Impact of River fluvial processes on arsenic enrichment in Mid Gangetic Plains: The coining of arsenic confirming pollution markers

The present study traces the geochemical occurrence of arsenic and heavy metals along the active oxbow formations of river Ganga in MGP. A total of 31 groundwater samples were collected, specifically in close proximity to the river profile section, to understand the high spatial enrichment pattern of arsenic. The bivariate plots reveal strong influence of silicate weathering and anthropogenic leaching of fertilizers occurring concurrently with pyrite oxidation, leading to high arsenic vulnerability. The bicarbonate enrichment plays a major role in the replacement of adsorbed arsenic while most of the carbonate minerals remain in a state of oversaturation, causing their ultimate precipitation. The steep changes in river directional profile as evident through the high bulk density of the soil (1587 kg/m³) near the oxbow formations of the river has caused high sediment deposition which is coherent with the spatial distribution of soil organic carbon stock (8–33 tons/hectare). Further, high concentration of arsenic (~100 ppb) traces the high availability of the clay content (18–40 %) and moderate iron concentration of the soil confirming the role of river led recharge in promoting oxidizing conditions. Low cation exchange capacity (9–52 mmol. c.kg⁻¹), indicative of illite as the dominant clay mineral, further supports our concern for groundwater vulnerability in terms of enhanced cation retention in the soil. Our study is a pioneering work in understanding arsenic spatial vulnerability under fluvial forcing through developing indicators which trace the arsenic mobilizing chemistry in a more coherent and direct ways.