Assessment of water quality by physico-chemical properties and nematodes as bio- indicators along river Sosiani in Uasin Gishu, Kenya

Abstract

Water quality in freshwater systems is increasingly threatened by industrial, domestic, and agricultural pollution, which introduces contaminants that degrade ecological integrity and pose risks to human health. River Sosiani is a critical water resource for domestic, agricultural, and industrial use; however, its quality has deteriorated due to increasing anthropogenic activities, necessitating more reliable and integrative monitoring approaches. Conventional chemical assessments provide only short-term snapshots of water conditions and fail to capture cumulative or long-term pollution effects. In contrast, biological monitoring using nematodes as bioindicators provides a more comprehensive assessment of both current and historical water quality. The general objective of this study was to apply nematodes as bioindicators for monitoring pollution in River Sosiani. Specifically, the study aimed to isolate and quantify nematodes from water and sediment samples and to examine the relationship between nematode community characteristics and pollution levels. The methodology involved collecting water and sediment samples from four key locations along River Sosiani: Kaptagat (control site), Kipkorgot, Kisumu Bridge, and Huruma. Nematodes were extracted from both water and sediment using a modified Baermann funnel technique. The densities of the nematodes were calculated as population densities (PD), expressed as the number of individuals per unit volume of water or per unit weight of sediment. The relationship between nematodes and pollution levels was assessed by correlating nematode population densities with physicochemical parameters, including dissolved oxygen and turbidity (as well as pH, temperature, and electrical conductivity). Results indicated a clear spatial trend in nematode abundance, with low nematode numbers in Kaptagat (93 individuals) and Kipkorgot (167), and significantly higher numbers in Kisumu Bridge (1344) and Huruma (1792), indicating a progressive increase along the pollution gradient, (P = 0.005). These trends corresponded with changes in physicochemical parameters, where pH decreased slightly from 7.39 at Kaptagat to 6.82 at Huruma, turbidity increased from 3.50 NTU to 8.36 NTU at Huruma, dissolved oxygen decreased from 5.45 mg/L to 3.55 mg/L at Huruma, temperature increased from 13.30 °C to 18.93°C at Huruma, and electrical to 18.93 °C to 18.93°C at Huruma, and electrical at Huruma, and electrical conductivity increased from 48.71 S/m to 174.35 S/m at Huruma, demonstrating a strong relationship between deteriorating water quality and increased nematode abundance, suggesting dominance of pollution-tolerant species. In conclusion, nematode-based assessments provide a reliable and integrative tool for assessing water quality and ecological changes. The study recommends their use alongside conventional chemical analyses for enhanced monitoring and sustainable management of River Sosiani and similar ecosystems.