Hydrochemical characterization of groundwater in geomorphic units using graphical and multivariate statistical methods in the Dimapur valley, Northeast India

Abstract

The present paper examines the potentiality of graphical and multivariate statistical methods in differentiating geomorphic units in terms of hydrochemical aspects. 275 shallow groundwater samples representing denudational hill (DH), piedmont zone (PZ), flood plain (FP) and alluvial plain (AP) were collected from 50 sites during pre and post monsoon seasons. Physicochemical parameters were measured in the field. Ca2+, Mg2+, K+, Na+, Fe, Mn were determined in ICP-AES while Cl−, SO4− and HCO3−, CO3− were measured in ion chromatography and titration, respectively. Trilinear plot indicates DH, PZ, FP units are characterized by Ca2+–Mg2+–Cl−–HCO3− facies while AP comprises Na+–Cl− facies in both the seasons suggesting progressive ionization process along the flow path. Durov diagram, Chebotarev anion model and Stiff diagram indicate that HCO3− and SO4− dominate DH, PZ and FP while Cl− signifies in AP suggesting the evolution of groundwater originates from DH and PZ and attains old stage in AP. Gibbs diagram reveals that hydrochemical constituents belong to geogenic origin which resulted from weathering of rock forming minerals. Box and scatter plots indicate elevations of dissolved ions in pre rainfall and simple ion mixing process. Pearson correlation shows that PZ is characterized by dissolution of clay minerals while FP and AP reflect dissolution of calcite and dolomite. Factor 1 represents high degree of dissolution, factor 2 indicates reaction of feldspar minerals with carbonic acid and factor 3 represents dissolution of carbonates leading to increase in hardness. Thus, such approach is found effective in characterization of hydrochemical parameters in geomorphic units/surfaces for better utilization of groundwater resource.