Journal Article

Impact of Dissolution of Saline‐Alkaline Soils on the Hydrochemistry and Erosion Rates of the Ganga River System

Singh, Sunil Kumar, Chatterjee, Jayati

2022

Overview

We characterize here the saline‐alkaline soils composed of Na2CO3 and NaHCO3 in the Ganga floodplain and the peninsular basin using various chemical proxies and the isotopic composition of Sr. Abundance of saline‐alkaline soils in the Ganga floodplain and their higher solubility make them an important source of non‐chloride Na and other dissolved ions including Sr to the river waters. Inverse model based source apportionment of dissolved ions indicates ∼26%–71% of Na at the Ganga outflow is influenced by the saline‐alkaline soils; however, in some of the tributaries of the Ganga in the floodplain, for example, in the Gomti, this contribution exceeds 85%. The estimated silicate erosion rate by correcting for the saline‐alkaline soil contribution in the Ganga floodplain (∼5 tons km−2 yr−1) is less than one third of that of the Himalayan headwaters (16 tons km−2 yr−1) emphasizing the important role of physical erosion in controlling the chemical erosion in the mountain catchments compared to higher temperature and residence time in the floodplain. The silicate sourced dissolved fluxes from the floodplains are comparable to those from the Himalaya because of the vast drainage area of the floodplains and peninsular catchment. The findings of this study have direct relevance to studies on the determination of silicate weathering rates of not only the Ganga system, but also of other basins infested by saline‐alkaline soils such as the Columbia, the Colorado, the upper Rio Grande, the Missouri‐Mississippi river system, the Parana river, the Niger, the Nile, and the Orange. Plain Language Summary The saline‐alkaline soils containing Na2CO3 and NaHCO3 are present abundantly in the plain and peninsular drainages of the Ganga. Their higher solubility contribute significantly to the dissolved ions budget of the river waters which was earlier considered as the part of silicate weathering resulting in overestimation of silicate weathering and hence the CO2 consumption in the Ganga System. Chemical and isotopic characterisation of these salts in the Ganga system allowed us to estimate actual silicate weathering of the system and associated CO2 consumption impacting the carbon cycle. This study estimates three times higher silicate erosion rate in the mountainous catchment of the Ganga, 16 tons km−2 yr−1 compared to its plain catchment, ∼5 tons km−2 yr−1. This study puts the hotly debated topic of importance of mountain versus plain erosion of the Ganga on rest and emphasizes the role of higher physical erosion in contributing to the higher chemical erosion in the hilly terrain compared to higher temperature and residence times in the plain catchment. Key Points The Ganga Plain is infested by saline‐alkaline soils, Na2CO3 and NaHCO3 minerals If not corrected, they overestimate the silicate erosion rates (SERs) in the Ganga Basin SER in the Ganga Plain is one third of that in the Himalaya

• Publisher: John Wiley & Sons, Inc,Wiley
• Subject: Alkaline soils / Carbon cycle / Carbon dioxide / Catchments / CO2 consumption rate / dissolved chemical composition / Drainage area / Erosion control / Erosion rates / Floodplains / Ganga river system / Headwaters / High temperature / Hydrochemistry / Ions / Isotope composition / Mountains / Outflow / Residence time / River water / Rivers / saline‐alkaline soils / Salts / silicate erosion rate / Silicates / Soil / Solubility / Sr isotopic composition / Temperature / Tributaries / Watersheds / Weathering