Geoscience Reference
In-Depth Information
of the European Communities, 2000) shows
that all is not well. For example, as a result of
pressures such as diffuse pollution, abstraction
and river engineering, 46% of rivers in Scotland
(http://www.sepa.org.uk/water/monitoring and
classification.aspx), 74% in England and Wales
(http://www.euwfd.com/02-SH091002 EA WFD
Update.pdf), and 75% in Northern Ireland
(http://www.doeni.gov.uk/niea/water-facts-book
let-2011.pdf) are currently at risk of failing to meet
the Directive's target of reaching 'good ecological
status' or better by December 2015. At a global
scale, V or osmarty
et al
. (2010) concluded that
65% of river discharge and the aquatic habitat
it supports are under moderate to high threat,
but that far less investment has been directed at
biodiversity conservation than to human water
security. In general, the pressures affecting rivers
in 1990 (Boon, 1992) are very similar to those
affecting rivers today (Table 1.3). Nevertheless,
there are some differences in emphasis and one
notable addition.
In 1990, there were 14 280 large dams
registered worldwide (International Institute
for Environment and Development and World
Resources Institute, 1987; Boon 1992). The
Worldwide Fund for Nature (WWF) reports that
the number has now increased to 48 000, about
half of which are in China, with a storage capacity
of about 6000 km
3
(http://wwf.panda.org/what we
do/footprint/water/dams initiative/quick facts/.).
Dam construction is no longer centred principally
in North America or in Europe but in countries
such as Iran and parts of Asia. With the growing
demand for water, both the numbers of dams and
their density on river networks have increased
substantially over the past 20 years. So has their
size, advances in engineering technology having
made possible dam projects on a previously
unimaginable scale, such as the Three Gorges Dam
in China (Plate 2).
Two specific human impacts on river systems
deserve particular mention:
have been substantial increases both in the number
of alien species recorded and the extent of their
invasions, as well as a greater awareness of the
damage that they cause. In the UK, some of
the most serious threats to rivers from invasive
alien species are from North American signal
crayfish (
Pacifastacus leniusculus
) (Crawford
et al
.,
2006) and from bankside species such as Japanese
knotweed (
Fallopia japonica
)and
Rhododendron
ponticum
(Hladyz
et al
., 2011). The management
response to these threats has been encouraging,
and marks a positive step in the right direction
over the past 20 years. In the UK, for example,
there are practical measures in place at a local and
regional scale to deal with invasive species, as well
as strategic planning at a national level. A recent
invasion shows that the importance of reacting
quickly is now recognized by government bodies
and others. In September 2010
Dikerogammarus
villosus
('killer shrimp') (Plate 3) was recorded for
the first time in the UK at a public water supply
reservoir in eastern England (Grafham Water,
Cambridgeshire) (http://www.environment-age
ncy.gov.uk/news/123209.aspx?page
=
8&month
=
9&year
=
2010). The shrimp is native to the Ponto-
Caspian region and spread across Europe following
the opening of the Danube-Main-Rhine canal in
1992. It is known to be a voracious predator on
other invertebrates and young fish and is a serious
threat to ecological integrity. The Environment
Agency responded immediately, and with the
water supply company, fishing organizations,
boating clubs and others quickly worked together
to put in place practical 'biosecurity' measures to
prevent further spread of the organism.
In Great Britain a strategy for tackling non-
native invasive species has been published (Defra,
2008) and a management structure set up to put
it into practice (https://secure.fera.defra.gov.uk/
nonnativespecies/home/index.cfm). Part of the
process involves carrying out detailed risk
assessments of alien invasive species. This is
undertaken by species experts and is based on
scientific evidence, so that the results can be used
to decide what action (e.g. eradication, control,
mitigation) to take in each situation. Many of the
risk assessments completed so far are for aquatic
Invasive alien species
The introduction of invasive alien species is not
a new phenomenon. Since 1990, however, there
