ADDING POLLEN TO THE RECORD: REFINING HOW SEDIMENTARY AQUIFERS FORM USING SEDIMENTOLOGY, PALYNOLOGY, AND OSL AGE DATING IN NEPAL’S TERAI

Like many of the other heterogeneously-afflicted arsenic regions of Asia, shallow aquifer sediments in the Nepalese Terai display extremely high variances of groundwater arsenic. Given that the degree of groundwater heterogeneity is often on the order of meters to 10’s of meters, understanding the small-scale aquifer differences and the evolutionary processes behind how these sedimentary units form is becoming increasingly necessary for managing and using local supplies of ground water—especially in developing countries like Nepal. Coupling previous sedimentological, geochronological and groundwater arsenic results from a 1-km transect in Parasi, Nepal with new palynological work, an effort is made to refine our understanding of how several processes (i.e., changes in climate and ecology) can affect modern groundwater arsenic distributions. Combining aquifer depositional dates with detrital zircon and titanite ages, stable O and C isotopes, and palynological separates, a more refined story of aquifer evolution emerges, with evidence suggesting that changes in source rock and climate can account for some of the arsenic heterogeneity we see today in Parasi’s shallow aquifer. While this work is still underway, the preliminary findings show that differences in climate (i.e., arid vs. humid periods) as well as sediment provenance (Siwalik vs. Crystalline Himalayan, etc.) can play a significant role in the distribution of Asia’s groundwater arsenic.