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

Abstract

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.