Spatial variation in the physico-chemical properties of Lake Naivasha, Kenya



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Lake Naivasha in Kenya is an important livelihood resource for its adjacent communities. However, thisfreshwater lake is under significant strain due to anthropogenic activities. The study aimed todetermine the water quality status of Lake Naivasha in order to establish its trophic state. Physico-chemical parameters were studied in seven pre-defined stations in the main lake from February to July2019 (autumn and winter months). Monthly samplings were done and sample analyses using standardprocedures were undertaken. Samples were collected in triplicates for the determination of nitratenitrogen, soluble reactive phosphorous, total nitrogen (TN), total phosphorous (TP), ammoniumnitrogen, silicates, and chlorophyll a . Water temperature, conductivity, dissolved oxygen (DO), and pHwere measured in situ using a multimeter probe. The results showed the mean water temperature to be22.73 ± 1.6°C, DO 8.5 1 ± 0.87 mg/L, conductivity 233.85 ± 26.94 μS/cm, pH 8.13 ± 0.3 , TN 471 ± 170.61µg/L, PO 4 5.88 ± 2.12 µg/L, TP 97.97 ± 49.06 µg/L, NO 3 -N 6.70 ± 3.55 µg/L, NH 4 -N 18.93 ± 10.91 µg/L, SiO 2 3.18 ± 2.99 mg/l and Chlorophyll a 21.51 ± 4.25 Mg/m³. The study revealed that secchi depth, totalphosphorous, and chlorophyll a showed significant differences spatially (P = 0.05). The results implythat Lake Naivasha is contaminated with pollutants from domestic wastewater, agricultural and/orsurface run off. A sewage discharge point and the R. Malewa mouth were identified as the main pointsources of pollution. Therefore, there is a need for measures to be put in place to reduce watercontamination from these points in order to improve the water quality of the lake