3. THE
IMPORTANCE AND
VALUE OF
COASTAL HABITATS
AND WETLANDS
3.1 The relevance of flood and coastal defence
to nature conservation can only be understood if the significance
of the coastal and wetland habitats that are affected is fully
appreciated.
3.2 Both tidal and fluvial wetland habitats
play an exceptionally important role in the maintenance of biodiversity.
The ecological work that these habitats do is, however, not only
important for maintaining wildlife. There are enormous socio-economic
benefits associated with these ecosystems. Their natural productivity
is an important source of food for commercial species; they dissipate
energy and control the magnitude of natural events; they maintain
the quality of the environment by absorbing and processing pollutants;
they provide bases for human communities; and they provide beautiful
landscapes which attract people and form the foundation of important
recreational and tourist economies.
3.3 The value of these functions to society
is very real. A recent study of the value of the world's ecosystem
services and natural capital compared the "value" of
different major ecosystems to society at large (Costanza et
al, 1997). While The Wildlife Trusts and WWF-UK question the
validity of attempting to attach monetary figures to non-market
values, the comparative results of this study are revealing. Figure
1 (see page 118), based on Costanza et al (1997), shows
the comparative values of major ecosystems on a global basis.
The ecosystems that are most adversely affected by current practices
and a legacy of unsustainable flood and coastal defence are shown
in black. Notwithstanding reservation about the attachment of
monetary values, it is clear to see that flood and coastal defence
directly impact on many of the highly valuable ecosystems.
3.4 The biological productivity of tidal
and freshwater wetlands is the foundation of much of their value.
It is rarely appreciated that these systems, even apparently bare
mud-flats, are highly productive. Figure 2 (page 119) shows the
comparative mean primary productivity of a number of ecosystems
with those systems that are most affected by flood and coastal
defences blocked in black.
3.5 The comparative significance of coastal
habitats and wetlands is immediately apparent. These habitats
are the biological engines that fuel the ecology and biodiversity
of so much of the naural and human world. The significance of
such habitats, in ecological terms, stretches far beyond their
boundaries. Migrating species of fish and birds, which may range
over thousands of miles, for example, depend on such places on
a seasonal basis or for key phases in their lifecycles.
3.6 These same coastal and fluvial wetland
habitats are also very effective sinks for both marine and river-borne
pollutants that would otherwise adversely affect the environment.
Accreting intertidal areas and healthy wetlands lock up and process
pollutants, thus buffering the wider environment. They are effective
carbon sinks that play an important role in the flux of CO2. It
has, for example, been estimated that reclamation of intertidal
areas in the Humber region alone has reduced the capacity of the
system to absorb 4.5 million tonnes of carbon per year. Vegetative
buffers in the coastal zone have been shown to be most effective
in removing pollutants. Desbonnet et al (1994) showed that
a 200 metre vegetative buffer in the coastal zone would remove
more than 90 per cent of total suspended solids, nitrogen and
phosphorus. Vegetative buffers are also effective processors of
hydrocarbons, PCBs, most metals and pesticides (Desbonnet et
al, 1995). Flood and coastal defence directly and indirectly
affect these vegetation buffers.
3.7 While these considerations are clearly
material to any integrated and sustainable flood management strategy,
the fact that coastal habitats and wetland actually reduce the
risks and probabilities of flooding by dissipating wave energy
and absorbing exceptionally high river flows has not escaped the
notice of water resources managers. The natural capacity of functional
flood plans to store and reduce the magnitude of downstream water
levels is also important. Meaningful monetary values can be placed
on some of these functions. For example, evidence from the National
Rivers Authority (now the Environment Agency) indicates that where
there is an 80 metre width of salt-marsh in front of a sea wall,
the necessary height of the wall is 3 metres and the cost is £400,000
per kilometre. Whereas, when there is no salt-marsh, a 12 metre
high wall is required to meet the same standard of defence and
the cost of providing that defence is £5,000,000 per kilometre—more
than 10 times the cost (NRA, 1995).
3.8 Wetland and coastal habitats are not
only exceedingly important wildlife habitats, they are also the
basis of local communities and are functionally very important
in the wider context. They help maintain the quality of the environment
and buffer both the land and the sea from the effects of natural
events such as floods and storms. The recreational and aesthetic
values of these habitats are also important. Their conservation
and restoration is a matter of practical significance, rather
than sentimental feeling.
4. THE
IMPACTS ON
NATURE CONSERVATION
4.1 Land drainage and land-claim have been
synonymous with wetland destruction. Most of our great wetlands
have been lost with appalling consequences for wildlife and a
concomitant loss of all the functions outlined above. Coastal
protection has sought, but largely failed, to control rather than
work with the forces of nature. The consequence has been protection
for some at the expense of undermining the ability of the coast
to adjust and maintain its own natural defences and ecological
functions. Important sediment sources have been locked up, for
example, by coast protection causing an increase in the rate of
erosion elsewhere. The reduction of sediment supply can also affect
the capacity of intertidal areas to maintain their levels and
extent as sea level rises. It has been estimated that sediment
inputs to the coastal environment may have declined by as much
as 50 per cent over the last 100 years due to cliff protection
works (Rendal Geotechnics 1998)[1].
4.2 Where the high tide mark has been fixed
or advanced by engineering works, the ability of intertidal areas
to adjust to rising sea levels has been damaged. Therefore, not
only have important habitats been lost directly as a result of
land claim, the sustainability of the remaining habitat has also
been impaired. This process, known as coastal squeeze, has far-reaching
cost implications for flood defence as the habitats' ability to
dissipate wave energy is seriously diminished. It is estimated
that 12,750 hectares of intertidal flats and marshes will be lost
in England alone as a result of the failure of intertidal areas
to adjust to sea level rise in the 20 years to 2013 (Pye &
French, 1993). Many of these areas are designated European sites[2],
which the UK has an international obligation to conserve. Coastal
habitats, such as sand-dunes and shingle ridges, have been fixed
or over-stabilised in coastal defence schemes, with serious adverse
impacts on their conservation interest and sustainability. A substantial
proportion of the active cliff resources has been stabilised by
engineering works. While land claim has slowed[3]
in recent years, these activities continue. A MAFF survey in 1994
identified more than 90 km of new cliff protection works likely
in the next 10 years, resulting in a potential loss of 36 per
cent of the remaining soft cliff resource.
4.3 Fens, peatlands and wet grasslands have
suffered the effects of drainage both directly, as a result of
reducing the water levels, and indirectly a result of ploughing
and stripping which drainage allows. Between 1947 and 1982 43
per cent of the country's freshwater marsh was destroyed. In the
East Anglian fens less than 1 per cent (EN, 1997) of the resource
remains. Reductions of ecologically valuable coastal and floodplain
marsh in the UK have been substantial. Outright losses from the
early 1930s to the mid-1980s include 64 per cent in the Greater
Thames, 48 per cent in Romney Marshes and 37 per cent in Broadland
(Cm2428 HMSO, 1995). Vast areas of tidal salt and brackish marshes
have been embanked, drained and converted to intensive agriculture.
4.4 Previous forms of anthropogenic exploitation
such as fisheries and wildfowling had depended on maintaining
the extent and quality of wetlands. In intertidal areas land claim
has had a disproportionately large impact on the upper part of
the shore which is the most biologically diverse. Upper salt-marsh
is now very scarce and in many places completely absent. Some
of the plants and animals that depend on these habitats are now
seriously threatened. Ninety-four per cent of lowland raised peatbog
has been destroyed or damaged.
4.5 As with coastal habitiats and tidal
wetlands, flood defence has had serious adverse impact on the
capacity of river systems to adjust and adapt. "In their
natural state, rivers are dynamic systems, continually modifying
their form. However, in many cases their ability to rejuvenate
and create new habitiats has been reduced or arrested by flood
defence structures and impoundments. Few rivers in the UK have
not been physically modified by man . . . Erosion of banks has
also been caused by canalisation. Such activities have resulted
in changes in the frequency and magnitude of flooding, altering
seasonal patterns of flow and hydrograph form. In addition, flow
regulation has altered the patterns of sediment exchange in river
systems." (Cm2428). The important point in this quotation
from the UK Biodiversity Steering Group Report is the acknowledgement
that flood defence works have not only led to habitat loss but
they have undermined the ability of the system to sustain itself.
The implications being that ever-greater sums of money need to
be spent on providing fundamentally unsustainable flood defences.
Results of the Environment Agency's River Habitat Survey (EA1998)
showed that less than 10 per cent of sampled river lengths on
4,500 sites in England and Wales were free from structural modification
of channel and banks.
1 More than 1,000 kilometres of active soft cliffs
in 1900 only 200 km remain unaffected by coast protection works. Back
2
Natura 2000 sites; ie Special Protection Areas or Special Areas
of Conservation. Back
3
But by no means stopped; English Nature projects 650 ha of loss
to land claim in the 20 years from 1992. Back
