ASSESSMENT OF POLLUTION LEVEL USING COMPOSITION, DISTRIBUTION AND ABUNDANCE OF MACRO-INVERTEBRATES IN ALA RIVER, AKURE, NIGERIA

Abstract

Anthropogenic activities are polluting the water resources thereby affecting the diversity of aquatic macro-invertebrates through indiscriminate waste disposal into the river. Macro-invertebrates serve as bio-indicators by providing a more accurate understanding of transition in the aquatic systems. The river was divided into three stations. The physico-chemical parameters and heavy metals were analyzed. Macro-invertebrates were collected with the use of the D-frame dip net and by directly handpicking of specimens from the biotopes. The result of the physico-chemical parameters showed that there was significant difference (P< 0.05) between the highest mean values for temperature, electrical conductivity, dissolved oxygen, pH, biochemical oxygen demand, nitrate-nitrogen, phosphate-phosphorus, total dissolved solids turbidity and least mean values of the months. The mean values for Copper were above World Health Organization (WHO) permissible limit while those for Zinc were below WHO permissible limit. Mean values for February were below detectible limit for all the heavy metals. A total of 1,101 macro-invertebrates comprising of 29 families, 12 orders and 4 phyla were identified. January had the highest number of individuals (213) and August being the least (61). Chironomidae (9.72%), order Diptera (23.43%) and phylum Arthropoda (70.94%) had the highest relative composition (%). In terms of distribution, Araromi (station 2) had the highest number of individuals (436). The diversity indices showed that the highest number of taxa (28) were recorded in the month of March. For the species diversity and species richness, March had the highest values. For the dominance and evenness, the highest value was obtained in the month of July and August respectively. From the study, it was concluded that Ala River was moderately polluted at the time the study was carried out. However, it is recommended that efforts should be intensified by relevant authorities to monitoring the level of pollution in the river so as to prevent destruction of the ecosystem, dumping of wastes into the river and any other water body.