University of Nigeria Research Publications
IBEMENUGA, Keziah Nwamaka Author PG/M.Sc/00/28091 The Ecology of Macro-Invertebrate Fauna of Ogbei Stream in Nkpologwu, Aguata
Title Local Government Area, Anambra State, Nigeria.
Physical Sciences Faculty
Zoology Department
March, 2005. Date
Signature Signature
THE ECOLOGY OF MACRO-INVERTEBRATE FAUNA OF OGBEI STREAM IN NKPOLOGWU, AGUATA LOCAL GOVERNMENT AREA, ANAMBRA STATE, NIGERIA
IBEMENUGA KEZIAH NWAMAKA
M.Sc. ZOOLOGY (HYDROBIOLOGY)
MARCH 2005 THE ECOLOGY OF MACRO-INVERTEBRATE FAUNA OF OGBEI STREAM IN NKPOLOGWU, AGUATA LOCAL GOVERNMENT AREA, ANAMBRA STATE, NIGERIA.
IBEMENUGA KEZIAH NWAMAKA PG/M.Sc.100/28091
A PROJECT REPORT SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENT FOR THE AWARD OF MASTER OF SCIENCE IN HYDROBIOLOGY TO THE DEPARTMENT OF ZOOLOGY, UNIVERSITY OF NIGERIA, NSUKKA.
DEPARTMENT OF ZOOLOGY UNIVERSITY OF NIGERIA NSUKKA
MARCH 2005 TITLE PAGE
THE ECOLOGY OF MACRO-INVERTEBRATE FAUNA
OF OGBEI STREAM IN NKPOLOGWU, AGUATA LOCAL
GOVERNMENT AREA, ANAMBRA STATE, NIGERIA CERTIFICATION
Miss Ibemenuga, K. N., a postgraduate student of Department of Zoology with
Registration Number PG/M.Sc./00/28091,has satisfactorily completed the requirements for course and research work for the degree of Master of Science in Zoology (Hydrobiology). The work embodied in this project report is original and has not been submitted in part or full for other diploma or degree of this or any other university.
...... Supervisor Head of Department (Dr. N M lnyan (Dr. H.M.G. Ezenwaji) Department of Zoology Department of Zoology University of Nigeria University of Nigeria Nsukka, Nigeria Nsukka, Nigeria DEDICATION
To my personal Lord and Saviour, Jesus Christ. ACKNOWLEDGEMENTS
I am highly indebted to my supervisor, Dr. N. M. Inyang, for his fatherly advice and constructive comments, which have contributed in no small measure to the successful completion of this study. He desires more gratitude from me than I can express here.
I would like to thank Dr, H. M. G. Ezenwaji, Dr. P. C. Ofojekwu and Mr. A. Ujah for their immense help in identifying the specimens collected and N. S. Oluah for laboratory chemical analyses.
I thank my relatives for their moral and financial support, which contributed to the success of this project.
My thanks also go to the Head of Department of Zoology, the lecturers and technical staff of the Department of Zoology, University of Nigeria, Nsukka, who made available the relevant equipment I needed for my project.
Finally, I wish to express my gratitude to Mr. A. 0. Ozioko (rtd) of the Department of
Botany for identifying the plant specimens collected during the fieldwork
Ibemenuga, K. N Department of Zoology University of Nigeria Nsukka. TABLE OF CONTENTS
TITLE PAGE
CERTIFICATION
DEDICATION
ACKNOWLEDGEMENTS iv
TABLE OF CONTENTS v
LIST OF TABLES vii .. . LIST OF FIGURES Vlll
ABSTRACT ix
CHAPTER ONE:INTRODUCTION AND LITERATURE REVIEW
1.0 Introduction
1.1 Justification of the study
1.2 Aims and objectives
1.3 Literature review
CHAPTER TWO: MATERIALS AND METHODS
2.1 The study area
2.2 Sample coIIections
2.3 Determination of physico-chemical parameters
2.4 Data analyses CHAPTER THREE: RESULTS
3.1 Physico-chemical parameters
3.2 Faunal composition, distribution and abundance 3. 2. 1. Variations in relation to stations
3. 2. 2. Monthly variations of macro-invertebrate population
3.2. 3. Seasonal variations of macro-invertebrate population
3. 2.4. Faunal diversity and dominance
3.2. 5. Faunal similarity of study stations
3.2.6. Relationship between macro-invertebrate fauna and
physico-chemical parameters
CHAPTER FOUR: DISCUSSION AND CONCLUSION
4.0 Discussion and conclusion
REFERENCES
APPENDIX vii
LIST OF TABLES
Table la: Mean monthly changes in the physical and chemical characteristics of Ogbei stream.
Table I b: Mean values of physical and chemical characteristics of the study stations.
Table 2: Mean of rainy and dry season values of physical and chemical characteristics of Ogbei stream.
Table 3: Composition and abundance of macro-invertebrates in Ogbei stream.
Table 4: Abundance of macro-invertebrates in relation to the study stations.
Table 5: Monthly variations of macro-invertebrates in Ogbei stream.
Table 6: Seasonal variations of macro-invertebrates in Ogbei stream.
Table7: Diversity of macro-invertebrates in the study stations.
Table 8: Test of significance of general diversity index (H) between pairs of stations. 80
Table 9: Similarity coefficients of pairs of study stations. 82
Table 10: Pearson's correlation coefficient between total macro-invertebrate abundance and physical and chemical parameters of Ogbei stream. 84 ... Vlll
LIST OF FIGURES
Fig. 1: Map of the study area showing Ogbei stream.
Fig. 2: Sampling equipment used for the study.
Fig. 3. Monthly variations in water temperature in the study stations.
Fig. 4: Percentage abundance of macro-invertebrates at the study stations. 47 ABSTRACT
The macro-invertebrate fauna of Ogbei stream in Nkpologwu, Aguata local Government Area,
Anambra State, Nigeria was studied between May 2002 and April 2003. six stations were selected for the study of physico-chemical and biological factors in relation to depth, human activities and land influence in the different stations. Analyses of the physico-chemical parameters indicated that water temperature fluctuated between 24.8' C and 28.7' C with an annual mean o f 2 7.47k0.79.Dissolved o xygen ranged from 3.8 mg/l in March to 6.5 mg/l in
August with an annual mean of 5.14*0.69. Depth ranged from 0.38 m in March to 0.72 m in
August with an annual mean of 0.54*0.07. Water transparency varied between 16.3 cm in
September and 33.9 cm in March with an annual mean of 26.73*3.59. Free carbon dioxide ranged from 4.0 mg/l to 39.2 mg/l in August and February respectively. The annual mean was
11 -60k6.49. Alkalinity fluctuated from 24.3 mgA CaC03 to 55.0 mg/l CaC03 in August and
October respectively with an annual mean of 33.25k6.53. A total of 11420 macro-invertebrates belonging to 4 classes, 13 orders, 29 families and 51 species were collected. Insecta (11225,
98.29%) was the most abundant class, followed by Arachnids (92, 0.81%), Oligochaeta (75,
0.66%) and Crustacea (28, 0.25%). Diptera was the most abundant order with a percentage composition of 42.62%, followed by Odonata (36.89%), Coleoptera (9.76%), Hemiptera (8.22%) and Plesiopora (0.66%). Composition and distribution of macro-invertebrates indicated that station 3 had the highest percentage composition and abundance of 28.56% (3262), followed by station 2 with 19.54% (2232). Station 5 had the least value of 9.39% (1072). There was a positive correlation between macro-invertebrate abundance and air temperature (r = 0.428), water temperature (r = 0.590), transparency (r = 0.422) and free carbon dioxide (r = 0.305). The effects of the physico- chemical parameters on the aquatic macro-invertebrate population in the stream were discussed. CHAPTER ONE
INTRODUCTION AND LITERAURE REVIEW
1.0 INTRODUCTION
The home of the ancient man was the waterside. The spring stops his thirst.
The bogs afforded his dependable supply of animal food. Water-hunting and fur- bearing animals provided his clothing. The rivers were his routes. Water sports were a large part of his relaxation, and the scenery of the shores was the food of his simple soul.
Although conditions of present life have greatly removed mankind from the waterside, and common needs have found other sources of supply, the ancient instincts still remain. Where invertebrates are abundant, and s warms o f may-flies hover, there we find life very interesting. The long-legged pond skater, Gerris sp. moving elegantly with great ease on the surface of the water attracts the attention of even the most casual observer (Olaniyan, 1978). The school boy stands on the border of a stream or even the pool, watching the caddis worms haul their lumbering cases about on the bottom, and the planktologist plies his nets recording each season the wax and wane of aquatic organisms, and both are satisfactory observers.
Aquatic bodies, be they marine, fresh water or estuary, and their flora and fauna have been a source of satisfaction to man.
Freshwater habitats are broadly classified into two main groups of environment, namely standing water or lentic, and flowing water or lotic. The lentic environments, sometimes known as the standing - water series, include all forms of inland waters (lakes, reservoirs, ponds, bogs, swamps, and their intergrades) in which
water motion is not that of continuous flow in a definite direction. ~ssentiallythe water is standing, although a certain amount of water movement may occur such as a
wave action, internal currents or water flow in the vicinity of inlets and outlets.
The lotic or running water series include all forms of inland waters whereby
the entire body of water moves continuously in a definite direction. The lotic
environment includes streams, rivers, springs and the heads of large impoundments
where the lotic conditions of streams grade into the lentic (Lagler et al., 1977).
The term invertebrates means "without or no backbone" (Cecie, 1975,
Kimbal!, 1974). Parker (1984) went further to say that such an animal in addition to
lacking a backbone also lacks internal skeleton.
Aquatic invertebrates have been in existence since creation and several species
inhabit fresh, marine and brackish waters. They can be classified according to their
habitats - the benthos and pelagic, as well a s according to their size - m acro and
micro-invertebrates. The benthic or benthonic invertebrates are found at the bottom
of a body of water (Reid and Wood, 1976). They may live in or on (and may move
slowly over) the substratum of water body (Olaniyan, 1978) and depend upon the
decomposition cycle for most if not all their basic food supply (Brinkhurst, 1974).
Benthic invertebrates may construct attached cases, tubes or nets in which they live in
or roam freely over rocks, organic debris, and other substrates during all or part of
their life cycle.
The pelagic invertebrates according to Olaniyan (1 978) were found away from
the bottom. They consist of plankton and nekton. The plankton consists of animals,
which float passively or swim on the water surface. The nekton consists of actively
moving or swimming numerous larvae of many invertebrates and small crustaceans,
which form the bulk of the zooplankton. Macro-invertebrates are considered by definition to be visible to the unaided eyes. Included among the macro-invertebrates are sponges, coelenterates, flatworms, roundworms, macro-crustaceans, aquatic insects and others, while the micro- invertebrates include rotifers, protozoans and tardigrades (water bears).
The benthic invertebrates can also be grouped according to size - the macro - benthos, micro-benthos and meio-benthos. The macro-benthic invertebrates are those that can be retained by mesh sizes greater than 200 mm but less than 500 mm (Slack et al., 1973; Rosenberg and Resh, 1993; Ajao and Fagade, 2002), although the early stages of some species are smaller than this size designation. The micro-benthic invertebrates are those organisms, which can pass through the sieves of 100 - 50mm mesh size. This grouping is not exclusive since the large protozoa and lichens are discussed most conveniently under the micro-benthos, even though they are exceptions to the general classification (Perkins, 1974). The meio-benthos refers to the group of living organisms that can pass through a sieve of 4 - 10 mm. There are two forms of meio-benthos: the interstitial and the benthic. The interstitial benthos inhabits pores of soil and move through the interstitial medium without disturbing the particles of substratum. This is unlike the benthic meio-benthos, which is made up of more bulky forms, and disrupts the soil structure by their passage through it.
1.1 Justification of the study
The study of aquatic invertebrates has become the subject of much research
because of their importance in the food chain of fishes, and as long-term indicators of
water quality (Ogbeibu and Egborge, 1995). Although much has been written on the Nigerian benthic flora and fauna
(Oyenekan 1987), nothing is known about the flora and fauna of the Ogbei stream as no studies have been done on the stream.
Ogbei stream has been proposed for impoundment for domestic, industrial and agricultural purposes. Since impoundments change water regime and create conditions affecting the stability of the aquatic vis-A-vis aquatic life, a pre- impoundment study is often necessary. The results of such studies can be compared with the results of post impoundment studies. Hence the urgent need for a complete inventory, distribution and abundance of aquatic macro-invertebrates of Ogbei stream.
The present study of physico-chemical parameters and the invertebrates of Ogbei stream will be the first comprehensive study of the stream and will be a useful contribution to the biology of the streams in the area.
1.2 Aims and Objectives
The aims and objectives of the study are to:
1. study the p hysico-chemical parameters of the stream and their seasonal
variations;
2. determine the species composition of the macro-invertebrates, their
abundance, richness and diversity in the stream; and
3. determine the e ffect of the p hysico-chemical p arameters s tudied o n the
aquatic macro-invertebrate population in the stream. 1.3 Literature Review
Hydrobiology 1 iterally means " the biology o f w aters". Life would be quite impossible without water and hence water is the pivot upon which all metabolic processes depend. Odum ( 1959) opined that since w ater is essential and the most abundant substance in protoplasm, it might be said that life is aquatic.
Hydrobiology was originally referred to as limnology, which deals with the study of lakes as a primary focus. Recently, the scope has been widened to include all types of inland waters, including lotic waters (running waters), such as streams and rivers.
Naturally, water is affected by a myriad of physical, chemical and biological variables, which in turn, affect the aquatic organisms. Freshwater of ponds, lakes and streams ultimately come from ground waters. Actual rainwater contributes very little of the water reaching these water bodies. Brown (1971) pointed out that most of the water arrives at water bodies as the result of drainage from the surrounding land and as the water travels towards a lake, pond, etc, gaseous and soIid substances become dissolved in it. Olaniyan (1978) reported that these substances are washed by rain water and swept into rivers, inland lakes, lagoons and sea. Suspended particulate
water settles out as a result of mild turbulence in a stream. Reactions take place
between water and muddy bottom (which consists of finer particles of silt and organic
material) and between dissolved suspended substances.
Temperature is a very important factor for an excellent physiological state of
the organisms in water especially since most of them are cold-blooded and will
require a certain degree of temperature to be physiologically active (Adeniji, 1986).
According to Odum (1959), water has unique thermal properties, which combine to
minimize temperature changes, thus the range of variation is smaller in water than in air. Brown (1971) reported that fluctuations in the temperature of water involve changes in the amount of dissolved oxygen present. Therefore, temperature is a major limiting factor in water as it affects the rates of chemical and biochemical reactions within aquatic organisms. Hach (1993) observed that at higher temperatures, processes, such as dissolved oxygen uptake by aquatic life, would increase. Dawson
(1992) in his study on physiological responses of animals at higher temperatures reported that sub-optimal conditions often lead to decreased growth, reproduction and increased mortality. Maitland (1990) concluded that the life cycles of many insects are closely linked with day length and / or temperature of their surroundings. Morgan and Waddell (1961), for instance, reported that the number of species of chironomid midge emerging from a Scottish loch was directly proportional to water temperature.
Depth is a very important factor in aquatic environment. The amount of oxygen varies with depth. Due to reduction in wind actions and amount of light as depth increases, oxygen content is low. With increase in depth goes increase in pressure, diminished light a nd fall in temperature. Living c onditions a re therefore very difficult in deep lakes. Absence of light renders water unsuitable for aquatic biota. Absence of light prevents photosynthesis and renders such waters relatively barren. Oxygen content decreases with depth of water. Deep waters, as a rule, are less productive of plankton.
Transparency of water is an important factor determining the depth at which light, essential for photosynthesis, can penetrate. All natural waters contain
suspended solids, which are both organic and inorganic and the organic components
are both plant and animal remains. Suspended inorganic matter a s a result o f t he
washing away of clay and silt from the hills into the stream causes the most marked
and sudden changes in turbidity. This reduces light penetration and thus food production. Light, therefore, controls the basis of animal food chains. Light enables animals to see and to be seen, which is important when considering food relationships and predation.
The hydrospheric media in which organisms live are not often completely still
for any period of time. Currents of varying degrees often stir them. Currents in water
greatly influence the concentration of gases as well as act as limiting factors. Rainfall plays a vital role in lotic fresh waters causing fast currents during the rainy season.
Current is increased by flood that, according to Grzybkowska and Witczak (1990),
completely washes much organic matter fiom deposited places. Currents may reduce
transparency (and increase turbidity) by agitating the sediment; causing constant
shifting of the bottom if it is soft, causing faunal reduction. Current also plays
important parts in the distribution of animals (Olaniyan, 1978). The speed of flow
determines whether the bottom of the stream will be composed of rubble, pebbles,
sand or silt, and the nature of this substrate largely governs the nature of the
vegetation that will grow there (Bardach, 1964). In the same way, the kinds,
distribution and abundance of macro-invertebrate fauna inhabiting a particular section
of the stream is determined by stream flow as well as the nature of the plant substrate.
Hydrogen ion concentration is a very important factor operating in aquatic
environments. Hydrogen ion concentration is related to the amount of carbonates
present in water and varies with habitats. Carbonate concentration increases as
carbon dioxide is withdrawn. Lind (1974) has reported that when enough carbonates
are available, hydrogen ion concentration tends to be neutral, with a value of
approximately 7, and when no carbonates are availabk as buffering material the
medium tends to be acidic with values of less than 7.0. Boyd (1982) has observed
that the removal of carbon dioxide from water body by aquatic plants increases the pH of natural waters. pH is low when photosynthesis is least. The types of rock substrate, and the amount of organic matter undergoing decay, sometimes have
important effect on pH (Vines and Rees, 1972). Ogbeibu (2001) working on
distribution, density and diversity of dipterans in a temporary pond in Okomu forest reserve observed that hydrogen ion concentration influenced temporal variation in
diversity of dipterans.
Dissolved oxygen is important and is required for the existence of aquatic life.
Dissolved oxygen is required for respiration and release of energy from food (Lagler
et a!., 1977). According to Adeniji (1986), its presence in good quantity in water will
improve the water quality by rendering poisonous gases like hydrogen sulphide,
ammonia, etc into their non-poisonous forms. Dissolved oxygen content of waters
results from the photosynthetic and respiratory activities of the biota in the open
water, and the aufwuchs and the diffusion gradient at the air-water interphase, and
distribution by wind.
Alkalinity is an important factor in natural waters. Boyd (1 982) has reported
that natural waters normally contain more carbonate than results from the ionization
of carbonic acid in waters saturated with carbon dioxide. Changes in alkalinity are
due to changes in the carbon dioxide concentration. During photosynthesis,
phytoplankton use more carbon dioxide for food production thereby reducing the
alkalinity of the environment. According to Vines and Rees (1972) alkaline waters
tend to support the greatest variety of organisms.
The determination of standing crop of dominant organisms has been a central
focus in the studies of limnetic communities in the last two decades (Lugthart et al.,
1990). Aquatic macro-invertebrates are very resourceful to man. Eyo and Ekwuonye
(1995) working on the macro-invertebrate fauna of pools in the flood plain (fadama) of the Anambra River observed that macro-invertebrates served as food. Also
Wissmar and Wetzel (1978), Boisclair and Legget (1985) and McQueen et al. (1986) reported the macro-invertebrate community in the littoral zone of lakes as a crucial link in the transfer of energy from primary producers to fish. Macro-invertebrates in the littoral zones of lakes are crucial link in the transfer of energy from producers and detritus to fish (Hanson, 1990) and to water fowl (Dane11 and Sjoberg, 1982). The food of Clarias ebriensis studied by Ezenwaji (2002) confirms this, although the fish also fed on algae, fruits and seeds. Since significant numbers of organisms exist deep in the bottom sediments of streams and rivers (Coleman and Hynes, 1970; Mbagwu,
1990), more interest has been directed to the evaluation of the ecological importance and significance of the macro-invertebrates.
Besides their importance to consumers, macro-invertebrates also play important role in the detrital dynamics of the entire system (Gladden and Smock,
1990). In their studies Kresaki et al. (1978) and Mbagwu (1990) observed that organisms living deep in the sediment are primary sediment mixers which influence regeneration of materials and energy within the sediment, circulation of materials within the water body and across the mid-water interface. Fisher and Likens (1973) and Anadu and Akpan (1986) considered macro-invertebrates as important component of stream ecosystem because they transform allochthonous materials into their body tissue, which are then utilized by higher levels. Also Tuchman (1 993) and
Pope et al. (1999) evaluated the relative importance of macro-invertebrate shredders in the processing of leaves in Michigan lakes of differing pH. The quality of
aIlochthonous and autochthonous food supply perform a significant role in determining the ecological niche and quality of macro-invertebrate faunal forms available.
Macro-invertebrates also play important roles in regulation of denuded or desiccated areas (Bishop, 1973; Mbagwu, 1990) and optimum utilization of available resources (Urilliams and Hynes, 1974, Mbagwu, 1990).
Oyenekan (1987) in his studies on benthic macro-faunal communities of
Lagos lagoon reported that coastal tribes in Nigeria collect snails known as periwinkles for food. He pointed out hrther that the collection and marketing of the adult periwinkles form an important industry in Niger Delta while juveniles form an important food item for many commercially important fishes in Lagos lagoon.
In terms o f water quality assessment, 0 gbeibu and E gborge ( 'I995) i n their hydrobiological studies of water bodies in Okomu forest reserve (Sanctuary in southern Nigeria) reported that macroinvertebrates are important as long-term indicators of water quality. Rutt et al. (1990). Rosenberg and Resh (1993) and Carter et al. (1996) observed that over the last severaI decades there has been increasing use of macroinvertebrates as indicators of the quality of lotic habitats. In Nigeria, Ajao and Fagade (2002) reported that macroinvertebrates have been employed as indicators of organic pollution. In Australia in recent years there have been many changes in water quality. The concern for ecological values has led to the emphasis on the use of aquatic biota to assess conditions more directly (Norris and Norris, 1995). These authors pointed out that the majority of the 30 or so publications in water quality employed the macro-invertebrates.
Studies by Ogbogu and Olajide (2002) have shown the effect of human
disturbances on stream macro-invertebrate community in Nigeria. That macro-
invertebrate communities are influenced by several human activities other than those that directly impinge on water quality is one of the problems for biologists.
Chessman (1995) reported that the removal of riparian vegetation, channelization and river regulation affect the aquatic biota by altering habitat availability, changing the physical but not necessarily the chemical properties of the water itself. Where the
intent o f biological assessment is to assess the health (CEPA, 1 992) or 'biological
integrity' (Karr 1991; Chessman, 1995) of a whole water body, this may not be an
issue. Faced with the need for a biological procedure for mutine assessment of water
quality Chessman (1995) developed a rapid assessment technique on macro-
invertebrates for four reasons. Firstly, they are ubiquitous and diverse (Pearson et al,
1986; Chessman, 1995) and the different taxa vary widely in their sensitivities to
pollutants. Therefore, it is probable that most types of pollution will change macro-
invertebrate community composition. Secondly, macro-invertebrates occupy a central
role in the ecology of rivers and their diverse feeding habits (Chessman, 1986) form
many of the key links in aquatic food chains. Their diversity and abundance are
therefore crucial to maintaining a balanced, functioning and healthy river ecosystem.
Thirdly, macro-invertebrates are generally sedentary and have life cycles ranging
from a few weeks to a few years (Marchant, 1986) so their communities recover only
slowly if damaged by a disturbance episode. The recent history of pallution, or other
disturbances in a river can therefore be inferred from macro-invertebrate assessment
even if the disturbance is not present at the time of sampling. Finally, macro-
invertebrates offer a convenient size for field examination, storage and lransport and
can be readily collected in large numbers with simple lightweight equipment. Rivers
and streams have been widely studied in recent years as they allow a large number of
sites to be examined at relativcly low cost (Resh and Jackson, 1993; Crowns et al.,
1995). For macro-invertebrates these procedures generally involve qualitative or semi-qualitative sampling and reduce the biological information to a metric or biotic index, which is easily interpreted by resource managers. As part of the development of these techniques it is essential to determine whether the sampling technique is adequate to describe the community occurring at a site. It is also essential to determine whether the index is affected by natural factors as well as by pollution levels. In Australia, it has been suggested that professional biologists should develop biological assessment programmes as a priority, tailoring them to specific circumstances existing in each waterway system (ANZECfAWRC, 1992; Crowns et al., 1995).
Chessman ( 1995), described a rapid procedure based on macro-invertebrates for assessment of water quality on rivers and streams of eastern Australia. This procedure involves obtaining standardized collections of 100 animals from up to six habitats at a site (riffles, pool, r mks, wood a nd soft sediments). The d istribution, structure and function of stream communities are influenced by a number of water quaIity characteristics. Townsend et al. (1983) while studying community in
Southern English streams observed collections, shredders and predators in acidic waters. The number of species in collector and predator categories increased in basic streams followed by grazers (scrappers) and filter feeders. They attributed these changes to the greater range of resources available in the less acid streams which led to i ncrease in species richness and e quitability. They a Iso reported an increase i n species richness within c ertain feeding categories such a s collectors, predators and grazers in the more basic streams. Vannote et a!. (19801, Anadu and Akpan (1986), indicated that the quality and quantity of organic particulates are of primary impottance in determining the macro-invertebrate community structure in stream systems. Coffinan et al. (1971), Anadu and Akpan (1986) observed that macro- invertebrate organisms, e specially those that o btain food by filtering. depend upon suspended particles as food. Hynes (1970), Anadu and Akpan (1986) found that the alteration of substrate composition associated with various types of organic pollution is believed to have a major impact on the macro-invertebrate community. Mayack and Waterhouse (1983), Anadu and Akpan (1986), however, thought that most organic pollutants affect other factors such as dissolved oxygen, biochemical oxygen demand (BOD), pH, nutrient availability, and temperature in addition to the quantity and quality of suspended or deposited particles. These will, in turn, affect the function and structure of the lotic system. CHAPTER TWO
MATERIALS AND METHODS
2.1 THE STUDY AREA
Ogbei stream is in Isioji village, Nkpologwu town in Aguata Local
Government Area of Anambra State, Nigeria. The study area is between latitude 5'
58'N and 6' 01'N and longitudes 7' 06'E and 7' 08'E (Fig.1).
The climate is tropical with a distinct rainy season (April-September) with an early peak in July and a later peak in September. Between the months is the short break of about two weeks in August. The dry season lasts from October to March.
Temperature ranges from 240 C - 32' C in rainy and dry seasons. (Emejulu et a/.,
1992).
The study area lies within the tropical rainforest region. However, the vegetation along the banks of the stream is characterized by the presence of macrophytes such as Pandanus tectorius, Costus afar, Marantochola leucantha,
Lepidagathis heudeiofiana, Rauvoljia vomitoria, Cyathea medullaris, Acioa barteri,
Canthiurn sp., Musa sp. and Raffia hookeri among others. The stream lies in a valley that slopes gradually from a high mountain of about 40.81 m high down to the swamp bordering the stream in its lower reaches. The stream arises from Umutzeagwu highlands, flows eastwards along its course and stretches to the west passing through
Akpo (in the south) before joining Otalu river in Anambra state (Fig. 1).
ACTIVITIES IN THE BASIN
The stream serves for bathing and drinking for the local populalion. Domestic activities in the stream include fermenting and sieving of cassava, soaking and washing of tapioca, washing of clothes, washing of breadfruit, mashing of bitterleaf, collection of sand, collection of Pandanus tectorius for mat production and collection of Marantl~oclzolaleucantha leaves for wrapping. It is also a source for subsistence fishing. It is suspected that dirt and remains fiom these activities may affect the lives of the organisms in the stream.
SAMPLING STATIONS
The stream was divided into six sampling stations (Fig. 1) along its stretch and each station was sampled once a month for 12 months (May 2002 to April 2003). The stations were selected on the basis of accessibility, human influence, type of habitat, e tc
Station 1
Station 1 was in the upper reaches with some swampy areas along the bank.
The substratum was characterized by both mud and sand. Water flow was generally slow. Plants along the banks included Cyathea medullavis, Dialiurn guineense, Acioa barteri, Costus afar, Alchornea cordilfolia, RauvotJia vomitoria, Cornnzelina sp.,
Landophia dulcis, Asplenium marinurn, Gyrfmperma senegalense and Stylochiton barteri. Washing of clothes, soaking of tapioca, fermenting and sieving of cassava and washing of breadfmit were among the common human activities that occurred in the station. Station 2
This station was characterized by dark and brownish mud, debris and sand in some places. Washing of breadfruits was carried out in this station. Plants along the I banks of the station #re Costus afar, Marantochola leucantha, Lepidagathis heudeiotiana, Eclipta alba, Asplenium marinum, Cyathea me~dullaris and
Chromolaerla odorata among others. Little light penetrates into the water in this station because of the over-hanging vegetation. The station is sloppier compared with station 3.
I Station 3 I Sand and o rganic d ebris occurred i n this s tation. The m acrophytes include
Alckornea cordifolia, Elaeis guineensis, Baphfa nitirla, Murantoclda leucarrrka,
Piptadeniastrum africanum, Ficus sp., Pentaclethra ntacrophylia, Baphia pubescens,
Canthiunt sp., Contmelina sp., Dialium guineense, Cissus sp., Dksotrs sp., Maratcia fr-axinea, Lygopodiunz sp. and Oxytenanthem abyssinica. The mjor part of the station is shady. Some human activities included subsistence fishing, lumbering of trees and tapping of palm wine. The station has a gentle slope down the stream.
Station 4
The station contained sand, mud and very few stones at the substratum.
Pandanus tectorius, Scleria boivinii, Uwria chanrae, Lepidagathis heudeiotiana,
Cisszls sp., Marantochoh leucantha, DaCbergia sp., Dioscorea sp. and Barteria nigritana. Rafia hookeri, inter-spaced along the bank. Little light penetrates the water as a result of over hanging-vegetation. Lumbering and palm wine tapping were the major human activities occurring in this station. Station 5
Both sand, debris and mud occurred in this station. Vegetation in this station included Pancianus tectorius, Costus afar, Ruffin kooken', Scleriu biovinii, and
Oxytenantkera abyssinica. It is sloppy. Little light penetrates in this area. Human activities occurring in this station included coHection of Panrlanus tectorius for mat production and palm wine tapping
Station 6
This station was a little bit swampy with sand and mud at the bottom and was rocky at the bank. The vegetation included Elaeis guitleensis, Costzcs afar, Dissotis sp, Strycknos sp., Cyathea rnedullaris, Dialiunz guineense, RaJf;a hookeri, Musa sp. and Selaginella sp. It was a bit sloppy and light penetration was relatively high.
Tapping of palm wine was the main human activity around the station. Each of the 6 stations was about 3.3 km apart.
2.2 SAMPLE COLLECTIONS
Macro-invertebrates were sampled with scoop net and serrated core sampler
(Fig. 2). The scoop net was u sed to collect organisms from the shallow shore by dragging it some distance upstream against water current. It was also used around the aquatic vegetation. The net was then brought out of the water and its contents emptied into a bucket. Iron handle
Serrated core sampler
Fig. 2: Sampling equipment used for the study The contents of the bucket were sieved using mesh size of 0.1 mm and 0.6 mm
Griffin net. The smaller mesh size was put into the larger one, so as to retain small organisms such as chironomid larvae. The sieving was carefully done to avoid inflicting injury on the organisms. They were then emptied into a large sorting white tray and spread out in a small amount of water to allow the macro-invertebrate specimens to be picked out with forceps and pipettes (Chessman, 1995). Collected specimens were preserved immediately in 10% formalin according to stations.
Some d ebris was c ollected from water using the sieves directly. The sieve contents were processed as for scoop net samples and specimens sorted and preserved also in 10% formalin.
Fallen branches and twigs in the water were removed and examined.
Specimens were picked off with forceps. Barks of fallen branches were lifted up and decaying organic matter pulled apart to reveal cryptic organisms when present.
The long serrated cylindrical sampler was also used to sample the benthos in shallow areas. The sampler was pushed into the substratum as fast as possible and the
contents within the sampler were scooped into a bucket with a cup. If the water
content was too much, 3/4 of the serrated cylinder sampler (SCS) from the mud level,
then some of the water was removed with a cup before scooping out the contents into
the bucket (Ofor, 1986). Thereafter, the bucket contents were shaken and stirred
vigorously with clean water to free smaller macro-invertebrates. The bucket contents
were allowed to settIe after which the animals were filtered carefully from the
supernatant through a fine-mesh. The sieving was carefully carried out to avoid
inflicting injury on the animals. The macro-invertebrates were then picked out into
plastic containers with forceps and pipettes. The macro-invertebrates collected were preserved in 10% formalin and labelled according to the sampling stations. The specimens were transported to the laboratory for identification.
In the laboratory the specimens were identified under the binocular dissecting microscope using Edmondson (1959), Mellanby (1963), Hynes (1970), Miles et al.
(1970), Pennak (1978), APHA, AWWA, WPCF (1985), Fitter and Manuel (1986) and
Egborge (1 993) as appropriate.
2.3 DETERMINATION OF PHYSICO-CHEMICAL PARAMETERS
TEMPERATURE
The temperature of water at each station was determined using centigrade thermometer dipped for five minutes into the water at a depth of 5 cm on each sampling day.
WATER CUWNTNELOCITY
A weighted cork was used to measure the rate of water flow per second using the formula:
D (m) Velocity = ---- T (sec)
where D = Distance, T = Time
Two fixed points were chosen and a weighted cork was dropped at a point
upstream at each station and the time it took the cork to reach a predetermined point
was noted. The time taken was used to divide the distance covered. 'This exercise
was repeated three times in each sampling station and the average was taken as the
velocity of the water at the station.
DEPTH
The depth of water at each sampling station was measured using a meter rule.
The meter rule was immersed in water until it touched the substratum. The reading was taken and recorded in meters. This method also helped in detemining the water level fluctuations during the study period.
WIDTH
The width of water at each study station was measured using a graduated stake. The stake was placed across from one edge of the water to the other in each station. The reading in meters was taken and recorded. TRANSPARENCY
The transparency of water at each station was determined using a 20 cm
diameter Secchi disc attached to a calibrated line lowered into the water and the depth
at which it disappeared was noted. It was then raised gradually until it reappeared.
The depth was also noted. The Secchi disc reading in centimeters was then taken as
the mean depths of disappearance on lowering and reappearance on hauling the disc
[Biswas, 1973).
pH The pH of the water was measured using battery operated tield pH meter
(Model EIL 3055). The probe was immersed in the water before it. was switched to
"on position" to measure the pH.
OXYGEN
The dissolved oxygen (DO) was determined using the Winkler's method
(APHA, 1976). A 250 ml stoppered reagent bottle was placed under water. The
stopper was removed under water to fill the bottle and stoppered again immediately
under water before bringing it out from the water. 1 rnl of manganous sulphate
solution was added to the sample water below the surface, foIlowed by addition of 1
ml of potassium iodide. The stopper was repIaced and the contents of the bottle
mixed rapidly by inverting the bottle several times. It was transported to the laboratory for further analysis. In the laboratory 1 ml concentrated sulphuric acid was added down the neck of the bottle and mixed well by inverting the bottle several times to dissolve the precipitate. The iodine released was allowed to stand for 5 to 10
minutes. Then 100 ml of the sample was transferred into a 250 ml conical flask and 8
drops of starch indicator was added. This was titrated rapidly with N/40 sodium
thiosulphate until the blue colour disappeared. Dissolved oxygen was calculated
using the equation:
(ml of titrant)(N)(1000) DO in mgll= Sample in mls
where N = Normality of the titrant.
All chemicals were freshly prepared
FREE CARBON DIOXIDE
The free carbon dioxide concentration of the water was determined in the
laboratory using sodium carbonate as the titrant. 100 ml of water sample was put into
a 250 ml conical flask and 5 - 10 drops of phenolphthalein indicator was added. The
water sample was then titrated against 0.0454 M sodium carbonate. The titration was
stopped when a pink colour, which lasts for 30 seconds, developed (end point). The
free carbon dioxide was then calculated using the formula;
A x N x 22,000 mg l lCuCO, Free carbon dioxide = 1 OO(vo1urneof water sample) - where A = volume of titre, N = Molarity of Na2C03 .+ (APHA, 1976)
The alkalinity of the water sample was determined in the laboratory using
methyl orange indicator. 100 ml of the water sample was put in a 250 ml volumetric
flask and 3 drops of methyl orange indicator was added and shaken thoroughly. This water samples. The optical density was read at 220 nm. The optical density was converted to nitrate equivalent by reading the nitrate value from the standard curve.
PHOSPHATE
This was determined using stannous chloride method (APHA, 1976).
One drop of phenolphthalein indicator was added to 100 ml of water sample.
After mixing thoroughly 4.0 ml of molybdate reagent and 0.5 ml (10 drops) of stannous chloride solution were added to induce colour development. Strong sulphuric acid solution was added drop by drop until the coIour disappeared. 8.0 ml of the mixed reagent was added to the sample, and mixed thoroughly. After 10 minutes the absorbance of each sample was measured at 690 nrn in the spectrophotometer, using the reagent blank as the reference solution. The phosphate was read from the standard curve prepared using standard phosphate. To obtain inference 1 - 2 drops of concentrated sulphuric acid was added to the sample.
2.4 DATA ANALYSIS
All statistical tests were based on a = 0.05 level of significance. Student's t- test and ANOVA were used for most of the statistical analysis.
Perceutage relative abundance
The total number of individuals in each macro-invertebrate group was
determined as percentage composition at each study station using the formula
a 100 Percentage relative composition = - X - b 1
where a = number of individuals recorded, b = total number of individuals of
all species in the station Faunal diversity and dominance
Faunal diversity index for species richness was analyzed usigg Margalef's diversity index for species (taxa) richness, Shannon Wiener index (11) for general diversity and Equitability or Evenness (E) of distribution.
Margalef's diversity index for species richness (d) was computed as follows:
S- I D= - LogN
where S = number of species recorded, N = total number of individuals
of all species (Maguman, 1988).
Shannon Wiener (H) which is the function devised to determine the amount of information in a code (Southwood, 1978), and Equitability (E) were use,d to calculate species diversity thus:
where H = information content of sample (bits/individuals) = index of species
diversity, S = number of species, Pi = proportion of total sample belonging to
ithspecies (Krebs, 1978).
Equitability (E) is calculated as follows:
Hmax = 1og~S
where H,,, = species diversity under conditions of maximal equitability,
S = number of species in the community (Krebs, 1978)
H Equitability index (E) = - Hm,
where E = Equitability, H = observed species diversity, H,,, =
maximum species diversity = logzS (Krebs, 1978) Hutcheson's t - test was performed to detect the significance difference between general diversity indices (Hutcheson, 1970; Victor and Tetteh, 1988; Victor and Meye, 1994) thus:
where Hi = General diversity in the ith station
Hj = General diversity in the jthstation
Var Hi = ithstation diversity variance
Var Hj = jth station diversity variance
pi(log - (cpi log pi)' S - I Var (H) = - -- N 2~~
N = total number of taxa in a station
S = Number of species recorded
Dominance was calculated using Simpson's index as follows:
I Simpson's index = - D
where D = xpi2, Pi = the proportion of individuals in the ith species
(Magurran, 1988).
Faunal similarity of study stations
Bellinger's coefficient was calculated to evaluate faunal similarity between
study stations (Wallwork, 1970) thus:
Bellinger's coefficient = (p-q) 'lp + q
where P = number of occasions in which the taxon occurs in one section than
the other, q = number of occasions where reverse is the case. Relationship between macro-invertebrate fauna and physico-chemical parameters
Relationship between macro-invertebrate fauna and physico-chemical parameters was evduated using Pearson's correlation coefficient (r) (Bishop, 197 1) as follows:
where x and y = variables, xand jJ = means of two sets of variables,
(x - E) and (y - 7) = deviations fi-om the means
(x- F) (y - 7) = the deviation of x from the mean P and
the deviation of y from the mean 7,and multiples of these
two deviations together.
One way and two-way analysis of variance (ANOVA) were used to determine whether there was any significant difference between the stations and the orders. The
Student's t-test was used to test the significance of each correlation coefficient a s
where r = correlation, n = number of samples. CHAPTER THREE RESULTS
3.1 Physico-chemical parameters
The mean monthly physico-chemical characteristics of Ogbei stream are shown in Tables la and b. The air temperature varied from 26.8'~ in August to
32.3'~ in March with an annual mean of 29.8*1.18 while the water temperature varied from 24.8'~in August to 28.7'~in March with an annual mean of 27.47~kO.79.
Although temperature varied slightly throughout the study period, the dry season mean temperature was significantly higher (P<0.05) than the mean temperature recorded during the rainy season (Table 2). The monthly water temperature in relation to stations is shown in Fig. 3. The temperature was lowest in the month of
August in all the stations.
Water velocity ranged from 0.03 ms-' in March to 0.22 ms-' in August with monthly velocity m ean values of 0.05zt0.2 a nd O.17ztO.03 respectively. The annual mean was 0.1 1*0.04 (Table la). Higher mean velocity values were recorded in rainy season months (0.13zt0.03) as against values recorded in dry season months
(0.09*0.03) (Table 2). Student t-test at 0.05 percent level of significance showed that there was a significant difference in mean velocity between dry and rainy seasons
(P<0.05).
The lowest depth (0.38 m) was recorded i n M arch while the highest depth
(0.72 m) was recorded in August with an annual mean value of O.54iO.07. The mean
depth of the water was significantly higher in rainy months (0.057i0.07) than the dry
months (0.5 1*0.05) b.05= 3.9092.064. Table la: Mean monthly changes in the physical and chemical characteristics of Ogbei stream (May 2002 -April 2003)
Parameters Jun Sept Oct
temperature'^(Air) 28.8h0.30 29.3rt0.32
(28.5-29.2) (28.8-29.5)
temperature'^
(Water)
Depth (m)
Width (m)
Velocity (ms-l)
Transparency (cm) Table la: Mean monthly changes in the physical and chemical characteristics of Ogbei stream (May 2002 - April 2003) (contd.)
Parameters Mar AP~ Annual mean I ~emperature'c (Air) 29.84~0.30
(Water) /(27.3-27.5)
((0.48-0.64)
Width (m) 2.32*0.4 1
Velocity (ms-') 0.1 13Z0.03
Transparency (cm) 26.3Ok3.3 7 Table la: Mean monthly changes in the physical and chemical characteristics of Ogbei stream (May 2002 - April 2003) (contd.) Parameters May Jun IJ~Y Aug Sept
Free carbon dioxide 7.87* 1.03 6.4BO. 15
Dissolved Oxygen 5.20i0.41 5.47M.68
Alkalinity (mgA 39.27*7.64 33.5k6.77
Phosphate (mdl) 0.28*0.03 0.28zt0.05
I I Nitrate (pg/l) Not detectable Table la: Mean monthly changes in the physical and chemical characteristics of Ogbei stream (May 2002 -April 2003) (contd.) - - Parameters 1Nov Dec 1Jan Feb Mar AP~ Annual mean I
5.5M.50
(5.2-6.5)
Free carbon dioxide 1 1.78ttO.62
(mg/l CaC03) (1 1.O- 12.4) (19.8-39.2)
4.58M.58 1 (3.7-5.2) 30.58*0.97
(29.0-3 1.5)
I Hardness (mgll ( 11S3iO.68 l6.5G.16 (13.0-20.0)
0.2M.03
(0.17-0.24)
Gtrate (pd) Not detectable Table Ib: Mean values of physical and chemical characteristics of the study stations, Ogbei stream, May 2002 -April 2003
Parameters Station 1 Station 2 Station 5 Station 6
TemperatureUc(Air) 30.1rtI.63 29.5&1.10 29.3M.79 29.5il. 1 1
(28.0-3 1.2) (28.1-30.5) (28.0-3 1.5)
~em~erature~~(Water) 27.3*0.99 27.5k0.77
(25.8-28.5)
Depth (m) 0.5&0.04 0.57kO.04
(0.50-0.64)
Width (m) 2.1 140.06 2.84*0.06
(2.75-2.81)
I Velocity (ms-') I O.O9H).O3 0.1 CkO.O3
(0.04-0.14)
Transparency (cm) 30.44rt2.62
I I I I- Mean *S.D. for 2 determinations. Minimum and maximum values in parenthesis X V,tt- 0 W ul
The mean width of the stream ranged between 2.22i0.39 in March and
2.44M.40 in August (Table la). Mcan width values during the rainy season months
(2.36rt0.37) were significantly higher than the values obtained during the dry season months (2.29H.37) (P<0.05).
Water transparency ranged from 16.3 cm in September to 33.9 cm in March with an annual mean value of 26.73h3.59. Higher water transparency values were recorded in dry season months as against the values recorded in rainy season months
(Table la). The mean transparency values for the rainy and dry season months were
25.48h3.56 and 27.99rt3.17 respectively (Table 2).
The dissolved oxygen concentration ranged from 3.8 mg/l in March to 6.5 mgA in August with monthly rn ean of 4.35i0.28 and 5.95i0.40 respectively. The mean dissolved oxygen values were 5.56~k0.66for rainy season months and 4.72h0.42 for dry season months (Table 2). Student's t-test at 0.05 percent level of significance showed that the difference between dissolved oxygen in the rainy and dry seasons is statistically significant (P Free carbon dioxide ranged between 4.0 mg/l CaC03 in August and 39.2 mg/l CaC03 in February (Table la). Free carbon dioxide concentration was lower in the rainy season months [7.12+2.58) than the dry season months (16.09*6.12) (Table 2). The stream was slightly acidic. The mean pH values varied from 5.3k0.38 in March to 5.8fO.18 in December. Higher mean pH values occurred in the rainy season (6.92rt8.08) than in the dry season (5.5k0.37). The difference was significantly different (P>0.05). Phosphate fluctuated during the study period from 0.16 mg/l in December to 0.36 mg/l in September with an annual mean value of 0.25f0.06. Equal mean monthly phosphate values of O.3O*O.O3 and 0.1%0.02 were recorded in the months of July and August; and December and March respectively. The mean values for hardness ranged from 9.83&1.08 mdl CaC03 in June to 19.9W3.27 mg/l CaC03 in January with an annual mean value of l3.06&13.18. The mean hardness values for rainy and dry seasons were 11.76h1.88 and 14.Xit3.64 respectively (Table 2) and these values were statistically significant (P<0.05). The nitrate - nitrogen was not detectable. 3.2 Faunal composition, distribution and abundance A total of 1 1420 macroinvettebrates were collected and identified into 5 1 species, 39 families, I3 orders and 4 classes (Table 3) The most abundant class was Insecta (1 1225) with percentage composition of 98.29, followed by Arachnids (92) with percentage c omposition o f 0.8 1 and 0 ligochaeta (75,O .66%). Crustacea was least (28) with a percentage composition of 0.25. The order Dipte~a(4867, 42.62%) was the most abundant order and had the highest number of species (I2 species), followed by Odonata (4213) with a percentage composition of 36.89 and was represented by I0 species. Coleoptera (1 115, 9.76%) and Hemiptera (939, 8.22 %) were the next in abundance with species composition of 4 and I0 respectively. Plesiopora (75, 0.66%) was represented by 3 species. Thc order Acari (52) represented by only 1 species had a percentage composition of 0.46. Plecoptera (47) with 2 species had a percentage composition of 0.41. Araneae (40) and Trichoptera (40) had equal percentage composition of 0.35 each and were represented by 2 and 3 species respectively. The order Decapoda (28,0.25 %) was represented by only 1 species. Neuroptera (1), Orthoptera (1) and Hymenoptera (1) had only 1 species each with a percentage composition of 0.01 each. Table 3: Composition and abundance of macroinvertebrates in Ogbei stream TAXA Total number % of total collected OLIGOCHAETA 75 Plesiopora 7 5 Naididae Lumbricidae Dugesiidae Dugesiu polychroa CRUSTACEA Decapoda Sudanonidae Sudanonautes sp. ARACHNIDA Araneae Dolomedidae Dolomedes fim hiatus Agronectidae Agronecta aquatica Acari Arrenuridae Arrenurus sp. Table 3: Composition and abundance of macroinvertebrates in Ogbei stream (contd.) TAXA Total number % of total collected Plecoptera 47 0.4 1 Perlidae 47 0.41 Odonata 4213 36.89 I I Aeshnidae 158 1.38 Aeshnu sp. Fabricus 158 1.38 I I I Corduliidae 437 3.8 Cordulia sp. 437 3.8 I I Macromiidae 27 0.24 I I Macronria tzfricana Sely 27 0.24 Gomphidae 159 1.39 Gomphus sp. 50 0.44 Haginus sp. 109 0.95 I I Libellulidae 1862 f 6.30 I Libellula sp. 1273 11.15 Sympetrum sp. 510 4.47 Tetragonatria sp. 79 0.69 Coenagrionidae 1570 13.75 42 Table 3: Composition and abundance of macroinvertebrates in Ogbei stream (contd.) TAXA Total number % of total collected Coenagrion scitulurn Rambur 12.69 Ischnura sp. Charpentier 3ernip tera Poissonia sp. Gemdae Gewis Iacustris Linn Hydrometridae Hydrometra sp. Mesoveliidae Microvelia sp. Weston Naucoridae Naucoris cimicoides Nepidae Nepa apiculata Ulher Ranatra fusca sp. Notonectidae Notonecia sp. 16 0.14 Table 3: Composition and abundance of macroinvertebrates in Ogbei stream (contd.) TAXA Total number % of total collected Neuroptera 1 0.01 Sialidae 1 0.01 I Sialis sp. LatreiIle 1 0.01 Trichoptera 40 0.35 Hydropsychidae 30 0.26 Hydropsyche sp. 30 0.26 Hydroptilidae 7 0.06 t I Ochrotrichia sp. Mosley 7 0.06 Philopotamidae 3 0.03 I I Philopotamus sp. 3 0.03 Orthoptera 2 0.02 I I Gryllotalpidae 2 0.02 Gryllotulpa robusta 2 0.02 Coleoptera 1115 9.76 Chrysomelidae 1I 0.10 Donacia sp. 11 0.10 Dytiscidae 3 0.03 Dytiscus sp. 3 0.03 Hydrophilidae 223 1.95 Hydrophilus sp. 223 1.95 44 Table 3: Composition and abundance of macroinvertebrates in Ogbei stream (contd.) TAXA Total number % of total collected Gyrinidae Gyrinus sp. Thaumaleidae Thatsmalia sp. Tabanidae Tabanus sp. Ceraptogonidae Culicoides sp. Stratiomyidae Tipulidae Tipula sp. 20 0.18 I I Simulidae 1 0.01 1 Sirnuliunz sp. 1 0.01 Syrphidae 13 0.1 1 EristaIis sp. 13 0.1 1 Chironomidae 480 1 42.04 Table 3: Composition and abundance of macroinvertebrates in Ogbei stream (contd.) TAXA Total number % of total I I collected 1 Chironornous transvalensis 2693 23.58 Polypedilunr sp. 1366 1 1.96 I Tarnytarsus sp. Hymenoptera 1 0.01 I I Caraphractus sp. 1 0.01 Total 11420 100 The most abundant family was Chironomidae (4801) with a percentage composition of 42.04. Next in abundance was Libellulidae (1862, 16.30%). Belostomatidae (I), Sialidae (I), Ceraptogonidae (I), Simulidae (1) and Mymaridae (1) had only one species each with percentage composition of 0.0 1 each. Chironomous transvalensis (2693, 23.58%) was the most abundant species, followed by Coeriagrion scitulurn Rambur (1449, 12.69%). Poissonia sp. (I), SiaIis sp. Latreille (I), Culicoides sp. (I), Sirnulium sp. (1) and Caraphractus sp. (1) had only one species each with a percentage composition of 0.01 each. 3.2.1 Variations in relation to stations The overall percentage abundance was highest at station 3 (28.6 %) followed by station 2 (19.5%), while the least (19.4%) was recorded at station 5 (Fig. 4). Stations Fig. 4: Percentage abundance of macroinvertebrates at the study stations A total of 51 species were recorded in the study. Of this, 40 species were recorded in station 3, 39 in station 2,38 in stations 4 and 6 and 37 species in station 5. Station 1 had the least number of species (33) (Table 4). The study reveaIed great variation in the abundance of major taxonomic groups among the study stations (Table 4). Oligochaeta was represented in all the stations with the highest abundance in station 4 followed by station 2 whereas very few individuals were collected in stations 6 and 1. Dero obstusa was the only ubiquitous taxon whereas the other taxa (Lumbricus sp. and Dugesia polychroa) were restricted in distribution, The decapod crustaceans represented by the genus Sudanonautes occurred in all the stations. Although equal number occurred in stations 2, 3 and 4, stations 5 and 6 had the least number followed by station 1. The Arachnids Arrenurus sp. (Acari) and Agronecta aquatica (Araneae) were the dominant taxa. Insecta was the most widespread and diverse fauna of all the taxonomic groups. The highest abundance was recorded in station 3, followed by station 2. Almost all the insect orders were represented although a few taxa were restricted in distribution (Table 4). Odonata, Hemiptera and Coleoptera were abundant. Chironomidae was the most abundant and ubiquitous taxa occumng in all the stations. Of all the individuak collected, station 1 had 13.7 % while stations 2, 3, 4, 5, and 6 had 19.5%, 28.6%, 15.8%, 9.4% and 12.9% respectively. The overall abundance was not significantly different among the six stations (ANOVA P'0.05). Table 4: Abundance of macro-invertebrates in relation to the study stations STATIONS TAXA 1 2 3 4 OLIGOCHAETA 3(0. 19)* 19(0.85) 14(0.43) 24(1.33) Plesiopora 3(0.19) 1g(0.85) 14(0.43) 24(1.33) Naididae 2(0.13) 1O(0.45) g(0.25) 12(0.66) Dero obtusa 2(0.13) 1O(0.45) 8(0.25) 12(0.66) I _ I I I Lumbricidae 1l(0.06) 1g(0.36) 16(0.18) / lO(O.55) Lurnbricus sp. l(0.06) g(0.36) 6(0.18) 10(0.55) Dugesia polychroa - l(O.04) - 2(0.11) CRUSTACEA 2(0.13) g(0.36) 8(0.25) S(0.44) I I I I Decapoda 2(0.13) g(0.36) 8(0.25) S(0.44) Sudanonidae 2(0.13) 8(0.36) S(0.25) g(0.44) Table 4: Abundance of macro-invertebrates in relation to the study stations(contd.) STATIONS TAXA 1 2 3 4 5 6 I I I I I I I I I Sudanonautes sp. 12(0.13) 1g(0.36) 1S(0.25) 1S(0.44) 1l(0.09) 1l(0.07) Araneae 8(0.5 1) 6(0.27) 7(0.21) 3(0.17) 9(0.84) 7(0.47) Dolomedes fimbriatus - l(0.04) l(0.03) - - - - Agronectidae S(0.5 1) 5(0.22) 6(0. 18) 3(0. 17) g(0.84) 7(0.47) Agronecta aquatica S(0.5 1) ----5(0.22) 6(0. 18) 3(0.17) 9C0.84) 7(0.47) I Acari lq1.02) 1(0.04) g(0.25) 4(0.22) g(0.75) 15(1.02) I I I I I Arrenuridae 116(1.02) 1l(0.04) 1g(0.25) 14(0.22) / S(0.75) 15(1.02) Arrenurus sp. 16(1.02) l(0.04) 8(0.25) 4(0.22) g(0.75) 15(1.02) INSECTA 154(198.15) 2198(98.48) 3225(98.87) 1769(97.84) 1041(97.11) 1451(98.31) Table 4: Abundance of macro-invertebrates in relation to the study stations (contd.) \ I STATIONS TAXA Plecoptera 4(0.25) Dinocrus sp. 4(0.25) NeoperIa sp. - Aeshna sp. Fabricus 13(0.83) Corduliidae 64(4.08) Table 4: Abundance of macro-invertebrates in relation to the study stations (contd.) STATIONS 1 1 Belostomatidae - - Poissonia sp. - - I .. I Gerris kacustris Linn 38(2.42) 51(2.28) Naboandelus sp. 21t1.34) l(0.04) Hydrometra sp. D(1.85) 2(0.09) MicrowIia sp. Weston 28(1.78) 49(2.20) Naucoridae I4(0.25) Table 4: Abundance of macro-invertebrates in relation to the study stations (contd.) f I STATIONS I Naucoris cimicoides 4(0.25) Nepidae 3 l(1.97) I Nepa apiculata Ulher / l(0.06) Ranatmfusca sp. 3(0. 19) I Notonectidae 6(0.38) Notonecta sp. 6(0.38) Neuroptera - I Sialis sp. Latreille - Trichoptera - Ld z zF. w 3 9-9 GTS a. 2 p p 2. ., 0;s. +Ei ' pz '4 t I I -Nu nnn8'8 P 'a V) w w w -NN h n n P warn808 VVW w I I h az V bvl- n n P 8 0 V) I0 w w 'NN n n P P w - P P w w Table 4: Abundance of macro-invertebrates in relation to the study stations (contd.) STATIONS TAXA I Donacia sp. - I I Dytiscus sp. - Hydrophilidae 56(3.57) Hydrophilus sp. 56(3.57) 1 Gyrinus sp. 1265(16.88) Thaumaleidae 3(0. 19) I Thaumalia sp. 3(0. 19) Tabanidae - Table 4: Abundance of macro-invertebrates in relation to the study stations (contd.) STATIONS TAXA 1 2 I 3 I 4 5 I I I 1 Tabanus sp. - l(O.04) - l(0.06) l(0.09) - Ceraptogonidae - - - - l(O.09) - Culicoides sp. - - - - l(O.09) - Stratiornyidae l(0.06) 3(0. 13) l(0.03) - 2(0.19) 4(0.27) Stratiomyia sp. l(0.06) 3(0. 13) l(0.03) - 2(0.19) 4(0.27) Tipulidae - 4(0. 12) g(0.44) - 20(1.36) Tipula sp. - - 3(0.09) 5(0.28) - 12(0.81) Megistocem longipinnis - - l(O.03) 3(0.17) - S(0.54) Simulidae ------l(0.07) Simulium sp. - - - - - l(0.07) Syrphidae 13(0.83) - - - - - I I Table 4: Abundance of macro-invertebrates in relation to the study stations (contd.) STATIONS TAXA Eristalis sp. Chironomidae Chironomous transvalensis Polypedilum sp. Strictochironomus Tarnytarsus sp. Hymenoptera Mymaridae Caraphractus sp. Total The percentage relative abundance was used to express the relative contribution of major macro-invertebrate orders, families and species to the overall faunal abundance at the various stations. Plesiopora contributed 0.19% at station 1, 0.85% at station 2,O .43% at station 3, 1 -33% at station 4, 1 .21% at station 5 and 0.14% at station 6. The order Araneae (Dolomedidae and Agronectidae) was quite insignificant contributing 0.51% at station 1, and 0.27%, 0.21%, 0.17%, 0.84% and 0.47% respectively at stations 2,3,4,5 and 6. The dominant species was Agronecta aquatica contributing 95% of all araneans. Acari were fairly represented at stations 1, 3, 5 and 6, but insignificant at stations 2 and 4. The genus Arrenurus was the only representative taxon. Plecoptera was not prominent; it contributed 0.25%, 0.18%, 0.21 %, 0.66%, 0.09% and 1.29% at stations 1, 2, 3, 4, 5, and 6 respectively. Dinocras (Perlidae) was the only dominant taxon contributing 83% of all plecopterans. Odonata was important at station 3 where it contributed 46.26% of the total invertebrate community. At station 1, its contribution was insignificant. The dominant species i n this order was Coenagrion s citulum Rambur (Coenagrionidae) with a percentage contribution of 34-40 of all odonatans. The order Hemiptera was fairly represented at stations 1, 2, 3, and 6, but insignificant at stations 4 and 5. It was represented by 10 taxa from seven families: Belotomatidae (1 species), Gerridae (2 species) Hydrometridae (1 species) Mesoveliidae (1 species), Naucoridae (1 species), Nepidae (3 species) and Notonectidae (1 species). Important species in this order included Microvelia sp. Weston, Gerris lacustris Linn, Lacotrephes sp, and Nepa apiculata Ulher. Neuroptera was only found in station 2 (0.04). Sialis sp. Latreille was the only species found. The order Trichoptera was not prominent. It contributed 0.27% at stations 2 and 6, 0.12%, 1.33% and 0.19% at stations 3, 4 and 5 respectively. Three families, Hydropsychidae, Hydroptilidae, and Philopotamidae represented by Hydropsyche sp., Ochrotrichia sp. Mosley and Philopotamus sp. respectively were encountered. The most dominant taxon in this order was Hydropsyche (1.27%). Coleoptera was prominently represented at stations 1 and 2 with 20.45% and 17.1 1% of the total fauna respectively while at stations 3,4, 5 and 6, its contributions were 4.60%, 5.64%, 4.01% and 7.93% respectively. Gyrinus sp (Gryrinidae) contributed 78.74% of all coleopterans. The order Diptera dominated the samples at all stations with percentage composition of 43.12%, 38.89%, 43.62%, 47.18%, 46.36% and 37.2% at stations I, 2, 3, 4, 5 and 6 respectively (Table 4). The most important species were Chironomous transvalensis, Polypedilum sp. and Strichironomous sp. Chironomous transvalensis, contributing 55.33% of all dipterans, was the most important species in station 1. Tarnytarsus contributed 0.51%, 0.18%, 0.03%, 0.28% and 0.37% at stations 1, 2, 3,4 and 5 respectively. It is absent at station 6. Analysis of variance indicates that the total abundance of the order was significantly higher (Pc0.05) than those of the other orders. 3.2.2 Monthly variations of macro-invertebrate population The monthly variations of macro-invertebrates are shown in Table 5. Table 5: Monthly variations of macro-invertebrates in Ogbei stream (Contd.) MONTHS Jun Jly Feb Range in monthly samples 4-T -4 1-19 2 - - Agnnrec tidae Agronecta aquatica Acari Arrenuridae Arrenurus sp. INSECTA Plecoptera Perlidae Table 5: Monthly variations of macro-invertebrates in Ogbei stream (Contd.) I 1 MONTHS * TAXA May Jun Jly Aug Sep Oct Nov Dec Jan Feb Mar Apr Rangein monthly samples Libellulidae 297 147 113 119 105 157 88 95 175 164 271 131 88-297 LibelIda sp. 131 ,89 /73 175 /70 (92 83 70 138 ,137 ,213 70-213 I 1 1lo2 1 5r ----45 8 33 49 - 25 34 21 46 24 21-136 Tetraganeuria sp. 30 - - - 2 16 5 - 3 6 12 5 2-30 Coenagrionidae 227 137 145 51 52 62 53 65 162 62 333 221 53-333 Coenagrion scituIurn Rambur 217 118 145 49 47 50 43 52 160 62 309 197 43-309 Ischnurn sp. Charpentier 10 19 - 2 5 12 10 13 2 - 24 24 2-24 Hemiptera 68 42 71 30 47 55 80 336 41 46 80 44 30-336 Belostomatidae ------1 - - 0- 1 - Poissonia sp. ------1 - 0- 1 Gemdae 11 7 41 1 15 28 53 103 17 5 20 9 1-103 Table 5: Monthly variations of macro-invertebrates in Ogbei stream (Contd.) MONTHS Aug I Sep 1Oct I Nov IDec I Jan 1Feb IMar / Apr / Range in monthly Gerris lacustris Linn Naboandelus sp. Hydrometridae Hydrornetra sp. Mesoveliidae MicroveZia sp. Weston Naucoridae Naucoris cimicoides Nepidae Nepa apiculata Ulher Table 5: Monthly variations of macro-invertebrates in Ogbei stream (Contd.) MONTHS Aug Sep Oct Nov Dec Jan Feb I Mar 1Apr I Range in monthly samples Lacotrephes sp. 7 12 16 5-26 Ranatra fusca sp. - Notonectidae Notonecta sp. Sialidae Trichoptera Hydropsychidae Hydropsyche sp. Hydroptilidae Table 5: Monthly variations of macro-invertebrates in Ogbei stream (Contd.) I I 1 MONTHS TAU May Jun Jly Ang Sep Oct Nov Dec Jan Feb Mar 1Apr 1Range in monthly Sam Ies Culicoides sp. ------1 - - Stratiomyidae 3 ------1 2 - Stratiomyia sp. 3 ------1 2 - 1 Tipulidae ------3 1 8 5 Tipula sp. ------3 1 8 5 Megistocera longipinnis ------1 5 4 Simulidae ------ Simulium sp. ------ Syrphidae 13 ------ Eristalis sp. 13 ------ Chironomidae 469 429 384 133 235 336 316 378 418 412 h) 'dl L h) 'dl - w 0 00 - w P - * w 00 During the study period the higher numbers of macroinvertebrates were recorded in the months of December, January and March than the lower numbers recorded in August and September. Out of 51 taxa recorded, Cfiironomous transvdensis out-numbered the others ranging between 87 in August and 393 in March (Table 5), thus indicating more abundance in the dry months. The least in the category were Poissonia sp. and Sialis sp. Latreille which occurred in February and July, and Gryllotalpa robusta and Cuiicoides sp. recorded in December each. Both Sirnulium sp. and Caraphractus sp. were recorded in March. 3.2.3 Seasonal variations of macro-Invertebrate population The seasonal variations in the population of macroinvertebrates are shown in Table 6. More macro-invertebrates were recorded during the dry season (6321) than during the rainy season (5099). Chironomous tranvalensis were almost equally represented in both rainy and dry seasons with a total number of 1278 and 1415 respectiveIy. Of the 51 macro-invertebrate species recorded during the study, 39 species were non-seasonal while 12 species were seasonal in occurrence. Of this 12 species, 8 species namely Piossonia sp., Notonecta sp., Hydropsyche sp., Philopotamus sp., Gryllotalpa robusta, Culicoides sp., Simulium sp. and Caraphractus sp. occurred only in the dry season, while 4 species namely Dolomedes fimbriatus. Sialis sp. Latreille, Tabanus sp. and Eristalis sp. were only present in the rainy season. Table 6: Seasonal variations of macroinvertebrates in Ogbei stream SEASONS TAXA t-- Rainy season Dry season OLIGOCHAETA 36 I Plesiopora 36 Naididae 20 Dero obtusa 20 I Lumbricidae 14 Lumbricus sp. I 14 Dugesiidae 2 Dugesia polychroa 2 I CRUSTACEA 13 Decapoda 13 Sudanonidae 13 Sudanonautes sp. 13 ARACHNIDA 35 Araneae 15 Dolomedidae 2 Dolomedes fim briatus 2 Agronectidae 13 Agronecta aquatica 13 Acari 20 Arrenuridae 20 Arrerturus sp. 20 Table 6: Seasonal variations of macroinvertebrates in Ogbei stream (contd.) SEASONS TAXA Rainy season Dry season INSECTA 5015 6210 Plecoptera 30 17 Perlidae Dinocras sp. 25 14 Neoperla sp. 5 3 I I Odonata 2009 2204 Aeshnidae 108 50 Aeshna sp. Fabricus 108 I 1 50 I Corduliidae 95 342 Cordulia sp. 95 342 Macromiidae 19 8 Macromia africana Sely 19 8 Gomphidae Gomphus sp. 12 38 Haginus sp. 30 79 Libellulidae 9 12 950 Libellula sp. Synzpetrum sp. Tetragoneuria sp. 37 42 Coenagrionidae 833 Coenagrion scitulum Rambur 773 676 Table 6: Seasonal variations of macroinvertebrates in Ogbei stream (contd.) SEASONS TAXA IRainy season Dry season Ischnura sp. Charpentier I 60 Hemiptera 301 Belostomatidae - Poissonia sp. - Gerridae Gerris Iacustris Linn 37 Naboandelus sp. 47 Hydrometridae 7 Hydrometra sp. Mesoveliidae 34 Microvelia sp. Weston 34 Naucoridae 6 Naucoris cimicoides Nepidae Nepa apiculata Ulher I 6 1 Lacotrephes sp. 105 Ranatra fusca sp. 4 Notonectidae - Notonecta sp. I Neuroptera 1 Sialidae 1 I SEASONS TAXA Dry season Sialis sp. Latreille 1 Hydropsychidae - Hydropsyche sp. - Hydroptilidae Ochrotrichia sp. Mosley Philopotamidae - Philopotanzus sp. - Orthoptera - Gryllotalpidae Gryllotalpa robusta - Coleoptera 399 Chrysomelidae 2 Donacia sp. 2 Dytiscidae 1 Dytiscus sp. I 1 Hydrophilidae 148 Hydropkilus sp . 148 Gyrinidae 248 Gyrinus sp. 248 Diptera 227 1 Table 6: Seasonal variations of macroinvertebrates in Ogbei stream (contd.) SEASONS TAXA Rainy season Dry season Thaumaleidae s Thaumalia sp. Tabanus sp. Ceraptogonidae Culicoides sp. I Stratiomyidae Stratiomyia sp. Tipulidae Tipula sp. I Megistocera longipinnis Simulium sp. L Syrphidae Eristalis sp. I Chironomidae I Chironomous transvalensis I Polypedilunz sp. Strictochironomus sp. Tarnytarsus sp. Hymenoptera Table 6: Seasonal variations of macroinvertebrates in Ogbel stream (contd.) SEASONS TAXA Rainy season Dry season Myrnaridae I - I 1 Caraphractus sp. Total 3.2.4 Faunal diversity and dominance Table 7 shows faunal diversity and dominance indices determined for the six stations. Margalef's species richness (d), Shannon Wiener diversity (H) and Equitability (E) were used in analyzing faunal diversity. Taxa richness (d) was highest in station 5 followed by stations 6 and 4 respectively. Station 1 had the least taxon richness. Shannon Wiener diversity index (H) was highest in station 6 and was significantly different from other stations (p<0.05), followed by stations 4 and 5 respectively. Station 3 had the least diversity index. The diversity index was not very different in stations 1 and 2.Maximum species diversity (Hmax) was highest in station 3 followed by station 2. Values for stations 4 and 6 were not statistically different (pXk05). Station 5 had maximum species diversity value of 1.568. Station I had the least value (1.5 19). The Equitability index (E) was highest in station 6 (0.784). Values for stations 4 and 5 were not very different. Stations 1 and 2 had Equitability index values of 0.684 and 0.655 respectively. Station 3 had the lowest Equitability index value of 0.632. Simpson's dominance index was highest in station 6 followed by station 4 and then station 2. Station 1 had the lowest value. Hutcheson's test was used to test diversity indices of the study stations (Table 8). The faunal diversity in station 6 was significantly higher (P4.05)than those of the other stations. Stations 1 and 2, 1 and 3, 1 and 5, 1 and 6, 2 and 5, and 4 and 5 were not significantly different (P>0.05). The other pairs of study stations were significantly different from one another (P<0.05). 79 Table 7: Diversity of macro-invertebrates in the study stations of Ogbei stream (May 2002 - April 2003) STATIONS No. of taxa No. of individuals 1570 Margalef s index (d) 10.013 I Shannon Wiener index (H) 1 1.038 Maximum species Diversity (H max) Equitability (E) Dominance (D) Table 8: Test of significance of general diversity index (H) between pairs of study stations (Hutcheson, 1970). 'STATIONS 1 2 3 4 5 6 1 2 NS 3 NS NS 4 S S S 5 NS NS S NS 6 NS SC S** S * S* S** indicates highly significant difference (P<0.05) S* indicates very significant difference (Pc0.05) S indicates significant difference (P4.05) NS indicates no significant difference (PO.05) 3.2.5 Faunal similarity of study stations Bellinger's coefficient, a similarity index was used to evaluate the faunal similarities between the sampling stations. The results are shown in Table 9. Station 5 was significantly different from the other stations in tenns of faunal similarity. With the exception of stations 5 and 6, which were significantly different (P<0.05),all the other pairs of study stations were not significantly different (P>O.OS). Table 9: Similarity coefficients of pairs of study stations, Ogbei stream (May 2002 - April 2003) BELLINGER'S COEFFICIENT STATIONS 1 2 3 4 5 6 1 2 0.143 3 0.57 1 0.533 4 0.143 1.286 0.133 5 0.3 10 5.538 6.533 6.259 6 0.667 0.133 0.133 0.048 9.143 3.2.6 Relationship between macro-invertebrate fauna and physico-chemical parameters Pearson's correlation c oefficient i ndicated a significant positive relationship between total macro-invertebrate population and air and water temperatures, transparency, free carbon dioxide and a significant inverse relationship with depth, current, dissolved oxygen and alkalinity, Correlations with other parameters were not significant (PM.05) (Table 10). Table 10: Pearson's correlation coefficient (r) between total macro-invertebrate abundance and physical and chemical parameters of Ogbei stream Parameter r Significance Air temperature 0.428 P<0.05* Water temperature 0.590 P~0.05* Depth -0.256 P<0.05* Width -0.058 P>0.05 Current -0.536 P<0.05* Transparency 0.422 P PH -0.059 P>O.OS Free carbon dioxide 0.305 Pdl.05* Dissolved oxygen -0.381 P<0.05* Alkalinity -0.283 P<0.05* Hardness -0.084 P>0.05 Phosphate-phosphorus -0.233 PB0.05 Nitrate-nitrogen Not detectable *significant correlation (r) CHAPTER FOUR DISCUSSION AND CONCLUSION Ogbei stream supports diverse macro-invertebrate fauna. The macro- invertebrates recorded consisted of 51 taxa represented by similar ecological biotopes that have been previously reported from similar bio-geographic zones (Bidwell and Clarke, 1977; Ogbeibu and Victor 1989; Victor and Ogbeibu, 1991, Ogbeibu and Egborge, 1995). In terms of species richness, mainly Diptera dominated the rnacro- invertebrate community. Among the dipterans, Chironomidae was the most prevalent group as is the case in both temperate and tropical streams (Williams and Hynes, 1971; Bishop, 1973; Towns, 1979; Lenat et al., 1981; Turcotte and Harper, 1982; Bylmakers and Sabolvarro, 1988; Victor and Ogbeibu, 1991; Ogbeibu, 2001). The relative percentage abundance of different species reveals that Ogbei stream favours the growth and survival of Libellula sp., Coenagrion scitulum Rambur and Chironomous tramvalensis more than Poissonia sp., Sialis sp. Latreille, Culicoides sp. and Grylldalpa robusta. This may be because Libellula sp., Coenagrion scitulum Rambur and Chirortomo~stranvalensis have better adaptations that permit them to attach to the substratum. Although factors which influence the a bundance and distribution o f m acro- invertebrate fauna include physical and chemical qualities of water, habitat area, immediate substrate of occupation, trophic condition, resource partitioning and predation (Dance and Hynes, 1980; Hart, 1983, Bromark et al.. 1984; Oscarson, 1987; Ogbeibu and Victor, 1989; Ogbeibu and Egborge, 1995, Ogbeibu and Oribhabor, 2001), the study revealed that temperature, depth, transparency, dissolved oxygen, free carbon dioxide, alkalinity and current were the major physical and chemical factors affecting the abundance and distribution of the macroinvertebrates in Ogbei stream (Table 10). The study further revealed that faunal assemblages showed great instability as a result of changes in the physico-chemical factors as well as habitat differences observed in the study. It was observed fiom the study that oligochaetes and hemipterans were associated with silt and muddy substrata rich in organic matter where they influence regeneration of materials and ecology as well as circulation of water within the water body. The naidid oligochaetes prevalent in water body with muddy substratum rich in organic matter (Petr, 1972; Carter, 1978) dominated in station 4 with muddy substratum. The hemipterans were mostly encountered in station 6 where the current was slow. The variation in habitat occasioned by water velocity, which eroded streambed and deposit silt and sand beside nearby objects accounted for the presence of flies such as crane fly (Tipulasp.) in silty and muddy stations of 3,4 and 6. Immediate substrate of occupation, water velocity and animals are closely related. Larger stones and pebbles were encountered in stations with low water velocity. On the other hand, smaller stones were encountered in stations with high water velocity. This brings about variation in substrata. The variation in water current velocity occasioned variation in habitat due to substrata and chemical composition. This influenced faunal distribution as well as explains why chironomid larvae were mostly collected where water velocity was quite high. Hydropsyche sp. occurred most in station 4 with high water velocity. To avoid being swept away, the hydropsyches cling to stone, which according to Ogbogu and Akinya (2001) is usually devoid of insects. It was observed during the study that hydropsyches preferred stonyhard substrate. This observation agreed with Chutter (1971) and Ogbogu (2001) who also reported that the hydropsyche genera Cheumatopsyche and Amphypsyche were common in stony runs. Phgsico-chemical parameters and the fauna The lowest and highest air temperatures recorded were 26.80~in August and 32.3'~in March respectively. Temperature decreased during the period of rains due to the lowering of solar heat radiation. Inundation by run-off water into the stream may also reduce temperature. Temperature plays important role in the abundance and distribution of macroinvertebrates. High temperature favours productivity. Energy is a limiting factor in aquatic ecosystem. The present investigation revealed that temperature has great effect on the abundance and distribution of macroinvertebrates as several of them were collected when temperature was relatively higher than when there was a drop in temperature. Pearson's correlation coefficient (r) calculated to assess relationship between macro-invertebrate and physico-chemical parameters confirmed a positive relationship between macro-invertebrate and water temperature (r 0.590, Table 10). Student t-test at 0.05 percent level of significance showed that macro-invertebrate abundance and water temperature were significantly related (P4.05). This may be attributed to adequate temperature, which, according to Tait (1981) and Dawson (1992), influences several major processes including feeding, respiration, osmoregulation, growtb and especially reproduction. Studying invertebrate fauna of New Zealand peat soil, Luxton (1983) observed that the activity of invertebrate fauna were slowed down by a drop in temperature with most of them reaching a state of virtual suspended animation during cold seasons. This study indicated that current exerts profound influence on substrata, abundance and distribution of macro-invertebrates in the stream. During the study, faunal abundance was high when the current was low. The reverse was the case when the current was high. Pearson's correlation coefficient (r) computed to assess macro- invertebrate abundance and physico-chemical parameters confirmed an inverse relationship between faunal abundance and current (r = -0.356) (Table 10). Table lb shows the fluctuation of Ogbei stream with respect to water velocity. The current was highest in station 2 and least in station 1. Less mud and debris occurred in the substratum of station 2 than station 1 with low water velocity. The high water velocity and adequate oxygen caused by water turbulence explains why Neoperla sp. were mostly collected fiom station 2. This is confirmed by the findings of Ogbeibu and Egborge (1995) who reported high current and suitable level of dissolved oxygen in streams as factors that likely influence the distribution of Neoperla sp. Dinocras was mostly collected in station 6 with muddy substratum due to siIt deposition brought by low current. It was observed from the study that silt - loving macroinvertebrates such as Gerris sp. and Nuboandelus sp., which fed upon rich deposits of animal and vegetable origin as well as water weeds occurred most in this station. Among such animals were the o ligochaetes and hemipterans, which were mostly encountered in stations 4 and 6 with low current speed. Seasonal changes in oxygen concentrations in Ogbei stream were simply more or less inversely related to changes in temperatures. Pearson's correlation coefficient (r) calculated to assess relationship between physical and chemical parameters confirmed an inverse relationship between dissolved oxygen and water temperature (r = -0.381). This observation agreed with Huet (1972) who also reported that increase in water temperature decreases dissolved oxygen. This is because as water temperature increases, dissolved oxygen decreases through respiration p rocesses of plants and animals, oxidation processes of breakdown and low dissolved oxygen solubility, hence the negative correlation between the two parameters. The high dissolved oxygen concentration in the rainy months may according to Olaniyan (1978) be attributed to a bloom of vegetation in the water as well as the high volume and turbulence, which enhance the solubility of oxygen in the water. The pH of Ogbei stream during the study ranged between 4.5 in March to 6.5 in June, January and February with an annual mean of 5.53~k0.35. The observed pH range indicates that the stream is acidic. The uneven distribution of fauna in the stream observed in this study expresses the impact of this factor on the aquatic life. There is low variability between the pH values and this is consistent with the findings of Hynes (1972) who reported that rivers and streams tend to be resistant to pH changes as a result of chemical buffering effects. However when rainwater runs into some tropical rivers, it may cause the water to be acidic because of its high carbon dioxide content and a fairly low pH. Therefore the investigation reveals that pH is not a major ecologica1 factor controlling faunal abundance and distribution in the stream (Table 10) Alkalinity was generalIy higher during the rainy season than during the dry season. The high alkalinity, which indicates good buffering capacity of the stream implies high productivity. The high alkalinity recorded during the rainy months may be related to reduction in evaporation, leaching of the bedrocks and rocks of the catchment area. Alkalinity reflects the geochemistry of the watershed (Kemdirim, 1993). The high alkalinity observed during the study was negatively correlated with high free carbon dioxide values (r = -0.121) (Table 11). Student's t-test performed at 0.05 percent leveI of significance indicated that there is no significant difference between the alkalinity and free carbon dioxide (D0.05). Winger (1981) in his review on physical and chemical characteristics of warm streams reported that excessive land use in the catchment area influences the quality of nutrients that enter receiving waters. According to Hynes (1975) majority of these nutrients entering water systems come from allocthonous organic input. Also Anderson and Sedell (1979) reported that input rates of aHochthonous material to rivers and streams range from 0.78 to 5.0 g dry weight particulate organic matter M~ day". The importance of allochthonous material in the functioning of streams and rivers has been documented (Anderson and Sedell, 1979; Allan, 1995; Pope er al.. 1999). Allochthonous organic materials are a source of energy to streams since it can cause increase in dissolved organic carbon and total phosphorus. This could in turn result in increased metabolic processes of stream plankton communities. Human activities like bush clearing around the stream lead to increase in organic matter and free carbon dioxide content of the system. Among the factors that influence the distribution of fauna in the stream was depth. Depth is a prime factor in aquatic environment. The study shows that depth increased during the rainy season. During the study, high and low faunal abundance occurred at periods of low and high depths respectively. Pearson's correlation coefficient (r) calculated to assess relationship between macro-invertebrate abundance and physico-chemical parameters confirmed an inverse relationship between faunal abundance and depth (r = - 0.256) (Table 10). Student's t - test performed at 0.05 percent level of significance showed a significant inverse relationship between faunal abundance and depth (Pc0.05). Faunal reduction encountered in the rainy season may be attributed to spate. Sudden torrential rain, which causes a rapid rise in the rate of flow beyond that against which some animal can maintain a foothold, explains the very low number of macro-invertebrates recorded in the rainy month of August (Table 5). This observation is supported by several works which have shown that spate reduce fauna. Hynes (1 975a) in his study of annual cycles of macroinvertebrates in a river in southern Ghana recorded a marked reduction of the benthos in a Ghanaian stream during the dry season because of the interruption of the flow. Petr (1970) and Turcotte and Harper (1982) noted greater densities of benthos in the Volta at the end of the dry season; the fauna was reduced by spate during the rainy season. Bishop (1973) attributed fluctuations in densities of benthos in a Malayan river to the recurrence of floods, which reduce the fauna. As spates are irregular and unpredictable, so are the variations in the abundance of the macroinvertebrates. The influential role of spates in the study stream was further echoed by the fact that smaller invertebrates such as Naboandelus sp. were subject to severe fluctuations in numbers than larger ones like Nepa apiculata Ulher. It is most likely that larger macroinvertebrates were more resistant to dislodging. Many of the invertebrates such as Libellula sp., Coenagrion scitulurn Rambur, Gyrinus sp., etc were non-seasonal in their life cycles and so their period of emergence and recruitment extend over the whole year; a few species such as Tipula sp. show limited seasonality and tend to concentrate emergence and / or recruitment in one half or so of the year. From my observations, Notonecta larvae in the order Hemiptera were first seen in November and appeared in samples until March, indicating that the life cycle is seasonal. A similar observation was made concerning Tipula larvae and Megistocera longipinnis larvae both of which belong to the order Diptera. Tipula larvae occurred from November to April. Megistocera longipinnis larvae on the other hand were encountered from December to April, although it was not seen in March. Therefore their life cycle is seasonal. Bishop (1973) observed a similar life cycle pattern in warm tropical environments. According to Turcotte and Harper (1982) this lack of synchrony in the life histories of most benthic dwellers in tropical areas eliminates 1 ife-cycle p attems as a major cause o f t he fluctuations of densities. Biological factors affect faunal distribution and abundance. Vertebrate predators such as carnivorous fish in the stream can affect macro-invertebrate abundance. Young and adult fish feed on macro-invertebrates and if their rate o f predation is higher than the rate of recruitment, this may bring about a reduction of the macroinvertebrates. Also since faunal abundance is often times resuscitated after rainfall, spate rather than predation may be the prime factor causing fauna1 reduction. The developmental rate of the small: macroinvertebrates can generally cause faunal recession. According to Ito (1980) most of the water animals are benthic only at larval stages and spend their adult lives outside the body of water. This can be true of all macroinvertebrates except Crustacea and water scorpion, which were found in the collection. Others, such as Poissonia migrate to live on land after they have developed to adult. The overriding influence of substrate omp position in macro-invertebrate faunal abundance and distniution can account for the significantly lower population in station 5. The presence of sand and macrophytes in all the stations, debris in stations 2, 3 and 5; stones in stations 4 and 6 ; and mud in a11 the stations except station 3 provided the right conditions for high faunal abundance in stations 1, 2,4, 5 and 6. Among the dipterans, Chimnomous transvalensis require a substratum with high organic matter c ontent. According to P etr (1972) Chironomous transvalensis prefer muddy bottoms to sandy substrata. Polypedilum sp. were abundant in station 3 as a result of adequate food supply. During his study on benthic fauna of a tropical man-made lake, Petr (1972) collected Polypedilum sp. mostly from the well- oxygenated shallow zone and r dated their abundance to the presence of r ich food supply rather than suitable substratum or oxygen concentration. The odonate nymphs are known to be associated with the macrophytes, such as Marantochola leucantha, Baphia nitida and Oxytenanthera abyssinica. This accounts for their high abundance in station 3 where the macrophytes abound. Naidid oligochaetes dominated by Dero obtusa were more abundant in station 4. According to Petr (19721, Carter (1978), Ogbeibu and Egborge (1995) the o!igochaetes dominate water bodies with muddy substratum, rich in organic matter. The substratum composed of sand, mud and very few stones seems probably to account for the abundance of Dero obtusa in this station. Several works like Milbrink (1973, I975), Jonasson and Thorhauge (19761, Mbagwu (1990) have shown that oligochaetes hide their c ocoons in the deeper sediment strata to protect them from predators and bacteria1 attack. The results obtained from this study indicate that diversity and equitability (E) measures calculated by Shannon Wiener index of general diversity (H) differed among the sampling stations. Diversity was significantly higher (PcO.05) in station 6, indicating a higher ecological stability. The higher Equitability (E) suggests this situation since according to Victor and Ogbeibu (1985) and Ogbeibu (2001) the higher the equitability the higher the diversity. Conclusively, macro-invertebrate abundance and distribution were affected by physico-chemical qualities of water. The main factors accounting for the difference were temperature, depth, transparency, spate resulting from rainfall, dissolved oxygen, free carbon dioxide and alkalinity; The aquatic macrophytes were also important. Turcotte and Harper (1982) noted that a close monitoring of non-seasonal lotic systems and the determination of the factors, which regulate them in the absence of the obvious cues would greatly increase our comprehension of running water systems. It is left for follow up studies to bridge these gaps in our knowledge of Ogbei stream and the factors, which regulate it in the absence of the obvious cues. 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