Observations of offshore freshened groundwater and saline groundwater discharge along continental shelves have important implications for water resources, ecosystem function, and the composition of the ocean, but they cannot be explained by basic theory. We show that these independent observations are linked and result from processes that drive variable‐density groundwater flow through the spatial heterogeneity that is ubiquitous in geologic formations. We use lithologic data to develop geostatistical models that mimic the architecture of coastal aquifers. Simulation of groundwater flow and salt transport through these random realizations shows that heterogeneity produces spatially complex subsurface salinity distributions that extend tens of kilometers offshore, even at steady state. The associated density gradients drive high saline groundwater circulation rates that cannot be predicted by equivalent homogeneous models. Results suggest that these phenomena may be common along continental shelves, potentially altering estimates of ocean chemical budgets and impacting coastal water management for future generations.

Many of the world's megacities depend on groundwater from geologically complex aquifers that are over-exploited and threatened by contamination. Here, using the example of Dhaka, Bangladesh, we illustrate how interactions between aquifer heterogeneity and groundwater exploitation jeopardize groundwater resources regionally. Groundwater pumping in Dhaka has caused large-scale drawdown that extends into outlying areas where arsenic-contaminated shallow groundwater is pervasive and has potential to migrate downward. We evaluate the vulnerability of deep, low-arsenic groundwater with groundwater models that incorporate geostatistical simulations of aquifer heterogeneity. Simulations show that preferential flow through stratigraphy typical of fluvio-deltaic aquifers could contaminate deep (>150 m) groundwater within a decade, nearly a century faster than predicted through homogeneous models calibrated to the same data. The most critical fast flowpaths cannot be predicted by simplified models or identified by standard measurements. Such complex vulnerability beyond city limits could become a limiting factor for megacity groundwater supplies in aquifers worldwide.

Medical students confront significant academic, psychosocial and existential stressors for coping with new college and schedule,. So assessment of the symptoms of depression, anxiety and stress among medical students are essential to take necessary steps to treat or prevent any psychiatric morbidity. The objective of the study was to assess depression, anxiety and stress among the first year MBBS students. This was a cross sectional and descriptive study conducted in Khulna Medical College, Bangladesh from December 2009 to July 2010. For this purpose, 105 students fulfilling inclusion and exclusion criteria were taken as sample. They filled up personal data and the short-form Bangla version of DASS (DASS-21 BV) scale. The results showed that, the mean age of students was 18.8 years with male predominance (54.3%). Symptoms of depression, anxiety and stress were found among 54.3%, 64.8% and 59.0% of students respectively. Eighty five (81%) students either had depression, anxiety or stress alone or in combination. Combination of depression, anxiety and stress was highest (36.2%). No significant association was found between gender difference and depression, anxiety or stress. Age was positively correlated with depression (p=0.004) and stress (p=0.001). Percentage of 1st year MBBS students suffering from depression, anxiety and stress were very high. Adequate psychiatric services should be provided to manage these symptoms among medical students.Bang J Psychiatry June 2015; 29(1): 23-29

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Sandy aquifers deposited >12,000 years ago, some as shallow as 30 m, have provided a reliable supply of low-arsenic (As) drinking water in rural Bangladesh. This study concerns the potential risk of contaminating these aquifers in areas surrounding the city of Dhaka where hydraulic heads in aquifers >150 m deep have dropped by 70 m in a few decades due to municipal pumping. Water levels measured continuously from 2012 to 2014 in 12 deep (>150m), 3 intermediate (90–150 m) and 6 shallow (<90 m) community wells, 1 shallow private well, and 1 river piezometer show that the resulting drawdown cone extends 15–35 km east of Dhaka. Water levels in 4 low-As community wells within the 62–147 m depth range closest to Dhaka were inaccessible by suction for up to a third of the year. Lateral hydraulic gradients in the deep aquifer system ranged from 1.7×10−4 to 3.7×10−4 indicating flow towards Dhaka throughout 2012–2014. Vertical recharge on the edge of the drawdown cone was estimated at 0.21±0.06 m/yr. The data suggest that continued municipal pumping in Dhaka could eventually contaminate some relatively shallow community wells.