Statistics and Data Analysis in Geology

The contamination of ground waters, abstracted for drinking and irrigation, by sediment-derived arsenic threatens the health of tens of millions of people worldwide, most notably in Bangladesh and West Bengal1,2,3. Despite the calamitous effects on human health arising from the extensive use of arsenic-enriched ground waters in these regions, the mechanisms of arsenic release from sediments remain poorly characterized and are topics of intense international debate4,5,6,7,8. We use a microscosm-based approach to investigate these mechanisms: techniques of microbiology and molecular ecology are used in combination with aqueous and solid phase speciation analysis of arsenic. Here we show that anaerobic metal-reducing bacteria can play a key role in the mobilization of arsenic in sediments collected from a contaminated aquifer in West Bengal. We also show that, for the sediments in this study, arsenic release took place after Fe(iii) reduction, rather than occurring simultaneously. Identification of the critical factors controlling the biogeochemical cycling of arsenic is one important contribution to fully informing the development of effective strategies to manage these and other similar arsenic-rich ground waters worldwide.

Role of metal-reducing bacteria in arsenic release from Bengal delta sediments

http://www.vliz.be/imisdocs/publications/242609.pdf

Seawater intrusion processes, investigation and management: Recent advances and future challenges

Over the past few decades, groundwater wells installed in rural areas throughout the major river basins draining the Himalayas have become the main source of drinking water for tens of millions of people Groundwater in this region is much less likely to contain microbial pathogens than surface water but often contains hazardous amounts of arsenic--a known carcinogen Arsenic enters groundwater naturally from rocks and sediment by coupled biogeochemical and hydrologic processes, some of which are presently affected by human activity Mitigation of the resulting health crisis in South and Southeast Asia requires an understanding of the transport of arsenic and key reactants such as organic carbon that could trigger release in zones with presently low groundwater arsenic levels

https://www.ldeo.columbia.edu/~avangeen/publications/documents/Fendorf_Sci_10.pdf

Spatial and Temporal Variations of Groundwater Arsenic in South and Southeast Asia

https://www.u-cursos.cl/usuario/7c1c0bd54f14c0722cefc0fa25ea186d/mi_blog/r/Lectura_clase_ingenieria_ambiental.pdf

Arsenic contamination, consequences and remediation techniques: a review

Safe and Sustainable Use of Arsenic-Contaminated Aquifers in the Gangetic Plain

The application of zero-water discharge system in treating diffuse village wastewater and its benefits in community afforestation

Retardation of arsenic transport by oxidized Holocene aquifer sediments of West Bengal, India

[1] Groundwater-dependent ecosystems (GDEs) in arid and semiarid environments play significant ecological roles, and, yet in many parts of the world, these ecosystems have been drained for agricultural use. In wetlands containing acid sulfate soils, the altered hydrology may trigger acidification and subsequent trace metal release. Quantifying shifts in hydrological regime and connectivity dynamics across wetlands is critical for understanding the resilience of these GDEs to anthropogenic impacts. Seasonal water balances for a wetland severely impacted by drainage and acidification were combined with laboratory geochemical data and field observations to develop a conceptual model describing hydrological connectivity across the wetland. The data indicated that, with the onset of the dry season, the superficial aquifer was lowered, exposing sulfides that oxidized to form sulfuric acid and dissolving metal salts. The following dry season enhanced capillary action causing upwelling of oxidized products to the surface where evaporative precipitation created acidity scalds. Subsequent winter rainfall and infiltration caused groundwater levels to rise, intersect with the ground surface, and form disconnected acidic pools. As the wet season progressed, connectivity was established between the pools, resulting in metal-rich acid discharge from the wetland. The degree of acid fluxes and metal release was controlled by the physicochemical characteristics of the soils, its exposure to the seasonally variable wetland hydrology, antecedent hydrological conditions, hydrological connectivity (both vertical and horizontal), and the resulting biogeochemical conditions.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2012WR012760

Hydrological and chemical connectivity dynamics in a groundwater‐dependent ecosystem impacted by acid sulfate soils

Groundwater contaminated with arsenic (As), when extensively used for irrigation, causes potentially long-term detrimental effects to surface soils. Such contamination can also directly affect human health when irrigated crops, such as rice, vegetable and fruits, are used for human consumption. Therefore, an understanding of the leaching behavior of As in surface soils is of high importance, because such behavior may increase the bioavailability of As in the soil horizon. In this study, we have investigated the role of phosphate ions in leaching and bioavailability of As in the soil horizon, where drinking groundwater contains elevated levels of As (≥50 μg/L). Soil and groundwater samples were characterized in the laboratory and measured for physical and chemical constituents. The soils are generally neutral to slightly alkaline in character (pH range 7.5–8.1) with low to moderate levels of free Fe2O3, Al2O3, CaCO3, organic carbon, and clay content. The measured electrical conductivity (mean 599 μS/cm) of the soils demonstrates their non-saline nature. The Eh values (range −37 to −151 mV) of the groundwater indicate anoxic condition with low to moderate levels of bicarbonate (range 100–630 mg/L) and phosphate (range 0.002–4.0 mg/L). The arsenic content (range 50–690 μg/L; mean 321 μg/L) in groundwater has exceeded both WHO recommended guideline values (10 μg/L) and the National safe drinking water limit (50 μg/L). Regression analyses demonstrate that the bioavailability of As in the soil horizon is mainly controlled by the composition of free Fe2O3 and CaCO3 content of the soils. However, application of P could increase bioavailability of As in the soil horizon and become available to plants for uptake.

Bibhash Nath

Papers

Safe and Sustainable Use of Arsenic-Contaminated Aquifers in the Gangetic Plain

The application of zero-water discharge system in treating diffuse village wastewater and its benefits in community afforestation

Retardation of arsenic transport by oxidized Holocene aquifer sediments of West Bengal, India

Hydrological and chemical connectivity dynamics in a groundwater‐dependent ecosystem impacted by acid sulfate soils

Bioavailability of arsenic in the soil horizon: a laboratory column study