ASSESSING WATER QUALITY USING PHYSICO-CHEMICAL PROPERTIES AND BENTHIC MACROINVERTEBRATE OF AWETU

Abstract

The surface water quality is a matter of serious concern today. Rivers due to their role in carrying off the municipal and industrial wastewater and run-off from agricultural land in their vast drainage basins are among the most vulnerable water bodies to pollution. Awetu river is subjected to different types of anthropogenic pressures varying in extent from upstream to downstream, thereby creating spatial variability of water and habitat quality in the stream segment. The main objective of this study was assessing water quality using physicochemical properties and benthicmacroinvertebrate metrics. The assessment were assessed using physicochemical parameters, physical habitat assessment, biotic indices /metrics , human activity by observation as well as macroinvertabretes samples from fifteen sampling sites coded AWS1 to AWS15 along the river using the standard procedures. Six water quality parameters were tested in situ, namely temperature, pH, dissolved oxygen, total dissolved solid, Electric conductivity and Turbidity by employing multi Prob analyzer. Other parameters namely ammonia, total suspended solid, nitrate, nitrite, Ortho phosphate, total Phosphate, total suspended solid, BOD5 and COD were tested in the laboratory. Benthic macroinvertebrates were sampled at each sampling site using a rectangular frame net (20 × 30 cm) with a mesh size of 300 μm, and identified to the family level following the standard methods in the laboratory. Water quality paramaters were analyzed using standard methods while the habitat quality class was quantified using the qualitative habitat evaluation index(QHEI). Multivariate statistical analyses were computed to describe the macroinvertebrate assembledge. Benthic macroinvertebrate assemblages were determined by, number of taxa, and the total number of individuals, by computing various indices. Detrended correspondence analysis (DCA) was also applied to evaluate the relationship between benthic macroinvertebrate community and physicochemical water parameters. The range values of surface water temperature was 19.6 to 23.6°C, dissolved Oxygen 3.2 to 7.8mg/l, BOD5 4.5 to 6.7 mg/l, EC 63 to 127μs/cm and NH4 -N 0.29 to 1.33 mg/l. A total of 1621 macroinvertebrates individuals within 33 taxas belonging to 13 orders were identified from the 15 sampling sites. The most abundant orders were: Ephemeroptera 31%, Trichoptera 18%, Odonata 15% and Diptera 10% represented by 14 families. The results revealed that macroinvertebrate distribution varied considerably with the change in anthropogenic activities and habitat conditions in the study area. Upstream sites were found to have significantly better ecological water quality than downstream sites based on indices and metrics. The downstream sites were the most impacted by urbanization, had the poorest water quality scores than upstream site