Impact of Seasonal Variation in Physico-Chemical Factors on Protozoa in Different Types of Water in Selected Areas of Kathmandu Valley, Nepal

Abstract

This study aims to assess how physico-chemical parameters influence protozoan populations across diverse drinking water sources in Kathmandu, analyzing the combined effects of seasonality, location, and water type on water quality dynamics. In 2021, 720 water samples were collected from municipal taps, wells, and deep tube-wells across four Kathmandu Valley sites during spring, summer, autumn, and winter. The physico-chemical parameters were analysed  (APHA). Samples (each1000 ml) were analyzed within 2–6 hours using centrifugation (2,500 r/min, 1–2 min) and microscopy (100x). Protozoan cysts and oocysts were confirmed with Lugol’s iodine and Modified Ziehl-Neelson stains. Analyses were conducted at Nepal Environmental and Scientific Service Pvt. Ltd. and KVWSMB laboratories, with data processed in Microsoft Excel. For water temperature, season emerged as the primary determinant (F = 1887.07, p < 0.001), underscoring pronounced seasonal fluctuations driven by climatic conditions, ambient temperature, and monsoonal precipitation, while branch (F = 7.80, p < 0.001) and Type (F = 5.15, p < 0.01) exhibited smaller but significant effects, reflecting spatial heterogeneity and treatment influences. Turbidity and color were primarily controlled by water type (F = 19.65, p < 0.001; F = 29.25, p < 0.001, respectively), indicating the effectiveness of treatment in reducing suspended particles and dissolved substances, whereas branch and season exerted weaker, non-significant effects. Chemical parameters including pH, alkalinity, hardness, iron, ammonia, and chloride, were significantly affected by both type and season, with type predominating for alkalinity (F = 23.79, p < 0.001), hardness (F = 23.54, p < 0.001), iron (F = 172.22, p < 0.001), ammonia (F = 103.60, p < 0.001), and chloride (F = 52.42, p < 0.001) whereas, pH was most strongly influenced by season (F = 24.04, p < 0.001). Branch effects were generally weaker, suggesting localized spatial variability. Microbiological quality, including pathogenic and non-pathogenic protozoa, was predominantly determined by Water Type (F = 5.10–5.69, p < 0.01), highlighting the critical role of treatment processes in mitigating protozoan contamination, with season and branch contributing minor effects.