Sediment geochemistry of the Krishna river system: Implications to Weathering pattern and elemental mobility

Abstract

Weathering of continental rocks is a key component in the global biogeochemical and climatic cycles. This land surface processes are found to be disproportionally higher (compared to their areal extent) in the tropical river basins, mainly due to their conducive climate (runoff and temperature). In particular, the rivers from the Peninsular India receive high rainfall mainly during south-west monsoon periods and also, predominantly flow through terrains dominated by silicate rocks. In this thesis work, the major oxide concentrations of the bed sediments from the Krishna mainstream and its major tributaries to infer chemical mobility of elements and sediment provenances for the basin. These samples, with good spatial-resolution covering samples from both Deccan traps and Archean Granitic terrains, have already been collected during high flow stages (August, 2015) of the river system and currently, archived at IISER, Pune. These data for the sediments from the Deccan trap regions fall between end-member compositions of Basalts and smectite. The concentrations of mobile elements show that the chemical weathering play a dominant role in influencing the sediment chemistry of these samples. In contrast, the sediment from the Archean terrain locations fall closer to the granitic composition and possibly retain the source signature. At the outflow, the Fe, Mg and P concentrations fall closer to the granitic endmember compositions than the basaltic compositions. This indicates that the sediment production in the basin is mainly restricted in the granitic terrains and in the lower reaches. The upper reaches i.e. north-western part of the basin(with high basin slope) composed of basaltic rocks (with faster dissolution kinetics) seem to play minimal role in the physical erosion in the basin. Outcomes from this study indicates that the lithology play a key role in the basin in regulating the sediment budget of the Krishna river basin.