Chemical Weathering in Jhelum River and its Tributaries, Kashmir Basin, Western Himalaya

The study describes the chemical analysis of water and sediment to understand the hydrogeochemical processes, chemical weathering rates and its intensities in the upper river Jhelum and its major tributaries in Kashmir Basin, Western Himalaya. A total of 50 water samples and 15 riverbed sediment samples were analyzed. It was found that Ca and Mg contribute 82% of the major cations and HCO3− contributes 92% of the anion budget with only 4% and 3% contributions from SO4 and Cl, respectively. The Chemical Weathering Rates (CWR) varied spatially among tributaries with Sukhnag showing the lowest and Sindh, the highest CWR during High Flow Period (HFP). However, during the Low Flow Period (LFP), Sukhnag recorded the lowest and Romush recorded the highest CWR thereby reflecting the influence of varied precipitation, discharge, basin lithology, topography and probably active tectonics. The CWR in the main Jhelum river ranged from 31.4 × 102 t/km2/month (LFP) to 107.0 × 102 t/km2/month (HFP) with an annual CWR of 11.1 × 102 t/km2/year. The Left Bank Tributaries (LBT) draining the tectonically active Pir-Panjal range showed higher CWR than the Right Bank Tributaries (RBT) draining the Great Himalayan range (except Sindh). However, in comparison to other Himalayan rivers and World averages (0.36 × 102 t/km2/year), the observed CWR in the main Jhelum river and its tributaries were also found to be higher. Furthermore, the main Jhelum river showed an average annual Silicate Weathering Rate (SWR) of 0.10 t/km2/year and Carbonate Weathering Rate (CrWR) of 0.35 t/km2/year. The Pohru tributary showed the lowest average SWR and CrWR of 0.04 t/km2/year, whereas the Sukhnag showed the highest SWR and CrWR of 0.41 t/km2/year and 0.48 t/km2/year respectively. The Chemical Index of Alteration (CIA) and Chemical Index of Weathering (CIW) support these findings and revealed a moderate weathering in the basin quite usual of cold regions.