fully integrated into planned landscapes without destroying valuable benefits provided by wetland ecosystems.
To gain public support for wetlands, their importance as a habitat needs to be communicated to the public. Public participation is a key factor to consider, and it is important to ensure greater public input into formal decision-making from the start of the planning process. The outcomes are improved guarantees for the public and better acceptance of plans and projects (Mermet, 1997).
Any greenspace- or habitat-creation scheme should take into account economic, environmental, biological, recreational and aesthetic issues. A good scheme should aim to protect and/or restore a healthy and biodiverse environment, create an interconnected infrastructure, and involve communities in the decision-making processes (De Sousa, 2003).
Sustainable Urban Brownfield Regeneration
An EPSRC-funded research project is being conducted by Forest Research and the University of Reading through the Sustainable Urban Brownfield Regeneration: Integrated Management (SUBR:IM Consortium). This aims to establish the best practice for the design and management of successfully engineered wetland habitats on brownfield land.
The research has identified key factors responsible for the success or failure of existing engineered wetlands on brownfield sites in the UK.
- Unsuitable location for wetland creation: in terms of substrate, surrounding land use, hydrological and ecological connectivity to similar habitats.
- Water quantity: sites located in areas where too much or too little water is available to maintain the structure and functioning of wetland habitats. This is compounded by a lack of control of water levels at some sites. Engineered solutions are often employed (e.g. pumping), but are not often sustainable.
- Water quality: water sources affected by run-off of polluted water, nutrients or sediments from the surrounding catchment, leading to eutrophication and excessive algae growth. There are problems at some sites with very high or low pH waters and heavy metal contamination.
- Invasive species: there are many opportunities for invasions in wetlands, as the range of terrestrial to aquatic habitats is so great. Of particular note are Japanese knotweed (Fallopia japonica), Himalayan balsam (Impatiens glandulifera), Australian swamp stonecrop (Crassula helmsii), parrot’s feather (Myriophyllum aquaticum) and floating pennywort (Hydrocotyle ranunculoides).
- Lack of resources: financial and human resources are needed for the ongoing maintenance of a site following creation (machinery, labour and repair).
- Public perception and participation: local support is needed from the planning stage, and involvement in maintenance (volunteer programmes) helps improve the success of a site. Negative public perception, and the litter, vandalism and crime that cause it, or are caused by it, is a major problem.
Russia Dock Woodland
Russia Dock Woodland was created on the infilled site of Russia Dock, formerly part of the Surrey Commercial Docks. It was developed in the late 1970s, and handed over to Southwark Council in 1982 as part of an overall regeneration plan by London Docklands Development Corporation to provide an area of amenity and ecology at the centre of the newly redeveloped housing areas in Rotherhithe.
Wetland areas and water features were included in the design as interconnecting streams and ponds, maintained by a water-pumping system. But the knowledge and resources required to maintain the water feature component of the restoration were not established at the outset, and following the drowning of a child there was an unwillingness to make it work, so many areas were allowed to deteriorate and dry up (Jackson, 1986).
Russia Dock still has problems today with eutrophication of stagnant water areas, invasive species in the form of Japanese knotweed (Fallopia japonica), and an often poor aesthetic quality due to litter and vandalism. But lessons have been learned from the early days of development, and increased resources and funding, together with a strong group of Friends, is helping to maintain and enhance the site. Positive developments include the introduction of community wardens to control litter and dog fouling, plus invaluable education work with local schools and community groups.
A strong science base is critical to address the issues surrounding the potential establishment of wetlands. The Forest Hydrology Programme at Forest Research involves a number of collaborative studies on the sustainable establishment of wetlands in the urban environment.
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