| Popis: |
The worldwide natural occurrence of high levels of arsenic (As) in groundwater and its deleterious effects on human health have inspired a great amount of related research in public health and geosciences internationally. With >100 million people in South and Southeast Asia exposed to >10 µg/L As in shallow groundwater that they use for drinking, the installation of deeper, low-As wells has emerged as a major strategy for lowering the exposure. As the magnitude of deep pumping continues to increase, this work focuses on the geochemical and hydrologic questions surrounding the vulnerability and sustainability of low-As aquifers in Bangladesh, the country most affected by As crisis. In an effort to better understand the residence time of groundwater in low-As aquifers at depth, radiocarbon (14C) and 13C in dissolved inorganic carbon, tritium (3H), stable isotopes of hydrogen (2H) and oxygen (18O), and noble gas concentrations were measured across a ~25 km2 area of Araihazar, ~30 km east of Dhaka. Groundwater from >120 m depth is shown to be ~10,000 years old and its isotopic signatures indicate that recharge occurred at the time of changing climate from the late Pleistocene to early Holocene, with little recharge occurring since. In contrast, the intermediate depth low-As aquifers |
