The response of macroinvertebrate communities to

1
The response of macroinvertebrate communities to
sediment clearance in a small canalised
stream Lisa King - BSc Biological Conservation
Physical Geography
Abstract Benthic macroinvertebrate communities
from a short, urban stretch of Dallington Brook,
Northampton, were sampled in November 2004 and
again in November 2005 in order to assess the
impact that the removal of silt from the stream
may have on water quality. For each year,
abiotic data was collected and the Biological
Monitoring Working Party (BMWP) score and average
score per taxon (ASPT) biotic indices were
calculated. Analysis of the results showed that
the removal of the silt, leaving a substrate
dominated by concrete, did not appear to have an
adverse effect on the water quality, as the BMWP
score and ASPT value increased in 2005. However,
differences in abiotic factors such as electrical
conductivity, current velocity and air and water
temperature may also have had some bearing on
this result.
Methods
Discussion Upon visiting the site in November
2005, we were initially struck by the visual
alteration that had occurred following the
removal of a large quantity of sandy sediment
from the sampling site (Figures 3 and 4).
Studies have suggested that there may
be a correlation between the amount and type of
sediment in a stream and the effect that it has
on the composition of the benthic
macroinvertebrate communities present (Grumiaux
et al., 1998 Kaller and Hartman, 2004).
Accumulations of sediment in the substrate of a
stream have a great capacity to absorb pollutants
such as metals which may be washed into streams
from agricultural, industrial or domestic
activities (Grumiaux et al. 1998). Many
macroinvertebrates live in or on sediments, and
consequently may be particularly susceptible to
accumulations of these pollutants. As the
sampling site lies downstream from an industrial
estate, it is possible that the accumulated
sediment contained high concentrations of
pollutants which may have had a deleterious
effect on the macroinvertebrate communities
present at the site. Indeed, the improvement in
the BMWP score and consequently the higher ASPT
value between the samples taken in 2004 and 2005,
suggest that the water quality in Dallington
Brook has improved following the removal of the
sediment from the stream. However, the
improvement may also have been affected by the
changes in certain abiotic factors identified in
the results further tests would be required to
verify this. Use of the BMWP score and ASPT value
in isolation may not provide an entirely accurate
interpretation of the results, as the index
values used differ according to the physical
features found at different sites (Clarke et al,
2002) for example, the removal of the sediment
at Dallington Brook has changed the physical
attributes of the site. In order to address this
limitation, the River InVertebrate Prediction And
Classification System (RIVPACS) site
classification computer model has been developed.
Based on 614 reference sites found in Great
Britain, this model uses environmental data
collected at the sample site to provide a
prediction of the fauna that could be expected to
be found in the absence of major environmental
stress (Clarke et al. 2002), thus allowing a more
objective basis for comparisons to be made when
assessing the water quality of a stream.
A 20m stretch of the stream was selected and the
following environmental measurements were
recorded stream width water depth substratum
characteristics electrical conductivity current
velocity water and air temperature. After
recording the environmental data, a sample of
macroinvertebrates was collected by utilising a
standardised 31 kick sampling technique.
Over a period of 3 minutes and using a standard
kick net, samples were taken from a number of
locations within the stretch that were considered
to be representative of the habitats present.
At each location, the net was placed in the water
with the bottom touching the substrate and the
area immediately in front of the net was
vigorously agitated for 10-20 seconds, thus
dislodging any invertebrates that were present in
the substrate. The contents of the net were
emptied into a container and removed to the
laboratory for identification to family level.
A further minute was spent searching the 20m
stretch by hand, paying particular attention to
microhabitats not sampled by the kick sampling.
Introduction Following the implementation of The
Water Framework Directive in December 2000, there
is a growing requirement for the quality of water
in inland and coastal waterways in the United
Kingdom and European Community member states to
be regularly monitored and assessed (Clarke et
al., 2003). Assessments may take the form of
either chemical analysis or biological assessment
methods. In isolation, chemical analysis is not
able to elucidate on the effects of pollution
and, therefore, it is becoming increasingly
important to use biological assessment methods to
identify the ways in which pollution affects
benthic macroinvertebrate communities (Clarke et
al., 2003). In this two year study of Dallington
Brook, Northampton, we used the Biological
Monitoring Working Party (BMWP) score system,
adopted in 1978 as the national standard for
biological monitoring of rivers in the United
Kingdom (Walley and Fontama, 1998), and the
average score per taxon (ASPT) to determine the
water quality of this stretch of urban stream.
Figure 3 Dallington Brook, November 2004
Figure 4 Dallington Brook, November 2005
Figure 2 Kick sampling
Results Following the removal of sediment from
Dallington Brook, the substrate characteristics
were altered from predominantly sand (65) in
2004 to predominantly concrete (70) in
2005. Analysis of the abiotic data collected for
2004 and 2005 revealed that there had been a
slight increase in the electrical conductivity
from 0.73µS cm-1 to 0.89µS cm-1 and that the
current velocity had increased from 0.44cm/s to
0.95cm/s. It was also noted that although the
data for 2005 was collected at the same time of
year as the 2004 data, the air temperature was
lower (4.1C compared to 11.7C) and the water
temperature was also lower (7.4C compared to
10C). The benthic macroinvertebrates that were
collected at the sampling site are shown in Table
1, together with the associated Biological
Monitoring Working Party (BMWP) scores and final
average score per taxon value for each sampling
year. Following the removal of the sandy
substrate from the sample site, the ASPT value
shows an increase from 3 in 2004 to 4.3 in
2005.
Site Description The source of Dallington Brook
is located in Brices Spinney, 5.3 km upstream
from the sampling site (Figure 1). From Brices
Spinney the stream meanders through agricultural
land before reaching the outskirts of New Duston,
where it follows the boundary of the Lodge Farm
Industrial Estate. The stream has been
canalised from where it borders the edge of the
industrial estate to beyond the area of the
sampling site, although this was not immediately
apparent in 2004 when the initial site visit was
conducted. The sampling site is a 20m
stretch of urban brook which lies downstream from
the industrial estate. There is a housing estate
and allotments to the south-west side of the
stream and Kings Heath, an area of open heath
land, lies to the north-east. The banks of the
stream are dominated by grasses, nettles (Urtica
dioica) and ivy (Hedera helix). Mature alder
(Alnus glutinosa) and willow (Salix) are also
present on both banks.
Table 1 Benthic macroinvertebrates found at
Dallington Brook with associated BMWP score and
ASPT value (xnot present)
Family 2004 2005
Asellidae 3 3
Baetidae x 4
Chironomidae 2 x
ClassDiptera larva x 5
Gammaridae 6 6
Glossiphonidae 3 x
Hydrobiidae x 3
Class Oligochaela 1 x
Panariidae x 5
BMWP score 15 26
N-Taxa 5 6
ASPT 3 4.3
References Clarke, R.T., Furse, M.T., Gunn,
R.J.M., Winder, J.M. and Wright, J.F. (2002)
Sampling variation in macroinvertebrate data and
implications for river quality indices.
Freshwater Biology 47 1735-1751. Clarke, R.T.,
Wright, F. and Furse, M.T. (2003) RIVPACS models
for predicting the expected macroinvertebrate
fauna and assessing the ecological quality of
rivers. Ecological Modelling 160
219-233. Grumiaux, F., Leprêtre, A. and
Dhainaut-Courtois, N. (1998) Effects of sediment
quality on benthic macroinvertebrate communities
in streams in the north of France. Hydrobiologia
385 33-46. Kaller, M.D. and Hartman, K.J. (2004)
Evidence of a threshold level of fine sediment
accumulation for altering benthis
macroinvertebrate communities. Hydrobiologia 518
95-104. Walley, W.J. and Fontama, V.N. (1998)
Neural network predictors of average score per
taxon and number of families at unpolluted river
sites in Great Britain. Water Research 32
613-622.
Figure 1 The course of Dallington Brook from its
source at Brices Spinney near Harpole to the
sampling site