Geoscience Reference
In-Depth Information
Although the HZ was not widely recognized
as a distinct habitat in its own right by many
researchers in the UK before 1990, there is a
relatively rich source of data on the biota of
the HZ in the form of historic biological records
collected by the Cave Research Group of Great
Britain and subsequently by the British Cave
Research Association 1938-1976 (Proudlove
et al
.,
2003). Fortuitously, the biological recorder and
team of collectors did not confine themselves to
caves and as a result accumulated an extensive
record of organisms from the HZ, including more
than 125 river sites where
Niphargus aquilex
was
known to occur. These historical records have
recently been compiled and mapped providing
the first comprehensive overview of hyporheic
and hypogean biodiversity and the presumed
geographical distribution of subterranean fauna in
the UK (Proudlove
et al
., 2003; Robertson
et al
.,
2009).
Many of the earliest records of fauna from
the HZ and other groundwater-dominated habitats
in the UK were collected from alluvial deposits
associated with chalk streams, springs and wells
within the chalk of Hampshire and Dorset. This
region has the highest biodiversity of hypogean
macroinvertebrate fauna recorded in the UK thus
far, but it also represents the region of greatest
sampling intensity. Two sites in particular are
notable for their historic hypogean biodiversity,
first the 'old town well' in Ringwood (Hampshire)
and second, the Waterston cress beds (Dorset). Five
macroinvertebrate taxa (Amphipoda:
Niphargus
aquilex
,
N. fontanus
,
N. kochianus kochianus
and
Crangonyx subterraneus
; Isopoda
: Proasellus cavaticus
)
and one copepod (
Acanthocyclops sensitivus
)were
recorded historically from Ringwood, although the
well does not exist today (Proudlove
et al
., 2003),
and five hyporheic macroinvertebrate taxa were
recorded from Waterston during a 5-year study
(1969-1974) examining the temporal variability in
the occurrence of hypogean taxa. The research on
the Waterston cress beds represents the only long-
term study of hyporheic faunal dynamics in the UK
to date and clearly demonstrates the strong link
between groundwater flow and the abundance of
obligate hypogean fauna (Gledhill, 1977).
A number of studies were carried out before
1990 examining meiofaunal groups (organisms
passing through a 1 mm mesh sieve but retained
on a 63
m sieve) recorded from the HZ,
including Ostracoda (Fox, 1964, 1967), Cladocera
(Fryer, 1993), Syncarida (Gledhill
et al
., 1993)
(Table 13.1) and water mites (Acari: Hydrachnidia
and Halacaridae) (Gledhill, 1979; Table 13.2).
This significant recording effort showed that the
biodiversity of the HZ and other hypogean habitats
was lower than in mainland Europe and appeared
to reflect the glacial history and hydrogeology of
the site. Sites in the south of the UK in karstic
rocks (chalk and limestone) generally support a
greater biodiversity of HZ and hypogean taxa than
those that are further north of the Devensian glacial
maxima and in non-karstic rocks. However, despite
this extensive period of sampling, few UK scientists
recognized or referred directly to the HZ and
there was limited acknowledgement of its wider
functioning. This historic sampling also left many
large 'holes' in the known geographical distribution
of organisms of the UK and, as a result, biodiversity
assessments of the HZ were incomplete.
The UK science and policy
context (1990-2010)
During the 1990s the importance of the dynamic
nature of interactions between surface water
and groundwater within the HZ began to be
acknowledged in the UK while its contribution to
the wider physical and ecological functioning of
river systems was gaining international recognition
(Stanford and Ward, 1993; Gibert
et al
., 1994).
As a result there was an international shift in
emphasis away from specific hypogean habitats
(caves, springs or HZ) and their unique fauna
and environmental characteristics towards stream
processes and organisms of varying sizes (spawning
fish through to meiofauna) that can use, or
migrate between, individual habitat units both
vertically and laterally (Gibert
et al
., 1994). This
also led to a growing appreciation of the need
for inter-disciplinary research at the interface of
hydrology, geomorphology and ecology for the
