Abstract:
Macroinvertebrates owing to their wide variation of response to environmental changes have been used to evaluate the water quality and health of aquatic systems. Presence and/or absence of macroinvertebrates can indicate the effects of anthropogenic activities on the aquatic environmental quality. The aim of the study was to assess the conditions in the Osia stream using benthic macro invertebrates as bio-indicators. Selected water quality parameters like dissolved oxygen (DO), pH, conductivity, and temperature were measured in-situ and turbidity in the laboratory using electronic meters. Habitat physical parameters like Stream width was measured using a tape measure and stream depth of the stream was determined using a wooden meter ruler.
Samples of benthic Macroinvertebrates were collected using a D-net of 30×60cm then transferred to the white tray for washing and finally preserved in 70% ethanol. The organisms were then taken to the laboratory for sorting. The mean and standard deviation for each physical chemical variable was calculated per sampling site. Here Species diversity, abundance and species evenness of benthic macroinvertebrates were evaluated. Physical chemical variables were compared using one-way analysis of variance (ANOVA). The physical chemical variable varied along Osia stream dissolved oxygen was highest at site 1 and lowest at site 3, temperature was slightly high at site 1, conductivity was highest at site 1 and lowest at site 2, PH decreased downstream, turbidity was highest at site 3 and lowest at site 2. A total of 12 families of macroinvertebrates from 5 orders were recorded. Thiaridae was the most dominant species.
Shannon wiener diversity index and Species evenness were highest (1.58) at site1, moderate (0.5) at site 3 and lowest (0.2) at site 2. These indicated good, moderate and fair water quality respectively. Water quality, habitat physical status and human activities varied along Osia stream which significantly affected the normal diversity and abundance of benthic macroinvertebrates and this indicated that the Osia stream is highly disturbed by human activities. There is need to educate the stake holders and the riparian community on effect of destroying the stream and other environmental related issues.
