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Water quality changes in relation to Diptera communitypatterns and diversity measured at an organic effluent
impacted stream in the Niger Delta, Nigeria
Francis O. Arimoro a,*, Robert B. Ikomi a, Chukwujindu M.A. Iwegbue b
a
Department of Zoology, Delta State University, P.M.B. 1 Abraka, Nigeriab Department of Chemistry, Delta State University, P.M.B. 1 Abraka, Nigeria
Received 20 February 2006; received in revised form 18 June 2006; accepted 21 June 2006
Abstract
Impact of abattoir effluents (characterized by intestinal and stomach contents of slaughtered animals, ashes from roasted
animals and blood stains) on water quality, distribution and abundance of Diptera were investigated in an urban stream, River
Orogodo, Southern Nigeria, from July 2003 to June 2004. Water quality changes indicated significant differences (p < 0.05) in
conductivity, dissolved oxygen, BOD5, COD, total hardness, nitrate-nitrogen and phosphate-phosphorus between the three
stations sampled. Higher values of these parameters were observed at the impacted station. The abundance and community
structure of Diptera patterns, especially Chironomidae, Culicidae and Syrphidae families (all indicative of poor water quality)showed strong evidence of impact from the abattoir effluents. Comparisons of abundance values demonstrated high significance
(p < 0.05) between the impacted station and the upstream (station 1) and downstream station (station 3). Shannon index and
BergerParker dominance were greater at the impacted station (station 2). Analysis of faunal similarities showed that upstream
station 1(unpolluted site) was significantly different from stations 2 and 3. The distinct taxa found in station 2 (the impacted
station) suggest that the organic input from the abattoir favoured their abundance as most of them were opportunistic species.
# 2006 Elsevier Ltd. All rights reserved.
Keywords: Diptera; Impact; Water quality; Orogodo stream; Nigeria
1. Introduction
The use of aquatic Diptera to assess water quality is
commonly a part of water assessment programmes. In
pollution-oriented studies, identification of taxa which
are tolerant or intolerant of pollution is important in
designating water quality (Nelson, 1994). Organic
pollution by domestic sewage and abattoir effluent areprominent factors threatening the quality of Nigerian
streams. Small streams in developing areas are not
only strongly affected by these regular organic inputs
but also by episodic inputs from farmland, non-point
sources, which are more difficult to control (Victor and
Ogbeibu, 1985; Brown, 1996). However, the rate of
dilution in these streams is great, as rainfall is high
This article is also available online at:www.elsevier.com/locate/ecolind
Ecological Indicators 7 (2007) 541552
* Corresponding author. Tel.: +234 8035615424.
E-mail address: [email protected] (F.O. Arimoro).
1470-160X/$ see front matter # 2006 Elsevier Ltd. All rights reserved.
doi:10.1016/j.ecolind.2006.06.002
mailto:[email protected]://dx.doi.org/10.1016/j.ecolind.2006.06.002http://dx.doi.org/10.1016/j.ecolind.2006.06.002mailto:[email protected] -
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during most part of the year (Matagi, 1996; Edokpayi
et al., 2000; Zabbey and Hart, 2006) and streams tend
to recover quickly from such impacts.
The Orogodo River flows through the town of Agborwith a population of 100,000 people in southern Nigeria
and is the main source of portable water for the riparian
communities. It is also the main drainage system of the
town accounting for most of the total runoff (Ikomi and
Owabor, 1997). The river at the middle reaches is
subjected to organic pollution arising from effluent
from an abattoir. The effluent of this abattoir comprises
of stomach and intestinal contents of slaughtered
animals as well as ashes of burnt animal parts and
associated bloodstains which are discharged regularly
into the river without treatment.
There have been several recent studies of Diptera
composition and structure in tropical freshwater
bodies (Victor and Dickson, 1985; Ogbeibu and
Egborge, 1995; Ogbeibu, 2001; Ndarunga et al.,
2004). However, there have been few studies on the
effects of abattoir effluents and livestock impacts on
the abundance and distribution of Diptera (Solimini
et al., 2000; Mathooko, 2001). Therefore, this research
was undertaken to investigate water quality and to
identify the groups of diptera that are present in the
organically polluted section of the river, in addition to
comparing the ecological characteristics upstream anddownstream of the abattoir effluent impacted area.
Here we aim to identify significant changes in the
composition, density and distribution of Diptera which
are attributed to this effluent.
2. Materials and methods
2.1. Description of the study area
The Orogodo River is a short stream (about 50 kmlength) located in the Delta State Nigeria. It lies
between latitude 580068200N and longitude 68100
68260E (Fig. 1). The stream is fed principally by
ground seepage from an aquifer in the thick rainforest
zone of Mbiri and also by precipitation, municipal
effluent and surface run off from the riparian
communities. It flows through the main town of
Agbor, Owa-Ofie, Ekuma-Abavo, Oyoko in Delta
State and ends in a swamp between Obazagbon-Nugu
and the oil rich town of Oben in Edo State, southern
Nigeria. Samples of Diptera were collected monthly
from July 2003 to June 2004 at three sampling
stations: the point of discharge of abattoir effluents
(station 2), upstream (station 1) and downstream(station 3) of the impacted station.
Station 1 is located about 15 km upstream from the
source. The marginal vegetation consists of few trees,
mainly oil palm Elaeis guineensis and Cocos nucifera
L., emergent vegetation, namely Pycreus lanceolatus
Poi and submerged vegetation, Ceratophyllum sub-
mersum L. The streambed consists predominantly of
clay and silt. Human activities here include sub-
sistence fishing and bathing. Mean water depth is
0.7 m and width 3.5 m.
Station 2 is the impacted station located behind the
Agbor town abattoir, where effluents are emptied into
the stream. The abattoir effluent is composed of
animal faeces from slaughtered animals, blood and
ashes from burning and roasting of animals, which
constitute an organic pollutant. Some of the water at
this station is eutrophicated with heavy algal growth.
The dominant macrophytes are Nymphae lotus, Azolla
sp., Utricularia sp. and Salvinia sp. Floating duck-
weed (Lemna minor) is also observed close to the river
banks. Mean water depth is 0.5 m and width 5.8 m.
Station 3 is located downstream of the impacted
area, 5 km from the Abattoir close to Abavo by Owa-fie town. The substratum is predominantly clay and
silt. It is flanked by Indian bamboo trees (Bambusa sp.)
and palm trees (E. guineensis). Abundant emergent
macrophytes, Pandanus sp. and Mitragyna ciliata.
Human activities here include bathing, fishing,
sacrifices by superstitious believers, etc. The average
water depth is 1.0 m and width 3.7 m.
2.2. Water quality analysis
Sampling for water quality parameters and Dipterawere carried out in the three study stations at monthly
intervals between July 2003 and June 2004, covering
dry and rainy seasons. Air and water temperatures
were recorded with a thermometer; conductivity, pH,
total alkalinity, dissolved oxygen (DO) and biochem-
ical oxygen demand (BOD5), total hardness were
determined according to APHA (1985) methods.
Monthly rainfall data were obtained from the
meteorological station in Agbor. Other parameters
measured included water velocity determined using
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the Ping Pong flotation technique; nitrate-nitrogen
(NO3-N) and phosphate-phosphorus (PO4-P) weremeasured spectrophotometrically after reduction with
appropriate solutions (APHA, 1985). Chemical oxy-
gen demand (COD) was determined after oxidation of
organic matter in strong tetraoxosulphate VI acid
medium by K2Cr2O7 at 148 8C, with back titration.
2.3. Sampling for Diptera
Samples of Diptera larvae were collected with
Surber net (30 cm 30 cm, mesh size 250 mm). Care
was taken to include all possible microhabitats over
representative sections of the stream. At each station,10 sampling units were taken and pooled for analysis.
Samples were fixed with 4% formalin in the field and
preserved with 70% ethanol in the laboratory.
Taxonomic identifications of most Diptera were made
to the generic level. Some members of the subfamily
chronominae were identified to the species level using
the larval head capsules, antennae and labial plates
(Pennak, 1978; Cranston, 2000). Diptera abundance
was obtained by counting all individuals in a taxon and
expressing the results as number m2.
F.O. Arimoro et al. / Ecological Indicators 7 (2007) 541552 543
Fig. 1. Map of River Orogodo showing the study stations.
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All statistical methods used in analyzing the water
quality parameters and diptera community were
adapted from Zar (1984) and Magurran (1988),
including taxa richness, diversity and evennessindices, using the Computer Basic Programme SP
DIVERS (Ludwig and Reynolds, 1988).
Jaccards similarity (Ravera, 2001) was used to
compare the sampling locations and to determine
which ones were similar in taxa composition.
sJ
C
A B C
where Cis the number of species found at both stations
being compared; A is the number of species found at
station 1; B is the number of species found at station 2.
BergerParker dominance index adopted from
(Ravera, 2001), dBP = Nmax/N, where Nmax is the
number of individuals in the most abundant taxon;Nis
the total number of individuals.
3. Results
3.1. Physical and chemical characteristics of the
water body
Table 1 summarizes the mean values of the various
parameters monitored at the three selected stations
over a 12 month time span (July 2003June 2004)
along the River.
Air and water temperatures were in the range of
2431 8C in the three stations sampled and were not
significantly different (p > 0.05) (Fig. 2A and B).
Mean water depth was also similar in all thestations (p > 0.05). Except that orthogonal compar-
ison using Duncans multiple range test revealed that
station 3 (down stream) of the impacted site showed
considerable higher depth 1.20 0.24 m as compared
with the other stations. Generally, water depth
(Fig. 2C) was considerably higher in the rainy season
than the dry season months.
Current velocity variation was also not significant
among the stations sampled (p > 0.05). Station 2,
however recorded high values of current velocity
especially in the rainy season months (Fig. 2D) as a
result of the runoff of storm water from the town which
empties a few kilometres from this station.
Conductivity values were significantly different
among the stations sampled (p < 0.05). The impacted
station (station 2) recorded higher conductivity values
throughout the study period (Fig. 2E).
Most of the chemical variables, that is dissolved
oxygen (Fig. 2F), biochemical oxygen demand
(BOD5), chemical oxygen demand (COD) (Fig. 2G
and H), nitrate-nitrogen (Fig. 2I), phosphate-phos-
phorus (Fig. 2J) and total hardness (Fig. 2K) were
significantly different among the various stationssampled (p < 0.05). Orthogonal comparison using
Duncans multiple range test showed that station 2 was
the cause of the observed differences in these
parameters.
F.O. Arimoro et al. / Ecological Indicators 7 (2007) 541552544
Table 1
Summary of some physical and chemical characteristics of the sampling stations of River Orogodo (values are mean S.E) from July 2003 to
June 2004
Variable Station 1 Station 2 Station 2 ANOVA F-value Probability (p)
1 Air temperature (8C) 26.2 0.38 27.4 0.44 26.4 0.32 1.42 >0.05
2 Water temperature (8C) 26.6 0.54 24.2 0.61 23.4 0.62 0.84 >0.05
3 Water depth (m) 0.7 0.12 0.54 0.08 1.02 0.24 2.49 >0.054 Current velocity (ms1) 0.36 0.02 0.48 0.09 0.38 0.05 2.62 >0.05
5 Conductivity (ms cm1) 121.06 41.66 426.8 96.11 91.02 11.10 21.46*
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Most of the water samples (from station 13) had a
pH value of between 7 and 8. Although slightly higher
values were observed at station 2, this was however
not significant (p > 0.05) between the stations
sampled (Fig. 2L).
Total alkalinity in mg L1 did not vary significantly
among the stations sampled. However orthogonal
comparison using Duncan multiple range showed that
station 2 was the cause of the difference in total
alkalinity among the stations sampled.
F.O. Arimoro et al. / Ecological Indicators 7 (2007) 541552 545
Fig. 2. (AL) Physical and chemical characteristics of River Orogodo from July 2003 to June 2004.
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3.2. Diptera composition, abundance and
distribution
The taxa composition, density and distribution
of Diptera in the study area are shown in
Table 2. The assemblage fall into eight families,
namely Chironomidae, Culicidae, Dixidae, Simu-
liidae, Ceratopogonidae, Tabanidae, Syrphidae and
Muscidae. The distribution of these organisms
varied from stations 13 as might be expected in
view of the different abiotic characteristics of the
stations.
F.O. Arimoro et al. / Ecological Indicators 7 (2007) 541552546
Fig. 2. (Continued).
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Twenty-four (24) taxa of Diptera comprising
10,047 individuals were recorded during the entire
study. The total number of taxa and individuals presentat stations 1, 2 and 3 were 13 (1845), 19 (5866), and 18
(2336), respectively.
The most abundant Diptera collected from the three
stations distributed along the Orogodo stream belong
to the following families: Chironomidae, Ceratopo-
gonidae and Culicidae. Less frequent were the
families Syrphidae and Tabanidae, with Muscidae,
Dixidae and Simuliidae sporadically present.
Of all the individuals collected, stations 1, 2 and 3
accounted for 18.2, 58.4 and 23.3%, respectively
(Fig. 3). The overall density of Diptera was
significantly different at the three stations sampled
(ANOVA, p < 0.05). An a posteriori test for multiple
comparison showed that the density at station 2 was
significantly higher than those at stations 1 and 3
(p < 0.05), which were not different from each other
(p > 0.05).
The family Chironomidae contributed 78.3% of
the total diptera density. The dominant taxon in this
family was Chironomus transvaalensis, others
included Chironomus fractilobus, absent in station
1, Tanypus sp., and Pentaneura, cricotopus sp. 1,
Tanytarsus sp. and Corynoneura sp. were completelyabsent in station 2. Pentaneura sp. 2 was limited to
station 2 only. Polypedilum sp. was more abundant in
stations 1 and 3, occurring only sporadically in
station 2.
The family Ceratopogonidae contributed 14.9% of
the total Diptera density. It was most important in
station 2 accounting for 53.2% of the total ceratopo-
gonid density. The dominant taxon in the family was
Allaudomyia sp. which was fairly distributed in all the
stations sampled.
The family Culicidae accounted for 3.6% of thetotal Diptera density. Station 1 recorded the least
Culicidae abundance. Culex pipiens, Anopheles sp.
and Chaoborus anomalus were completely absent in
station 1. C. anomalus was the dominant culicid,
closely followed by C. pipiens.
The family Simuliidae was represented by one
genus, Simulium sp. (0.08%), which was restricted to
station 1 alone. The same applied to the family
Dixidae (0.11%), represented by Dixa sp. and
restricted to station 3 alone.
F.O. Arimoro et al. / Ecological Indicators 7 (2007) 541552 547
Table 2
Distribution and abundance (individuals per m2) of Diptera in River
Orogodo study stations, July 2003June 2004
Diptera Stations
1 2 3
Family Chironomidae
Chironomus transvaalensis 21 3658 38
Chironomus fractilobus 498 71
Tanypus sp 28 182 17
Pentaneura sp. 1 4 62 12
Pentaneura sp. 2 21
Cricotopus sp. 1 43 72
Cricotopus sp. 2 11 4 14
Polypedilum sp. 862 71 1456
Tanytarsus sp. 565 104
Corynoneura sp. 16 6
Family Culicidae
Theobaldia sp. 26 8 39
Culex pipiens 98 5
Anopheles sp. 62 6
Mansonia sp. 4 14
Chaoborus anomalus 96 8
Family Dixidae
Dixa sp. 11 17
Family Simuliidae
Simulium sp. 8
Family Ceratopogondae
Palpomyia sp. 16 28 11
Allaudomyia sp. 241 592 427
Forcipomyia sp. 176 4
Family TabanidaeChrysops sp. 27
Tabanus sp. 48 5
Family Syrphidae
Eristalis sp. 203
Family Muscidae
Musca sp. 18
Number of individuals 1845 5866 2336
Number of taxa 18 13 19
Fig. 3. Percentage distribution in density of Diptera in the study
stations.
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Tabanidae (0.8%) was represented by two genera
Chrysops, and Tabanus sp. and restricted to stations 2
and 3. Station 2 accounted for 93.8% of the total
Tabanid density.Family Syrphidae and family Muscidae occurred
sporadically with overall percentages of 2.0 and 0.2%,
respectively. They were represented by Eristalis sp.
and Musca sp., respectively. These species were
restricted to station 2 alone.
Analysis of variance (ANOVA) showed that the
density of Chironomidae was significantly higher
(p < 0.05) than those of other families. Also analysis
of variance revealed that there were differences in the
abundance of Diptera among the stations sampled
(p < 0.05) and orthogonal comparison using Duncan
multiple range test showed that station 2 means was
quite different from the means of stations 1 and 3.
3.3. Spatialtemporal dynamics in population
density
The spatialtemporal distribution in abundance of
Diptera in the study stations is shown in Fig. 4. In the
three stations sampled, the highest densities were
recorded during the dry season months, January in
station 1, February in stations 2 and 3. Lower densities
were recorded in July and October for station 1 and in
August for stations 2 and 3. These were periods of high
water level. Analysis of variance however reveals that
Diptera abundance with season was not significant
(p > 0.05).The Ecological relationship between mean abun-
dance and water quality variables at each station using
Pearsons correlation coefficient (Table 3) revealed
that in station 1, water depth, current velocity, and
dissolved oxygen were negatively correlated with the
mean abundance of Diptera, whereas conductivity and
total hardness were positively correlated with the
mean abundance of Diptera. In station 2, water depth,
current velocity, dissolved oxygen were negatively
correlated with the mean abundance of Diptera,
whereas BOD, COD, NO3-N, PO4-P, total hardness
and pH were positively correlated with the mean
abundance of Diptera. Station 3 was similar to station
1; however water depth was negatively correlated with
the mean abundance of Diptera.
3.4. Diversity, dominance and similarity indices
Table 4 shows the summary of the diversity and
dominance indices calculated for the three stations.
The taxon richness calculated as Margalef index (d)
was highest in station 3 (2.190), closely followed by
station 2 (2.074) and station 1 accounted for the least
F.O. Arimoro et al. / Ecological Indicators 7 (2007) 541552548
Fig. 4. Spatial temporal distribution of Diptera density in the study area of River Orogodo, Southern Nigeria.
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(1.595). Shannon diversity (H) and maximum possible
diversity were higher in station 2 although this was
statistically not significant (p > 0.05). Evenness
values were closely similar in all the three sampling
stations. BergerParker dominance value was lowest
in station 1 and similar in both stations 2 and 3.Faunal similarities between sampling stations
evaluated by Jaccards coefficient are given in
Table 5. This test showed that the pair of stations 2
and 3 (0.61), were more similar than other pairs of
sampling stations. Stations 1 and 2 were dissimilar
(0.39), while stations 1 and 3 were fairly similar
(0.55).
4. Discussion
The water quality changes observed especially the
high BOD5 levels, Conductivity, COD, and low
dissolved oxygen values obtained in station 2 portends
the abnormality of the water at this station as a result
of the impact arising from the untreated abattoir
effluents. Nitrate-nitrogen and phosphate-phosphorus
levels of the water obtained from the abattoir
discharge indicate a substantial amount of organic
input coming from the abattoir. These values were
significantly higher than the levels of the control
stations, upstream and downstream of the impacted
sites. The values of nutrients obtained for this study
were very high compared with low titre value reported
for similar natural unimpacted stream within southern
Nigeria (Ogbeibu and Oribhabor, 2002; Edema et al.,2002).
The relatively high velocity reported in station 2,
especially during the rainy season months is attributed
to surface runoff and storm water especially when it
rains.
The pH of an aquatic system although not definitive
is an indicator of the water quality and the extent of
pollution in the watershed (Jonnalagadda and Mhere,
2001). Unpolluted streams normally show a near
neutral or slightly alkaline pH. Most of the water
samples had a pH of about 7 and 8. Station 2, hadslightly higher values of pH which again could be
traced to the nature of the effluent which is slightly
alkaline.
BOD5 values indicate the extent of organic
pollution in aquatic systems, which adversely affect
the water quality (Jonnalagadda and Mhere, 2001). In
all the water samples BOD5 was less than 4 mg L1
except in station 2 where BOD was in the range of 8
14 mg L1, indicating that the effluent from the
abattoir was organic in nature. This high BOD5 value
F.O. Arimoro et al. / Ecological Indicators 7 (2007) 541552 549
Table 3
Pearson correlation coefficients between mean abundance and some
physicochemical parameters at each station
S/N Parameter Stations
1 2 3
1 Air temperature (8C) 0.50* 0.12 0.31
2 Water temperature (8C) 0.59* 0.20 0.43
3 Water depth (m) 0.88* 0.89* 0.85*
4 Current velocity (m s1) 0.66* 0.69* 0.72*
5 Conductivity (ms cm1) 0.87* 0.40 0.77*
6 Dissolved oxygen (mg l1) 0.53* 0.74* 0.28
7 BOD5 (mg L1) 0.05 0.85* 0.03
8 COD (mg L1) 0.65* 0.79* 0.09
9 Nitrate-nitrogen (mg L1) 0.64* 0.62* 0.10
10 Phosphate-phosphorus
(mg L1)
0.62* 0.54 0.54*
11 Total hardness
(mg L1 CaCo3)
0.85* 0.60* 0.16
12 pH 0.23 0.63* 0.02
13 Total alkalinity (mg L1) s 0.45 0.05 0.11
* Significant difference at probability level (p < 0.05).
Table 4
Diversity of Diptera in the study stations of River Orogodo, 2003
2004
Station 1 Station 2 Station 3
Number of samples 12 12 12
Number of taxa 13 19 18
Number of individuals 1845 5866 2336
Margalef index (d)
(taxa richness)
1.595 2.074 2.190
Shannon diversity (H) 0.611 0.654 0.631
Maximum possible
diversity (Hmax)
1.114 1.279 1.255
Evenness (E) 0.548 0.511 0.503
BergerParker dominance 0.467 0.624 0.623
Table 5
Jaccards similarity Index for pairs of sampling stations in River
Orogodo, July 2003June 2004
Stations
1 2 3
Stations
1 0.39 0.55
3 0.61
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recorded in station 2 reflect high burden of organic
pollution.
Water hardness reported for stations 1 and 2 were in
the range of 62.496.45 mg L1
CaCO3 which is inthe range of soft waters by Lind (1979) classification.
Station 2 with an average hardness of 146
7.39 mg L1 CaCO3 is classified as hard water.
The total number of Diptera taxa reported in the
study (24) is high when compared with earlier studies
by Ogbeibu and Victor (1989), Edokpayi et al. (2000)
and Adakole and Anunne (2003), which reported 19,
13 and 18, respectively, in Nigerian freshwater
streams. The probable reason for this high number
of taxa in this report may be due to the organic
materials from the abattoir effluents, whose substrate
is mostly covered by bacteria and sewage fungi which
are the main food source for most diptera (Rueda et al.,
2002). Again, the shallow nature of the stream at this
station must have favoured the growth of pollution
tolerant species such as Eristalis, which extends its
breathing tube outside the water surface. Related
studies elsewhere include those ofMiserendino (2001)
which reported 27 taxa in Andean Patagonian Rivers
and Ogbeibu (2001) recorded 26 taxa in Okomu forest
ponds in southern Nigeria. The principal taxa, in the
present study, Chironomus sp., Polypedilum sp.,
Allaudomyia sp., Culex and Tanytarsus sp. haveearlier been reported in Nigerian waters (Ogbeibu and
Victor, 1989; Edokpayi et al., 2000; Adakole and
Anunne, 2003; Zabbey and Hart, 2006).
Station 2 recorded high abundance of individual
Diptera as compared to the upstream and downstream
stations. Probably this high abundance could be as a
result of the opportunistic species monopolizing the
available resources or further exhibiting certain
adaptations to survive these conditions (Mason,
1991). Again, it is possible that the organic pollutant
has been directly or indirectly used as a food resource,and probably there could have been a reduction in
competition and predation for the remaining species.
Similar studies elsewhere Solimini et al., 2000;
Brown, 1996; Ravera, 2001; Rueda et al., 2002)
revealed that Diptera abundance is due to considerable
load of organic particles from untreated sewage and
livestock effluents.
The overall composition and density of fauna
varied both spatially and temporarily in response to
physical, chemical and biological factors of the
environment. The family Chironomidae especially
C. transvaalensis, C. fractilobus, Tanypus sp. and
Pentaneura sp. 1 and Pentaneura sp. 2 were abundant
taxa especially in station 2. The long reproductiveperiod, the absence of growth synchronization of egg
or larval diapause and a better adaptation to low
oxygen conditions are probably the reasons for the
preponderance of these species. Furthermore, Chir-
onomids are known to build up large populations
quickly and can tolerate sudden changes in habitat
conditions (Solimini et al., 2003). Tanytarsus sp.,
Cricotopus and Corynoneura sp. were completely
absent in station 2. This is an indication that these taxa
are representative of pollution intolerant species and
could not survive the very low oxygen concentration
of that station. Ogbeibu (2001) was of the opinion that
Tanytarus and Cricotopus species are prominent in
stations of permanently high oxygen saturation. These
species are therefore incapable of resisting the harsh
environmental changes and are recommended as
indicator species for freshwater streams in southern
Nigeria.
C. pipiens, Mansonia sp., Anopheles sp., Theobal-
dia sp. and Chaoborus anomalous all belonging to the
family Culicidae were more abundant in station 2.
These organisms are characteristic of polluted waters.
They have been reported in grossly polluted shallowwaters (Hynes, 1978). They are known to exist in
waters in high density that is depleted of oxygen
(Hellawell, 1986). Their abundance is also presum-
ably favoured by the rich supply of particulate organic
matter on which they feed.
The family Ceratopogonidae was represented in all
stations. The larvae of this family are common among
aquatic plants (Ogbeibu, 2001).
Tabanus sp. and Chrysops sp. were the representa-
tive genera of the family Tabanidae. They were more
abundant in the impacted site. Their dominance in thisstation is also traceable to their ability to tolerate and
survive adverse environmental conditions and low
oxygen concentration.
The family Syrphidae was represented by Eristalis
sp. alone and was recorded in station 2 only. This
organism has been implicated in sewage polluted
streams (Ravera, 2001; Rueda et al., 2002). Their
ability to survive is their possession of delicate
retractile anal skills for respiration, and the presence
of decaying organic matter which they feed on
F.O. Arimoro et al. / Ecological Indicators 7 (2007) 541552550
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(Pennak, 1978). They are also known to thrive well in
shallow waters; this is to permit the tip of the extended
caudal respiratory tube to be projected just above the
surface.Dixidae was represented by one genus, Dixa. These
midges are found resting on vegetation (Pennak,
1978). In consonance with our study they were more
abundant in station 3, the site with abundant
vegetation.
The diversity and evenness of species calculated by
Shannon function were similar among the stations
however, station 2 recorded slightly higher Shannon
diversity, maximum possible diversity and dominance
than the upstream and down stream stations. This may
be a reflection of the state of pollution, which was
favourable for the abundance of opportunistic species.
The relatively low number in taxa richness (Margalef
index) in stations 1 and 3 was due to the relatively low
number of representative individuals. This is not a
consequence of environmental degradation but of the
natural selection of Diptera by scarce organic matter
input in these stations.
Jaccard similarity index revealed that stations 2 and
3 were similar. Probably, the discharge of organic
matter/particles at station 2 must have affected the
faunal characteristics downstream with minor changes
as a result of dilution and recovery. Stations 1 and 2were dissimilar, whereas stations 1 and 3 were fairly
similar, indicating that the latter were unimpacted sites.
From the results obtained in this study, there was
restoration downstream of pollution intolerant Dip-
tera. This is evidenced by the natural depuration
process. According to Miserendino and Pizzolon
(2000) organic load dilution is known to occur
downstream generating a species composition and
abundance similar to upstream station.
In conclusion, the perceived effects of the abattoir
waste discharges on the aquatic water body can bemitigated, if these wastes are properly channeled and
treated before discharge into the water surface.
Acknowledgements
We are grateful to Drs. A.E. Ogbeibu and O.J.
Olomokoro who gave their expertise and assistance in
identifying most of the diptera larvae and the
Department of Zoology, Delta State University,
Abraka, Nigeria, for providing some of the materials
used in this study.
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