Assessment of water quality status using planktonic diatoms on river Kisat, Lake Victoria catchment, Kisumu County, Kenya
Otieno, Anna Adoyo
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Information on the quality of water is important as it forms a vital baseline for among others the detection of undesirable change in water quality. Diatoms often are used as water quality bio indicators in European countries, however there is limited use of these microalgae in most African countries yet they are suitable for quantitative research as they respond strongly to environmental changes. The physico-chemical and diatom properties were investigated along River Kisat that drains into Lake Victoria over a period of six months between March and August 2014. The aim of the study was to determine the levels of physico-chemical parameters and diatom properties along River Kisat. Sampling was done during the day and analyzed within four hours of sampling at the Kenya Marine Fisheries and Research Institute, Kisumu. The parameters measured were temperature, electrical conductivity, pH, dissolved oxygen, flow rate, turbidity measured on site and alkalinity, total nitrogen, total phosphorus, silicates and diatom composition measured in the laboratory. Mean EC along the river ranged from 390.75±18.40 μ𝑠 cm-1 to 839.65±33.01 μ𝑠 cm-1. Mean temperature ranged from 24.63±0.42 0C to 25.07±0.78 0C and pH was from 7.08±0.17 to 7.60±0.24. Mean DO ranged from 3.42±0.40 to 5.92±0.75 mg l-1. The lowest mean turbidity recorded was 32.37±5.16 NTU while the highest was 122.98±18.97 NTU. Flow rate ranged from 0.00 ms-1 to 0.37±0.08 ms-1. Mean total alkalinity ranged from 107.23±20.37 mg l-1 to 199.67±28.93 mg l-1 along the river. Mean TN was within 400.77±124.50 μg l-1 to 857.88±363.96 μg l-1. TP concentration ranged from 342.17±112.49 μg l-1 to 1227.38±424.29 μg l-1. Silicates and chlorophyll a concentrations were from 3.8±0.37 mg l-1 to 4.46±1.02 mg l-1 and 95.82±21.15 mg l-1 to 213.14±74.30 mg l-1 respectively. The study revealed that only four parameters including DO, pH, alkalinity, and silicate showed significant differences along the river (P˂0.05). A total of 22 taxa belonging to 10 genera were identified in all the five sampling sites along the river. Nitzschia genus had the largest number of taxa (4) whereas gomphonema and Stephomodiscus were represented by one taxon each. Species diversity indices (richness, diversity, evenness) were generally low and showed no significant difference along the river (P˃0.05). Weak correlations, less than 0.5, were also found between these indices and the physico-chemical parameters. A canonical correspondence analysis was used to determine correlations between individual diatom species and the physico-chemical parameters and revealed correlations among all the identified species and the parameters. The study showed that five parameters (conductivity, alkalinity, silicates, TN and TP) were the most important environmental variables influencing the species composition. It is concluded that diatom assemblages are influenced by changes in water quality and can successfully be used as bio indicators.