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- Coomar, Poulomee, et al.
(författare)
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Contrasting controls on hydrogeochemistry of arsenic-enriched groundwater in the homologous tectonic settings of Andean and Himalayan basin aquifers, Latin America and South Asia
- 2019
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Ingår i: Science of the Total Environment. - : Elsevier BV. - 0048-9697 .- 1879-1026. ; 689, s. 1370-1387
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Tidskriftsartikel (refereegranskat)abstract
- High groundwater arsenic (As) across the globe has been one of the most well researched environmental concerns during the last two decades. Consequently, a large scientific knowledge-base has been developed on As distributions from local to global scales. However, differences in bulk sediment As concentrations cannot account for the As concentration variability in groundwater. Instead, in general, only aquifers in sedimentary basins adjacent to mountain chains (orogenic foreland basins) along continental convergent tectonic margins are found to be As enriched. We illustrate this association by integrating observations from long-term studies of two of the largest orogenic systems (i.e., As sources) and the aquifers in their associated foreland basins (As sinks), which are located in opposite hemispheres and experience distinct differences in climate and land-use patterns. The Andean orogenic system of South America (AB), an active continental margin, is in principle a modern analogue of the Himalayan orogenic system associated with the Indus-Ganges-Brahmaputra river systems in South Asia (HB). In general, the differences in hydrogeochemistry between AB and HB groundwaters are conspicuous. Major-solute composition of the arid, oxic AB groundwater exhibits a mixed-ion hydrochemical facies dominated by Na-Ca-Cl-SO4-HCO3. Molar calculations and thermodynamic modeling show that although groundwater of AB is influenced by cation exchange, its hydrochemical evolution is predominated by feldspar dissolution and relationships with secondary clays. In contrast, humid, strongly reducing groundwater of HB is dominated by Ca-HCO3 facies, suggestive of calcite dissolution, along with some weathering of silicates (monosiallitization). This work demonstrates that although hydrogeochemical evolutionary trends may vary with local climate and lithology, the fundamental similarities in global tectonic settings can still lead to the elevated concentrations of groundwater As.
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- Skelton, Alasdair, et al.
(författare)
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Coupling Between Seismic Activity and Hydrogeochemistry at the Shillong Plateau, Northeastern India
- 2008
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Ingår i: Pure and Applied Geophysics. - : Springer Science and Business Media LLC. - 0033-4553 .- 1420-9136.
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Tidskriftsartikel (populärvet., debatt m.m.)abstract
- Transient hydrogeochemical anomalies were detected in a granite-hosted aquifer, which islocated at a depth of 110 m, north of the Shillong Plateau, Assam, India, where groundwater chemistry is mainlybuffered by feldspar alteration to kaolinite. Their onsets preceded moderate earthquakes on December 9, 2004(MW = 5.3) and February 15, 2005 (MW = 5.0), respectively, 206 and 213 km from the aquifer. Theratios [Na+K]/Si, Na/K and [Na+K]/Ca, conductivity, alkalinity and chloride concentration began increasing3–5 weeks before the MW = 5.3 earthquake. By comparison with field, experimental and theoretical studies, weinterpret a transient switchover between source aquifers, which induced an influx of groundwater from a secondaquifer, where groundwater chemistry was dominantly buffered by the alteration of feldspar to smectite.This could have occurred in response to fracturing of a hydrological barrier. The ratio Ba/Sr began decreasing3–6 days before the MW = 5.0 earthquake. We interpret a transient switchover to anorthite dissolution causedby exposure of fresh plagioclase to groundwater interaction. This could have been induced by microfracturing,locally within the main aquifer. By comparison with experimental studies of feldspar dissolution, we interpretthat hydrogeochemical recovery was facilitated by groundwater interaction and clay mineralization, which couldhave been coupled with fracture sealing. The coincidence in timing of these two hydrogeochemical events withthe only two MW C 5 earthquakes in the study area argues in favor of cause-and-effect seismichydrogeochemicalcoupling. However, reasons for ambiguity include the lack of similar hydrogeochemicalanomalies coupled with smaller seismic events near the monitoring station, the >200 km length scale of inferredseismic-hydrogeochemical coupling, and the potential for far-field effects related to the Great Sumatra–Andaman Islands Earthquake of December 26, 2004.
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| 4. |
- Skelton, Alasdair, et al.
(författare)
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Seismic-hydrogeochemical coupling in north-eastern India
- 2008
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Ingår i: 33rd International Geological Congress Oslo August 6 -14th 2008 General Proceedings. - : EurekaMag.com. ; , s. CD-ROM
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- We report the result of a hydrogeochemical monitoring program, which has been operational north of the Shillong Plateau, Assam, India from December 2003. The aim of this ongoing study is to test for coupling between the groundwater chemistry collected from a granite-hosted aquifer, located at a depth of 110m, and seismic activity. Based on molar Na+/Ca2+ and molar HCO3-/SiO2 ratios after Garrels (1967), we interpret that groundwater chemistry is normally buffered by the alteration of feldspar (plagioclase) to kaolinite.During the study, we monitored transient chemical changes which coincided temporally with a period of increased seismic activity. This included (1) MW = 5.3 and MW = 5.0 earthquakes which occurred on December 9, 2004 and February 15, 2005, south of the Shillong Plateau and 206 and 213 km from the sampling station, respectively, and (2) the Great Sumatra – Andaman Islands Earthquake of December 26, 2004. These are the only three MW > 5 earthquakes which have occurred during our study and for which our monitoring site is within their respective strain radii as given by Dobrovolsky et al. (1979).The most dramatic chemical change was a coincident and approximately 2-fold increase of the ratios [Na+K]/Si, Na/K and [Na+K]/Ca. This was accompanied by significant increases of conductivity, alkalinity and chloride concentration. The onset of this chemical shift occurred 3-5 weeks before the first (MW = 5.3) earthquake. We interpret a transient switchover between source aquifers, which induced an influx of groundwater from a second and probably deeper aquifer, where groundwater chemistry was dominantly buffered by the alteration of feldspar to smectite. This could have occurred in response to fracturing of a hydrological barrier. We also recorded a rapid drop in the ratio Ba/Sr, which occurred 3-6 days before the final (MW = 5.0) earthquake. We interpret a transient switchover to anorthite dissolution caused by exposure of fresh plagioclase to groundwater interaction. This could have been induced by microfracturing, locally within the main aquifer. Both of these changes were transient and “recovery” occurred over periods of 2-4 weeks. By comparison with experimental studies of feldspar dissolution, we suggest that hydrogeochemical recovery was facilitated by groundwater interaction and clay mineralization, which could have been coupled with fracture sealing.The main argument in support of seismic-hydrogeochemical coupling is the coincidence in timing of two hydrogeochemical events with two MW 5 earthquakes. Reasons for ambiguity include the lack of similar hydrogeochemical anomalies temporally coupled with smaller seismic events which occurred much closer to the monitoring station, the >200 km length scale of inferred seismic-hydrogeochemical coupling, and the potential for far-field effects related to the Great Sumatra – Andaman Islands Earthquake of December 26, 2004. The hydrogeochemical anomalies reported in this study meet some of the validation criteria of the IASPEI (International Association of Seismology and Physics of the Earth’s Interior) sub-commission on earthquake prediction (Wyss, 1991; 1997) in that a relation to pre-seismic stress and that some dependence on distance from the earthquake foci is inferred. However, hydrogeochemical data was collected from only one site, and even although the hydrogeochemical anomalies are recorded using several instrumental methods the reported anomalies are not truly independent of one another.
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