Groundwater recharge affects water budgets and groundwater quality on the deltas and floodplains of South and Southeast Asia. Rain and flooding rivers recharge groundwater during the monsoon; irrigated rice fields and surface water bodies recharge aquifers during the dry season. Groundwater throughout the region is severely contaminated by arsenic, and recent research suggests that quantifying and characterizing recharge is important to understand whether recharge flushes or mobilizes arsenic from aquifers. At a field site in Bangladesh, we found that burrows of terrestrial crabs short-circuit low-permeability surface sediments, providing the primary conduit for recharge. We combine field observations along with a model that couples isotope and water balances to quantify the effect of crab burrows on aquifer recharge. Given the wide distribution of burrowing crabs and the surficial geology, we suggest that crab burrows provide widespread conduits for groundwater recharge.

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BACKGROUND: Layered double hydroxide compounds (LDHs) have been applied for the removal of oxyanions including arsenate (As(V)). However, the aim of this present research is to develop a LDH to treat arsenite (As(III)). Both batch and column sorption studies were conducted to assess the effect of LDH dosage, contact time, solution pH and initial As(III) concentrations on the As(III) removal performance. The potential re-use of this sorbent was also investigated.

Application of the Tropical Rainfall Measuring Mission (TRMM) can be an efficient method for precipitation measurement in Bangladesh. The TRMM was a joint US−Japan space programme used to measure tropical rainfall with spatial and temporal distribution. This study analyses the reliability of TRMM data by comparing them with the rain gauge data of Bangladesh Meteorological Department at 35 different locations. The comparison is made for the data from 1998 to 2010. Extensive analyses were performed on the basis of different temporal scales (daily, monthly, seasonal and yearly). Both datasets were compared for average, peak and total values. The correlation co‐efficient and bias of TRMM rainfall data with respect to rain gauge values were also determined. However, the rainfall products are also compared at the two most extreme elevation stations to observe the influence of station topography (if any). Results show that TRMM rainfall data closely match with rain gauge data for average values on an annual basis, and the correlation co‐efficient is found to be greater than 0.90. However, significant deviation is found for daily peak rainfall values. Again, a seasonal comparison shows that the TRMM data outputs match with station data except during the dry season. The rainfall data at the highest and lowest elevations show that the TRMM data follow a similar trend to the station data but they underestimate the value to some extent, especially during the wet season. Finally, it is inferred that the TRMM data are reliable in estimating the average rainfall in Bangladesh for hydrological analyses of watersheds.

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