Spatio-temporal variations in hydrochemistry and quality of surface water in Bharathapuzha River Basin, Kerala, India

ABSTRACT The Bharathapuzha river (Length = 209 km; Area = 6186 km2; order (N) = 8th) is the second-largest river in Kerala State, India. The midland part of the river (Area = 1854 km2) has been studied to bring out the variation in hydrochemistry and quality due to anthropogenic and geological influences. The study area is the ‘rice-bowl’ of the State and is characterized by its unique geography, sub-humid to semi-arid climate, industrial activities, and intense agricultural practices. The major ion chemistry of the Bharathapuzha river, based on surface water from 27 locations for three seasons, is mainly controlled by carbonate weathering, with Ca2+ and HCO3 − ions dominating the composition. Gibbs plots revealed rock–water interaction as the major mechanism controlling the surface water chemistry, and scatter diagrams revealed carbonate weathering significantly and silicate weathering marginally contributing the ions to the surface water. Majority of the water quality parameters exhibited values within the desirable limits of WHO guidelines and Bureau of Indian Standards for drinking purposes, and showed distinct seasonal variations. Quality degradation was observed at some locations, where the tributaries were close to industrial units and domestic dwellings. Strong correlation results of K+ with Cl− and PO4 3-, and the presence of organochlorine pesticides aldrin and heptachlor indicate the use of nutrients and pesticides in the study area. The quality assessment revealed that 44% of samples in monsoon, 67% in post-monsoon, and 33% in pre-monsoon were suitable for drinking and domestic purposes, and almost all samples except one were found to be suitable for irrigational purpose.