Geoscience Reference
In-Depth Information
Chironomidae
Chironomids (non-biting midges) have been
widely used in the study of palaeoenvironments
to assess the trophic status of lakes (Langdon
et al
., 2006). Since the early 1990s the sub-
fossil chitinous head capsules have been used
as indicators of palaeo-temperature, dissolved
oxygen, pH, salinity and wider palaeo-climate
characteristics (Brooks, 2006). The sub-fossilized
head capsule remains of chironomid larvae have
received considerable attention in lakes; although
they were initially overlooked and ignored in
rivers because of the assumption that larval head
capsules were not well preserved and/or present
in very low abundances (Elias, 1994). However,
this assumption has recently been challenged by
Gandouin
et al.
(2005) and Howard (2007) who
reported that chironomid remains are typically
more abundant than those of either Coleoptera
or Trichoptera. Both Gandouin
et al.
(2005) and
Howard
et al
. (2010) have successfully linked
palaeochannel chironomid assemblages with
channel evolution, and instream habitat and flow
variability.
been greatly enhanced through the use of
multiple indicator groups/organisms (a multi-
proxy approach). Individual proxies, such as
Trichoptera or Coleoptera, may be sensitive to
specific environmental factors such as temperature,
pH or stream flow velocity. Each proxy provides
a record of variability which, when combined,
may facilitate the identification of common/
contemporaneous trends across different faunal
groups that may be overlooked or obscured if
examined independently. For example, Trichoptera
remains are typically more abundant in the fossil
record when the channel was flowing actively
and Coleoptera usually occur more frequently
under lentic conditions, with the exception of
Elmidae(r fflebee les).Asaresu tthesetwo
proxies can be used effectively to indicate the
timing of channel cut-off or oxbow lake formation
(Figure 17.2). If the floral or faunal remains from
the palaeochannel sediments can be identified
to an appropriate taxonomic level, knowledge
regarding the preferences for individual species
that influence the distribution and abundance can
aid interpretation and allow an environmental
reconstruction of the past riverine conditions to be
made.
Gastropoda
Gastropod shells are preserved in a wide range of
sediments where there is a sufficient amount of
calcium carbonate. Non-marine molluscs are one
of the most common groups of macrofossils to
be found in palaeo-deposits and dominate fossil
assemblages in freshwater tufas (Lozek, 1986).
Larger species have characteristic shells that can
be easily identified in the field, and in general
where gastropods are found they are usually
found in large numbers, providing easy and
accurate analysis (Lozek, 1986). Compared with
insect proxies, fossil gastropod shells are readily
transported and eroded in flowing environments.
However, they can provide a clear indication of
channel isolation/cut-off and the transition from
flowing to standing water conditions.
Case study - River Eye,
Leicestershire, England
Several rivers designated as Sites of Special
Scientific Interest in England have been identified
provisionally as potential candidates for future
restoration (Mainstone, 2007). Following initial
screening, the River Eye (Leicestershire) was
selected for a pilot study of the proposed method
outlined above. The River Eye has been designated
as an exceptional example of a semi-natural
lowland clay stream (Natural England: http://
www.sssi.naturalengland.org.uk/citation/citation
photo/1001178.pdf).
The
River
Eye
rises
at
Bescaby,
approximately
10
km
north
east
of
Multi-proxy analysis
Melton
Mowbray
in
Leicestershire,
later
to
become
the
River
Wreake,
downstream
of
The
potential
accuracy
of
reconstructing
past
Melton
Mowbray.
The
river
flows
for
21
km
riverine
environments
and
communities
has
before
joining
the
River
Soar.
The
geology
of
