Seasonal Dynamics of Physico-Chemical Characteristics and Water Quality Index of the River Ghaghara at Azamgarh, Uttar Pradesh, India

Abstract

The River Ghaghara is a major Himalayan tributary of the Ganga that supports irrigation, fisheries and domestic use along the northern boundary of Azamgarh district, Uttar Pradesh. This study assessed the seasonal and spatial variation of 23 physico-chemical variables (21 measured directly; total dissolved solids and magnesium derived) and the overall water quality of a 9.6 km reach of the river. Water was sampled monthly for one year at five sites, with three replicates per visit (n = 180), and analysed by standard methods. Data were evaluated by two-way ANOVA, the Kruskal–Wallis test, Spearman correlation, principal component analysis (PCA) and a weighted arithmetic Water Quality Index (WQI). The water was mildly alkaline (pH 7.48–8.29), well oxygenated (DO 5.33–8.18 mg/L) and moderately mineralised (EC 184–363 µS/cm), with a calcium–bicarbonate ionic composition. All variables differed significantly between seasons (p < 0.001). Major ions were diluted during the monsoon, whereas turbidity (up to 183 NTU), BOD, COD, phosphate and silicate increased and nitrate peaked after the monsoon. Site effects were small and limited to BOD, COD and nutrients, which were highest at one site with visible human activity. BOD exceeded the CPCB Class B criterion of 3 mg/L in 32.2 % of samples. The WQI averaged 76.4 and ranged from 64.4 ('poor') in winter to 85.6 ('very poor') in summer, mainly because of BOD and dissolved oxygen; both season (p < 0.001) and site (p = 0.015) affected it significantly. PCA extracted ionic–flow, thermal–organic and runoff-nutrient components that together explained 92.5 % of the variance. The river is well oxygenated and its mineral content meets Indian drinking-water standards, but seasonal organic enrichment, reflected in BOD and the WQI, is its main water-quality concern.