Reductive Dissolution of Fe-oxyhydroxides a Potential Mechanism for Arsenic Release into Groundwater in the Alluvial Plain of River Brahmaputra

Abstract. An integrated hydrogeochemical study was carried out to realize the occurrence of arsenic (As) in a saline aquifer. Saline groundwater was mostly concentrated in the uppermost aquifer, and non-saline water was in the lower aquifer in the study area. High As concentrations were found in both the uppermost and lower aquifers. No correlation among salinity, well depth and As concentration was observed. Various forms of Fe oxyhydroxides were identified in the magnetic fractions, which were concentrated by high gradient magnetic separation (HGMS) technique, revealing that the redox cycling of Fe occurred in the subsurface. High levels of Fe, HCO3-, DOC and NH4+ concentrations accompanying alkaline pH in the As-rich groundwater were consistent with the mechanism triggered by the microbially mediated reductive dissolution of Fe oxyhydroxides. A proposed threshold value of 50μg L-1 As concentration was used as an indicator for identification of active proceeding reductive dissolution of As-bearing Fe oxyhydroxides in the saline aquifer. Desorption behaviors of As were relevant to its valence in the sediments and the co-existence of anions. Experimental and numerical results showed that additions of Cl- and SO42-, which represent the main anions of saline water, had minor effect on leaching sedimentary As. Although bicarbonate addition resulted in less As desorption than that of phosphate on a molar basis, the contribution of bicarbonate to the total release of As was greater than phosphate due to the much higher concentration of bicarbonate in shallow groundwater and the associated microbial mediation. Collectively, the chemical effect of saline water on the As release to groundwater is mild in the coastal aquifer.

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Identifying sources and controlling factors of arsenic release in saline groundwater aquifers

Hydrology and Earth System Sciences Discussions ◽

10.5194/hessd-10-10565-2013 ◽

2013 ◽

Vol 10 (8) ◽

pp. 10565-10603 ◽

Cited By ~ 1

Author(s):

C.-W. Liu ◽

K.-L. Lu ◽

Y.-H. Kao ◽

C.-J. Wang ◽

S.-K. Maji ◽

...

Keyword(s):

Saline Water ◽

Threshold Value ◽

Chemical Effect ◽

Reductive Dissolution ◽

Minor Effect ◽

Saline Aquifer ◽

High Gradient Magnetic Separation ◽

Saline Groundwater ◽

Groundwater Aquifers ◽

Fe Oxyhydroxides

Abstract. An integrated hydrogeochemical study is carried out to realize the occurrence of arsenic (As) in a saline aquifer. Saline groundwater was mostly concentrated in the uppermost aquifer and non-saline water was in the lower aquifer in the study area. High As concentrations were found in both uppermost and lower aquifers. No correlation among salination, well depth and As concentration was observed. Both reducing and oxidizing forms of Fe oxyhydroxides were identified in the magnetic fractions, which were concentrated by high gradient magnetic separation (HGMS) technique, revealing that the redox cycling of Fe occurred in the subsurface. High levels of Fe, HCO3-, DOC and NH4+ concentrations accompanying alkaline pH in the As-rich groundwater were consistent with the mechanism triggered by the microbial-mediated reductive dissolution of Fe oxyhydroxides. A threshold value of 50 μg L−1. As concentration was used as an indicator for identification of active proceeding reductive dissolution of As-bearing Fe oxyhydroxides in the saline aquifer. Desorption behaviors of As were relevant to its valence in the sediments and the co-existence of anions. Experimental and numerical results showed that additions of Cl- and SO42-, which represented the main anions of saline water, had minor effect on leaching sedimentary As. Although bicarbonate addition resulted in less As desorption than that of phosphate on a molar basis, the contribution of bicarbonate to the total release of As was greater than phosphate due to the much higher concentration of bicarbonate in groundwater and the associated microbial mediation. Collectively, the chemical effect of saline water on the As-release to groundwater is mild in the coastal aquifer.

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Emotional Impact Feedback Changes How We Remember Negative Autobiographical Experiences

Experimental Psychology (formerly Zeitschrift für Experimentelle Psychologie) ◽

10.1027/1618-3169/a000042 ◽

2010 ◽

Vol 57 (5) ◽

pp. 354-359 ◽

Cited By ~ 10

Author(s):

Melanie K. T. Takarangi ◽

Deryn Strange

Keyword(s):

Well Being ◽

The Other ◽

Personal Perspective ◽

Emotional Impact ◽

Potential Mechanism ◽

Negative Experiences ◽

Negative Memory ◽

The Relationship ◽

Negative Memories ◽

Over Time

When people are told that their negative memories are worse than other people’s, do they later remember those events differently? We asked participants to recall a recent negative memory then, 24 h later, we gave some participants feedback about the emotional impact of their event – stating it was more or less negative compared to other people’s experiences. One week later, participants recalled the event again. We predicted that if feedback affected how participants remembered their negative experiences, their ratings of the memory’s characteristics should change over time. That is, when participants are told that their negative event is extremely negative, their memories should be more vivid, recollected strongly, and remembered from a personal perspective, compared to participants in the other conditions. Our results provide support for this hypothesis. We suggest that external feedback might be a potential mechanism in the relationship between negative memories and psychological well-being.

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