Geoscience Reference
In-Depth Information
sediments to reconstruct historic flow regimes in
the
in-situ. However, they are not resistant to
erosion and if subject to transportation usually
experience severe degradation and fragmentation
(Williams and Eyles, 1995). Each family and
most species of Trichoptera display distinctive
patterning and arrangement of setal pores on the
frontoclypeal apotome, allowing identification
to species level in many instances (Plate 22).
These factors, when combined with knowledge
of their ecology, provide an accurate means of
reconstructing past environmental conditions
within palaeochannels (Greenwood
et al
., 2003,
2006). This may be particularly valuable in
identifying the timing of channel cut-off or
isolation following anthropogenic diversion, by
observing the change in characteristic fauna of
lotic (e.g.
Hydropsyche contubernalis
) to lentic (e.g.
Phryganea bipunctata
) conditions (Figure 17.2).
River
Trent
catchment
(Greenwood
et al
.,
2006).
Trichoptera larvae
Trichoptera (caddis flies) are associated with
almost all types of water body and are widely
used as environmental indicators (Chessman
et al
., 2006; Greenwood
et al
., 2006). Trichoptera
are comparatively under-used in the field of
palaeohydrology and palaeoecology although
the head capsule (especially the frontoclypeal
apotome) and thoracic plates (from the mesonotum
and pronotum) are well preserved in both river
and lake sediments (Greenwood
et al
., 2003).
Trichopteran head capsules and thoracic plates
are sclerotized and are well preserved if deposited
Trichoptera
Coleoptera
10-0
20-10
30-20
40-30
50-40
60-50
70-60
80-70
90-80
100-90
Transition
110-100
120-110
130-120
140-130
150-140
160-150
170-160
180-170
0 10 0 10 20 30 0 10 20 30 40 50 0 10 0 10 0 10 20 30 0 10 20 30 40 0 10 20 0 10 20 30 0 10 20 0 10
Figure 17.2
Vertical distribution of sub-fossil Trichoptera and Coleoptera from an idealized palaeochannel deposit
indicating the transition in community structure from a predominantly lotic to lentic community (between 110-100 cm
depth) resulting from channel cut-off (after Howard, 2007).
