Characterizing temporal and spatial trends in soil geochemistry on Polder 32, southwest Bangladesh

Abstract

Soil samples were collected during three field campaigns to determine seasonal and spatial trends of soil salinity, soil acidity and arsenic concentrations on Polder 32 in coastal Bangladesh. Many farmers on Polder 32 use a crop rotation of rice cultivation in the wet season and shrimp farming in the dry season, and studies have shown that this rotation can increase soil salinity and acidity. Soil samples were collected from rice paddies and shrimp ponds on the polder, from adjacent tidal channels, and from the Sunderbans mangrove forest to the SE of the polder, and analyzed for both geochemical and physical parameters and then subjected to statistical tests and mapped using geographic information system software to find correlations. Results support the belief that soil salinity, acidity and arsenic concentration exhibit spatial variation, and soil salinity and acidity show seasonal variation. Rice grown in paddies should be unaffected by salt concentrations in the wet season, while arsenic concentrations in soil may be high enough to cause unsafe As levels in produced rice. Future studies should measure the As concentration in rice to determine the risk of bioavailable arsenic transmitted from soil in the area. No evidence of soil acidification was found, most likely due to the presence of soil carbonate.