Download Conservation, restoration, and effects of climate change on wetlands

Conservation, restoration, and effects of climate change on
wetlands
Deborah V. Chapman
School of Biological, Earth and Environmental Sciences, University College Cork, Ireland
1. Introduction
Wetlands are unique ecosystems that exhibit permanent or regular inundation or saturation with
fresh or saline water. Marginal wetlands are created at the edges of rivers, lakes and the sea and
are characterised by rooted vegetation that is permanently, or occasionally, partially submerged.
Other wetlands, such as bogs, swamps and marshes, exist without direct connection to a large
water body and depend on groundwater and precipitation. All types of wetland are usually dominated by vegetation that has adapted to survive with its roots in saturated soil conditions.
Wetlands serve many important hydrological and biological functions in the natural environment and provide many essential services to human communities and yet they have been degraded and even destroyed by human activities for decades. The importance of wetlands was
recognised by the Ramsar Convention on Wetlands signed in Iran in 1971 (UNESCO 1994).
This intergovernmental treaty provides a framework for wise use and conservation of all types of
wetlands. The Convention currently has 159 contracting parties and 1,886 designated wetlands
(Ramsar Convention Secretariat, 2010).
All wetlands are intricately linked with the hydrological cycle and thus they may be vulnerable to some of the potential impacts of global climate change, such as increased flood and
drought events or storm surges. In addition, wetland vegetation can make an important contribution to the sequestration of carbon, thereby contributing to the mitigation of climate change. The
need to consider conservation and restoration activities will be, therefore, even more important
in the future.
2. Benefits from wetlands
Wetlands are an essential component of the natural environment helping to maintain a natural
balance in hydrological systems and their associated habitats. In addition, they provide many additional benefits to human communities, such as food (e.g. fisheries) and fibre (e.g. from reeds).
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Other benefits include habitats for rare and endangered species, natural water purification,
overwintering habitats for waterfowl, flood control and many more (Barbier et al., 1997). An
initial attempt at placing a monetary value on the functions of natural ecosystems, including
wetlands, was carried out by Constanza et al. (1997). As an example, the potential benefits from
swamps and floodplains were estimated to have a value of US$ 19,580 per hectare per year and
the value of the goods and services arising from coastal areas and inland wetland ecosystems
combined was approximately 46% of all ecosystems worldwide. It is mainly as a result of appreciating the role and potential value of wetlands that many restoration and conservation
programmes have been initiated.
Being able to place a value on the benefits from a particular wetland often strengthens the
case for conservation and even restoration and makes the need for such actions more apparent to
managers and the public. There is a need therefore to assign values to a wetland before any degradation occurs. It can be particularly difficult to assign monetary values to services such as aesthetic beauty or recreational use and the present lack of scientific understanding of wetlands is
tending to lead to undervaluation of many benefits. However, the role of wetlands in maintaining
fisheries is fairly well understood. As an example, IWWR (2003) argue that approximately 75
per cent of commercially harvested fish and shellfish in the USA are dependent on estuaries and
their associated wetlands. In the year 2000, commercial fisheries were worth US$3.5 billion and
thus any loss of wetlands could result in a substantial economic loss to the fishing industry. In
1996, recreational anglers in the USA spent US$38 billion fishing for species that are dependent
to some degree on wetlands, often for spawning (IWWR, 2003).
3. Climate change and other pressures on wetlands
Wetlands are dynamic ecosystems that would normally adapt slowly to changing environmental
conditions such as precipitation and sea level. Over time many wetlands would undergo a natural succession where some areas would become terrestrial systems, while other new wetland
areas would be created. However, over the last few centuries vast areas of wetland have been lost
as a result of human activities, particularly drainage and reclamation to create agricultural land.
It has been estimated that more than 54 per cent of the original 215 million acres of wetlands in
the USA were lost over the 200 year period 1780s to 1980s (Dahl 1990, cited in IWWR, 2003)
and between 1637 and 1954 an estimated 3,380 km2 of wetland in the UK East Anglian fens was
reduced to about 10 km2 (Wade and Lopez-Gunn, 1999).
Wetlands all over the world are still under threat from a range of human activities and are
being degraded or lost altogether (Moser et al., 1996). Direct threats include draining and filling
for land reclamation and indirect threats include impacts from water regulation activities, such
as groundwater extraction, impoundment of rivers, and coastal development. In addition,
wetlands are vulnerable to invasive species and both point and diffuse sources of pollution.
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Table 1 Principal impacts on wetlands arising from, or compounded by, climate change
Inland wetlands
Coastal wetlands
Changes in wetland plant communities
Invasion or spread of alien species
Tropical wetland floodplains replaced with salt water
habitats and salt tolerant species
Loss of feeding and breeding grounds for fish
and birds
Loss of staging grounds on bird migration routes
Landward intrusion of seawater
Coastal inundation and storm surge flooding
Inland and upstream salinity intrusion
Changes in ecosystem structure
Reduced coastal protection through loss of
coastal wetlands
Source: Ramsar Convention 2002a, based on Gitay et al. 2001 and McLean et al. 2001
It is likely that the vulnerability of wetlands from past and present human activities will be
compounded by the impacts of global climate change. Anticipated changes in rainfall duration
and intensity will affect local hydrological regimes which, in turn, will affect both inland and
coastal wetlands. The timing and duration of inundation with freshwaters may change and saline
regimes may be altered. These, together with future temperature changes, will affect species distributions. Coastal wetlands may also be at additional risk from sea level rise and from the impact of more intense storms and tidal surges. Nicholls et al. (1999) predict that the effects of
sea-level rise combined with other human-related pressures could result in the loss of 70 per cent
of coastal wetlands by the 2080s. The impacts of the combined pressures of climate change and
human activities are likely to vary regionally and even locally (Ramsar Convention, 2002a).
However, on a global scale, the actual impacts of climate change on water resources would probably be rather small in the short term (i.e. less than 20 years) relative to the impacts of other
human activities (Arnell and Chunzen, 2001, cited in Ramsar Convention, 2002a).
The principal effects on inland and coastal wetlands that may be associated with climate
change are summarised in Table 1. Within Europe the likely impacts of climate change will differ
from region to region, with some regions suffering from increased flooding in winter and others
experiencing a greater difference between summer and winter flows. There are also expected to be
differences in water temperature. Where water temperature increases are coupled with decreased
summer flows there could be deterioration in water quality, especially as a result of reduced dissolved oxygen concentrations. This will have impacts on the fauna and flora of wetland systems,
such as a gradual change from salmonid communities to cyprinid and percid communities in the
north and west of Europe. Migratory birds may also be affected by the possible loss, or change in
ecosystem structure, of the isolated inland wetlands of central and southern Europe on which
they depend for food during their migration (Ramsar Convention 2002a).
European coastal deltas, estuaries and salt marshes are likely to be threatened by sea level
rise, particularly in the Mediterranean, Black and Baltic seas where the tidal range is low (< 1 m).
The intensive development along much of these coast lines has reduced the capacity of wetlands
to adapt naturally to any changes (Ramsar Convention, 2002a). Evidence also exists for changes
in the distribution of estuarine birds in the UK as a result of changing patterns of minimum
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temperatures along the coasts (Austin and Rehfisch, 2005). There are approximately 3,000 km2
of salt marshes and more than 6,500 km2 of other unvegetated intertidal habitat within Europe,
much of which has been designated under the Ramsar Convention. The loss of these habitats, together with mangrove swamps, has been estimated to reach 31–100 per cent for the Mediterranean, 84–90 per cent for the Baltic and 0–17 per cent for the Atlantic coasts (Ramsar Convention,
2002a). The associated loss of habitats and feeding areas could have significant impacts on fish,
wildlife and birds.
4. Conservation and restoration
Whether as a result of human activities or climate change, impacts on wetlands need to be
reduced and preferably prevented. In some cases it may be possible to restore degraded wetlands
to a condition that closely resembles the previous habitat. All such activities require financial
and human resources, as well as the participation and involvement of local communities and
stakeholders.
Conservation is the long-term preservation and protection of the functions and values of
wetlands and should involve a combination of activities, including legislation, development of
wetland policy, agreements and treaties, stakeholder and landowner involvement and volunteer
projects (Canadian Wildlife Service, 2002). Designation of reserves and protected areas form an
important part of conservation activities. An example of a wetland conservation plan is Lake
Engure in Latvia, where the lakeshore meadow vegetation was being taken over by willows and
reeds and damaged by other human activities. The undesirable vegetation succession in this
Ramsar site is being controlled by regular cutting of the reeds and grazing the meadow with traditional domestic herbivores such as horses and cattle. Undesirable economic activities are also
being prohibited in the area (Raèinska, 2004). Approaches to conservation of coastal wetlands
could involve removing sea defences so that wetland habitats re-establish themselves naturally
landwards to replace areas lost through sea-level rise.
Restoration is the process of returning a degraded wetland (rehabilitation) or former wetland (re-establishment) to its pre-existing condition, or as close to that condition as possible.
Restoration often involves activities such as construction work and re-planting in order to restore the hydrological regimes and biological communities. Knowledge of the hydrological
regime is often lacking or poorly understood. For a restoration project to succeed it must consider (Canadian Wildlife Service, 2002):
+
The position of the wetland in its watershed,
+
Natural sources of seed in the area that will allow recolonisation,
+
The hydrological connection between the wetland and its surrounding water table,
+
The wetland sediment, and
+
The water level fluctuations that may be required to support the new wetland vegetation.
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Table 2 Examples of possible restoration activities for different wetland problems
Problem
Cause
Restoration action
Poor water quality
Nutrient/sediment run-off,
sediment erosion
Change land-use practices, install vegetation
buffers/sediment traps
Altered hydrology due
to drainage
Presence of ditches and
drains, embankment cutting
off wetland from water source
Fill ditches, remove embankment, install
gates/weirs
Raised elevation
Dumping or in-fill
Remove surplus material
Subsidence
Removal of soil, depletion
of groundwater
Allow natural sedimentation, add sediment
Loss of biodiversity
Change in habitat
Planting of native species, allow species to
recolonise
Loss of native plants
Change in hydrology, change
in land use, invasive species
Restore hydrological regime, remove invasive
species and alter conditions that favour them
Source: IWWR (2003)
In addition to considering the environmental benefits of any restoration project, the technical
and economic feasibility needs to be considered carefully and the relevant stakeholders should
be consulted.
There are two approaches to restoration: passive and active. Passive restoration fundamentally involves removing the cause of degradation and allowing the wetland to regenerate
naturally. This approach is only likely to work if there are other water and wetland species
nearby that will gradually colonise the area being restored. The approach is low cost and the final
outcome is a wetland that is likely to resemble the surrounding environment. By contrast, active
restoration usually involves considerable design work and the building of structures such as
weirs and culverts and intensive planting with native species, combined with substrate creation
and control of invasive species (IWWR, 2003). Such methods can be expensive and labour intensive. Examples of methods suitable for different wetland problems are given in Table 2 and
further information is available in the many guidebooks available detailing methods and approaches to conservation and restoration in different wetland habitats (Payne, 1992;
Galatowitsch and van der Valk, 1994; USEPA 1994, 2000; Zedler, 2000).
If active restoration is likely to involve engineering work, it is recommended that bioengineering or “soft” engineering solutions should be used rather than the traditional “hard” engineering approaches that replace natural ecosystem functions with designed and constructed
structures (IWWR, 2003). Bioengineering is more natural and is often more economical. Examples of soft engineering solutions to stream bank erosion are (IWWR, 2003):
+
Planting native species, such as willows that are fast growing.
+
Using logs to stabilise banks. The logs decompose over time.
+
Using geotextile materials to stabilise banks. These materials can be covered in soil and
roots can penetrate through them.
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Table 3 Examples of qualitative and quantitative monitoring techniques for wetlands
Qualitative techniques
Quantitative techniques
Aerial photographs of extent of plant cover,
channelisation, etc.
Ground-level photographs of water levels, plant
communities, etc.
Field observations, e.g. bird species, presence of
invasive plants, erosion, evidence of grazing or
human use
Water level using a gauge
Water quality measurements, e.g. nutrients, salinity
Surface elevations at fixed transects
Plant species and cover over random quadrats or
transects
Diversity and abundance of wildlife using random
trapping for vertebrates and invertebrates
Source: Based on IWWR (2003)
Conservation or restoration activities can be expensive and may involve the co-operation
of many groups of stakeholders. Therefore an important prerequisite to any potential project is
an evaluation of the importance of the wetland and of the various benefits and goods that it supplies. This can be achieved through an assessment of the existing extent and condition of the
wetland combined with a valuation of its anticipated environmental benefits (Canadian Wildlife
Service, 2001). The key questions to be asked as part of an assessment of the feasibility and potential usefulness of any restoration project are (Ramsar Convention, 2002b):
+
Will there be environmental benefits (e.g. improved water quantity, reduced
eutrophication, biodiversity conservation, flood control)?
+
What is the cost effectiveness of the proposed rehabilitation?
+
What options, advantages or disadvantages will the restored area provide for local
people and the region?
+
What is the present and possible future ecological status of the project?
+
What is the status of the area in terms of present land use?
+
What are the main socio-economic constraints?
+
What are the main technical constraints?
Assessment of the extent and current status of any wetland prior to commencing a restora-
tion project involves surveying and monitoring techniques, which may be either qualitative or
quantitative (see Table 3). Typically assessment would include determination of: hydrological
regime, topography and evidence of erosion, vegetation patterns, use by wildlife especially
birds, structural developments and adjacent land use. An important aspect of the implementation
of any restoration project is the continuation of monitoring and assessment activities in order to
determine whether actions are achieving the desired objectives. Monitoring should be based on
careful selection of appropriate indicators that are related to the specific objectives of the restoration project over relevant spatial or temporal scales, such as changes in breeding bird populations, changes in areal extent of specific plant species or communities, species diversity, water
quality and sediment accretion or erosion. For example, if the objective is to improve the habitat
Conservation, restoration and effects of climate change on wetlands
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Box 1 Example of restoration project objectives, targets and associated monitoring:
Stevens Creek Tidal Marsh, California
Goal:
Restore deep pit with ponds to salt marsh in order to provide vegetated tidal marsh habitat
for rare species
Objectives:
+
Restore natural tidal influence
+
Return mudflat to appropriate level for vegetation
+
Re-establish native tidal salt marsh vegetation
Targets:
+
Re-establish tidal influence
+
Develop mudflat on 50 percent of the site within three years, at an elevation available to
vegetation
+
Restore native salt marsh vegetation on 50 per cent of the site within five years
Monitoring and assessment:
+
Automatic tide gauge measurement, interpreted by a hydrologist
+
Annual quantitative measurements of mudflat elevation by a qualified surveyor
+
Annual vegetation survey along transects on the ground together with aerial photographs interpreted by an ecologist
+
Annual aerial photographs of channel formation, interpreted by a hydrologist
+
Qualitative observations on tidal flow and the presence of non-native species
Source: IWWR (2003)
for migratory waterfowl, monitoring should include bird counts, nest sites and the number of
juveniles of key species. Success of the project can be measured against a performance standard
or target, such as a specified number of breeding pairs of key species that are expected to use the
site once restoration is complete. An example of a restoration project with objectives and monitoring programme outline is given in Box 1. A detailed framework for creating inventories, monitoring and assessing wetlands has been produced by the Ramsar Convention (Ramsar
Convention Secretariat, 2007).
5. Conclusions
Wetlands are being degraded and destroyed by many human activities, despite providing a wide
range of important and valuable goods and services. The economic value of these habitats has
only recently been appreciated and has highlighted the necessity of conserving and restoring
them. The impacts of climate change, specifically the changes in hydrological regimes, that are
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expected to arise from increased rainfall and sea-level rise, may contribute to the degradation
and loss of wetlands in some world regions. Conservation and restoration projects are necessary
to preserve these valuable habitats but they require financial and technical resources, as well as
stakeholder and community participation. With careful planning and implementation, followed
by monitoring and assessment, restoration projects can be extremely successful and can lead to
increased social and economic benefits for local communities.
6. References
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Canadian Wildlife Service 2001 Putting a Economic Value on Wetlands – Concepts, Methods and
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Canada, 12 pp.
Canadian Wildlife Service 2002 Great Lakes Coastal Wetlands – Science and Conservation.
Great Lakes Fact Sheet. Minister of Public Works and Government Services Canada, 12 pp.
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