Geoscience Reference
In-Depth Information
Some of the problems associated with river
engineering may have been inadvertent because
little if anything was known about the presence of
rare and endangered species such as pearl mussels
beforehand. In theory, heightened awareness, full
legal protection, control over physical alteration
of river channels and good information on the
distribution and presence of pearl mussels means
that such damage is now preventable. Indeed,
specific online guidance for river managers working
in and around Scottish pearl mussel rivers is
now provided by SNH. Such adaptive management
responses should be carefully informed so as not
to compromise pearl mussel conservation. Flood
management/prevention should be carried out at
the catchment scale and use sustainable, natural
management techniques that seek to work with the
river's natural processes by maximizing ecosystem
services such as floodplain storage that will allow
adequate flood protection and accommodate pearl
mussels.
One of the main opportunities to prevent or
reduce the severity of climate change effects
on pearl mussels is the restoration of riparian
and catchment woodland. The roots of native
broadleaved trees help to reduce erosion and
stabilize edge habitats (Parrot and MacKenzie,
2000) and research has shown a positive
correlation between pearl mussel beds and
tree cover (Baer, 1981; Hastie
et al
., 2003b). It is
believed pearl mussels (and their host fish) benefit
through the shading of watercourses, reducing
the extremes of hydrothermal fluctuations and
preventing excessive algal growth which can
smother the river bed. Woodlands (as well as
catchment lakes) can dramatically 'dampen down'
or ameliorate the effects of flood and spate
events, by accumulating and releasing water over
greater lengths of time than denuded or treeless
catchments where runoff is greater and faster.
The use of dappled shade is important because
neither freshwater pearl mussels nor their host fish
benefit from dark, tunnelled shade. The mussels
need enough light to be able to gape sufficiently
and filter effectively and this ability is lost in deep
shade. Therefore, native tree planting needs to be
carefully planned and managed on a long-term
basis. This will not only benefit the downstream
aquatic communities but also human settlements
through reductions in the severity of flooding.
Today, woodland cover in Scotland is currently at
a tiny fraction of what it was previously (Parrot and
MacKenzie, 2000; Smout
et al
., 2007) and many
pearl mussel populations occur in catchments
denuded of native woodland cover. Consequently,
carefully targeted (riparian) woodland restoration
schemes within pearl mussel catchments probably
offer the best chance for river managers to mitigate
against the worse climate change scenarios.
The UK forestry service has produced detailed
guidance, with specific focus on conserving and
enhancing aquatic species, for managers both when
replanting and managing existing forestry (Forestry
Commission, 2003). These
Forests & Water Guidelines
advise owners and managers how woodlands and
forests influence freshwater ecosystems. They give
guidance to managers on how forests should
be designed and operations planned, and to
practitioners on how field operations should be
carried out in order to protect and enhance the
water environment.
Mitigation
Just as there is political pressure to adapt
and manage rivers to prevent flooding, there
is societal pressure (e.g. Kyoto Protocol treaty
to the United Nations Framework Convention
on Climate Change) to prevent the worst-case
climate change scenarios from occurring in the
first place by developing preventative schemes such
as windfarms, tidal barrages and hydro-electric
schemes, which reduce emissions of climate change
gases. During the past two decades, under the
Scottish Renewables Obligations, Scotland has seen
a huge expansion in applications for windfarms
and hydro-electric schemes and these must be
developed carefully so as not to compromise pearl
mussel conservation. If not, they can destroy
instream habitats and adversely affect pearl mussels
by producing short-term near-flood and near-
drought conditions, which are incompatible with
maintaining pearl mussel populations (Cosgrove
and Hastie 2001; Hastie
et al.,
2003a). According
to Ziuganov
et al
. (1994), a number of freshwater
