To identify the causes of salinization and arsenic contamination of surface water on an embanked island (i.e., polder) in the tidal delta plain of SW Bangladesh we collected and analyzed water samples in the dry (May) and wet (October) seasons in 2012-2013. Samples were collected from rice paddies (wet season), saltwater ponds used for brine shrimp aquaculture (dry season), freshwater ponds and tidal channels (both wet and dry season), and rainwater collectors. Continuous measurements of salinity from March 2012 to February 2013 show that tidal channel water increases from ~0.15 ppt in the wet season up to ~20 ppt in the dry season. On the polder, surface water exceeds the World Health Organization drinking water guideline of 10 μg As/L in 78% of shrimp ponds and 27% of rice paddies, raising concerns that produced shrimp and rice could have unsafe levels of As. Drinking water sources also often have unsafe As levels, with 83% of tubewell and 43% of freshwater pond samples having >10 μg As/L. Water compositions and field observations are consistent with shrimp pond water being sourced from tidal channels during the dry season, rather than the locally saline groundwater from tubewells. Irrigation water for rice paddies is also obtained from the tidal channels, but during the wet season when surface waters are fresh. Salts become concentrated in irrigation water through evaporation, with average salinity increasing from 0.43 ppt in the tidal channel source to 0.91 ppt in the rice paddies. Our observations suggest that the practice of seasonally alternating rice and shrimp farming in a field has a negligible effect on rice paddy water salinity. Also, shrimp ponds do not significantly affect the salinity of adjacent surface water bodies or subjacent groundwater because impermeable shallow surface deposits of silt and clay mostly isolate surface water bodies from each other and from the shallow groundwater aquifer. Bivariate plots of conservative element concentrations show that all surface water types lie on mixing lines between dry season tidal channel water and rainwater, i.e., all are related by varying degrees of salinization. High As concentrations in dry season tidal channel water and shrimp ponds likely result from groundwater exfiltration and upstream irrigation in the dry season. Arsenic is transferred from tidal channels to rice paddies through irrigation. Including groundwater samples from the same area (Ayers et al. in Geochem Trans 17:1-22, 2016), principal components analysis and correlation analysis reveal that salinization explains most variation in surface water compositions, whereas progressive reduction of buried surface water by dissolved organic carbon is responsible for the nonconservative behavior of S, Fe, and As and changes in Eh and alkalinity of groundwater.

中文翻译：

---

孟加拉国西南部地表水的盐碱化和砷污染。

为了确定孟加拉国西南部潮汐三角洲堤岸（即island田）上地表水盐化和砷污染的原因，我们收集并分析了2012年干季（5月）和湿季（10月）的水样， 2013。从稻田（湿季），用于盐水虾养殖的咸水池塘（旱季），淡水池塘和潮汐渠道（湿季和旱季）以及雨水收集器收集样品。从2012年3月到2013年2月对盐度的连续测量显示，潮汐通道的水从湿季的约0.15 ppt增加到旱季的约20 ppt。在the田中，78％的虾塘和27％的稻田中的地表水超过了世界卫生组织的饮用水准则10μgAs / L，引起关注的是，生产的虾和大米可能具有不安全的砷含量。饮用水源中的砷含量通常也不安全，其中83％的试管井和43％的淡水池塘样品的As / L> 10μg。水的成分和现场观察与在干燥季节从潮汐渠道获取的虾塘水一致，而不是来自管井的局部含盐地下水。稻田的灌溉水也可以从潮汐渠道获得，但是在潮湿的季节，地表水比较新鲜。盐分通过蒸发浓缩到灌溉水中，平均盐度从潮汐源中的0.43 ppt增加到稻田中的0.91 ppt。我们的观察结果表明，在田间进行稻米和虾的季节性交替耕种对稻田水盐度的影响可忽略不计。另外，虾塘也不会显着影响相邻地表水体或地下地下水的盐度，因为不可渗透的浅层淤泥和粘土表面沉积物大多数将地表水体彼此隔离，也与地表浅层含水层隔离。保守元素浓度的双变量图表明，所有地表水类型都位于旱季潮汐通道水和雨水之间的混合线上，即，所有这些都与盐碱化程度有关。干旱季节潮汐河道水和虾塘中的As含量较高可能是由于干旱季节的地下水渗入和上游灌溉造成的。砷通过灌溉从潮汐通道转移到稻田中。包括同一地区的地下水样品（Ayers等人，Geochem Trans 17：1-22，2016），主成分分析和相关分析表明，盐碱化解释了地表水成分的大部分变化，而溶解引起的地下地表水逐渐减少有机碳是造成S，Fe和As的非保守行为以及Eh和地下水碱度变化的原因。