Geoscience Reference
In-Depth Information
the catchment consists primarily of Jurassic and
glacial clays, although there is also a groundwater
influence on river flow from the underlying
Jurassic limestone (Natural England: http://www
.sssi.naturalengland.org.uk/citation/citation photo/
1001178.pdf). The study site in this investigation
is a 1.4 km reach of the river, which flows
through pasture land and is dissected by a flood
alleviation impoundment and a railway line.
Parts of the SSSI are considered to be in an
unfavourable condition due to the operation of
impoundments, dredging activities and diffuse
agricultural runoff, all resulting in sedimentation
and nutrient enrichment.
downstream. As a result of the ponding, the natural
pool-riffle sequence had changed and the number
of riffles had been reduced, particularly at the
downstream end of the reach. More recently a
flood alleviation dam had been constructed which
was used to retain water and prevent flooding
of Melton Mowbray during periods of high water
flow.
Analysis of contemporary and
palaeo communities
The contemporary instream macroinvertebrate
community was examined from a representative
range of instream habitats (pools, riffles, runs and
marginal vegetation) using both semi-quantitative
kick samples and quantitative Surber samples. The
palaeochannel sediments and community were
sampled using a sediment pit on an instream island
(dated by the presence of a large willow tree at
least 47 years old). In addition, sediment cores
(1 m long) were extracted from palaeochannel
depressions on the adjacent floodplain using
a Cobra corer. Ongoing research is aimed at
confirming the chronology using lead 210 (
210
PB)
and caesium 137 (
137
Cs) dating techniques. These
data, in association with data obtained from
the Environment Agency of England and Wales,
provided a contemporary baseline dataset. A total
of 50 taxa were recorded, including five Coleoptera,
12 Trichoptera and 14 Gastropoda taxa.
Examination of the Coleoptera, Trichoptera
and Gastropoda present in both contemporary
and palaeo-samples from the River Eye showed
that a greater number of taxa were recorded in
the contemporary samples (31 taxa) compared
with the historic palaeo-sample (26 taxa). The
palaeo-community from sediments beneath the
instream island indicated that before isolation/
terrestrialization the site was a relatively fast-
flowing riffle. A total of four Coleoptera and
five Trichoptera taxa were common to both the
palaeo and contemporary samples. Two riffle
beetle taxa (Elmidae -
Limnius volckmari
and
Riolus
subviolaceus
)
Contemporary conditions and
archival data
A survey of the river was undertaken to determine
contemporary hydromorphological features
and to identify suitable sedimentary deposits
for palaeoenvironmental analysis. This survey
identified an in-channel island, which had been
stabilized by terrestrial vegetation, including a large
willow tree. Using an increment borer this tree
was examined to determine its minimum age (47
annual growth rings) an indication that the latest
date of initiation of tree growth, and earliest date
of flow cessation and terrestrialization of the site
(latest date of island formation was 1962).
The nature and magnitude of recent/historic
natural channel movement and/or anthropogenic
modification of the channel shape and form was
examined using historic Ordnance Survey maps
with survey dates of 1887, 1959, 1977 and the most
recent survey. This information was complemented
by records of land use and changes associated
with land drainage and flood alleviation, provided
by the landowner/tenant, dating back for more
than 75 years. Detailed examination of historic
maps indicated that the channel had not moved
laterally throughout the 123-year period since the
first survey and that its form had remained stable.
However, significant ponding of the study reach
occurred owing to the presence of a weir in the
town of Melton Mowbray, approximately 2 km
and
three
Trichoptera
(
Hydropsyche
sp.,
Brachycentrus
subnubilus
and
Athripsodes
