- Email: [email protected]
Ecological integrity of upper Warri River, Niger Delta using aquatic insects as bioindicators
ecological indicators 9 (2009) 455–461
available at www.sciencedirect.com
journal homepage: www.elsevier.com/locate/ecolind
Ecological integrity of upper Warri River, Niger Delta using aquatic insects as bioindicators Francis O. Arimoro *, Robert B. Ikomi Department of Zoology, Delta State University, P.M.B. 1, Abraka, Nigeria
article info
abstract
Article history:
Aquatic insects are bioindicators of water quality. Their structure and species composition
Received 11 March 2008
is used in assessing the ecological integrity of streams and rivers. Their composition and
Received in revised form
density of the upper Warri River, Niger Delta, Nigeria were assessed and the influence of
15 June 2008
different physical and chemical variables on their distribution was explored at three
Accepted 24 June 2008
designated stations. A total of 57 taxa were recorded with station 2 accounting for the greatest Ephemeroptera–Plecoptera–Trichoptera (EPT) richness. Abundance of the aquatic insects was affected by the nature of the substrate, macrophytes and canopy cover at the
Keywords:
various stations examined. Generally, the upper Warri River is a fairly clean water body rich
EPT organisms
in EPT organisms. Pollution tolerant insect taxa such as chironomids and culicids larvae
Substrate
were only sporadically present. # 2008 Elsevier Ltd. All rights reserved.
Aquatic insects’ macrophyte indicators Warri River Niger Delta
1.
Introduction
The study of the composition and structure of aquatic insects is vital in monitoring the changes of water quality and the ecological integrity of streams and rivers. Ecological integrity can be expressed as the maintenance of all internal and external community processes and attributes so that high ecological integrity corresponds to a natural state and where the natural community is preserved by regulation, and resilience to environmental stress (Karr, 1991). Aquatic insects are among the most directly affected and vulnerable organisms with respect to surface water pollution and constitute an important component of biodiversity in lotic systems (Verneaux et al., 2003). They are diverse, sensitive and respond to both natural and man-induced changes in the environment (Ndaruga et al., 2004). Curiously, the significance of aquatic insects in indicating the ecological integrity of running waters
has been neglected in the past (Karr, 1991), especially when compared to the traditionally popular environmental indicators, such as fish and birds (Bauernfeind and Moog, 2000).Currently, emphasis is shifting to the use of the socalled Ephemeroptera–Plecoptera–Trichoptera (EPT)—philosophy for describing environmental conditions (Atobatele et al., 2005; Arimoro et al., 2007a). The assessment of ecological integrity provides information for environmental managers and decision makers to take accurate and justifiable actions as well as to evaluate the effectiveness of legislative regulations already in force (Bauernfeind and Moog, 2000). Published work on the use of aquatic insects for evaluating the ecological integrity of streams is far from adequate in tropical Africa (Ogbogu and Akinya, 2001; Dobson et al., 2002; Mafuyai et al., 2004). This present work was carried out to investigate the composition and distribution of aquatic insects in relatively unperturbed reaches of the upper Warri River in an attempt to
* Corresponding author. Tel.: +234 8035615424. E-mail address: [email protected] (F.O. Arimoro). 1470-160X/$ – see front matter # 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.ecolind.2008.06.006
456
ecological indicators 9 (2009) 455–461
evaluate their possible relevance as indicators of clean water conditions.
2.
Materials and methods
2.1.
Description of the study area
The upper Warri River lies in the northern outskirts of the fresh water zone in the Niger Delta, Nigeria (58210 –68000 N; 58240 –68210 E) (Fig. 1). The river is fed principally by ground seepage from an aquifer in the thick rainforest of Utagba-Uno in Ndokwa, Southern-Nigeria and flows southwest for about 74 km, through Akoku, Eziokpor, Amai and Umuebu, Abraka and Warri before emptying into the Atlantic Ocean through the Forcados estuary. The water in the stream is the black type and the flow is nontidal. For the purpose of this study three marked out stations were chosen proceeding downstream from the source of the river. Station 1 was located 10 km, from the river source, station 2 was located 7 km, from station 1 at Amai, while station 3 was located another 7 km from station 2 at Umuebu.
2.2.
Water sampling
Water samples were collected monthly between July and December 2006 at each station. Surface water temperatures
were recorded with a mercury-in-glass thermometer. Water velocity was measured in the mid channel on three occasions by timing a float (average of three trials) as it moved over a distance of 10 m (Gordon et al., 1994). Depth was measured in the sample area using a calibrated stick. Other parameters were determined according to APHA (1985) methods. Substratum composition in each 25 m sampling reach was estimated visually as percentage of silt, loam and sand (Ward, 1992).
2.3.
Aquatic insects sampling
Kick samples of macroinvertebrates were collected monthly (July–December 2006) with a D-frame net (800 mm mesh) within an approximately 25-m wadeable portion of the river. Four 3-min samples were taken on each sampling visit to include all different substrata and flow regime zones. Samples collected from the net were preserved in 70% ethanol. In the laboratory, samples were washed in a 500mm mesh sieve to remove sand and macroinvertebrates were then picked from the substrate with the aid of a forceps and microscope. All animals were enumerated and identified under a binocular dissecting microscope and identification using regional keys (Durand and Leveque, 1981; Gerber and Gabriel, 2002), and keys from elsewhere; Merritt and Cummins (1996).
Fig. 1 – Map of the study area showing the sampling stations in the upper reaches of Warri River.
457
ecological indicators 9 (2009) 455–461
Table 1 – Environmental factors measured at three sampling sites of upper Warri River (July–December 2006) Parameter Features of the reach Riparian vegetation Land use Substrate type Air temperature (8C) Water temperature (8C) Water depth (m) Flow velocity (ms1) Dissolved oxygen (mg/L) pH Alkalinity (mg/L) BOD5 (mg/L) Total nitrogen (mg/L) Total phosphorus (mg/L)
Station 1
Station 2
Station 3
Constrained Native Forestry Silt/sand 25.2 1.34 (23.0–27.0) 23.3 1.24ab (22.0–25.0) 1.40 0.61ab (0.58–1.98) 0.33 0.09a (0.20–0.43) 4.49 0.36a (4.02–5.01) 7.01 0.36 (6.90–7.09) 2.67 0.56 (2.00–3.43) 1.43 0.21 (0.90–1.72) 24 10a (21–38) 4 1a (2–6)
Unconstrained Mixed forest-pasture Agriculture Silt/clay 27.8 2.11 (25.0–31.0) 25.2b 1.77 (23.0–28.0) 1.21 0.60a (0.40–1.76) 0.52 0.21b (0.26–0.78) 8.68 0.64b (7.36–10.80) 7.01 0.06 (6.91–7.08) 2.85 0.85 (2.16–4.21) 0.94 0.11 (0.72.1–1.10) 41 14b (32–52) 9 3b (6–12)
Unconstrained Native Native forest Silt/clay 26.0 1.63 (23.0–28.0) 22.3a 1.11 (21.0–24.0) 1.65 0.50b (0.98–2.20) 0.29 0.09a (0.16–0.38) 4.89 0.56a (4.30–5.62) 7.07 0.05 (7.03–7.10) 3.00 0.83 (2.19–4.23) 1.34 0.48 (0.92–1.24) 80a 24 (69–111) 10 4b (7–12)
F-value ANOVA Probability
3.12 5.55* 0.88 4.50* 11.59* 3.75 2.28 1.62 16.42* 3.21
P > 0.05 P < 0.05 P > 0.05 P < 0.05 P < 0.05 P < 0.05 P > 0.05 P < 0.05 P < 0.05 P > 0.05
Note: values are mean S.E. (minimum and maximum values are in parentheses). Different superscript letters in a row show significant differences (P < 0.05) indicated by Tukey Honest significant difference tests. * indicates significantly calculated F-value.
2.4.
Statistical analyses
Community attributes and physicochemical parameters of the sampling stations were compared using repeated measures ANOVA. Fixed effect ANOVAs were performed using dates as replicates on log(x + 1) transformed data. Significant ANOVAs (P < 0.05) were followed by Tukey Honest significant difference (HSD) tests to identify differences between stations means. The components metrics used in assessing the ecological integrity of the upper Warri River were species composition and community structure. Taxa richness (Margalef index), diversity (Shannon–wiener Index) and evenness indices were calculated using the computer BASIC programme SP DIVERS (Ludwig and Reynolds, 1988).
3.
Results and discussion
The physical and chemical conditions of the study stations, that is, air temperature, water depth, pH, alkalinity, BOD, and total phosphorus were not significantly different among the stations examined (Table 1). Water temperature, flow velocity and dissolved oxygen were, however, significantly different (P < 0.05). Station 2 means was greater than the other two stations. Total nitrogen increased progressively from station 1 (upstream) and was greater at station 3. This was also significantly different (P < 0.05) among the stations examined. The physicochemical qualities of water, immediate substrate and food availability are important factors for determining the abundance and distribution of benthos including aquatic insects (Dance and Hynes, 1980). Current velocity was greater in station 3 and greatest in station 2. The nonuniformity can be traced to the wall of the modern bridge constructed in station 2 that reduced the cross-sectional area of the channel, consequently increasing the water volume and flow velocity. According to Nelson and Liebermann (2002), flow velocity is important both directly and indirectly as it influences the type of river bed and amount of silt deposition that in turn affects the distribution of benthic organisms. All the stations had relatively high flow velocity. Hence, they were dominated
by the Ephemeroptera particularly Baetis, Afrobaetodes and the trichopteran, Hydropsyche. This is similar to other studies in Nigeria (Ikomi et al., 2005) and elsewhere (Griffith et al., 2001; Nelson and Liebermann, 2002). More chironomids were found in station 3 where flow velocity was less. This is in accordance with the findings of Doisy and Rabeni (2001) who reported that chironomid abundance is related to the amount of detritus, which in turn is negatively correlated with flow velocity. The detritus material that they feed on does not accumulate in areas of high velocity. The significant role of dissolved oxygen in the diversity of benthic insects was well collaborated in our study. Species diversity was greater at station 2 with the highest dissolved oxygen levels. The plausible reason for high dissolved oxygen in station 2 could be due to large surface area of the station which exposed the site to atmospheric air and sunlight as well as the abundance of organic debris which favoured the photosynthetic activities of aquatic plants. Similar observation was reported by Ikomi et al. (2005) in the River Ethiope, Niger Delta. In addition, the solubility of oxygen in water is primarily governed by water temperature (Imoobe and Oboh, 2003; Ikomi et al., 2005). There was a significant difference (P < 0.05) in water temperature among the stations. This may have contributed to the differences noticed in the amount of dissolved oxygen levels in the stations. The dense tree canopy cover in station 3 contributed to the low water temperature at that site subsequently some species, e.g. Tricorythus and certain Trichoptera were abundant in this site. Nutrients, alkalinity and BOD values were positively correlated with aquatic insects density. It is likely that input of nutrients to the river enhanced primary productivity and was reflected by an increase in aquatic insects’ density. It has been reported that increase inputs of nutrients can significantly increase secondary production, especially in open-canopied reaches where the main pathway of energy flow is through periphytic production (Zalewski et al., 1998). Fiftyseven (57) taxa of aquatic insects were identified, with Ephemeroptera (8), Plecoptera (1), Trichoptera (8), Odonata (12), Hemiptera (9), Coleoptera (14) and Diptera (5) being the representative orders (Table 2). Ephemeroptera was represented by five families. Afrobaetodes was the preponderant ephemeroptera and was present in all the three stations
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ecological indicators 9 (2009) 455–461
Table 2 – The overall composition and distribution of aquatic insects in the upper Warri River study stations, July– December Station 1
Station 2
Station 3
All sites combined
No. of taxa
No. of individuals.
No. of taxa
No. of individuals
No. of taxa
No. of individuals
No. of taxa
Ephemeroptera Baetidae Caenidae Potamanthidae Heptageniidae Tricorythidae
2 – 1 1 1
21 – 2 4 4
2 1 1 2 –
71 8 3 13 –
3 1 – 2 1
37 5 – 9 12
3 1 1 2 1
129 13 5 26 16
Plecoptera Perlidae
1
14
1
9
1
17
1
40
Trichoptera Hydropsychidae Ecnomidae Leptoceridae Hydroptilidae
1 1 2 1
7 6 3 3
2 1 1 2
18 12 4 5
2 1 2 2
23 7 15 20
2 1 2 3
48 25 22 28
Odonata Calopterygidae Lesticidae Coenagrionidae Gomphidae Libellulidae Macromiidae Cordulegasteridae Aeschnidae
1 2 1 1 3 – 1 –
2 7 3 2 14 – 4 –
1 2 1 1 3 1 – 1
7 5 17 24 36 17 – 8
– – – 1 3 – 1 1
– – – 17 42 – 11 4
1 2 1 1 4 1 1 1
9 12 20 43 92 7 15 12
Hemiptera Belostomatidae Corixidae Mesoveliidae Gerridae Notonectidae Nepidae Naucoridae Pleidae
1 1 1 1 1 2 1 1
7 4 11 12 14 19 4 4
1 1 1 1 1 2 1 1
4 3 14 14 7 20 14 2
1 1 – 1 1 1 1 1
3 3 – 15 12 2 13 3
1 1 1 1 1 2 1 1
14 10 25 41 33 41 31 9
Coleoptera Dytiscidae Gyrinidae Hygrobiidae Hydrophilidae Hydraenidae Dryopidae Elmidae
3 1 – 1 1 – 3
16 6 – 4 2 – 16
3 1 – 1 2 1 –
25 7 – 3 13 3 –
2 2 1 – 2 – 2
30 18 3 – 6 – 11
4 2 1 1 2 1 3
71 31 3 7 21 3 27
Diptera Chironomidae Ceratoponidae Tabanidae Culicidae
2 – 1 1
3 – 2 3
1 1 1 1
3 14 2 2
2 – 1 1
8 – 7 4
2 1 1 1
14 14 11 9
sampled. Coloen was restricted to station 3 only. Odonata was the dominant group in station 2. It was represented by ten genera with Coenogrion, Gomphus, Macromia, Oxythemis gamblesi and Aeschna being abundant (Appendix A). Station 3 had very low Odonata density, and it was significantly different among the stations (P < 0.05). The multiple comparison test showed that odonata densities were greatest at station 2, where macrophytes dominated the site (F = 23.6, P < 0.05). Odonata nymphs are usually associated with macrophyte (Carchini et al., 2004). Diptera formed a minor component of fauna in this study. Only five genera were recorded. Chironomidae were represented by two taxa, Chironomus and Pentaneura occurring
No. of individuals
in very limited numbers in the study stations. Tabanus (Tabanidae) and Allaudomyia (Ceratopogonidae) were the other represented taxa. They occurred only sporadically in the study stations. Diversity, taxa richness and dominance indices are shown in Table 3. Values were similar in all stations sampled, however, station 2 recorded higher number of individuals and higher EPT richness. The EPT richness was quite high in all the stations sampled (27.4–34.8%). The EPT richness portrays the river to be well oxygenated and clean as compared to other water bodies in the Niger Delta area of Nigeria with low EPT richness and high chironomid % (Arimoro et al., 2007b;
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ecological indicators 9 (2009) 455–461
Table 3 – Diversity and other indices of aquatic insects in the study stations of upper Warri River
Number of taxa Number of individuals/catch Taxa richness (d) (Margalef index) Shannon-Wiener diversity (H) Evenness (E) Simpson dominance % EPT % chironomids
Station 1
Station 2
42 223 7.60 1.52 0.933 0.038 27.4 3.58
44 397 7.19 1.47 0.892 0.054 34.8 5.28
Chindah et al., 1999). Generally, the high abundance and distribution of sensitive orders of aquatic insects reflects the relative cleanliness of the upper Warri River. Moreover with special reference to Margalef’s water quality index, values greater than 3 indicate clean conditions (Lenat et al., 1980). The value was far greater than 3 at all sites further lending more evidence to the relative ‘clean water’ stations of the study area. In other words, the stretch of the upper reaches
Station 3 41 357 6.81 1.51 0.957 0.035 32.3 5.32
were minimally disturbed from anthropogenic activities. Much work is needed on the life histories and distributional ecology of stream insects and to confirm their potential value for biological monitoring of water quality in lotic systems of the Niger Delta area and other developing countries. In the meantime, there is need to adhere strictly to adequate conservation measures to protect the state of this water body for its beneficial uses.
Appendix A. Taxa and percentage density contribution in the different sampling stations of upper Warri River between July and December 2006 (+ present, S absent) ORDER
Taxa
Station 1
Station 2
Station 3
%Mean abundance
Ephemeroptera
Afrobaetodes Centroptilum Coloen Caenis cibaria Potamanthus Afronurus Ecdyonurus Tricorythus
+ + + + +
+ + + + + +
+ + + + + + +
10.7 1.7 0.7 1.3 0.5 1.4 1.2 1.6
Plecoptera
Neoperla spio Hydropsyche Leptonema Ecnomus Triaenodes Mystacides Agraylea Hydroptila Oxyethira
+ + + + + +
+ + + + + + +
+ + + + + + + +
4.1 2.9 2.0 2.6 0.5 1.7 1.5 0.6 0.7
Odonata
Calopteryx sympecma Lestes Coenagrion Gomphus Orthetrum Oxythemis gamblesi Sympetrum navasi Libellula Macromia Cordulegaster Aeschna
+ + + + + + + + +
+ + + + + + + + + +
+ + + + + +
0.9 0.6 0.7 2.0 4.4 0.4 1.5 4.1 3.4 1.7 1.5 1.3
Hemiptera
Belostoma flumineae Corixa Mesovelia Gerris lacustris Notonecta Ranatra linearis Nepa cinerea Naucoris Plea leachi
+ + + + + + + + +
+ + + + + + + + +
+ + + + + + +
1.4 1.0 1.5 4.3 3.4 3.5 0.7 3.2 0.9
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ecological indicators 9 (2009) 455–461
Appendix A (Continued ) ORDER Coleoptera
Diptera
Taxa
Station 1
Station 2
Station 3
Hydrovatus Laccomphilus Dytiscus Derovatellus Gyrinus Orectochilus Hygrobia tarda Hydrophilus Hydraena Ochthebius Dryops Stenelmis Promeresia Limnius
+ + + + + + + + +
+ + + + + + +
+ + + + + + + + +
4.1 0.8 2.3 0.2 3.1 0.2 0.3 0.8 1.3 0.9 0.4 1.1 1.0 0.4
Chironomus Pentaneura Allaudomyia Tabanus Culex pipiens
+ + + +
+ + + +
+ + + +
1.1 0.3 1.4 1.1 0.9
references
APHA., 1985. American Public Health Association. Standard Methods for the examination of water and waste water’ Ed. APHA, Washington, DC, 1244 pp. Arimoro, F.O., Ikomi, R.B., Erebe, E., 2007a. Macroinvertebrate community diversity in relation to water quality status of River Ase, Niger Delta. Nigeria. J. Fish. Aquat. Sci. 2 (5), 337–344. Arimoro, F.O., Ikomi, R.B., Iwegbue, C.M.A., 2007b. Water quality changes in relation Diptera community patterns and diversity measured at an organic effluent impacted stream in the Niger Delta, Nigeria. Ecol. Indicators 7, 541–552. Atobatele, O.E., Morenikeji, O.A., Ugwumba, O.A., 2005. Spatial variation in physical and chemical parameters of benthic macroinvertebrate fauna of River Ogunpa, Ibadan. The Zoologist 3, 58–67. Bauernfeind, E., Moog, O., 2000. Mayflies (Insecta: Ephemeroptera) and the assessment of ecological integrity: a methodological approach. Hydrobiologia 135, 155–165. Carchini, G., Pacione, T., Tanzilli, C.I., Di Domenico, M., Solimini, A., 2004. Temporal variation of an Odonata species assemblage (Rome, Italy). Odonatologica 33, 157–168. Chindah, A.H., Hart, A.I., Atuzie, B., 1999. A preliminary investigation on the effects of municipal waste discharge on the macrofauna associated with macrophytes in a small freshwater stream in Nigeria. Afr. J. Appl. Zool. 2, 29–33. Dance, K.W., Hynes, H.B.N., 1980. Some effects of agricultural land use on stream insect communities. Environ. Pollut. Ser. A 22, 19–28. Dobson, M., Magana, A., Magana, A., Mathooka, J.M., Ndegwa, F.K., 2002. Detitivores in Kenyan highland streams: more evidence for the paucity of shredders in the tropics? Freshwater Biol. 47 (178), 909–919. Doisy, K.E., Rabeni, C.F., 2001. Flow conditions, Benthic Food resources, and invertebrate community composition in a low-gradient stream in Missouri. J. N. Am. Benthol. Soc. 20 (1), 17–32. Durand J.R. and Leveque C. 1981. Flore et faune Aquatiques De l’Afrique Saholo – Sou danienne editions de l’office de la
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Recherche Scientifique et Technique aetre – mercollection initiatins. Documentations Technique No. 45, Paris. Gerber A. and Gabriel M.J.M. 2002. Aquatic invertebrates of South African Rivers. Field Guide. Institute for Water Quality Studies, vol. I and II, 150 pp. Gordon, N.D., Mc Mahon, T.A., Finlayson, B.L., 1994. Stream Hydrology, An Introduction for Ecologists. John Wiley and sons, New York, 526 pp. Griffith, M.B., Kaufmann, P.R., Herlihy, A.T., Hill, B.T., 2001. Analysis of macroinvertebrate assemblages in relation to environmental gradients in Rocky mountain streams. Ecol. Appl. 11, 489–505. Ikomi, R.B., Arimoro, F.O., Odihirin, O.K., 2005. Composition, distribution and abundance of macroinvetebrates of the upper reaches of River Ethiope, Delta State, Nigeria. The Zoologist 3, 68–81. Imoobe, T.O.T., Oboh, I.P., 2003. Physical and chemical hydrology of River Jamieson, Niger Delta, Nigeria. Benin Sci. Digest 1, 105–119. Karr, J.R., 1991. Biological integrity: a long-neglected aspect of water resource management. Ecol. Appl. 166–184. Lenat, D.R., Smock, L.A., Penrose, D.L., 1980. Use of benthic macroinvertebrates as indicators of environmental quality. In: Biological Monitoring for Environmental Effects, Lexinton Books, Toronto, Canada, pp. 7–114. Ludwig, J.A., Reynolds, J.F., 1988. Statistical Ecology. A Primer on Methods and Computing. Wiley/interscience, Wiley, New york, 337 pp. Mafuyai, H.B., Wade, J.W., Agoom, A.K., Audu, B.S., 2004. Aquatic insect composition at a Simulium breeding site on the River Assob, Plateau State, Nigeria. J. Aquat. Sci. 19 (1), 9–15. Merritt, R.W., Cummins, K.W., 1996. An Introduction to the Aquatic Insects of North America 3rd Ed. Kendall-Hunt, Dubuque, IA, 862 pp. Ndaruga, A.M., Ndiritu, G.G., Gichuki, N.M., Wamicha, W.N., 2004. Impact of water quality on the macroinvertebrate assemblages along a tropical stream in Kenya. African J. Ecol. 42 (3), 208–216. Nelson, S.M., Liebermann, D.M., 2002. The influence of flow and other environmental factors on the benthic invertebrates in Sacramento River, USA. Hydrobiologia 489 (1), 117–129.
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Ogbogu, S.S., Akinya, T.O., 2001. Distribution and abundance of insects orders in relation to habitat types in Opa stream reservoir, Nigeria. J. Aquat. Sci. 16 (1), 7–12. Verneaux, J., Schmitt, V., Verneaux, V., Prouteau, C., 2003. Benthic insects and fish of the Doubs River systems: typological traits and the development of a species continuum in a theoretically extrapolated watercourse. Hydrobiologia 490, 63–74.
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available at www.sciencedirect.com
journal homepage: www.elsevier.com/locate/ecolind
Ecological integrity of upper Warri River, Niger Delta using aquatic insects as bioindicators Francis O. Arimoro *, Robert B. Ikomi Department of Zoology, Delta State University, P.M.B. 1, Abraka, Nigeria
article info
abstract
Article history:
Aquatic insects are bioindicators of water quality. Their structure and species composition
Received 11 March 2008
is used in assessing the ecological integrity of streams and rivers. Their composition and
Received in revised form
density of the upper Warri River, Niger Delta, Nigeria were assessed and the influence of
15 June 2008
different physical and chemical variables on their distribution was explored at three
Accepted 24 June 2008
designated stations. A total of 57 taxa were recorded with station 2 accounting for the greatest Ephemeroptera–Plecoptera–Trichoptera (EPT) richness. Abundance of the aquatic insects was affected by the nature of the substrate, macrophytes and canopy cover at the
Keywords:
various stations examined. Generally, the upper Warri River is a fairly clean water body rich
EPT organisms
in EPT organisms. Pollution tolerant insect taxa such as chironomids and culicids larvae
Substrate
were only sporadically present. # 2008 Elsevier Ltd. All rights reserved.
Aquatic insects’ macrophyte indicators Warri River Niger Delta
1.
Introduction
The study of the composition and structure of aquatic insects is vital in monitoring the changes of water quality and the ecological integrity of streams and rivers. Ecological integrity can be expressed as the maintenance of all internal and external community processes and attributes so that high ecological integrity corresponds to a natural state and where the natural community is preserved by regulation, and resilience to environmental stress (Karr, 1991). Aquatic insects are among the most directly affected and vulnerable organisms with respect to surface water pollution and constitute an important component of biodiversity in lotic systems (Verneaux et al., 2003). They are diverse, sensitive and respond to both natural and man-induced changes in the environment (Ndaruga et al., 2004). Curiously, the significance of aquatic insects in indicating the ecological integrity of running waters
has been neglected in the past (Karr, 1991), especially when compared to the traditionally popular environmental indicators, such as fish and birds (Bauernfeind and Moog, 2000).Currently, emphasis is shifting to the use of the socalled Ephemeroptera–Plecoptera–Trichoptera (EPT)—philosophy for describing environmental conditions (Atobatele et al., 2005; Arimoro et al., 2007a). The assessment of ecological integrity provides information for environmental managers and decision makers to take accurate and justifiable actions as well as to evaluate the effectiveness of legislative regulations already in force (Bauernfeind and Moog, 2000). Published work on the use of aquatic insects for evaluating the ecological integrity of streams is far from adequate in tropical Africa (Ogbogu and Akinya, 2001; Dobson et al., 2002; Mafuyai et al., 2004). This present work was carried out to investigate the composition and distribution of aquatic insects in relatively unperturbed reaches of the upper Warri River in an attempt to
* Corresponding author. Tel.: +234 8035615424. E-mail address: [email protected] (F.O. Arimoro). 1470-160X/$ – see front matter # 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.ecolind.2008.06.006
456
ecological indicators 9 (2009) 455–461
evaluate their possible relevance as indicators of clean water conditions.
2.
Materials and methods
2.1.
Description of the study area
The upper Warri River lies in the northern outskirts of the fresh water zone in the Niger Delta, Nigeria (58210 –68000 N; 58240 –68210 E) (Fig. 1). The river is fed principally by ground seepage from an aquifer in the thick rainforest of Utagba-Uno in Ndokwa, Southern-Nigeria and flows southwest for about 74 km, through Akoku, Eziokpor, Amai and Umuebu, Abraka and Warri before emptying into the Atlantic Ocean through the Forcados estuary. The water in the stream is the black type and the flow is nontidal. For the purpose of this study three marked out stations were chosen proceeding downstream from the source of the river. Station 1 was located 10 km, from the river source, station 2 was located 7 km, from station 1 at Amai, while station 3 was located another 7 km from station 2 at Umuebu.
2.2.
Water sampling
Water samples were collected monthly between July and December 2006 at each station. Surface water temperatures
were recorded with a mercury-in-glass thermometer. Water velocity was measured in the mid channel on three occasions by timing a float (average of three trials) as it moved over a distance of 10 m (Gordon et al., 1994). Depth was measured in the sample area using a calibrated stick. Other parameters were determined according to APHA (1985) methods. Substratum composition in each 25 m sampling reach was estimated visually as percentage of silt, loam and sand (Ward, 1992).
2.3.
Aquatic insects sampling
Kick samples of macroinvertebrates were collected monthly (July–December 2006) with a D-frame net (800 mm mesh) within an approximately 25-m wadeable portion of the river. Four 3-min samples were taken on each sampling visit to include all different substrata and flow regime zones. Samples collected from the net were preserved in 70% ethanol. In the laboratory, samples were washed in a 500mm mesh sieve to remove sand and macroinvertebrates were then picked from the substrate with the aid of a forceps and microscope. All animals were enumerated and identified under a binocular dissecting microscope and identification using regional keys (Durand and Leveque, 1981; Gerber and Gabriel, 2002), and keys from elsewhere; Merritt and Cummins (1996).
Fig. 1 – Map of the study area showing the sampling stations in the upper reaches of Warri River.
457
ecological indicators 9 (2009) 455–461
Table 1 – Environmental factors measured at three sampling sites of upper Warri River (July–December 2006) Parameter Features of the reach Riparian vegetation Land use Substrate type Air temperature (8C) Water temperature (8C) Water depth (m) Flow velocity (ms1) Dissolved oxygen (mg/L) pH Alkalinity (mg/L) BOD5 (mg/L) Total nitrogen (mg/L) Total phosphorus (mg/L)
Station 1
Station 2
Station 3
Constrained Native Forestry Silt/sand 25.2 1.34 (23.0–27.0) 23.3 1.24ab (22.0–25.0) 1.40 0.61ab (0.58–1.98) 0.33 0.09a (0.20–0.43) 4.49 0.36a (4.02–5.01) 7.01 0.36 (6.90–7.09) 2.67 0.56 (2.00–3.43) 1.43 0.21 (0.90–1.72) 24 10a (21–38) 4 1a (2–6)
Unconstrained Mixed forest-pasture Agriculture Silt/clay 27.8 2.11 (25.0–31.0) 25.2b 1.77 (23.0–28.0) 1.21 0.60a (0.40–1.76) 0.52 0.21b (0.26–0.78) 8.68 0.64b (7.36–10.80) 7.01 0.06 (6.91–7.08) 2.85 0.85 (2.16–4.21) 0.94 0.11 (0.72.1–1.10) 41 14b (32–52) 9 3b (6–12)
Unconstrained Native Native forest Silt/clay 26.0 1.63 (23.0–28.0) 22.3a 1.11 (21.0–24.0) 1.65 0.50b (0.98–2.20) 0.29 0.09a (0.16–0.38) 4.89 0.56a (4.30–5.62) 7.07 0.05 (7.03–7.10) 3.00 0.83 (2.19–4.23) 1.34 0.48 (0.92–1.24) 80a 24 (69–111) 10 4b (7–12)
F-value ANOVA Probability
3.12 5.55* 0.88 4.50* 11.59* 3.75 2.28 1.62 16.42* 3.21
P > 0.05 P < 0.05 P > 0.05 P < 0.05 P < 0.05 P < 0.05 P > 0.05 P < 0.05 P < 0.05 P > 0.05
Note: values are mean S.E. (minimum and maximum values are in parentheses). Different superscript letters in a row show significant differences (P < 0.05) indicated by Tukey Honest significant difference tests. * indicates significantly calculated F-value.
2.4.
Statistical analyses
Community attributes and physicochemical parameters of the sampling stations were compared using repeated measures ANOVA. Fixed effect ANOVAs were performed using dates as replicates on log(x + 1) transformed data. Significant ANOVAs (P < 0.05) were followed by Tukey Honest significant difference (HSD) tests to identify differences between stations means. The components metrics used in assessing the ecological integrity of the upper Warri River were species composition and community structure. Taxa richness (Margalef index), diversity (Shannon–wiener Index) and evenness indices were calculated using the computer BASIC programme SP DIVERS (Ludwig and Reynolds, 1988).
3.
Results and discussion
The physical and chemical conditions of the study stations, that is, air temperature, water depth, pH, alkalinity, BOD, and total phosphorus were not significantly different among the stations examined (Table 1). Water temperature, flow velocity and dissolved oxygen were, however, significantly different (P < 0.05). Station 2 means was greater than the other two stations. Total nitrogen increased progressively from station 1 (upstream) and was greater at station 3. This was also significantly different (P < 0.05) among the stations examined. The physicochemical qualities of water, immediate substrate and food availability are important factors for determining the abundance and distribution of benthos including aquatic insects (Dance and Hynes, 1980). Current velocity was greater in station 3 and greatest in station 2. The nonuniformity can be traced to the wall of the modern bridge constructed in station 2 that reduced the cross-sectional area of the channel, consequently increasing the water volume and flow velocity. According to Nelson and Liebermann (2002), flow velocity is important both directly and indirectly as it influences the type of river bed and amount of silt deposition that in turn affects the distribution of benthic organisms. All the stations had relatively high flow velocity. Hence, they were dominated
by the Ephemeroptera particularly Baetis, Afrobaetodes and the trichopteran, Hydropsyche. This is similar to other studies in Nigeria (Ikomi et al., 2005) and elsewhere (Griffith et al., 2001; Nelson and Liebermann, 2002). More chironomids were found in station 3 where flow velocity was less. This is in accordance with the findings of Doisy and Rabeni (2001) who reported that chironomid abundance is related to the amount of detritus, which in turn is negatively correlated with flow velocity. The detritus material that they feed on does not accumulate in areas of high velocity. The significant role of dissolved oxygen in the diversity of benthic insects was well collaborated in our study. Species diversity was greater at station 2 with the highest dissolved oxygen levels. The plausible reason for high dissolved oxygen in station 2 could be due to large surface area of the station which exposed the site to atmospheric air and sunlight as well as the abundance of organic debris which favoured the photosynthetic activities of aquatic plants. Similar observation was reported by Ikomi et al. (2005) in the River Ethiope, Niger Delta. In addition, the solubility of oxygen in water is primarily governed by water temperature (Imoobe and Oboh, 2003; Ikomi et al., 2005). There was a significant difference (P < 0.05) in water temperature among the stations. This may have contributed to the differences noticed in the amount of dissolved oxygen levels in the stations. The dense tree canopy cover in station 3 contributed to the low water temperature at that site subsequently some species, e.g. Tricorythus and certain Trichoptera were abundant in this site. Nutrients, alkalinity and BOD values were positively correlated with aquatic insects density. It is likely that input of nutrients to the river enhanced primary productivity and was reflected by an increase in aquatic insects’ density. It has been reported that increase inputs of nutrients can significantly increase secondary production, especially in open-canopied reaches where the main pathway of energy flow is through periphytic production (Zalewski et al., 1998). Fiftyseven (57) taxa of aquatic insects were identified, with Ephemeroptera (8), Plecoptera (1), Trichoptera (8), Odonata (12), Hemiptera (9), Coleoptera (14) and Diptera (5) being the representative orders (Table 2). Ephemeroptera was represented by five families. Afrobaetodes was the preponderant ephemeroptera and was present in all the three stations
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Table 2 – The overall composition and distribution of aquatic insects in the upper Warri River study stations, July– December Station 1
Station 2
Station 3
All sites combined
No. of taxa
No. of individuals.
No. of taxa
No. of individuals
No. of taxa
No. of individuals
No. of taxa
Ephemeroptera Baetidae Caenidae Potamanthidae Heptageniidae Tricorythidae
2 – 1 1 1
21 – 2 4 4
2 1 1 2 –
71 8 3 13 –
3 1 – 2 1
37 5 – 9 12
3 1 1 2 1
129 13 5 26 16
Plecoptera Perlidae
1
14
1
9
1
17
1
40
Trichoptera Hydropsychidae Ecnomidae Leptoceridae Hydroptilidae
1 1 2 1
7 6 3 3
2 1 1 2
18 12 4 5
2 1 2 2
23 7 15 20
2 1 2 3
48 25 22 28
Odonata Calopterygidae Lesticidae Coenagrionidae Gomphidae Libellulidae Macromiidae Cordulegasteridae Aeschnidae
1 2 1 1 3 – 1 –
2 7 3 2 14 – 4 –
1 2 1 1 3 1 – 1
7 5 17 24 36 17 – 8
– – – 1 3 – 1 1
– – – 17 42 – 11 4
1 2 1 1 4 1 1 1
9 12 20 43 92 7 15 12
Hemiptera Belostomatidae Corixidae Mesoveliidae Gerridae Notonectidae Nepidae Naucoridae Pleidae
1 1 1 1 1 2 1 1
7 4 11 12 14 19 4 4
1 1 1 1 1 2 1 1
4 3 14 14 7 20 14 2
1 1 – 1 1 1 1 1
3 3 – 15 12 2 13 3
1 1 1 1 1 2 1 1
14 10 25 41 33 41 31 9
Coleoptera Dytiscidae Gyrinidae Hygrobiidae Hydrophilidae Hydraenidae Dryopidae Elmidae
3 1 – 1 1 – 3
16 6 – 4 2 – 16
3 1 – 1 2 1 –
25 7 – 3 13 3 –
2 2 1 – 2 – 2
30 18 3 – 6 – 11
4 2 1 1 2 1 3
71 31 3 7 21 3 27
Diptera Chironomidae Ceratoponidae Tabanidae Culicidae
2 – 1 1
3 – 2 3
1 1 1 1
3 14 2 2
2 – 1 1
8 – 7 4
2 1 1 1
14 14 11 9
sampled. Coloen was restricted to station 3 only. Odonata was the dominant group in station 2. It was represented by ten genera with Coenogrion, Gomphus, Macromia, Oxythemis gamblesi and Aeschna being abundant (Appendix A). Station 3 had very low Odonata density, and it was significantly different among the stations (P < 0.05). The multiple comparison test showed that odonata densities were greatest at station 2, where macrophytes dominated the site (F = 23.6, P < 0.05). Odonata nymphs are usually associated with macrophyte (Carchini et al., 2004). Diptera formed a minor component of fauna in this study. Only five genera were recorded. Chironomidae were represented by two taxa, Chironomus and Pentaneura occurring
No. of individuals
in very limited numbers in the study stations. Tabanus (Tabanidae) and Allaudomyia (Ceratopogonidae) were the other represented taxa. They occurred only sporadically in the study stations. Diversity, taxa richness and dominance indices are shown in Table 3. Values were similar in all stations sampled, however, station 2 recorded higher number of individuals and higher EPT richness. The EPT richness was quite high in all the stations sampled (27.4–34.8%). The EPT richness portrays the river to be well oxygenated and clean as compared to other water bodies in the Niger Delta area of Nigeria with low EPT richness and high chironomid % (Arimoro et al., 2007b;
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Table 3 – Diversity and other indices of aquatic insects in the study stations of upper Warri River
Number of taxa Number of individuals/catch Taxa richness (d) (Margalef index) Shannon-Wiener diversity (H) Evenness (E) Simpson dominance % EPT % chironomids
Station 1
Station 2
42 223 7.60 1.52 0.933 0.038 27.4 3.58
44 397 7.19 1.47 0.892 0.054 34.8 5.28
Chindah et al., 1999). Generally, the high abundance and distribution of sensitive orders of aquatic insects reflects the relative cleanliness of the upper Warri River. Moreover with special reference to Margalef’s water quality index, values greater than 3 indicate clean conditions (Lenat et al., 1980). The value was far greater than 3 at all sites further lending more evidence to the relative ‘clean water’ stations of the study area. In other words, the stretch of the upper reaches
Station 3 41 357 6.81 1.51 0.957 0.035 32.3 5.32
were minimally disturbed from anthropogenic activities. Much work is needed on the life histories and distributional ecology of stream insects and to confirm their potential value for biological monitoring of water quality in lotic systems of the Niger Delta area and other developing countries. In the meantime, there is need to adhere strictly to adequate conservation measures to protect the state of this water body for its beneficial uses.
Appendix A. Taxa and percentage density contribution in the different sampling stations of upper Warri River between July and December 2006 (+ present, S absent) ORDER
Taxa
Station 1
Station 2
Station 3
%Mean abundance
Ephemeroptera
Afrobaetodes Centroptilum Coloen Caenis cibaria Potamanthus Afronurus Ecdyonurus Tricorythus
+ + + + +
+ + + + + +
+ + + + + + +
10.7 1.7 0.7 1.3 0.5 1.4 1.2 1.6
Plecoptera
Neoperla spio Hydropsyche Leptonema Ecnomus Triaenodes Mystacides Agraylea Hydroptila Oxyethira
+ + + + + +
+ + + + + + +
+ + + + + + + +
4.1 2.9 2.0 2.6 0.5 1.7 1.5 0.6 0.7
Odonata
Calopteryx sympecma Lestes Coenagrion Gomphus Orthetrum Oxythemis gamblesi Sympetrum navasi Libellula Macromia Cordulegaster Aeschna
+ + + + + + + + +
+ + + + + + + + + +
+ + + + + +
0.9 0.6 0.7 2.0 4.4 0.4 1.5 4.1 3.4 1.7 1.5 1.3
Hemiptera
Belostoma flumineae Corixa Mesovelia Gerris lacustris Notonecta Ranatra linearis Nepa cinerea Naucoris Plea leachi
+ + + + + + + + +
+ + + + + + + + +
+ + + + + + +
1.4 1.0 1.5 4.3 3.4 3.5 0.7 3.2 0.9
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Appendix A (Continued ) ORDER Coleoptera
Diptera
Taxa
Station 1
Station 2
Station 3
Hydrovatus Laccomphilus Dytiscus Derovatellus Gyrinus Orectochilus Hygrobia tarda Hydrophilus Hydraena Ochthebius Dryops Stenelmis Promeresia Limnius
+ + + + + + + + +
+ + + + + + +
+ + + + + + + + +
4.1 0.8 2.3 0.2 3.1 0.2 0.3 0.8 1.3 0.9 0.4 1.1 1.0 0.4
Chironomus Pentaneura Allaudomyia Tabanus Culex pipiens
+ + + +
+ + + +
+ + + +
1.1 0.3 1.4 1.1 0.9
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