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human impacts have affected natural processes
over large spatial scales, palaeoenvironmental
and palaeoecological approaches may provide a
valuable insight into past instream conditions and
a direct comparison with contemporary channel
hydromorphology and the associated instream
community (Brown, 2002; Greenwood and Smith,
2005). Historic palaeoecological studies centred on
rivers, such as the Rhine, have demonstrated that
sub-fossilized insect remains (material that has not
been fossilized/mineralized owing to lack of time
or inappropriate conditions) within abandoned
palaeochannel sediments can be used successfully
to characterize the 'original/natural habitats' of the
River Rhine (Klink, 1989). Detailed examination
of the sub-fossilized aquatic insect community
and contemporary river fauna clearly indentified
the increasing impact of thermal pollution and
changes in nutrient status and increasing sediment
accumulation rates.
This chapter explores the potential use
of palaeoenvironmental and palaeoecologial
techniques in developing the concept of the
'reference condition' for river ecosystems.
It describes a range of biological proxies
available within riverine sediments to assess
palaeoenvironmental/ecological conditions and
outlines a method for examining the contemporary
channel, instream ecology and historic archival
data (maps and land drainage records). The
approach is illustrated with reference to a pilot
study undertaken on the River Eye (Leicestershire),
and shows how palaeochannel sediments may be
used to inform the conservation, management and
future restoration of lowland rivers in the UK.
Figure 17.1 Idealized representation of channel change
(straightening) typically identified from examination of
historic maps or aerial photographs between historic
surveys of the river.
channel management or realignment activities
(Plate 21). Once abandoned, the cut-off channel
may be subject to natural sedimentation processes,
although this may be punctuated by periodic
reactivation of flow during spates (Brown, 1997;
Howard et al ., 2009).
Many rivers have been modified extensively
for centuries for a variety of purposes, although
some of the most significant modification of
rivers in Europe took place during the industrial
revolution (1760-1850) and in the UK during
the decades following World War II (post-1945),
in a drive to increase food security through
improved land drainage and associated flood
management (Mainstone, 2008). Historic river
channelization, involving straightening, deepening,
widening and re-profiling resulted in greatly
reduced habitat heterogeneity and significant,
although largely unquantified, changes in riverine
and floodplain biodiversity (Davis et al ., 2007).
A better understanding of the geomorphological,
hydrological and biodiversity elements that have
been compromised or lost is required in order
to characterize the benefits of planned measures
to restore and reinstate channel form and
function (Newson and Large, 2006). To generate
this
Reference conditions
The need to identify ecological reference conditions
in freshwater ecosystems has occurred as a
result of legislation such as the European Union
Water Framework Directive (WFD; Council of
the European Communities, 2000) and the
United States Environmental Protection Agency
guidelines (USEPA, 2006). Historically, reference
conditions for river restoration have been based
primarily
understanding
in
an
environment
where
on
routine
physical
and
biological
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