Geoscience Reference
In-Depth Information
make a significant contribution to species richness,
biomass, abundance and productivity (Reiss and
Schmid-Arraya, 2008).
works affecting river beds), flow regulation
(including abstraction), nutrient enrichment (with
consequential effects on algal growth) and siltation
(leading to clogging of substrates and reductions in
oxygen concentration).
Not only has the monitoring and management
of hyporheic zones been neglected, but their
evaluation and protection for nature conservation
has not yet been attempted explicitly. The
Wildlife and Countryside Act 1981 (which applies
to England, Wales and Scotland) requires the
designation of Sites of Special Scientific Interest
(SSSIs) (Boon, 1991); similar legislation applies in
Northern Ireland. These sites are selected using
published guidelines (JNCC, 1995) which draw
on the principles set out in
A Nature Conservation
Review
(NCR) (Ratcliffe, 1977). The NCR was
the first comprehensive attempt in Britain to
produce an evaluation of nationally important
nature conservation areas using criteria such
as representativeness, naturalness, diversity and
rarity. These criteria have achieved a broad level of
acceptance, and they have continued to influence
conservation evaluations, including those of rivers
(Boon
et al
., 1997; Boon and Freeman, 2009).
However, the NCR contained just three short
paragraphs on 'subterranean rivers and streams',
mainly with reference to underground waters and
the invertebrates in caves; only one sentence might
be taken to include hyporheic zones: 'Subterranean
water also exists in the interstices of gravel and
in fissures in chalk and limestone where a highly
specialised microflora and fauna is found' (Ratcliffe,
1977). In the 34 years since the NCR was published
no evaluations of rivers for conservation have
mentioned specifically hyporheic zones and their
communities. The Geological Conservation Review
has a volume devoted to karst features (Waltham
et al
., 1997) listing almost 100 important cave sites
(mainly in England and Wales) most of which have
been designated as SSSIs. However, these have
been selected for their geological rather than their
biological interest.
The European Habitats Directive (Council of
the European Communities, 1992) also lacks
any reference to hyporheic habitats, although
Annex I, which lists threatened habitats requiring
Management and conservation
Although hyporheic zones play an important
role in the functioning of river systems, the
environment agencies in the UK do not include
these areas in routine survey, monitoring or
management. Monitoring water chemistry is
carried out mainly on the water flowing within
river channels, while most biological monitoring
covers only benthic macroinvertebrates living
on the river bed. The EC Water Framework
Directive (WFD) has encouraged an expansion
of monitoring taxonomically (to include fish,
macrophytes and diatoms) but not spatially, so
it is still an activity directed predominantly at
the river channel and the bed surface. The WFD
does include a requirement to assess the status of
groundwater bodies, but this only covers chemistry
and microbiology (Arnscheidt
et al
., 2009). The
European Groundwater Directive (Council of the
European Communities, 2006) deals specifically
with subterranean waters; however, the Directive
is aimed at preventing groundwater pollution
(e.g. from pesticides) and does not have an
ecological component, although the introduction
does refer to the need for further research into
groundwater ecosystems (Knight and Penk, 2010).
Thus, at present the classification of ecological
status of rivers in the UK does not take account
of the vertical dimension (downwards into the
hyporheic) or the lateral dimension (outwards into
the floodplain) even though the importance of
these is well known (Ward, 1989).
The lack of routine monitoring of hyporheic
zones means that environmental impacts in those
areas may not be adequately recorded or managed.
In general, threats to hyporheic habitats are
those that apply to rivers as a whole, but some
are more important than others because they
directly affect sediments or the movement and
quality
of
water
within
them.
These
include
gravel
extraction,
river
engineering
(especially