Volume 2 † Number 2 † June 2009
10.1093/biohorizons/hzp015
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Research article
The effects of riparian habitat quality and
biological water quality on the European Otter
(Lutra lutra) in Devon
Susannah J. Bedford*
School of Agriculture, Policy and Development, The University of Reading, Whiteknights, Reading RG6 6AR, UK.
* Corresponding author: Millside, Middle Mill Lane, Cullompton, Devon EX15 1JP, UK. Tel: þ44 1884 32987. Email: [email protected]
Supervisor: Dr Julian Park, School of Agriculture, Policy and Development, The University of Reading, Whiteknights, Reading RG6 6AR, UK.
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After a period of decline, European Otter (Lutra lutra) populations are showing signs of recovery throughout the UK. Populations in
Devon are thought to be almost fully recovered, although exact numbers are unknown; however, there are still rivers within Devon
that do not appear to support Otter populations. The aim of this research was to determine the relationship between environmental
condition and the presence of Otters by comparing the quality of riparian habitat of rivers with and without evidence of Otters. The
research was undertaken in four rivers in Devon, the Rivers Culm, Ken, Coly and Otter: the first two being river stretches with no documented evidence of Otter populations, and the latter two having documented evidence of Otter populations. Along each of the rivers,
10 sections of 50 m were sampled. In each section, the riparian habitat quality was recorded using the Qualitat del Bosc de Riberia index.
The biological water quality was determined by calculating Biological Monitoring Water Party scores, and water chemical concentrations
were obtained from Environment Agency data. The riparian habitat quality and biological water quality were found to be of significantly
lower quality in the river stretches that did not have evidence of Otter populations when compared with those with Otter populations.
The chemical water quality was correlated to biological water quality: the quality being worse in the rivers without evidence of Otter
populations. The results of this research suggest that rivers with no evidence of Otter populations are generally of worse riparian
quality than those supporting Otter populations.
Key words: Lutra lutra, riparian, QBR, BMWP, Devon.
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Introduction
The European (or Eurasian) Otter (Lutra lutra) is part of the
Mustelidae family (Mammalia: Carnivora).1, 2 One of the
nine Otter species, it has the widest distribution throughout
Europe and Asia.1, 3
The Otter, once widespread across the UK, became mainly
confined to upland areas between the 1950s and 1970s. Four
main causes of population decline have been identified: pollution of freshwater systems, insufficient prey, habitat degradation and disturbance, and incidental mortality.
Pollution of Freshwater Systems
It is believed that water pollution is the most usual cause of
UK Otter population declines.4 – 7 In the 1950s, persistent
organochlorine pesticides and polychlorinated biphenyls
(PCBs) became intensively used in agriculture. In one investigation, PCBs were found in every Otter, spraint and
fish tested; these chemicals are known to affect the reproduction and immune systems of mammals and bioaccumulate
within tissues.7 Otters, which eat 15–20% of their own
weight in fish daily, are likely to have high concentrations
of these bioaccumulating contaminants in their tissues.8
The introduction of the pesticide dieldrin offers a specific
example. Dieldrin, thought to be the most important cause
of Otter declines,9 came into use in 1956 in sheep dips in
the South West: western Otter populations began to decrease
in 1958. A complete ban on dieldrin in sheep dips was introduced in 1966: the western Otter populations began to
increase with effect from 1968.6, 10, 11
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#
2009 The Author(s). This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License
(http://creativecommons.org/licenses/by-nc/2.0/uk/) which permits unrestricted non-commercial use, distribution, and reproduction in any
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Insufficient Prey
The main prey of Otters is fish, forming 70– 92% of their
diet,1, 5, 12 which is, however, known to include other organisms depending upon habitat and prey availability. Frog
(Rana temporaria) remains were found in Otter spraints in
woodland habitats,2, 12 another study found bird remains
in 41% of spraints analysed,13 whereas spraints from agricultural areas contained higher percentages of fish.14
Another study found seasonal variation of prey: during the
summer, spraints were found to contain more non-fish
food than during the winter when fish move more slowly.1
Despite this, a lack of prey is thought to be a major factor
in the decline of Otter populations as many of the species
they depend upon were adversely affected by the use of pesticides and decreases in water quality.15
Habitat Degradation and Disturbance
It was the Joint Otter Group who first recognized that
habitat destruction coincided with Otter population
decline.16 Population densities of Otters are known to be
low due to their linear habitats and territoriality.12
Erlinge17 found that in stream habitats, the Otter density
was one Otter per 4– 5 km stream length. Research estimates
that Otter territories are roughly 10–20 km, depending upon
the quality of the habitat and resources.3, 18 A eutrophic
river, with a high carrying capacity and plentiful food and
habitat cover, could support a higher Otter density.17
Habitat requirements for the Otter include the provision
of resting-up sites, in the form of reeds and sedges, and
mature vegetation in which holts can be established;18, 19
however, research into these requirements has been contradictory. Kruuk et al. 19 found no significant relationship
between vegetation cover and Otter distribution.12, 18, 20
Conflicting research found that Otters were dependent on
bankside vegetation cover.14 A significant relationship was
found between Otter signs and the density of European
Ash (Fraxinus excelsior) and Sycamore (Acer pseudoplatanus);7 furthermore, a river stretch with abundant food was
unused by Otters due to the absence of sufficient cover for
resting sites.7
After the Second World War, riparian land was reclaimed
for agricultural production, contributing significantly to the
decline in Otter populations.15 Additionally, urbanization
led to the loss of riparian land. The location of dwellings
closer to rivers has required flood prevention schemes.
These can reduce water flow, leading to a reduction in prey
available; or alternatively increase flow, resulting in flooded
holts and increased infant mortality.
Incidental Mortality
Urban expansion has forced Otters to become more tolerant
of humans, Otters are now present in 49 towns, including
London,21 and breeding in nine of these.16 Consequently,
road accidents are still the main cause of recorded Otter
deaths in the South West.21
In addition to incidental mortality, Otters have previously
been vulnerable to persecution.9, 22 Although not thought to
be a main factor behind Otter population decline, it is often
suggested that Otter hunting was a contributing factor, as it
reduced populations to an unstable level.9, 15
Four national Otter surveys have been carried out in the UK
with the aim of determining the extent of and main causes
behind the decline of Otter populations and also the recovery
of Otter populations across the country. The first was 1977–
1979,23 the second 1984–1986,10 the third 1991– 199415
and the fourth 2000–2002.4 Prior to this, there was little
monitoring of UK Otter populations. Much of the monitoring of Otter populations has been undertaken via the assessment of sprainting activity along rivers, including these
national surveys, either to provide evidence or suggestion
of Otter abundance, or indicating the absence of Otter
activity.12, 14, 18 However, research by Conroy and
French24 shows that sprainting varies seasonally and thus
may not give an accurate assessment of population
distribution.25
Rather than using spraint counts, this paper outlines
research to assess Otter habitat preferences by comparing
the quality of riparian habitat of Devonian rivers with evidence and without evidence of Otters, with the aim of determining the relationship between environmental condition and
the presence of Otters. Due to the elusive nature of the Otter
and the fact they do stray beyond their normal territories, it is
not possible to state categorically that Otters are not present
because no evidence of their presence has been found.
Two river stretches with known Otter populations were
compared with two river stretches where Otters were
believed to be absent. Results of the national Otter surveys
suggest that populations in Devon have increased more
rapidly than many other regions of the UK. In the first
Otter survey, 23.5% of sites surveyed had evidence of
Otter presence; this percentage increased consistently
throughout the surveys, and by the most recent survey,
83% of sites had evidence of Otters.26 Otter populations
are now at their highest recorded levels for 50 years.4 The
most recent surveys have shown that Otter population
increases in Devon have begun to slow, suggesting that
Otters are now present in most of the suitable riparian habitats.26 However, there are still rivers in Devon that do not
appear to support Otter populations and it is unclear why
Otters have not moved into these.
Against this backcloth, the research reported here compares the quality of riparian habitat vegetation, the biological
water quality and the chemical characteristics of
four Devonian rivers (two that are known to be
populated by Otters and two that have no recorded presence
of Otters).
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Four main hypotheses tested in this study are as follows:
(1) The riparian vegetation of rivers with Otters is significantly different from those with no recorded Otter
presence.
(2) There is a difference between the biological water quality
and invertebrate composition of rivers with Otters and
those with no recorded Otter presence.
(3) The chemical water quality differs between rivers with
Otters and those with no recorded Otter presence.
(4) There is a significant correlation between the Qualitat
del Bosc de Riberia (QBR) and Biological Monitoring
Water Party (BMWP) scores.
Location and external factors
Four river locations for sampling were chosen through an
analysis of environmental data and local public surveying.
Each reach of the rivers surveyed needed to be easily accessible
so that samples could be taken at a number of points and sites
were selected with similar surrounding land uses to limit wider
environmental variability. The River Ken and a diverted
stretch of the River Culm were identified as the rivers
without evidence of Otter populations, and the Rivers Coly
and Otter were identified as the rivers with Otter populations.
The River Culm was surveyed to the east of the town of
Cullompton. Bordering the east of the stretch were open
fields with a public footpath. To the west of the river were
open fields and the outskirts of the town. The River Ken
was surveyed to the west of the village of Kentisbeare and
was bordered by an area of newly established woodland
used for recreation on the south and arable land (in the
Organic Entry Level Stewardship Scheme) to the north.
The River Coly was surveyed west of the town of Colyton
where it runs around the northern boundary of the town.
The north side of the river was used for rough grazing and
was part of the Catchment Sensitive Farming Delivery
Initiative through which runs the East Devon Way. To the
south of the river were open paddocks. The River Otter was
surveyed south of Ottery St Mary. The land to the west of
the river was part of the Countryside Stewardship
Scheme with open fields used for rough grazing. To the east
of the river, there was unmanaged woodland which borders
arable land in the Entry Level Environmental Stewardship
Scheme, all of this area was a Nitrate Vulnerable Zone.
The sampling took place over 3 weeks, the River Otter
sampled 8 September 2007, the River Ken 15 September
2007, the River Coly 22 September 2007 and the River
Culm 27 September 2007. Precipitation rates during May,
June and July 2007 were significantly higher than previous
years. August was drier, compared with the preceding
months, and September drier still. Less than 5% of the
month’s precipitation fell before the Rivers Otter and Ken
were sampled, and the majority of monthly precipitation
occurred during the period in which
Culm were sampled. River flows in
than average as a result of previous
September river flows had returned to
the Rivers Coly and
August were higher
precipitation, yet by
average.27
Materials and Methods
Ten sections of 50 m were selected for sampling along each
river, at equal distances of 100 m. If sections allocated
were seen to be too deep to be sampled safely, then the
section began at the nearest safe access point. Grid references
of the sections sampled are shown in Table 1.
The QBR index was used to measure the quality of riparian habitat.28 The index relies on four indicators of quality:
total vegetation cover, vegetation cover structure, cover
quality and river channel alteration. For each indicator, a
maximum of 25 points can be awarded, based on a set of criteria. For example, evidence of .75% tree cover would be
awarded 25 points. If less abundant, then 0, 5 or 10 points
could be awarded, depending on the percentage of tree
cover present. Additionally, extra points could be awarded
for positive riparian signs and negative points for signs of
poor riparian quality. The four indicators were assessed at
each river section sampled and the scores from the four indicators were totalled to give an overall QBR score for the
section ( providing 10 QBR scores for each river). The QBR
scores were then classified to a quality class (Table 2).
This index was chosen as it is quick to carry out in comparison to other riparian sampling methods. It requires no detailed
taxonomic knowledge but a basic knowledge of native
species and the ability to answer questions in the survey.29
The biological water quality was sampled by active 3 min
kick samples, as standardized by the River Invertebrate
Prediction and Classification System (RIVPACS).30 These
samples were taken at sections one, three, five, seven and
nine of each river, providing five freshwater invertebrate
Table 1. Ordnance Survey grid references of the 10 sections
sampled along each of the four rivers
Section number
Grid reference
River Culm
River Ken
River Coly
River Otter
1
ST027067
ST064084
SY245942
SY094952
2
ST026066
ST063085
SY244941
SY094948
3
ST027068
ST063083
ST243943
SY095946
4
ST028069
ST062085
SY241945
SY096945
5
ST028070
ST062083
ST239944
SY097944
6
ST027071
ST061084
SY238942
SY094942
7
ST028072
ST061082
SY236943
SY097941
8
ST026073
ST060083
ST235944
SY096938
9
ST027074
ST059084
SY234943
SY094937
10
ST029075
ST057083
SY233944
SY093936
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Table 2. Quality classes assigned to final QBR index scores28 and BMWP index scores51
Habitat quality class
QBR
Water quality class
BMWP
101 – 120
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Riparian habitat in natural condition
95
Very clean water
Some disturbance, good quality
75 –90
Evidence of mild pollution effects
61 –100
Disturbance important, fair quality
55 –70
Polluted waters
36 –60
Strong alteration, poor quality
30 –50
Very polluted waters
16 –35
Extreme degradation, bad quality
25
Strongly polluted waters
,15
samples for each river. The invertebrates collected were
identified to family level and assigned a score, as set by the
BMWP, to classify the biological water quality (Table 2).31
These scores are based upon the invertebrate’s tolerance to
pollution on a scale from 1 to 10, 1 being the most tolerant
and 10 the least tolerant.
From these scores, the Average Score per Taxa (ASPT) was
calculated for each sample, providing five ASPT results for
each river, by dividing the total BMWP score by the
number of taxa recorded. The observed ASPT results were
compared with the expected ASPT results32 to calculate the
Ecological Quality Index of the river and compare it with
standards set by the European Union Water Framework
Directive (WFD). The WFD’s objective is to achieve good
ecological status in rivers through the implementation of
river catchment management plans.31 The expected ASPT
results were based on data from the River Quality section
of the Environment Agency website. The sites sampled by
the Environment Agency were more widely spaced than the
samples in this study; however, three Environment Agency
sites overlapped with this study’s sampling sections for the
River Culm (referred to as Sites 1, 2 and 3) and two for
the River Otter (referred to as Sites 1 and 2) so
Environment Agency data were compared with those from
the closest sampling site. No data sets were available for
the River Ken or Coly. The dissolved oxygen content,
ammonia, phosphate and nitrate levels for the Rivers Otter
and Culm were also obtained via the Environment Agency.32
The nature of the ecological investigation described here
does raise the issue of pseudo-replication, and in particular,
the fact that downstream samples are not fully independent
of those upstream. Hurlbert33 provides a detailed insight
into this issue in relation to ecological studies. In essence,
pseudo-replication is difficult to overcome in a limited investigation of this nature and its importance is still debated in the
ecological literature. Indeed Oksanen34 suggests that provided
sampling regimes are clearly explained and that the data collected are interpreted with regard to the limitations of that
design then ‘pseudo-replication may be a pseudo-issue’.
the analyses gave mixed results; therefore, it was considered
safest to use non-parametric statistical tests. The Kruskall–
Wallis test was used to test for significant differences in
both QBR and BMWP data. The Mann–Whitney U-test
was used to compare observed and expected ASPT results,
and a non-parametric correlation was used to compare the
QBR data with BMWP data.
Results
Riparian Habitat Quality
The QBR scores of the four rivers were significantly different
(P , 0.001) (Fig. 1). The QBR scores of the River Culm were
significantly lower than the Rivers Coly and Otter (P , 0.01).
There was a significant difference in QBR scores of the Rivers
Ken and Otter (P , 0.05); however, there was no significant
difference between the QBR scores of the Rivers Ken and
Coly. Coefficients of variance (COVs) in QBR scores along
each individual river were also calculated (Table 3).
Biological Water Quality
BMWP Scores
The BMWP scores of the four rivers were significantly different (P , 0.05) (Fig. 2). The BMWP scores of the River Culm
were significantly lower than those of the Rivers Coly (P ,
0.05) and Otter (P , 0.01). The BMWP scores of the
River Ken were significantly lower than the River Otter
Statistical Analysis
The Kolmogorov–Smirnov test was used to check for normality in data. As is often the case in ecological studies,
Figure 1. Mean QBR index scores for each river showing the standard
deviation around the mean.
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(P , 0.05) but there was no significant difference between
the Rivers Ken and Coly.
ASPT Scores
When compared with the expected results,32 the River Otter
observed ASPT results from this study were higher, but the
difference was not significant (Fig. 3). In contrast, the observed
results collected by the Environment Agency were lower than
the expected ASPT, but not significantly different, nor was
there a significant difference between the Environment
Agency’s observed results and the results of this study.
Table 3. Minimum, maximum and mean QBR results and standard
deviation from the mean, with COV
River
Minimum
QBR
Maximum
QBR
Mean
QBR
Standard
deviation
Coefficient of
variance (%)
Culm
25
55
45.00
10.27
22.82
Ken
50
80
58.00
10.33
17.81
Coly
40
85
67.50
15.68
23.23
Otter
55
75
68.50
7.84
11.45
The observed ASPT results from this study were lower
than the expected ASPT for the River Culm, although not
significantly different (Fig. 3). Similarly, the observed ASPT
results obtained by the Environment Agency were lower
than the expected ASPT, although not significantly different,
nor were the Environment Agency’s observed results and the
observed results of this study significantly different.
Species Composition
The invertebrate species varied between rivers (Table 4).
Only 4.1% of the species in the River Culm samples were
of BMWP score 7 or higher and 41.9% of the species in
the River Ken. In contrast with the rivers without
evidence of Otters, the Rivers Coly and Otter had a higher
percentage of these less tolerant species, 57.3% and
72.4%, respectively.
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Chemical Water Quality
The highest BMWP scores coincided with the highest dissolved
oxygen contents. In general, as phosphate concentrations
increased, the BMWP score increased, higher ammonia concentrations corresponded to lower BMWP scores and increased
nitrate levels caused a decrease in BMWP score.
Interaction of Riparian Quality and Biological Quality
There was a general trend such that as the QBR score
increased, the BMWP score increased; however, this relationship was not significant.
Table 4. Mean occurrence of macroinvertebrate families in kick
samples, ordered by BMWP tolerance score
BMWP score
Figure 2. Mean BMWP scores of the rivers showing the standard deviation
around the mean.
Mean occurrence (%)
Culm
Ken
Coly
Otter
Hydrobiidae
2.19
0.58
0.54
0.00
Sphaeriidae
6.03
2.91
6.49
0.92
Erpobdellidae
7.67
6.98
4.32
3.67
Glossiphoniidae
3.01
6.40
6.49
1.38
Asellidae
0.27
0.00
0.00
0.00
Gyrinidae
1.64
0.00
0.54
0.00
Hydropsychidae
0.82
4.07
2.16
5.53
Gerridae
3.01
11.05
14.05
10.14
4.15
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3
5
6
Figure 3. Observed ASPT, RIVPACS expected ASPT and Environment
Agency observed ASPT results for the Rivers Culm and Otter.
Family
Gammaridae
70.68
26.16
5.95
Viviperidae
0.58
0.00
0.54
0.00
Ancylidae
0.00
0.00
1.62
1.84
7
Caenidae
1.64
9.30
15.68
25.35
8
Astacidae
0.00
0.00
0.00
10.60
10
Ephemeridae
1.92
13.95
16.76
9.22
Ephemerellidae
0.27
9.30
21.08
20.74
Leptoceridae
0.27
9.30
3.78
6.46
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Discussion
This research has used a range of data to test four hypotheses
relating to Otters and their habitats. Some of these data have
been accessed via the Environment Agency website and used
alongside or in combination with primary data collected
from four Devonian rivers. This primary data set is of a
limited nature because of time and resource constraints,
and thus the results need to be interpreted with some
caution.
of precipitation would have been similar in each of the rivers
due to their proximity.
The water quality may have been affected by the increased
precipitation resulting in increased runoff and the addition of
debris from the surrounding land. Runoff can increase the
suspended silt content making the river less suitable for sensitive macroinvertebrates requiring clean water, which may
explain why the lowest BMWP scores for each of the rivers
were all directly downstream from busy roads.
ASPT Scores
Riparian Habitat Quality
The riparian habitat quality of the Otter-inhabited rivers was
of significantly better quality than those with no recorded
Otter presence; therefore, the first hypothesis can be
accepted. The standard deviation in the QBR results for
each river suggests that the riparian vegetation varied along
the stretches sampled; however, the COV suggests that the
vegetation cover along each river was not highly variable.
The Rivers Otter and Coly had an abundance of bankside
vegetation, channel vegetation and mature trees, all of which
have been suggested as habitat requirements for Otters.5, 7, 14
The bankside vegetation and mature trees along the Rivers
Culm and Ken were sparse and fragmented, the main species
found on these river banks were grasses, of little benefit to
Otters.35, 36 The River Culm was heavily managed along
its eastern side, reducing vegetation further. The vegetation
of the River Ken was of higher quality and abundance;
however, sections had no mature trees. The bankside vegetation in both the Rivers Culm and Ken was directly adjacent to heavily accessed areas; this may make them
unsuitable as resting-up sites due to disturbance.14, 18, 35
Previous research suggests that Otters can tolerate poor vegetation cover, provided human disturbance is not high.7
Other research found no relationship between the vegetation
density and the presence of Otters, or between human disturbance and Otter presence;12, 18 – 20 therefore, the lack of
vegetation may be one of many factors contributing to the
apparent absence of Otters.
Biological Water Quality
BMWP Scores
The BMWP scores of the rivers without evidence of Otters
were significantly lower than those with Otters; therefore,
the second hypothesis can be accepted.
Above average precipitation in the months prior to
sampling may have increased flow rate, affecting the macroinvertebrates. Sensitive species such as Leptoceridae and
Ephemeridae cannot tolerate fast water so abundance may
have been reduced due to increased flow speeds.37
This rapid entry of water may have decreased river water
temperature. Some macroinvertebrate species are sensitive to
temperature, so may have left the area;31 however, the effects
The River Otter observed ASPT results were higher than the
expected ASPT results,32 suggesting that the water quality
could be improving. The surrounding land is part of the
Countryside Stewardship Scheme; implementation of this
scheme may have improved the management of the surrounding land to conserve the riparian habitat. The
Environment Agency’s observed results were lower than
expected at Site 1 and as expected at Site 2, this suggests
that the biological water quality of the River Otter may
have improved since sampled by the Environment Agency.
The observed ASPT results for the River Culm from this
study and from the Environment Agency were lower than
the expected results, indicating a potential reduction in
water quality. Many of the sampled stretches of the River
Culm had signs of disturbance, river bank erosion or proximity to roads. An increase in precipitation and these factors
may have increased the debris, silt and soil entering the river,
decreasing the water quality and making it less suitable for
intolerant species, therefore reducing the ASPT.4, 15
Species Composition
The least tolerant species were more abundant in the rivers
with Otter populations; therefore, the hypothesis can be
accepted. The macroinvertebrate species found in the River
Culm were of higher pollution tolerance than the species
found in the rivers inhabited by Otters. This is likely to be
due to the silty substrate and the stationary water, indicative
of low dissolved oxygen content; when sampling was carried
out in riffles, more sensitive species were found.
The overhanging vegetation of the River Culm may also
affect the invertebrate species. This overhanging vegetation
provides shade which can reduce the water temperature;38
this can be beneficial for fish during warm summers;
however, some macroinvertebrate species are temperaturesensitive. One study found an increase in shade to 60–
90% caused a significant reduction in invertebrate
abundance and that 90–98% shade reduced invertebrate
taxa richness.39 The overhanging vegetation also creates
leaf litter providing a food source for fish.40, 41 However,
once in the watercourse, leaf litter can cause eutrophication
as microorganisms decompose the leaf litter, increasing the
biochemical oxygen demand and depleting the available dissolved oxygen content for invertebrates and fish. One study
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found a significant decrease in wet-weight of macroinvertebrates after the addition of plant litter to a lake.42
In comparison, the Rivers Otter and Coly had a more suitable substrate for sensitive species intolerant of silt. The
wider channels meant that there were both shallow riffles
and deeper pools, providing habitat for all types of macroinvertebrates and a mixture of water temperatures, features not
present in the Rivers Culm or Ken.
Ecological Water Quality
Based upon the observed and expected ASPT results, the
River Otter can be deemed of high ecological quality. The
River Culm was of poorer quality, and given the lack of evidence of Otters along this river, this suggests that Otters
probably do have a preferred riparian habitat as the thriving
Otter populations are known to be in the river of better ecological water quality.
Chemical Water Quality
Dissolved Oxygen Content
The lower BMWP scores coincided with lower dissolved
oxygen contents. Erpobdellidae and Asellidae are both tolerant of low dissolved oxygen contents,43 and both species
were found in their highest abundance in the river with the
lowest oxygen content. The results of this investigation
concur with previous research showing that the BMWP
scores in dissolved oxygen contents of ,97% were lower
than in dissolved oxygen contents of .97%.31 The
samples with the highest dissolved oxygen content also
relate to those with a higher abundance of sensitive species,
such as Leptoceridae and Ephemerellidae, which require
.97% dissolved oxygen.31
Additionally, the introduction of nutrients such as phosphates and nitrates can cause eutrophication as plant
matter growth increases.38, 44 If the dissolved oxygen
content falls too low, the river can become anoxic, suffocating aerobic organisms. When compared, the samples with
the highest nitrate and phosphate levels were found to have
the lowest dissolved oxygen saturation and BMWP scores.
Ammonia Levels
Previous studies have found ammonia concentration to be
inversely related to the BMWP score45 as high ammonia concentrations adversely affect water ecology.46, 47 This may
explain the low BMWP scores in samples with a high
ammonia concentration.
Nitrate Levels
Nitrates can mobilize heavy metals contained within the sediment.48 The mobilization of heavy metals can significantly
decrease species richness and abundance.47 Sensitive species
such as Caenidae, Ephemeridae and Leptoceridae are highly
sensitive to heavy metals;49 the only species that survive in
most cases are Oligochaeta and Chironomidae.37, 47, 49
Heavy metals are often found in the sediments of rivers downstream from busy roads, which could explain the low BMWP
scores for the first section of the River Culm sampled directly
downstream from a major road.
Phosphate Levels
The phosphate concentrations were higher in the River Otter
than the River Culm, which was unexpected as a high phosphate level would suggest pollution in the form of eutrophication. However, the samples with high phosphate
concentrations were also those with high BMWP scores.44
The phosphate levels in the River Otter did not appear to
affect the biological quality; this may be due to limited
additional pollution; if the nitrate and ammonia concentrations had been higher, effects may have been more noticeable. However, the water phosphate content may not reflect
the true phosphate concentration of the river as phosphate
can bind with sediment.50 Phosphate concentrations within
the sediment and plant life were not taken into account in
this investigation; therefore, the results may not be an accurate indication of the true concentration.
These results show that the chemical water quality did
differ between the Rivers Culm and Otter and the third
hypothesis can be accepted.
Interaction of Riparian Quality and Biological Quality
A high QBR score suggests a river of good riparian quality,
and a high BMWP score is a sign of a river of good water
quality. It could therefore be predicted that the higher the
BMWP score, the higher the QBR score. This is the general
result found; however, the relationship was not significant
and the fourth hypothesis cannot be accepted.
This interaction was investigated in a search to improve
sampling efficiency; assigning a BMWP score can be timeconsuming and assigning a QBR score is quicker. If a
direct relationship had been found, the QBR score could be
recorded and used to predict the BMWP score; however,
this would need to be studied further.
The limited nature of this study, the use of ‘absence of presence’ as a surrogate for the absence of Otters and, in particular, the issue of pseudo-replication must be considered
when interpreting the research presented here. Although difficult to overcome in this type of study, the robustness of the
analysis could have been improved by increasing the number
of samples at each point, sampling the same stretches of river
at different points in time and by increasing the number of
rivers sampled.
Conclusion
The quality of the riparian habitat and the biological water
quality of the rivers with Otters were found to be
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significantly better than the rivers without evidence of
Otters. The low QBR scores of the River Culm suggest an
exposed river and the low BMWP scores suggest poor
water quality. Few fish tolerate water of poor quality
suggesting that the River Culm may lack prey for Otters.
The BMWP scores of the River Ken suggest a slightly polluted watercourse with a lack of prey; however, the QBR
score gave evidence of fair quality riparian habitat.
The Rivers Coly and Otter proved to be of good riparian
habitat quality with evidence of only mild water pollution.
Both rivers had exposed areas but abundant bankside vegetation
for resting-up sites and mature trees with potential as holts.
Encouraging Otters to the uninhabited rivers may be possible through the planting of trees and bankside vegetation to
provide additional cover, and widening of narrow sections.
The River Culm had some mature trees with potential for
holts; however, the banks lacked additional vegetation
cover. The planting of bankside vegetation may make the
riparian habitat more suitable and prevent addition of silt
and debris during precipitation; nevertheless, this is unlikely
to counteract the sections of poor water quality, the proximity of water pollution sources and the heavily used footpath. It is unlikely that this diverted stretch of the River
Culm will ever support Otter populations.
The River Ken had abundant bankside vegetation that
could provide cover and resting sites for Otters, but few
mature trees were present. Planting of trees may increase suitability for Otters, although it will take time for the trees to be
appropriate for use as holts. In addition to this planting, a
reduction in surface runoff from roads may improve water
quality and increase prey abundance. The footpath along
the stretch of the River Ken sampled was heavily used; nonetheless, bankside vegetation is sufficient to provide cover for
Otters and if local Otter populations were to reach the River
Ken, then with the planting of mature trees, it may be suitable as a habitat for Otters.
It is essential to understand the habitat requirements of
Otters in order to ensure that re-establishment of Otter
populations is successful. Many factors known to have contributed to the population decline are now controlled,
agro-chemical use is regulated, Otters are legally protected
and water quality standards are in place. Yet little is done
to protect the riparian habitat unless part of an
agri-environment scheme. This suggests that in the future,
habitat degradation may be the main limiting factor for
Otter populations. This study shows that riparian habitat
quality is likely to affect a river’s ability to support Otter
populations and habitat regeneration is likely to encourage
their return to areas where they currently appear absent.
throughout the development of this research. My thanks
are due, too, to my family and friends for their encouragement throughout the sampling and writing of this study.
Funding
This project was funded by The University of Reading.
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Author Biography
Susannah Bedford recently graduated with a BSc (Hons) in Rural Environmental Sciences from the University of Reading. Her
main interests lie in the development of environmental policies through the use of sustainability appraisal and environmental
assessment. Susannah is looking to further her knowledge of the environmental sector, and to pursue a career in the field of
environmental policy. She hopes that following this career path will allow her to build on the voluntary work that she carried
out in Honduras, enabling her to raise awareness of the fragility and importance of our natural environment and to minimise
potential anthropogenic impacts.
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Submitted on 30 September 2008; accepted on 18 December 2008; advance access publication 5 April 2009
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