Hydrochemical variations of a tropical mountain river system in a rain shadow region of the southern Western Ghats, Kerala, India. (December 2015)

• Record Type: Journal Article
• Authors: Thomas, Jobin; Joseph, Sabu; Thrivikramji, K.P.
• Is Part Of: Applied geochemistry. Volume 63(2015:Dec.)
• Page Start: 456
• Page End: 471
• Publication Date: 2015-12
• Subjects: Hydrochemistry -- Rain shadow rivers -- Weathering -- Downstream hydrochemical trend -- Southern Western Ghats; Environmental geochemistry -- Periodicals; Water chemistry -- Periodicals; Geochemistry -- Social aspects -- Periodicals; Geochemistry -- Periodicals; 551.9
• DOI: 10.1016/j.apgeochem.2015.03.018
• Languages: English
• ISSNs: 0883-2927

Abstract

Abstract: River water chemistry of Pambar River Basin (PRB), draining a rain shadow region of the southern Western Ghats, India, with granite gneiss and hornblende-biotite-gneiss lithology, was monitored for three sampling seasons, such as monsoon (MON), post-monsoon (POM) and pre-monsoon (PRM) to ascertain the spatio-temporal trends in hydrochemistry. In PRB, upstream and downstream areas have differing climate (i.e., tropical-wet–dry/humid upstream, while semi-arid downstream) and land use (plantations and farmland dominate the upstream, while pristine forest environment covers the downstream). The hydrochemical attributes, except pH and K +, exhibit distinct temporal variation mainly due to monsoon-driven climatic seasonality. Relative abundance of cations between upstream and downstream samples of PRB shows noticeable differences, in that the upstream samples follow the order of abundance: Ca 2+ > Mg 2+ > Na + > K +, while the downstream samples are in the order: Na + > Mg 2+ > Ca 2+ > K + . Ca 2+ + Mg 2+ /Na + + K +, Si/Na + + K +, Cl − /Na + and HCO3 − /Ca 2+ ratios suggest multiple sources/processes controlling hydrochemistry, e.g., atmospheric supply, silicate weathering, dissolution of carbonate minerals and soil evaporites as well as anthropogenic inputs (domestic and farm/plantation residues). Even though weathering of silicate and carbonate minerals is the major hydrochemical driver in both upstream and downstream portions of PRB, Gibbs diagram and scatter plot of Mg 2+ /Na + vs. Mg 2+ /Ca 2+ imply the importance of evaporation in the downstream hydrochemistry. Piper diagram and partial pressure of CO2 ( p CO2 ) values suggest that a groundwater dominated discharge exerts a significant control on the downstream hydrochemistry, irrespective of sampling season. Although spatial variability of rainfall in PRB shows a linear downstream (decreasing) trend, the best-fit model for the dissolved load suggests that the downstream hydrochemical variability in PRB (i.e., an increasing trend) follows a power function ( f ( x ) = ax k ). This study suggests that climate has a significant role in the spatio-temporal variability of hydrochemistry in PRB. Highlights: Hydrochemistry of a tropical-mountainous-rain shadow river basin was addressed. Hydrochemistry differs between upstream and downstream mainly due to climatic variability. Monsoon-driven climatic seasonality controls temporal variation of hydrochemistry. Downstream variations in rainfall and hydrochemistry show differing trends.