Open AccessTemporal Variations in Water Chemistry of the (Lower) Brahmaputra River: Implications to Seasonality in Mineral Weathering
Author(s) -
Samanta Anupam,
Tripathy Gyana Ranjan,
Das Ritima
Publication year - 2019
Publication title -
geochemistry, geophysics, geosystems
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.928
H-Index - 136
ISSN - 1525-2027
DOI - 10.1029/2018gc008047
Subject(s) - weathering , seasonality , monsoon , surface runoff , drainage basin , geology , silicate , hydrology (agriculture) , massif , period (music) , mineralogy , geochemistry , climatology , chemistry , ecology , geography , physics , cartography , geotechnical engineering , organic chemistry , acoustics , biology
Dissolved major ions and Sr concentrations of the Brahmaputra River at Guwahati, India, have been investigated on weekly basis for one year to understand the seasonality in weathering pattern and relative contributions from possible solute sources. Comparison of major ion data sets from present and earlier studies for this location shows no appreciable change during last ~50 years. Elemental concentrations and Ca/Na* (Na* = Na − Cl) ratio of the Brahmaputra covary (inversely) with the water discharge; the degree of seasonality, however, is less pronounced compared to other Himalayan (e.g., Ganga and Salween) rivers. The monthly averaged Ca/Si ratios of the Brahmaputra (3.7 ± 0.2), which is lower by ~2 times than those reported earlier for the Ganga outflow (6 ± 1), show minimal (~6%) seasonal changes. Seasonal variability in Na*/K with higher ratios during non‐monsoon period has been attributed to proportionally higher Na supply from hot springs and/or alkaline salts. The silicate‐derived cations (Cat s ) and Sr (Sr s ) have been estimated using an inversion method. Although these estimated values broadly show seasonal changes, the average Cat s and Sr s values for the monsoon (26 ± 4% [Cat s ]; 26 ± 6% [Sr s ]) and non‐monsoon (27 ± 3% (Cat s ); 24 ± 4% (Sr s )) seasons are statistically same. These estimates indicate a weak runoff‐weathering linkage for the Brahmaputra river. Outcomes from this study suggest that the chemical weathering intensity of this basin is more dominated by regional rapid weathering around the eastern syntaxis than the climatic (runoff) parameters.