RICE FIELD HYDROCHEMISTRY: IMPLICATIONS FOR THE ARSENIC CONTAMINATED AQUIFERS OF BANGLADESH

The shallow aquifer in Bangladesh that provides drinking water for millions and irrigation water for numerable rice fields is severely contaminated with naturally occurring arsenic. Near-surface soil processes likely play a crucial role in the fate and transport of arsenic through the subsurface. To quantify the potential impact of these processes on the shallow aquifer, we studied the movement and chemistry of water in an irrigated rice field. Rice fields cover approximately 65% of the land area in our study area and water-balance calculations show that irrigation return flow is an important component of the hydrologic system. Presented results incorporate both hydrologic data from a tracer test and a transect of vertically profiled water content and water tension sensors, as well as chemical data from collected soil cores and soil water samples. The data elucidate the rice field's aquifer recharge behavior; clarify the extent to which water preferentially moves through cracks, root channels and bunds; and track the chemical impact of seasonal flooding and aeration cycles on the field's soil and infiltrating water.