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Abstract
Understanding the seasonal variation of arsenic occurrence in shallow groundwater system is one of the challenges and hot spots concerning the research on high arsenic groundwater, which plays an important role in evaluation of safe groundwater availability and remediation of arsenic-affected aquifer. To investigate the seasonal variation of arsenic speciation in the shallow aquifer from the endemic arsenicosis area in the Jianghan plain, groundwater from shallow phreatic aquifer and unconfined aquifer were monitored for arsenic speciation (As(III), As(V) and acid-leacheable particulate As) and water level during pre-monsoon (May), monsoon (July-August) and post-monsoon (November-December) seasons. Arsenic concentration and speciation in groundwater varied temporally: the concentration of As(V) and particulate As were higher, together with higher particulate Fe in most samples during the pre-monsoon seasons; As(V) and particulate As decreased significantly during monsoon seasons, while dissovled As and Fe increased dramatically. Higher As concentrations were associated with an increasing percentage of As(III) in rainy season and a decrease towards the end of dry season, indicating a reductive moblization responding to groundwater level fluctuation. © 2015, Editorial Department of Earth Science-Journal of China University of Geosciences. All right reserved.
... High-arsenic groundwater continues to threaten the safety of water supplies for drinking, farming and irrigation (Fendorf et al., 2010;Nordstrom, 2002;Rodriguez-Lado et al., 2013). In addition to the wellknown endemic arsenicosis areas such as Bengal Delta, Inner Mongolia and Datong basin (Guo et al., 2013a;He and Charlet, 2013;Smith et al., 2000), Jianghan Plain in the middle reaches of Yangtze River has been identified as a new arsenicosis area (Chen et al., 2017;Deng et al., 2015;Duan et al., 2015;Gan et al., 2014;Schaefer et al., 2016Schaefer et al., , 2017. As the activities like grain planting, fish breeding and poultry feeding are intensive in Jianghan Plain, the local people have been striving to seek safe water supplies. ...
... The aqueous chemical compositions observed at 10 m depth in all wells were used as the chemical boundary conditions at the top of the simulation domain. Initial groundwater arsenic species and other aqueous chemical concentrations were taken from the field monitoring data (Table 3; Deng et al., 2015;Duan et al., 2015;Li et al., 2015;Schaefer et al., 2017). ...
The arsenic concentration in groundwater varies significantly with time and space in groundwater-surface water exchange zones. Various processes have been identified that control arsenic concentration distribution and mobility in laboratory systems. However, it is still challenging to identify important processes controlling arsenic concentration distribution at the field scale due to the complex coupling of hydrobiogeochemical processes. In this study, a reactive flow and transport model was used to identify dominant processes controlling arsenic distribution and seasonal variations in groundwater-surface water exchange zones using Jianghan Plain, China, as an example. The results revealed the importance of river water and groundwater interactions on seasonal changes in arsenic concentration; however, the affected region is limited to within 50-m distance to the river. The modeling results, unexpectedly, revealed the predominant importance of groundwater extraction to the seasonal variation in arsenic concentration. The groundwater extraction changed the groundwater flow pattern and induced vertical leakage of oxygen-containing surface water into the aquifer, which triggered a series of biogeochemical reactions that changed groundwater redox conditions and promoted arsenic sorption, resulting in a rapid decrease in arsenic concentrations in groundwater. After groundwater extraction ceased, aquifer recovered to anoxic condition, promoting arsenic release from the sorbed phase, leading to a rapid rebounding in groundwater arsenic concentrations. Overall, this study provided a tool to identify coupled hydrobiogeochemical processes on arsenic spatiotemporal distribution and migration in groundwater.
... During the wet summer monsoon when surface water levels are higher than groundwater levels, a groundwater recharge flow gradient develops; during drier, winter months, surface water levels drop below groundwater levels, and groundwater flow reverses and moves toward surface water. Further details of the field area are provided in previous publications Deng et al., 2015;Schaefer et al., 2016). ...
At Jianghan Plain of central Yangtze basins where the health of >73, 000 people has been affected by long term intake of high arsenic groundwater, over 100 sediment samples from four boreholes at the field monitoring sites were collected and analyzed to delineate the distribution and speciation of As in the shallow aquifer sediment. Results showed that sediment As concentration is generally dependent on the lithological conditions, with the higher As concentration present in fine particle sediment, especially in the silty sand layers underlying clay or silty clay layers. High As concentration in the sediment mainly occurred in three different depth ranges: <5m, 15-35m, and >35m. Both the groundwater regime and redox conditions played important roles in controlling sediment As speciation. Arsenate (86%) was the dominated As species in the near surface sediment. As the redox turned to be reducing, arsenite (64%) became the dominant species in the underlying clay and silty clay layers. But in the silty sand aquifer near the boundary of unconfined aquifer and confined aquifer, arsenate (85%) became the dominant species again as results of redox potential elevation. In the deep medium to coarse sand aquifers (>35m deep), As-sulfides (49%-63%) were the main species of As. The speciation and reactivity of sediment As strongly controlled the spatial distribution of groundwater As concentration, while seasonal variation in groundwater As concentration and speciation affected the content and speciation of sediment As.
Arsenic is abundant in the earth’s crust and has been found in more than 300 minerals in nature. As a compound with other elements such as oxygen, chlorine, and sulfur, arsenic is widely distributed in minerals and ores that contain copper or lead. Arsenic present in the minerals is usually mobilized through geogenic and anthropogenic activities. Anthropogenic sources of arsenic pollution originate in several industries, such as mining, smelting or refining of metal, fossil fuel combustion, and wood preservation.
To investigate geochemical and mineralogical features of sediments from aquifers containing high levels of dissolved arsenic (As) in western Hetao Basin, Inner Mongolia, sediment samples were collected for XRD (X-ray diffraction), amorphous Fe/Mn oxides, and humic/fulvic acid analyses, in addition to As determination. In the study area, the total As contents in the sediments were in the range 5.3-28.8 mg/kg; while that associated with humic substances in the range 4-9 mg/kg, accounting for 26%-47% of the total As. The results of XRD analysis suggest that clay and silt contain certain small amounts of iron oxides minerals, such as ferrihydrite, hematite and goethite, whereas have higher As and Fe2O3 contents. Up to one third of As in the sediments could be extracted by ammonium oxalate, and high As contents were generally found in organic-rich clay or silty clay samples with high FA/HA ratio. As is strongly associated with humic substances and Fe oxyhydroxides, which may be the major sink and source of As in the aquifer sediments. © 2017, China University of Geosciences and Springer-Verlag GmbH Germany.
The stress imposed on groundwater resources due to intensively exploited aquifer has resulted in groundwater depletion in the North China Plain (NCP). Management of groundwater resources needs to understand the changes or dynamic responses due to the exploitation. The response of groundwater systems to intensive exploitation and groundwater availability were assessed by the combined use of conventional hydrochemical data and environmental isotopes in Shijiazhuang, NCP. The generally increased concentration of total dissolved solids (TDS), major cation and anion of groundwater in the past 40 years indicated high vulnerability of aquifer system but a short turn over time by intensive groundwater exploitation, which also was proved by changes of groundwater renewal rate estimated by tritium. The vertical distribution of tritium in aquifers showed that the active groundwater recharge zone has been extended from the depth of 100 to ~150 m since 1985, indicating an enhancement of active groundwater flushing of local groundwater system due to intensive groundwater abstraction. The enrichment trend of δ¹⁸O and δ²H value with groundwater abstraction, suggested the impacts of local recharge from irrigation return. The increase concentrations of nitrate with time indicated high aquifer vulnerability. A comprehensive effort should be developed for effective management strategies that ensure long-term, stable, and flexible water supplies to meet water demands in the NCP. © 2017, China University of Geosciences and Springer-Verlag GmbH Germany.
Objective: To investigate the basic distribution of endemic areas in the type of drinking water arsenism and in Xiantao City, Hubei Province, and to offer a scientific basis for control and prevention. Methods: According to "the Chinese Scheme of Implementing Surveillance of Distribution of Endemic Arsenism", considering with the special geography feature of Xiantao, both sampling and overall survey were used in 7 towns chosen. The water arsenic content was determined by half quantitative fast reagent-box method. We began to search for clues and patients according to the endemic areas and the families with high arsenic wells. Results: High endemic arsenic water sources were distributed in 7 the towns (districts or farms). In 81 villages of Xiantao City, 35 villages had drinking water arsenic content exceeding 0.05 mg/L, accounting for 43.21% (35/81). In 4020 screened wells, 269 had arsenic content higher than the national standard, the detective rate of high arsenic wells (more than 0.05 mg/L) was 6.69%(269/4020), with the highest rate in Shahu Seed Plant being 13.56% (115/848). The population exposed to high arsenic was 1091, in a rate of 5.75%(1091/18 975), in which 281 children were exposed in a rate of 5.82% (281/4826). In Shahu Seed Plant, 467 people including 129 children were exposed to high arsenic, accounting for 13.26%(467/3522) and 12.91%(129/999), respectively. Conclusions: High arsenic sources widely exist in Xiantao City, especially in Shahu Seed Plant, where arsenic content, the exposed rate of population and children are high. Therefore, prevention and control should be carried out in the southeast as soon as possible, as well as in other places where situation is less serious.