PHYSICO-CHEMICAL ANALYSIS OF OGUTA LAKE WATER AND ITS EFFECT ON PHYTOPLANKTON POPULATION

Samples were collected from the three sampling stations namely; Up, Mid and Downstream respectively to investigate the effect of nutrients concentration on the phytoplankton in Oguta Lake. The methods used were electrometric, argentometric titration, phenate spectrophotometric, colorimetric, cadmium reduction and acetone extraction spectrophotometric methods were used to determine the pH of water sample, chlorides, sulphate, ammonia, phosphorus, nitrate, nitrite, chlorophyll-A, conductivity, turbidity, chemical oxygen demand, copper, colour, total dissolved solid, respectively. However, serial dilution was carried out using the spread plate or pour plate method was used to determine the microbial analysis of the sample. At the end of these researches, the Physico-chemical parameters analysed showed that Oguta Lake had total dissolved solids values of 6.50 ± 0.06mg/l, 6.50 ± 0.14 and 6.50 for upstream, mid stream and downstream respectively. The result showed there was no significance total dissolved solids difference between the various stream points (P0.05). the colour of the Lake showed significant difference ranging from 17.00 ± 1.41 and76.00 V 1.41 in upstream and downstream and the lowest value at upstream. The pH range in this study indicates that the water may be acidic (5.54-7.31). Phytoplankton assemblages obtain across the three stream points showed only three divisions and 78 species. The identified divisions and species are comprised of Eurcharyta (44), Cyanophyta (25) and Chlorophyta (9). Eurkaryta recorded 100%, 5% and 15% abundance in upstream, midstream and downstream respectively, while Cyanophyta recorded the highest abundance at downstream with 75%, Chlorophyta only was identified at the midstream and was least abundance with 23%. The phytoplankton diversity indices done showed that downstream was most diverse having the highest Shannon Weiner Index and Evenness Index of 3.631 and 1.212 respectively. In relation to physicochemical and phytoplankton abundance, the findings in this study is contradictory to some researches. They reported positive correlation of phytoplankton with phosphate and nitrate. There was negative correlation of phosphate with Eurkaryta and Chlorophyta, except for Cyanophyta that showed positive correlation with phytoplankton but not very significant. These low levels of phosphate and nitrate may be the cause of low phytoplankton levels.