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Qualitative sampling of the floral and fauna composition in a temporary pond was carried out during the dry and rainy seasons for two years. The floral communities consist of Phytoplankton of which Blue-green algae and diatoms were the most predominant and the macrophytes, which were classified into Emergent. Submerged and floating plants. The Fauna communities include the Zooplankton with Daphnia na Cypris species being the most abundant, while the neustons, nektons and benthos were also sampled. The effect of sedimentation, moisture and humus contents of the substratum soil on both plants and animal life and the tactics employed by these organisms to survive drought in the pond were also investigated. Various ways by which resources of temporary ponds can be of benefit are discussed.
The study of the functional relationship and productivity of standing (lentic) freshwater biotic communities as they are affected by the dynamics of physical, chemical and biotic environmental parameters forms the basis of the ecology of inland water otherwise known as limnology. Hydrobiological study of temporary water such as pools, paddocks and ponds or large water bodies such as lakesw, streams and rivers most often predict the course of biological events in such habitats and generally give an insight into the composition and productivity of the water.
An understanding of the Community structure of a body of water is dependent upon the ability to differentiate between species population changes and variations in spatial and temporal distribution (Wetzel and Likens, 1998). Changes in species composition and biomass may affect photosynthetic rates, assimilation efficiencies, rate of nutrient utilization, grazing rates, productivity and catch per effort. Thus the knowledge of species composition and abundance in a body of wter is essential for sustainable exploitation, conservation and management of such water body. It also helps for a better understanding of the ecological interrelationships amongst the population of the community.
Several studies have been conducted on the floral and fauna of large water bodies in Nigeria. These include Imevbore (1970) on Lake Kainji, Holden and Green (1960) on River Sokoto. and Egbore (1979) on River Oshun. Little attention has been paid to the Limnology and hydrobiology of seasonal temporary water bodies. This might be attributed to the fact that temporary water occurs for a short time to support life and only during the rainy season.
Biological studies of organisms in the temporary ponds start from the time when the pond is dry. This is to observe the physiological and behavioural tactics employed by species in the pond to survive drought. Williams (1987) and Mclachan (1983) have reported a number of physiological and behavioural tactics of organisms of temporary ponds to survive abiotic conditions during the dry season. In the rainy season, the distribution composition and abundance of these organisms is influenced by the temperature and nutrient levels of the water harbouring them (Mulford and Norcross, 1971).
The role of biotic community in Aquatic food cycle is known, their deleterious effect on other organisms in the water body such as excessive bloom which may cause anoxia and mortality is also known. These biological communities have been used in water quality analysis, biological indicators of pollution and to determine the average ecological conditions of water bodies.
This paper therefore aims at identifying the organisms prevalent in a seasonal temporary pond and the tactics they employ to survive drought in the pond. The study also intends to note the effect of soil on the benthic organisms. This will contribute to the knowledge of the ecology of organism inhabiting temporary waters with a view of making good use of the species for teaching, research and industrial purposes.
Materials and Methods
The study site
The temporary pond is located on the South-Eastern side of the University of Ilorin, Kwara State. It is a shallow pond with a maximum length and width of 11m and 5m respectively, 1.5m deep, surface area of 470.5m2 and volume of 611.75cm2.
The pond si always dry at the peak of the dry season i.e. between December to February; it becomes gradually filled with water with the onset of the rain in March. The pond is surrounded by hornblende biotite gneiss rock.
Collection of samples
Dry soil samples were collected from two sites designated A and B (A is on the Western end of the pond while B is on the Eastern side) by digging 10cm into the substratum using a hand trowel during the peak of the dry season when the pond was devoid of water. The samples were collected into two tins and taken to the laboratory. Plankton samples were collected by sweeping plankton net gently across the water surface , fixed and preserved in 4% formalin. The benthic organisms were collected using the van veenâ€™s bottom grabs. The contents poured on to a dissecting tray. The vascular rooted plants (emergents), the submerged and floating plants species were all collected by hand and put into a polythene bag where they were taken to the University of Ilorin Herbarium for identification.
Analysis of samples
Fixed plankton (Phytoplankton and Zooplankton) and fauna (nektons and neustons) samples were analyzed qualitatively by separating them from one another and identifying the organism to generic level using the light microscope and appropriate texts. Their relative abundance was estimated by counting the species in 50ml of the sub sample. The benthos were recovered from the soil using a forceps, separated and identified up to Generic level using the binocular microscope and relevant texts. The aquatic macrophytes from different zones were identified to species level at the University of Ilorin Herbarium.
Soil analysis in the laboratory
Floatation method(Madge and Sharma, 1969) for extraction of plant and animals life.
Sedimentation done by arranging a series of graded sieves on top of one another in decreasing order of mesh sizes and shaken thoroughly.
Gravirnetic method (Brady, 1985) for determination of moisture and humus contents.
The floatation experiment carried out on the dry soil sample produced eggs, spores, cysts of various organisms and seeds of aquatic macrophytes. Insects such as ants, beetles and mites were also observed, while earthworm, nauplius larva and Chironomous larva were collected.
The variation in the particle size composition of the soil from the two sites is presented in Table 1. Site A contains much of sand particles and the type of sand found was the sandy loamy.
Table 1: Particle size composition of the soil from study sites
The moiosture and umus content of the soil is shown in Table 2. Site B has the higher moisture and humus contents than site A. Site B is characterized with loamy sand soil. A relationship exists between the moisture and humus contents of the soil. As the moisture content increases, the humus contents also increases and vice-versa.
Table 2: Moisture Humus contents of the soils from study sites
Characteristics, Composition and abundance of Zooplankton and fauna, (neustons, nektons and benthos)
The zooplankton and fauna communities weresampled in the rainy seasons. The zooplankton consisted mainly of Daphnia. Bosmina and Cypris. 70% of the zooplankton was Arthropod, the protozoa 20% and Rotifers were represented by only 2% Genera (Table 3).
Table 3: Phytoplankton Composition and Abundance
The fauna communities were highly diverse and consisted of Neustons which are organisms associated with the surface film of water, the Nektons are large swimming or gliding animals and the benthos which are organisms living on the bottom substrate. The Neustons were mainly insects that lay their eggs among clusters of aqutic vegetation. The Nektons collected were frog Rana sp. and water turtle Chresmy sp. that feed on the insect and breed in the water. The benthos were highly diverse and included worms in substrate detritus. Table 4 shows the composition and abundance of the fauna.
Characteristics, Composition and Abundance of Phytoplankton and floral (Aquatic macrophytes)
The phytoplankton and floral communities were sampled during the rainy seasons. The Green algae (Chlorophyceae) was the most abundant phytoplankton class with 7 Genera while Euglenophyceae had least with 3 Genera. The Bacillariophyceae (Diatoms) were the most abundant in terms of number (Table 5).
The floral communities were divided into three based on the zones where they occur in the pond. The Emergents are rooted in the bottom qand grow to produce long sinuous leaves and flowers above the water surface. Three plant species were found in this category. The submerged have their foliage seldom reaching the surface. They possess long slender stems with leaves.
Two plant species occur as submerged and were not very many in the pond. The floating leaf plants occur on the water surface. They were highly abundant and explosive at certain periods that they cover the entire surface of the pond. Eichhornia and pistia species were the only floating plants identified in the pond (Table 6).
Organisms inhabiting seasonal ponds are known to survive dry periods with the aid of some adaptations (Mclachan, 1983). The presence of ants, beetles, mites and earthworm proved that these organisms live active lives during the period of drought in the pond. The formation of spores, eggs, cysts, and seeds is a mechanism employed by organisms of the pond to survive dry season. The presence of good loamy sand soil especially on site B, must have promoted the survival of the insects, earthworms, spores, cysts, eggs, and seeds. Edward (1968) and Amos (1969) reported that larvae of chironomous, Rotifers and protozoans survive in encystment stage and Algae survive in form of spores in desiccated rock pools and ponds. Both moisture an humus contents of the soil have a major effect on the distribution and abundance of benthic organisms like Earthworm and beetles. The moisture prevents desiccation and the organic matter (humus) serves as food.
With the onset of the rains and subsequent flooding of the pond, the spores, eggs, cysts and seeds either germinate, hatch or grow to give rise to the phytoplankton, zooplankton and floral communities respectively. The phytoplankton in this pond is highly diverse and composed mainly of algae. This agrees with Round (1973) who reported that ponds often have a rich phytoplankton of flagellates such as Euglena Phacus and Scenedesmus. The eutrophic nature of the pond supported many of these flagellates. The stability of the water column during the rains and conditions for mixing of water might also be responsible for the high species diversity of the phytoplankton as observed by Calijuri and Dos Santos (1996) in a small reservoir.
Table 4: Zooplankton Composition and Abundance
Table 5: The Fauna Communities in the Pond
Table 6: The Floral Communities in the Pond
There is a positive relationship between zooplankton and phytoplankton biomass as evident from the dominance of cladocerans amongst the zooplankton. McCauley and Kalff (1981) had already reported this type of relationship. The phytoplankton like diatoms which are the primary food producer in plankton cycles, were highly abundant, and they served as the primary food source for the Zooplankton. Pizzolon et al (1995) had already reported such dominance of Diatoms in Lake Futalanquen, Argentina during the rainy season. The absence of fish and the presence of large number of phytoplankton contributed to the high population of Zooplankton especially Daphnia. This has an advantage of helping to control the algal biomass. Thus predator-prey relationship exists in the pond.
The nature of the substratum and the availability of food supported a great number of benthic species such as Libyodrilus and Tubifex. The high population of chironomous larva is typical of the characteristics of benthic fauna of stagnant waters. The lentic and stagnant nature of the water provided a good breeding and gliding surface for mosquitoes and neustons, like dragonfly, pond skaters and water boat man. The nektons, frog and water turtle breed in the pond during the rains, while insects and the larvae serve as food for them.
The aquatic macrophytes are sites for egg laying by insects. The submerged rooted plants are sources of dissolved and organic compounds into the water as reported by Wetzel (1996) and Allen (1971), while the contributions of emergent vegetation such as Typha to productivity is largely indirect as detritus. The floating plant Eichhornia and Pistia often lead to deoxygenation and turbidity as a result of their explosiveness. Aquatic macrophytes can also be used as indicators of water quality (Urtans, 1995).
The study of the biotic communities of this seasonal pond, have shown that the pond is a microcosm that supported a large and diverse species of organisms. The pond could be developed to a level whereby the organisms in it are harvested and put into economic use.For example, diatomite used in industrial filtration, sugar refining and brewing industries could be obtained from diatoms which are highly abundant in the pond. Organic fertilizers, Agar, corrageenin and antibiotics could be obtained from Algae (Round, 1973). Water hyacinth, Eichhornia can be formulated into animal fodder while Zooplankton can be turned into fish pellets.