Comparative study of physico-chemical parameters with national and international standard and the insect community of Erelu Reservoir in Oyo town, Oyo State, Nigeria

摘要

Assessment of water bodies is very crucial to determine its quality and proffer solution before it has an adverse impact on its biota and direct users of the water body. Insect communities and physico-chemical parameters in comparison with national and international criteria of Erelu Reservoir were investigated to determine their impacts on insect community of the reservoir. Water and insect macro-invertebrates sampling was done once in every month from June 2013-May 2015 from each station of Erelu Reservoir. Insects were collected using net of mesh size of 250 m to swap the surface of water. Insects collected were identified with standard identification guide. Water samples were analyzed using standard method. Data collected from physico-chemical parameters were analysed using descriptive statistics. Relationship between physico-chemical parameters and insect macro-invertebrates was determined using pearsons correlation coefficient (r). Species diversity, evenness and richness were examined using Margalef, Shannon Weinner and Equitability indexes. The results of physico-chemical parameters revealed that turbidity values (12.483.00 Ntu) were higher than the required limits of WHO and NESREA (5.00 Ntu) criteria, while nitrate (1.140.15 mg/L) and phosphate (0.210.08 mg/L) values were below the recommended standard of NESREA (9-10 and 3.50 mg/L). A total of 4 orders (Coleoptera, Diptera, Hemiptera and Odonata) having 72,276 individual insect macro-invertebrates were collected. Hemiptera were the most abundant (91.57%) among the insects encountered. Transparency had positive significant relationship with Hemiptera (0.880) and Odonata (0.675), Ca2+, Mg2+, DO, TDS, NO3-, TA. Turbidity, pH, Temp. and EC had negative correlation with orders of Coleoptera, Diptera and Odonata at (P0.05). Turbidity had direct correlation with Diptera (0.0731) at (P0.05). The present study revealed that the water quality parameters value were within standard limits and had little impacts on the insect abundance and richness. The low nutrients and high turbidity indicate low productivity of water body, thus, tending towards deterioration if proper management of the reservoir is not adopted.