Spatial-temporal assessment of water quality and assimilative capacity of river Ramganga, a tributary of Ganga using multivariate analysis and QUEL2K.

Abstract Water quality of river Ramganga, a major tributary of the Ganga, was monitored by monthly sampling at selected 23 stations (17 on the main stem and 6 on tributaries) during two calendar years 2014 and 2015 for 24 parameters. Cluster analysis grouped the sites in three statistically significant clusters, highly polluted, moderately polluted and less polluted, based on the similarities or differences in water quality parameter values. Discriminant Analysis helped in identifying the most representative discriminant parameters in entire dataset with more than 86% correct assignment in both temporal and spatial analysis. Despite high organic load in the middle stretch of Ramganga, the observed dissolved oxygen values were higher than 4 mg/l at almost all sampling stations on the main stem, even in lean flow period of a year. About 16–49% BOD load reduction from various point sources was estimated to maintain the desired dissolved oxygen levels (5–6 mg/l) for aquatic species during lean flow season in river Ramganga. This implies that primary treatment alone of discharge from these sources is sufficient from the point of view of sustenance of indigenous aquatic flora and fauna. Comparison of water quality of Ramganga and Ganga (before and after the confluence with Ganga) for lean flow season revealed that Ramganga does not significantly contribute to the decline in water quality of river Ganga in terms of parameters such as dissolved oxygen and heavy metals. Highlights • Discriminant analysis identified 6 parameters with more than 86% correct assignment. • Observed DO values were found higher than 4 mg/l at all sampling stations on main stem. • Reduction of 31%, 30%, and 49% BOD loads to maintain DO values more than 6 mg/l. • Dhela and Kosi are the most polluted tributaries of Ramganga. • Ramganga does not significantly contribute to the decline in water quality of Ganga. [ABSTRACT FROM AUTHOR]