Research papers
Impact of differential surface water mixing on seasonal arsenic mobilization in shallow aquifers of Nadia district; western Bengal Basin, India

https://doi.org/10.1016/j.jhydrol.2022.128270Get rights and content

Highlights

  • The study provides a comprehensive effort of understanding the role of multiple factors driving seasonal As mobilization in shallow groundwater.

  • Increasing anoxia and dissolved As concentration is prominent in shallow GSA groundwater during dry pre-monsoon period than in post-monsoon time.

  • Magnitude of seasonal changes in groundwater As concentrations (ΔAs = AsPRM – AsPOM) vary over years due to variable hydrological conditions.

  • Variable rainfall, excess groundwater withdrawal, mixing, surface water infiltration, and local lithology are marked as probable seasonal redox drivers for As mobilization in shallow aquifer.

  • Excess withdrawal in pre-monsoon time acts as a conduit for organic-rich surface water infiltration or aquifer intercalated clay-pore water expulsion by compaction and mixing in the adjoining groundwater; promotes high As release.

Abstract

Arsenic (As) mobilization in groundwater is linked to the dissimilatory reductive dissolution of As(V) coated Fe(III)-oxy-hydroxides from the aquifer sediment coupled with the degradation of available dissolved organic carbon (DOC) due to the presence of anaerobic microbes under anoxic conditions. Understanding the seasonal pattern of As mobilization in the shallow groundwater of the Bengal Basin remains a challenging task due to the heterogeneous character of the shallow aquifers and the involvement of multiple factors. To resolve this issue, in the present study, we showcased a comprehensive effort to advance understanding of the seasonal As mobilization process in the shallow groundwater, utilizing multiple geochemical tracers (i.e., the abundance of dissolved total As, Fe, Mn, NO3, SO42-, DOC, Cl-, and δ18O, δ2H, δ13C-DOC isotopic tracers) between post-monsoon and pre-monsoon periods over multiple years from Nadia district, West Bengal, India. We quantified and explained the seasonal variation of dissolved total As concentrations in the groundwaters with the nature of the aquifer lithology (i.e., grey sand aquifer or ‘GSA’ and brown sand aquifer or ‘BSA’). The present study reported elevated dissolved total As concentrations in the shallow groundwater samples during dry pre-monsoon (‘PRM’) periods compared to post-monsoon (‘POM’) time. However, the magnitude of such seasonal changes in groundwater As concentrations (denoted as ΔAs = AsPRM-AsPOM) varied between years depending on the extent of rainfall, surface water infiltration, mixing, and groundwater withdrawal. Our current findings are different from the past studies that reported elevated As concentrations in the shallow groundwater during the monsoon and post-monsoon periods compared to the dry pre-monsoon periods. However, the limitations of the past findings are that most of the previous studies were carried out between seasonal intervals over a single annual cycle without reinvestigating the seasonal trends over different years under variable hydrological conditions. We proposed that the excess groundwater withdrawal during the dry pre-monsoon period drive draw-down and, therefore, trigger infiltration of surface-derived deep pond water into the shallow aquifer. Such surface water infiltration introduces fresh labile organic matter into the shallow aquifer, promoting high As mobilization during the dry pre-monsoon period. A viable alternative approach of ‘squeezing’ of aquifer intercalated clay-peat sedimentary lenses and mixing of organic-rich pore water in the adjoining groundwater can also enhance high As mobilization during the dry time, as examined in this study. This process is triggered by the excessive groundwater withdrawal practices and drawdown encountered during dry time, driving the aquifer intercalated clay-pockets compaction.

Introduction

High As concentrations (>10 µg/L; permissible guideline value recommended by WHO) are documented in the groundwater of the shallow grey sand aquifers (‘GSA’) (at depths < 70 m bgl) of the Bengal Basin (Dowling et al., 2002, Harvey et al., 2002, Fendorf et al., 2010, Biswas et al., 2012, Chatterjee et al., 2013, Biswas et al., 2014). Frequent patterns of seasonal variations in As concentrations are documented mainly in the shallow GSA groundwaters of the Bengal Basin (Cheng et al., 2005, Savarimuthu et al., 2006, Planer-Friedrich et al., 2012, Biswas et al., 2014, Majumder et al., 2016, Majumder et al., 2017). In contrast, the brown sand aquifers (‘BSA’) (at depths 35–70 m bgl) provide nearly As-free groundwater (<10 µg/L As) (McArthur et al., 2008, Ghosal et al., 2015). Arsenic is commonly found in As(V) sorbed on the surfaces of Fe(III)-oxy-hydroxide phases in the fine sand grains and silty/clay-rich sediments of the Bengal Basin, which is characterized by the high organic contents (Bhattacharya et al., 1997, Nickson et al., 1998, McArthur et al., 2001, Dowling et al., 2002, McArthur et al., 2004). These sediments were part of palaeo-Ganges river flood-delta plain sedimentation events and were strongly influenced by sea-level fluctuations during the Quaternary periods (Acharyya et al., 2000). The principle mechanisms involved in As mobilization from these sediments include dissimilatory reductive dissolution of As(V) coated Fe(III)-oxy-hydroxides, liberating As(III) and Fe(II) in the presence of microbes that facilitate consumption of bioavailable dissolved organic carbon (DOC) in the groundwater for growth and metabolism. DOC in groundwater actively participates during As mobilization process as energy source for microbes and can originate from multiple sources, such as aquifer intercalated organic-rich clay-peat lenses (McArthur et al., 2001, McArthur et al., 2004, Sengupta et al., 2008, Datta et al., 2011) and the natural surface water bodies (ponds, rivers, lakes), that are rich in fresh, labile organic matter (Harvey et al., 2002, Neumann et al., 2010, Lawson et al., 2013).

Seasonal variation in As concentrations in the shallow groundwater of the Bengal Basin is documented highly heterogeneous due to the involvement of multiple factors, including variable rainfall, surface water recharge, mixing, groundwater withdrawal, aquifer redox state, and local lithology (Cheng et al., 2005, Savarimuthu et al., 2006, Planer-Friedrich et al., 2012, Biswas et al., 2014, Majumder et al., 2016, Majumder et al., 2017). However, the subject remains poorly addressed due to the lack of comprehensive knowledge on the interconnected roles of multiple factors driving As distribution over time in the shallow groundwaters of the Bengal Basin. Therefore, an advanced understanding of this topic is needed to identify the potential causes of excessive As in the shallow groundwater and its seasonal fluctuations to better manage the groundwater resources.

The South-West Monsoon (SWM) rainfall (June through September) which accounts for 82 % of the annual rainfall over India, significantly recharges the shallow aquifers of the Bengal Basin (Mukherjee et al., 2007b). The time interval between October and May is designated as the dry period when the freshwater abundance due to the interplay of the meteorological parameters is less prominent, and the demand is high for the groundwater. The dry period is further divided into three periods: post-monsoon (October-December), winter (January- February), and pre-monsoon (March-May). After the SWM, the groundwater level remains high in the post-monsoon period due to the monsoon recharge effect. However, during the pre-monsoon period, the groundwater level recedes maximum due to excessive abstraction practices for irrigation and drinking purposes. Pre-monsoon showers (‘Norwester’ or locally known as ‘Kalbaisakhi’) and rainfall due to cyclonic activities account for 18 % of the annual precipitation over India (Mukherjee et al., 2007a, Mukherjee et al., 2007b). Such rain provides occasional hydrological input to the shallow aquifers during dry periods by percolation through unsaturated soil and sedimentary desiccation features like mud cracks. In dry periods, groundwater provides the only potential water resource (∼50–60 % from shallow aquifers), essentially meeting the agricultural demand (Sikdar et al., 2018). Excessive groundwater abstraction during dry periods causes a sharp drop in the local groundwater level of the shallow aquifers (Harvey et al., 2002, Neumann et al., 2010, Lawson et al., 2013, Biswas et al., 2014, Mukherjee et al., 2018), which generates local depression zones in the groundwater levels (Sikdar et al., 2018). The drawdown in the groundwater level of the shallow aquifer is often compensated by the a) infiltration of organic-rich surface water from the base of ponds, lakes, and rivers (Harvey et al., 2002, Neumann et al., 2010, Lawson et al., 2013, Mukherjee et al., 2018) or b) mixing of organic-rich pore-water from the adjoining intercalated clay-pockets. Mixing of such organic-rich water into the shallow aquifer is likely to trigger anoxic conditions and higher As mobilization by driving the anaerobic microbial activity. There has been evidence of land subsidence in the adjoining areas of the Bengal Basin due to the compaction of sub-surface fine-grained sedimentary strata by excessive pumping (Sahu and Sikdar, 2011, Planer-Friedrich et al., 2012, Mihajlov et al., 2020, Mozumder et al., 2020, Pathak et al., 2022a). Seasonal changes in the storage volume of the shallow aquifers occur due to the cycles of monsoonal recharge and dry time groundwater abstraction (Planer-Friedrich et al., 2012). The process generates an expansion and squeezing effect in the aquifer intercalated clay-peat layers, which may perturb the sub-surface aqueous chemistry by expulsion and mixing of the organic-rich pore-water. Approximately ∼20 % mixing of organic-rich pore water derived from the squeezing of aquifer intercalated clay pockets caused high As release via excess supply of DOC to the adjoining groundwater (Mihajlov et al., 2020).

A variable temporal pattern of dissolved total As concentration in the shallow groundwater has been explained based on the seasonal recharge cycles. Multiple studies, registered higher dissolved total As concentrations in shallow groundwater during the wet periods compared to the dry periods in an annual cycle (Cheng et al., 2005, Savarimuthu et al., 2006, Planer-Friedrich et al., 2012, Biswas et al., 2014, Majumder et al., 2016, Majumder et al., 2017). Such an observation is commonly attributed to the monsoonal recharge bringing anoxia either through the inflow of DOC or saturation of sediment pore spaces; conducive for high As release. In contrast, Government agencies like Central Ground Water Board (CGWB) and other studies (Cheng et al., 2005, Biswas et al., 2014) reported elevated dissolved total As concentrations in the shallow groundwater during dry periods compared to the wet period. The possible dilution effect in the shallow groundwater during the wet time due to the mixing of rainwater and surface runoff as input can explain such temporal distribution of dissolved total As concentrations. In addition, the introduction of organic-rich anoxic water from the bottom of the natural surface water bodies into the shallow aquifer during the dry period facilitated by excess groundwater withdrawal can lead to high As mobilization.

The majority of the past studies reporting heterogeneous As distribution in the shallow groundwater over time were conducted between seasonal time intervals over only an annual cycle. Therefore, repeated seasonal observations on the same set of bore-wells over multiple years are required to understand better the seasonal As mobilization process in the shallow groundwater under variable hydrological conditions in yearly cycles. A comprehensive effort to monitor the seasonal As trends in the shallow groundwater (mid-screen depth < 70 m bgl) over multiple years (2016–2019) was carried out in this study to address the interconnected roles of multiple factors responsible for As release. In this study, the groundwater sampling was done from one of the As hot spot regions of the Bengal Basin, situated in the Nadia district, West Bengal, India. We focused our observations between the post-monsoon and pre-monsoon periods (coinciding with the period of maximum abstraction of shallow groundwater). Our current objectivity focused on a quantitative understanding of the source of recharge water contributing to labile organic matter and responsible for high As mobilization in the shallow groundwater at the seasonal time intervals by inducing anaerobic microbial activity. For this purpose, we measured the abundance of conservative solute (dissolved Cl-) and stable isotopic ratios (δ18O, δ2H) in the seasonal shallow groundwater samples along with δ13C-DOC signatures in the groundwater. For a better understanding of the active redox-biogeochemical processes responsible for the seasonal release of As in the shallow aquifer, we simultaneously measured multiple dissolved redox-sensitive solutes and redox-parameter (i.e., dissolved total As, Fe, Mn, SO42-, NO3, DOC concentration, Oxidation Reduction Potential ORP value) with emphasis on their seasonal patterns.

Section snippets

Study area

The field area (∼48 km2 in Haringhata and Chakdaha blocks, Nadia district, West Bengal) (Fig. 1a) selected in the present study has received significant attention due to excess As concentrations in the shallow groundwaters inspected for over > 30 years. It falls under the Gangetic alluvial plain and belongs to the Sonar Bangla Aquifer (Mukherjee et al., 2007a) (elevation: 0–20 m above MSL) in proximity to the Hooghly River (also known as Hugli River).

Groundwater modeling over the study region

Materials and methods

Here we monitored bore-well waters tapping the shallow GSA (mid-screen depths < 70 m bgl) and BSA (mid-screen depths 35–70 m bgl). The groundwater sampling from shallow GSA included n = 11 bore-wells each during Nov-16, Apr-17, Feb-18, and May-18; n = 35 bore-wells each during Dec-18, and Apr-19 time periods. However, the groundwater sampling from BSA included n = 6 bore-wells each during Nov-16 and Apr-17; n = 1 bore-well each during Dec-18 and Apr-19 period (Fig. 1a). We provided a

Vertical distribution pattern of As and As mobilizing solutes in groundwater:

The vertical distribution pattern of dissolved total As concentrations in the integrated seasonal groundwater samples (mid-screen depths: 4–70 m bgl) over multiple years was compared with the adjoining lithological characteristics of the aquifers. The groundwater samples in the present study from mid-screen depths <70 m bgl mainly originated from the shallow GSA, and a few groundwater samples from mid-screen depths of 39.6–51.8 m bgl represented BSA. Dissolved total As concentrations in the

Identification of the possible mineral phases in the shallow GSA groundwater from the calculated saturation indices values

In the geochemical modeling, the Saturation Index value or SI > 0 implies a supersaturation condition, which indicates precipitation of mineral phases from the solution is thermodynamically favorable. However, precipitation of mineral phases can be inhibited by slow rates of reactions. Whereas SI < 0 indicates an undersaturation condition, which suggests dissolution of mineral phases into the solution without further precipitation (Drever, 1997). The calculated SI values of the shallow

Conclusion

This study highlights the interconnected roles of multiple factors driving seasonal variation in As release in the shallow aquifer between the post-monsoon and pre-monsoon periods over 2016–2019. We analyzed groundwater samples from the shallow reducing grey sand aquifers (GSA) and a few samples from less reducing brown sand aquifers (BSA) that showed distinct seasonal variation patterns in the dissolved total As concentrations over multiple years. Unlike previous findings, our current

CRediT authorship contribution statement

Pousali Pathak: Conceptualization, Methodology, Formal analysis, Data curation, Investigation, Visualization, Validation, Writing – original draft. Prosenjit Ghosh: Conceptualization, Funding acquisition, Writing – review & editing. Abhijit Mukherjee: Resources, Writing – review & editing. Utsab Ghosal: Resources, Writing – review & editing. Mao-Chang Liang: Formal analysis, Writing – review & editing. Pradip K. Sikdar: Resources, Writing – review & editing. Ritika Kaushal: Formal analysis,

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgment

The work is supported by the Indian Institute of Science Ph.D. fellowship. We express our gratitude to Mrs. Ranita Banerjee, Mrs. Noor Muzakkira (Centre for Earth Science, IISc, Bangalore, India), and Dr. Sumanta Bagchi (Centre for Ecological Sciences, IISc, Bangalore, India) for helping in the analytical measurements of dissolved total Arsenic (As) and dissolved organic carbon (DOC) concentration in the water samples needful for this study. We are thankful to Mr. Kathiravan Merran (Centre for

References (59)

  • J.M. McArthur et al.

    Natural organic matter in sedimentary basins and its relation to arsenic in anoxic ground water: the example of West Bengal and its worldwide implications

    Appl. Geochem.

    (2004)
  • J.M. McArthur et al.

    Waste-water impacts on groundwater: Cl/Br ratios and implications for arsenic pollution of groundwater in the Bengal Basin and Red River Basin, Vietnam

    Sci. Total Environ.

    (2012)
  • A. Mukherjee et al.

    Deeper groundwater chemistry and geochemical modeling of the arsenic affected western Bengal basin, West Bengal, India

    Appl. Geochem.

    (2008)
  • A. Mukherjee et al.

    Regional-scale stable isotopic signatures of recharge and deep groundwater in the arsenic affected areas of West Bengal, India

    J. Hydrol.

    (2007)
  • A. Mukherjee et al.

    Hydrogeochemical comparison and effects of overlapping redox zones on groundwater arsenic near the Western (Bhagirathi sub-basin, India) and Eastern (Meghna sub-basin, Bangladesh) margins of the Bengal Basin

    J. Contam. Hydrol.

    (2008)
  • A. Mukherjee et al.

    Geologic, geomorphic and hydrologic framework and evolution of the Bengal basin, India and Bangladesh

    J. Asian Earth Sci.

    (2009)
  • P. Pathak et al.

    Role of carbon and sulfur biogeochemical cycles on the seasonal arsenic mobilization process in the shallow groundwater of the Bengal aquifer

    J. Appl. Geochem.

    (2022)
  • B. Planer-Friedrich et al.

    Organic carbon mobilization in a Bangladesh aquifer explained by seasonal monsoon-driven storativity changes

    Appl. Geochem.

    (2012)
  • A.A. Seddique et al.

    Arsenic release from biotite into a Holocene groundwater aquifer in Bangladesh

    Appl. Geochem.

    (2008)
  • P.K. Sikdar et al.

    Geochemical evolution of groundwater in the Quaternary aquifer of Calcutta and Howrah, India

    J. Asian Earth Sci.

    (2001)
  • E. Stopelli et al.

    Carbon and methane cycling in arsenic-contaminated aquifers

    Water Res.

    (2021)
  • D. Stüben et al.

    Arsenic enrichment in groundwater of West Bengal, India: geochemical evidence for mobilization of As under reducing conditions

    Appl. Geochemistry

    (2003)
  • Y. Zheng et al.

    Redox control of arsenic mobilization in Bangladesh groundwater

    Appl. Geochem.

    (2004)
  • Y. Zhou et al.

    Characteristics and implication of stable carbon isotope in high arsenic groundwater systems in the northwest Hetao Basin, Inner Mongolia, China

    J. Asian Earth Sci.

    (2018)
  • S.K. Acharyya et al.

    Arsenic toxicity of groundwater in parts of the Bengal basin in India and Bangladesh: the role of Quaternary stratigraphy and Holocene sea-level fluctuation

    Environ. Geol.

    (2000)
  • R.A. Berner

    A new geochemical classification of sedimentary environments

    J. Sed. Petrol.

    (1981)
  • P. Bhattacharya et al.

    Occurrence of arsenic-contaminated groundwater in alluvial aquifers from delta plains, eastern India: options for safe drinking water supply

    Int. J. Water Resour. Dev.

    (1997)
  • S. Biswas

    Groundwater flow direction and long term trend of water level of Nadia District, West Bengal: a statistical analysis

    J. Geol. Soc. India

    (2003)
  • Z. Cheng et al.

    Limited temporal variability of arsenic concentrations in 20 wells monitored for 3 years in Araihazar, Bangladesh

    Environ. Sci. Technol.

    (2005)
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