Effects of Anthropogenic Activities on Water Quality of Ngong River, Nairobi County, Kenya

Abstract

Water quality is one of the major aspects of water availability affected by the problem of water pollution. Water pollution has recently become rampant due to an increase in urbanisation, population and industrialisation. It is therefore crucial to understand the degree of water quality in rivers that flow through urban areas in order to develop the necessary rehabilitation strategies and measures to alleviate this problem. This study evaluated the effects of anthropogenic activities on water quality of Ngong River in Nairobi County, Kenya. The study was aimed at identifying the different anthropogenic activities along Ngong River, measuring the pollution levels in Ngong River with respect to selected Physico-Chemical Parameters, and establishing the relationship between the anthropogenic activities and water quality along the Ngong River. The hypotheses that guided the study were that anthropogenic activities had no effect on the water quality of Ngong River and that there were no significant differences between physicochemical parameters at different study sites. Anthropogenic activities observed were recorded for different sites. The river was divided into three segments in which twelve water samples were collected. Water samples were analysed for pH, electrical conductivity, temperature, TDS, Total suspended solids, oil and grease, BOD, COD, nitrate, lead and Cadmium and faecal coliforms (Total Coliforms and E.coli). Secondary data was collected from official government reports, water sector, NEMA, and scientific publications. Water quality data set obtained was subjected to Accumulation Factor, River Recovery Capacity, Cluster Analysis and ANOVA test (p<0.05). Accumulation Factor (AF) indicated that E.coli, Total Coliforms, BOD and COD significantly built up downstream of Ngong River. The river recovered significantly from several physicochemical parameters: COD, BOD, Total Coliforms, E.coli, Turbidity and TSS for wet and dry seasons. E.coli and Total coliforms had the highest recovery value of 99% during both seasons. Cluster analysis indicated that Ngong River’s water quality was highly influenced by dumpsites, domestic and industrial effluents on the river basin. Lindi Mosque site had the highest pollution levels while Ngong Forest site had the lowest pollution levels. The ANOVA test results showed that majority of the parameters were not significantly different for the different sites (BOD, E. coli, pH, Total suspended solids, Total coliforms, Turbidity, Conductivity, Nitrates, Oil and grease and TDS) except COD. All the water quality variables except COD showed similar characteristics throughout the Ngong River. The non-significant difference observed in the majority of parameters indicate contribution of anthropogenic sources in the Ngong River basin. Lead (Pb) levels were all below the detectable limit (0.001ppm) for both seasons. Cadmium (Cd) was detectable during the dry season with high levels of 0.113ppm at Ngong Forest Boundary indicating upstream pollution of Ngong River with regards to Cd. The findings of this study revealed that the parameters causing variations on water quality are mainly related to anthropogenic pollution. It is recommended that anthropogenic activities, such as domestic effluents and industrial effluents discharge, be closely monitored to reduce their probable pollution of Ngong River basin.