View article

Arsenic is contaminating the groundwater of Holocene aquifers throughout South and Southeast Asia. To examine the biogeochemical and hydrological processes influencing dissolved concentrations and transport of As within soils/sediments in the Mekong River delta, a ∼50km² field site was established near Phnom Penh, Cambodia, where aqueous As concentrations are dangerously high and where groundwater retrieval for irrigation is minimal. Dissolved As concentrations vary spatially, ranging up to 1300μg/L in aquifer groundwater and up to 600μg/L in surficial clay pore water. Groundwaters with high As concentrations are reducing with negligible dissolved O₂ and high concentrations of Fe(II), NH₄⁺, and dissolved organic C. Within near-surface environments, these conditions are most pronounced in sediments underlying permanent wetlands, often found within oxbow channels near the Mekong River …