Effects of Anthropogenic Activities on Water Quality within Ngong River Sub-Catchment, Nairobi, Kenya

Abstract

Anthropogenic activities often compromise the water quality of natural water systems, rendering it unfit for domestic and agricultural use. This paper evaluates the effects of anthropogenic activities on the water quality of Ngong River in Nairobi County, Kenya. It aimed to assess the river’s physico-chemical parameters, identify major anthropogenic activities that act as pollutant sources and establish the relationship between the anthropogenic activities and water quality along the Ngong River. Twelve water samples were systematically collected in each of the twelve study sites in April and August 2021 and analyzed in the laboratory for various water quality parameters. The accumulation factor (AF) indicated that E. coli, total coliforms, BOD and COD were found to significantly build up downstream of Ngong River. The ANOVA test results showed that all the physicochemical parameters studied (BOD, E. coli, pH, total suspended solids, total coliforms, turbidity, conductivity, nitrates, oil and grease and TDS), except COD, were not significantly different (p ≤ 0.05) for the different sites. Measured heavy metals, such as lead (Pb) levels at different sampled points, were all found to be below the detectable limit (0.001 ppm) for both seasons. Cadmium (Cd) was detectable during the dry season with the highest levels (0.113 ppm) being recorded at Ngong Forest Boundary. The findings of this study revealed that anthropogenic activities, such as raw sewage disposal, industrial activities, solid waste dumping and small-scale agriculture, had adverse effects on Ngong River’s water quality. The study recommends a need to closely monitor anthropogenic activities along Ngong River to reduce their probable pollution of the water in the River basin. This will ensure the sustainability of the water resources.