Geoscience Reference
In-Depth Information
CHAPTER 17
The Use of Palaeoecological Techniques
to Identify Reference Conditions for
River Conservation Management
Emma L. Seddon
1
,PaulJ.Wood
1
, Chris P. Mainstone
2
, Malcolm T. Greenwood
1
and Lynda C. Howard
1
1
Department of Geography, Loughborough University, UK
2
Natural England, Northminster House, Peterborough, UK
Introduction
and depositional units may vary in extent and
thickness owing to the variation in the magnitude
of sediment transport or depositional events. In
addition, the sedimentary record of past/historic
rivers may be biased by the erosion of pre-
existing deposits (Brown, 2002). River channel
changes may reflect high magnitude floods and in
particular human channel management activities,
including dredging, channel straightening and
widening (Figure 17.1). Owing to the potential
reworking of riverine sediments, obtaining suitable
stratigraphically dated sediment sequences can
be problematic when compared with lakes.
Riverine sedimentary sequence development
may be episodic because of alternating periods of
erosion and deposition (Greenwood
et al.
, 2006).
In addition, owing to channel migration these
sequences typically represent relatively limited
periods of time (
500 years) compared with
lake chronologies. However, when evidence of
short-term changes is required fluvial sediments
provide a rich and diverse archive of aquatic
and terrestrial environmental change (Amoros
et al
., 1987; Greenwood and Smith, 2005). These
records can be extracted from palaeochannels
produced as the river channel migrated across its
floodplain or from deposits isolated as a result of
It is widely recognized that human activities
have resulted in significant changes to the
hydromorphology (flow characteristics and
fluvial geomorphology) and ecology of riverine
ecosystems globally and that to reinstate
morphological diversity, physical river restoration
may be required in many instances (Jansson
et al
., 2007). However, significant questions
remain regarding the ecological 'benefits' resulting
from physical restoration measures on their
own (Harrison
et al
., 2004). Several species of
riverine flora and fauna have been extirpated or
disadvantaged by historic channel modifications
across much of lowland England (Brown, 2002;
Mainstone and Clarke, 2008). In many instances
river restoration (physical and ecological) may
not be possible without direct intervention or
re-establishment of target habitat features and/or
organisms (Jones
et al
., 2009; Thompson and Lake,
2010).
Floodplains are ecologically complex
environments that are frequently subjected
to change from both natural and anthropogenic
forces (Brown, 1997). Some natural river processes,
such as sedimentation and erosion, are episodic
