Assessment of hydrogeochemistry and water quality index (WQI) in some wetlands of the Brahmaputra valley, Assam, India

Abstract

In the present study, geochemical characteristics of surface water have been studied considering seasonal variation. Water samples from 10 different wetlands of the Brahmaputra valley were collected and analyzed for pH, electrical conductivity, total dissolved solids, bicarbonate, chloride, sulfate, nitrate, calcium, magnesium, sodium, potassium and total hardness. The order of the abundance of the major cation and anion is as follows: HCO3- > SO42- > Cl– > Na+ > Ca2+ > K+ > Mg2+ > NO3- in pre-monsoon and HCO3- > SO42- > Cl– > Na+ > Ca2+ > Mg2+ > K+ > NO3- in post-monsoon. Both carbonate and silicate weathering occur in the wetlands although carbonate weathering was found to be dominant in post-monsoon. According to Gibbs diagram, the predominant samples fall in the rock–water interaction dominance. The Piper-trilinear diagram shows that the water samples belong to Ca2+–Mg2+–Cl–-SO42- type or facies in pre-monsoon, while in post-monsoon, most of the sample show temporary and permanent hardness due to Ca2+–Mg2+-HCO3-, and Ca2+–Mg2+-SO42-, respectively, indicating a mixed type of water. Based on the water quality index, Deepor Beel and wetlands of Kaziranga National Park shows poor water quality. Principal component analysis used for source apportionment of the parameters indicated pH, HCO3-, TH, EC, TDS, Cl–, Ca2+, Mg2+, Na+, and K+ as the mineral component of the wetlands, whereas Mg2+, NO3-, and SO42- originated from anthropogenic sources such as agricultural run-offs, nearby tea gardens and sewage sludge.