Seasonal Dynamics of Water Quality and Pollution in Urban Streams of Tunduma, Tanzania

Understanding seasonal water quality variation is essential for sustainable water resource management in rapidly urbanising towns such as Tunduma, Tanzania. This study investigated temporal dynamics in physicochemical and microbial quality across six surface water points (SWPs) through monthly sampling over one year. Parameters analysed included pH, electrical conductivity (EC), turbidity, total dissolved solids (TDS), nitrate, phosphate, biochemical oxygen demand (BOD), and microbial indicators (faecal and total coliforms). Descriptive statistics revealed distinct wet-season increases in turbidity (up to 25.24 NTU), total suspended solids (> 44.17 mg/L), nitrate (11.59–25.57 mg/L), phosphate (1.40–1.49 mg/L), BOD (13.96–24.53 mg/L), and microbial contamination (faecal coliforms 10.58 CFU/100 mL; total coliforms 26.00 CFU/100 mL). Shapiro–Wilk tests (W = 0.64–0.95) confirmed non-normality of most variables, reflecting event-driven pollution. Pearson correlation (r > 0.65) indicated strong associations between nutrients and microbial indicators, suggesting agricultural runoff, pit latrines, and greywater as common sources. Mann–Kendall trend tests identified increasing trends in EC, TDS, and nitrate, with declining turbidity and sulphate at some sites. Principal Component Analysis (PCA) extracted three components explaining 77.9% of total variance: Component 1 linked nitrate, phosphate, BOD, and coliforms to nutrient and organic pollution; Component 2 captured turbidity and suspended solids, indicating sediment inputs during rainfall; while Component 3 reflected site-specific variability. PCA biplots revealed clear seasonal clustering, with wet-season months (March–May, November) associated with elevated contaminant loads, and dry-season months near baseline conditions. Several parameters exceeded World Health Organization (WHO) drinking water guidelines, particularly during peak rainfall, posing risks to human health and aquatic ecosystems. These findings underscore the need for continuous monitoring, seasonally adaptive management, and pollution control strategies to safeguard surface water quality in Tunduma and similar rapidly growing urban environments.