Plankton diversity in Oriyanrin lower Ogun river water body

Introduction

All over the world, freshwater resources have been subjected to an increasing pollution load from contaminated runoff water originating from anthropogenic activities like domestic and industrial (Banetti and Garrido, 2010) [5] . The adverse effects of human impacts on the aquatics include water-borne diseases, alteration of aquatic biota composition, eutrophication, and reduction or destruction of ecosystem integrity (Ekpo et al., 2013) [8] . Bio-monitoring programs that employ indices and metrics of community structure (Udoidiong and King, 2000) have been used to assess the potential impacts or non-impacts of these alternations on the aquatic ecosystem (Aiwerioghene and Adedolapo, 2016) [1] . The richness of macro invertebrate community composition in a water body can be used to provide an estimate of water body health (Argerich et al., 2004) [4] . The physical and chemical qualities of water and substratum occupied by macro invertebrates determine their occurrence and distribution (Danes and Hynes, 1980) [6] . Macro invertebrates play an important role in the aquatic community icluding mineralization, mixing of sediments and flux of oxygen into sediment, cycling of organic matter and assessing the quality of inland water (George et al., 2009) [9] . Human development pressures point to adverse consequences for water quality and general environmental degradation, which in the Lagos lagoon have manifested in declining fisheries, visible aesthetic nuisance, and loss of recreational amenities (Ajoa et al., 1996) [2] .

Methodology

The study area The Oriyanrin Lagoon, Abeokuta, Ogun State, is approximately 60 km long and 3 km wide and lies between longitudes 3°0′ and 3°45′ E and between latitudes 6°25′ and 6°30′ N. It is part of a continuous system of lagoons and creeks along the coast of Nigeria from the border with the River Ogun to the Niger Delta. Its water depth ranges from 1 m to 10m. The lagoon experiences two seasons: the dry season (December -May) and the wet season (June -November). (Williams, 1962). Most of the year, it is characterized by fresh and slightly brackish water. The lagoon is approximately equidistant from the entrances of Ogun and Cotonou harbors. Therefore, it is influenced by tides and floods from the Ogun Lagoon and Cotonou harbour through Lake Nokue and Lake Porto-Novo (Anyanwu and Ezenwa, 1988) [3] . The river with its tributaries Italu and Itomo is the major river emptying into the lagoon. Creeks connected to the lagoon include Bawa and Doforo. Major weeds occurring in the lagoon yearly in December and January include the common water hyacinth (Eichiorniacrassipes) and ceratophyllum and pistia sp. The lagoon is surrounded by large areas of swamps covered with vegetation, among which the raphia palm (Raphia sudanica), the African oil palm (Elaeis guineensis), and the coconut palm (Cocos nucifera) are dominant (FAO, 1969).

Plankton

Plankton net (mouth area = 40 cm, mesh size =500 um) with a 10ml bottle attached to the apex was used to collect plankton samples. Ten vertical and horizontal hauls were made, and the net was dragged over a distance of 5 m to make a semi-lunar area. Concentrated samples were poured into a labelled 150 ml bottle, and 4% formalin was added to preserve the phytoplankton, and 70% ethanol was used to preserve zooplankton.

The bottle was covered and properly labeled at each location. Plankton species were identified with illustration by Jeje and Fernando (1986), and the number of plankton was estimated using the Sedgwick Rafter counting chamber as described by Boyd (1979).

Results

Plankton composition of Oriyanrin Lagoon, Ogun State

Forty taxa of plankton were encountered.

Discussion

Sources of dissolved oxygen in the aquatic environment include the atmosphere and photosynthesis. This depends on its solubility, while a loss of oxygen includes respiration, decay by aerobic bacteria, and decomposition of dead decaying sediments (Gupta and Gupta, 2006) [10] . Accumulation of free carbon dioxide due to little photosynthetic activities of phytoplankton will lower the pH value of the water, while intense photosynthetic activities of the phytoplankton will reduce the free carbon dioxide content resulting in increased pH values (Egborge, 1981; Gupta and Gupta, 2006) [7,10] .

Conclusion

Although considerable interest has been directed towards research and development of fisheries in Nigerian waters, surprisingly little effort has been directed at the association of non-fisheries resources (Aquatic microflora and fauna). Apart from their ecological role, plankton contributes greatly to the economic and scientific importance of Nigerian water bodies. The present tendency to annihilate these resources through anthropogenic activities, importance, water physical and chemical tolerance level, will spell doom to aquatic organisms which depend on them.

The ecological system should be maintained, which supports high plankton diversity, and its pollution should be discouraged to continue providing healthy habitat for its aquatic inhabitants.

Recommendation

There is a need to study the primary production of the water, know their population dynamics and diversity as most aquatic organisms are dependent on plankton. The uncontrolled use of the water body should be checked through the enforcement of variation regulation by the implementing agencies involved, as there will be a serious biodiversity loss if this situation should continue. Any management programme put in place should be such that it will address the issues of environment protection, integrated management, and sustainable development, as well as the conservation of the living resources of the system. So far, no work has been published on the diversity of plankton in Oriyanrin lagoon. Therefore, this study provides baseline data for Oriyanrin lagoon.

References

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