Chemical-weathering rates of aquifers and the mixing of soils: the role of optical dating in quantifying near-surface processes on earth and their timescales

Abstract

In arsenic-prone regions, an important question is the provenance of arsenic in shallow groundwaters (< 30 m). Some studies suggest that arsenic is sourced from the overlying local soils of an aquifer, whereas others surmise it to be due to weathering of the underlying aquifer matrix. Most work on chemical weathering suggests that 'younger/fresher' material 'weathers' faster than 'older/indurated' material. New optical dates suggest that the depositional-age of the sediments comprising an aquifer is an important parameter in arsenic groundwater chemistry. Here, we re-introduce the concept of the critical zone, explain how Asia's shallow groundwater arsenic is a process occurring within the critical zone and show a new application of optical dating methods to help determine critical zone chemical weathering rates, such as the release of arsenic into Asia's groundwaters.