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  • 1
    Language: English
    In: Environmental Earth Sciences, 2013, Vol.69(2), pp.429-441
    Description: The impact of diffuse pollution, agricultural land use and climate change on the long-term response of subsurface–surface water quality is not well understood, but is a prerequisite for evaluation of water management options. The goal of this study is to model geochemical evolution of water chemistry from the infiltration through soil into the unsaturated zone, transport through bedrocks and granular aquifers to a river in order to identify zones of steep concentration gradients and high dynamics under transient flow conditions. A numerical model was constructed comprising a 2-D 1,500 m × 150 m vertical cross-section of typical sedimentary rock formations, a glacio-fluvial quaternary gravel aquifer in the valley and soil layers. The model coupled saturated/un-saturated flow and reactive transport under steady state and transient conditions. Geochemical interactions, include intra-aqueous kinetic reactions of oxygen with dissolved organic matter, as well as kinetics of carbonate dissolution/precipitation. This model section was chosen to provide insight in to the principal processes and time scales affecting water chemistry along different flow paths. The numerical simulator MIN3P was used, a finite volume program for variably saturated subsurface flow and multi-component reactive transport. The results show that subsurface water residence times range from approximately 2 to 2,000 years. Different zones are to be expected with respect to the development of mineral equilibria; namely, purely atmospherically influenced, as well as open and closed system carbonate dissolution. Short-term responses to daily averaged changes in precipitation, however, are only visible to some extent in the shallower and near-river parts of flow system and solute loads. This can most likely be explained by directional changes in flow paths, indicating that equilibrium geochemical condition predominate at the hillslope scale, i.e. water quality depends on transport pathways rather than on kinetic effects. The extent of reducing conditions is controlled by the presence of organic-rich layers (i.e. peat deposits), the dissolution kinetics of aquifer organic matter and the subsequent mixing with oxygenated water by hydrodynamic dispersion.
    Keywords: Rock water interaction ; Water chemistry evolution ; Hydrogeochemical modelling ; Water residence time ; Catchment hydrology
    ISSN: 1866-6280
    E-ISSN: 1866-6299
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  • 2
    Language: English
    In: Environmental Geochemistry and Health, April, 2009, Vol.31(2), p.69(16)
    Description: Byline: Anwar Zahid (1,2), M. Q. Hassan (1), G. N. Breit (3), K.-D. Balke (4), Matthias Flegr (4) Keywords: Adsorption; Arsenic distribution; Iron oxides; Soil and sediments; Trace metals Abstract: Accumulations of iron, manganese, and arsenic occur in the Chandina alluvium of southeastern Bangladesh within 2.5 m of the ground surface. These distinctive orange-brown horizons are subhorizontal and consistently occur within 1 m of the contact of the aerated (yellow-brown) and water-saturated (gray) sediment. Ferric oxyhydroxide precipitates that define the horizons form by oxidation of reduced iron in pore waters near the top of the saturated zone when exposed to air in the unsaturated sediment. Hydrous Fe-oxide has a high specific surface area and thus a high adsorption capacity that absorbs the bulk of arsenic also present in the reduced pore water, resulting in accumulations containing as much as 280 ppm arsenic. The steep redox gradient that characterizes the transition of saturated and unsaturated sediment also favors accumulation of manganese oxides in the oxidized sediment. Anomalous concentrations of phosphate and molybdenum also detected in the ferric oxyhydroxide-enriched sediment are attributed to sorption processes. Author Affiliation: (1) Department of Geology, University of Dhaka, Dhaka, Bangladesh (2) Ground Water Hydrology, Bangladesh Water Development Board, Dhaka, Bangladesh (3) United States Geological Survey, Denver Federal Center, Denver, CO, USA (4) Institute for Geology and Paleontology, University of Tuebingen, Tuebingen, Germany Article History: Registration Date: 01/12/2008 Received Date: 11/08/2007 Accepted Date: 17/10/2008 Online Date: 19/12/2008
    Keywords: Iron (Metal) ; Arsenic ; Adsorption ; Groundwater ; Manganese Compounds ; Iron Compounds ; Sediments (Geology) ; Hydrology ; Molybdenum ; Paleontology ; Phosphates ; Iron Oxides
    ISSN: 0269-4042
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  • 3
    Language: English
    In: Environmental Geology, 2008, Vol.54(6), pp.1247-1260
    Description: Dissolved major ions and important heavy metals including total arsenic and iron were measured in groundwater from shallow (25–33 m) and deep (191–318 m) tube-wells in southeastern Bangladesh. These analyses are intended to help describe geochemical processes active in the aquifers and the source and release mechanism of arsenic in sediments for the Meghna Floodplain aquifer. The elevated Cl − and higher proportions of Na + relative to Ca 2+ , Mg 2+ , and K + in groundwater suggest the influence by a source of Na + and Cl − . Use of chemical fertilizers may cause higher concentrations of NH 4 + and PO 4 3− in shallow well samples. In general, most ions are positively correlated with Cl − , with Na + showing an especially strong correlation with Cl − , indicating that these ions are derived from the same source of saline waters. The relationship between Cl − /HCO 3 − ratios and Cl − also shows mixing of fresh groundwater and seawater. Concentrations of dissolved HCO 3 − reflect the degree of water–rock interaction in groundwater systems and integrated microbial degradation of organic matter. Mn and Fe-oxyhydroxides are prominent in the clayey subsurface sediment and well known to be strong adsorbents of heavy metals including arsenic. All five shallow well samples had high arsenic concentration that exceeded WHO recommended limit for drinking water. Very low concentrations of SO 4 2− and NO 3 − and high concentrations of dissolved Fe and PO 4 3− and NH 4 + ions support the reducing condition of subsurface aquifer. Arsenic concentrations demonstrate negative co-relation with the concentrations of SO 4 2− and NO 3 − but correlate weakly with Mo, Fe concentrations and positively with those of P, PO 4 3− and NH 4 + ions.
    Keywords: Salinization ; Iron-oxyhydroxides ; Adsorption ; Paddy soil ; Arsenic mobility
    ISSN: 0943-0105
    E-ISSN: 1432-0495
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  • 4
    Language: English
    In: Environmental Geology, 2006, Vol.50(4), pp.495-504
    Description: Hazaribagh is a densely populated area of Dhaka city where about 185 leather processing industries have been operating and discharging solid and liquid wastes directly to the low-lying areas, river and natural canals without proper treatment. The area is covered by alluvial deposits of Holocene age and is underlain by Pleistocene Madhupur clay. The Dupi Tila Formation of Mio-Pliocene age underlain by this yellowish gray to brick red clay bed serves as the main water-bearing aquifer of Dhaka city. To assess the environmental degradation as well as the groundwater environment, major anions, cations and heavy metals of water samples, heavy metals and organic carbon content of sediment samples were analyzed in this study. Analyses of tannery effluent detect high concentration of Na + , Mg 2+ , Cl − and SO 4 2− followed by Ca 2+ , NH 4 + and K + with remarkable contents of some trace elements, mainly Cr, Fe, Mn, S, Ni and Pb. Higher accumulations of Cr, Al and Fe are observed in topsoil samples with significant amounts of Mn, Zn, Ni and Cu. Concentrations of ions and all the investigated trace elements of sampled groundwater were within the maximum allowable limit for drinking water of the Department of Environment, Bangladesh (DoE), and World Health Organization (WHO). However, excessive concentrations of Cr, Pb, etc., have already been reported in the shallow groundwater (10–20 m) of the area. Due to excessive withdrawal the vulnerability of groundwater contamination in deeper parts cannot be avoided for the future.
    Keywords: Tannery ; Solid waste ; Effluent ; Groundwater ; Chromium ; Bangladesh
    ISSN: 0943-0105
    E-ISSN: 1432-0495
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  • 5
    Language: English
    In: Environmental Geochemistry and Health, 2009, Vol.31(Supplement 1), pp.69-84
    Description: Accumulations of iron, manganese, and arsenic occur in the Chandina alluvium of southeastern Bangladesh within 2.5 m of the ground surface. These distinctive orange-brown horizons are subhorizontal and consistently occur within 1 m of the contact of the aerated (yellow-brown) and water-saturated (gray) sediment. Ferric oxyhydroxide precipitates that define the horizons form by oxidation of reduced iron in pore waters near the top of the saturated zone when exposed to air in the unsaturated sediment. Hydrous Fe-oxide has a high specific surface area and thus a high adsorption capacity that absorbs the bulk of arsenic also present in the reduced pore water, resulting in accumulations containing as much as 280 ppm arsenic. The steep redox gradient that characterizes the transition of saturated and unsaturated sediment also favors accumulation of manganese oxides in the oxidized sediment. Anomalous concentrations of phosphate and molybdenum also detected in the ferric oxyhydroxide-enriched sediment are attributed to sorption processes.
    Keywords: Adsorption ; Arsenic distribution ; Iron oxides ; Soil and sediments ; Trace metals
    ISSN: 0269-4042
    E-ISSN: 1573-2983
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  • 6
    Language: English
    In: Environmental geochemistry and health, 2009, Vol.31(1), pp.69-84
    Description: Accumulations of iron, manganese, and arsenic occur in the Chandina alluvium of southeastern Bangladesh within 2.5 m of the ground surface. These distinctive orange-brown horizons are subhorizontal and consistently occur within 1 m of the contact of the aerated (yellow-brown) and water-saturated (gray) sediment. Ferric oxyhydroxide precipitates that define the horizons form by oxidation of reduced iron in pore waters near the top of the saturated zone when exposed to air in the unsaturated sediment. Hydrous Fe-oxide has a high specific surface area and thus a high adsorption capacity that absorbs the bulk of arsenic also present in the reduced pore water, resulting in accumulations containing as much as 280 ppm arsenic. The steep redox gradient that characterizes the transition of saturated and unsaturated sediment also favors accumulation of manganese oxides in the oxidized sediment. Anomalous concentrations of phosphate and molybdenum also detected in the ferric oxyhydroxide-enriched sediment are attributed to sorption processes. ; Includes references ; p. 69-84.
    Keywords: Carbon ; Carbon ; Sediment ; Sediment ; Data Management ; Data Management ; Arsenic ; Arsenic ; Trace Elements ; Trace Elements ; Iron ; Iron ; Water Pollution Control ; Water Pollution Control ; General ; General;
    ISSN: 0269-4042
    Source: AGRIS (Food and Agriculture Organization of the United Nations)
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