Geochemistry of dissolved loads and chemical weathering in the Upper Jhelum River Basin (UJRB) of western Himalayas: Isotopic and chemical constraints

Abstract

Hydrochemistry and carbon isotopic (δ¹³C_DIC) compositions of dissolved inorganic carbon (DIC) were investigated in the Upper Jhelum River Basin (UJRB) in the western Himalayan region, to better understand the mechanisms and controlling factors of chemical weathering and carbon dynamics. A forward model was used to estimate the contributions of various sources of dissolved loads. Carbonate weathering dominated the riverine solute generation with a contribution of 69.5 ± 5.9%, and ions derived from carbonate weathering show strong chemostatic behavior in response to changes in discharge. Ions derived from silicate weathering demonstrate a significant dilution impact and silicate weathering contributed 8.9 ± 3.1% of the riverine solutes. We estimated the annual discharge weighted weathering rates of carbonate (52.8 t/km²/y) and silicate (12.0 t/km²/y), and then estimated CO₂ consumption rates by carbonate weathering (7.0 10⁵ mol/km²/y), silicate weathering (2.2 10⁵ mol/km²/y), and net CO₂ consumption flux (6.5 mol/km²/y). The cation flux of 126.5 × 10⁴ t/km²/y accounts for 0.1% of the total cation budget of ocean water. The δ¹³C_DIC values are primarily controlled by carbonate weathering by carbonic acid and show a lower sensitivity than DIC contents in response to various hydrological conditions. However, biological carbon influx during higher temperatures in summer and autumn and evasion to the atmosphere during spring are secondary processes controlling DIC and δ¹³C_DIC in the region. This study provides insights into chemical weathering processes and carbon dynamics, highlights the impacts of hydrological variability that controls the generation and transport of solutes and aids in understanding of the global carbon cycle.