Elevated fluoride (F⁻) levels in groundwater, primarily due to geogenic processes, pose significant health risks, including dental and skeletal fluorosis and neurological disorders. This study aimed to quantify source-dependent F⁻ exposure at the community level in selected tropical dry regions of Andhra Pradesh, India. These locations include Chintal Cheruvu, Rompicharala, Shantamangalur, Thimmapur, and Nadendla. Community surveys and drinking water sample analyses were conducted in these regions. Dental Fluorosis Index (DFI) was used to estimate exposure levels across age and sex groups. Findings of surveys indicate that groundwater consumption with high F⁻ (4.3 mg/L) results in the highest exposure dose (0.62 mg/kg/day), with Chintal Cheruvu identified as the most affected. A strong positive correlation was observed between exposure dose, water F⁻ content, and the Community Fluorosis Index (CFI), with R² values of 0.98 and 0.97, respectively. Dental fluorosis prevalence exceeded 80% across all age groups, and household surveys revealed 100% unawareness of F⁻ exposure risks. Though there exist many ways to determine the impact of fluoride, the hierarchy of regions may change with the type of parameter chosen. To address this, we developed the Fluoride Impact Index (FII), a multi-criteria index computed considering various parameters indicating the impact of fluoride in a region. The magnitude of FII for Chintal Cheruvu is 0.563 which is highest among the considered regions indicating that it is most impacted region that needs remedial measures first in the hierarchy. Rompicharala with FII as 0.252, Nadendla (0.223), Shantamangalur (0.214), and Thimmapur (0.188) follows the hierarchy. These findings highlight the urgent need to raise awareness about F⁻ exposure risks and to identify sustainable alternative water sources. Immediate interventions, including human health risk assessments using the USEPA approach and the provision of safe drinking water, are critical to achieving SDG-6 of safe drinking water for all by 2030.

Arsenic (As) accumulation in rice plant from arsenic contaminated groundwater has now become an emerging global concern. The main objective of the present study was to evaluate the accumulation pattern of As in different parts of rice plants grown in an As affected area of in order to the make appropriate and safe selection of suitable rice varieties to be cultivated in the As affected areas. The study was conducted by collecting twelve different varieties of rice and soil samples from four arsenic affected villages of Purbasthali II block, West Bengal, India. The soil As level varies between 5.88 and 71.33 mg/kg and soil enzyme activity was recorded 0.215–0.724 µg/24 h/kg soil of amylase, 0.187–4.598 µg/24 h/kg soil of invertase, and 0.103–4.406 µg/24 h/kg soil of cellulose and these activators of soil enzymes were also observed to be affected by arsenic. The highest arsenic accumulation was recorded in root, shoot and leaf of the variety R6 (Voganti) and in rice husk and grain of theR11 (Nayanmoni) and R1 (Miniket), respectively. The overall accumulation pattern of arsenic in different parts of rice plants were in the order of root > shoot > leave > rice husk > rice grain. However, arsenic accumulation varied widely in different cultivars. The mean value of arsenic in rice grain was recorded < 1.0 mg/kg, which was much closer to FAO/WHO prescribed safe limit (1.1 ppm by weight according to FAO, 2019). Our study can be concluded by suggesting varieties like R4 (Miniket) and R8 (Sada Sorno) can be safely cultivated in the As affected areas.

Plastic-aggregates are made up from unused or waste plastic and natural aggregates which have recently been emerged as a significant addition to the existing emerging contaminants list mainly in the coastal environment. The transformation from plastics/microplastics to Plastic-aggregates signifies a crucial shift in our understanding and use of plastics and prompting us to reconsider their fundamental characteristics along with possible environmental threats. When plastic waste is incinerated for the purpose of disposal, it combines with organic and inorganic substances present in the surrounding environment, leading to a new type of material. Besides, some natural factors (physical, chemical, biological or in combination) also act upon discarded plastics to combine with rocks and other earthen materials to form plastic-aggregates. Our research aims to build fundamental knowledge and critically review the possible formation process, classification, and possible degradation of all such polymer-rock compounds along with their impact on the ecosystem. The knowledge gap related to the degradation and release of secondary pollutants from these agglomerates is to be addressed urgently in future research. Development and standardization of proper sampling and reporting procedures for plastic-aggregates can enhance our understanding related to their impacts on human health as well as to the entire environment as these aggregates contain different toxic chemicals.

Occurrence of fluoride (F−) at elevated levels in groundwater (GW) has become a major concern as it is associated with serious health issues like dental-skeletal fluorosis, severe neurological disorders, and abnormal enzymatic activities. This study conducted, in Purulia district in West Bengal, India, to understand the factors influencing F⁻ enrichment in GW in the context of hydroclimatic variability, its suitability for drinking water and irrigation purposes, and associated health risks. Results show that 37.5% of collected GW samples (n = 24) exceed the permissible limit of WHO (1.5 mg/L). The average and highest F⁻ concentrations recorded at 1.4 mg/L and 2.2 mg/L, respectively. A positive correlation between F⁻, Ca²⁺, and Na⁺ indicates that rock weathering significantly contributes to F⁻ mobilization. GW in this area is of Na-Mg-Cl type as indicated by the piper plot. The trend of rainfall and temperature shows an inverse relationship with F− content and GW level is one of the major aggravating hydroclimatic factors for mobilization of F− in GW. The study showed that, GW is suitable for irrigation based on geochemical indices, but elevated fluoride and moderate salinity have degraded its quality, raising concerns about increased F− exposure through dietary intake. Consequently, Dental fluorosis prevalence is notably higher among individuals aged 10–20, 21–30, and over 50, with males consuming more F⁻-rich water than females across all age groups. So, it can be concluded that, hydroclimatic variability plays a key role in driving geochemical processes that mobilize fluoride in groundwater. Therefore, identifying safe aquifers while considering demographic and climatic factors is essential for managing fluoride contamination and mitigating health impacts.

In the past 20-30 years, deterioration in soil quality has become a serious environmental issue. Rapid industrialization and mining activities have triggered the deterioration of soil quality. Owing to these anthropogenic activities, soil is exposed to contaminants, such as heavy metals (HMs) (Xiao et al., Land Degradation & Development 31:1969-1989, 2020; Raj and Maiti, Environmental Monitoring and Assessment 191:566, 2019), which, in turn, result in the degradation of soil quality as well as soil fertility.

Coastal groundwater is susceptible to physico-chemical modification from interaction with seawater and other surface waters. Surface water-groundwater (SW-GW) interaction can alter the Sr concentration and radiogenic 87Sr/86Sr signature of both seawater and groundwater from multi-depth aquifers. In this study, we document such an interaction between a tropical ocean (Bay of Bengal [BoB]) and the coastal aquifers of a large mega-deltaic system formed by the Himalayan-sourced Ganges River, at shallow (10–50 m below ground level [bgl]), and deeper (115 and 333 m bgl) depths, using radiogenic strontium isotopes (87Sr/86Sr), stable isotope ratios (δ18O and δD), salinity and dissolved solutes. The mean 87Sr/86Sr for shallow coastal aquifers (10–50 m bgl: 0.71094) suggests that seawater mixes with the terrestrial-sourced shallow groundwater, modifying them to brackish water. This is further supported by the stable isotope signatures (14–25 m bgl: −3.63 to −0.7 ‰ and 30–50 m bgl: −3.5 to −1.2 ‰ δ18O). The radiogenic 87Sr/86Sr (115 m bgl: 0.71681 and 333 m bgl: 0.71995) and depleted δ18O (115 m bgl: −5.04 to −1.61 ‰ and 333 m bgl: −4.43 to −2.38 ‰) suggest relatively less to negligible mixing between seawater and terrestrial-sourced resident groundwater at greater depths. The mixing process is additionally characterized by a significant Sr flux discharged from these coastal aquifers to the BoB, which ranges between 7.7 × 104 and 12 × 105 mol/year for shallow aquifers, and between 1.78 × 104 and 8.26 × 104 mol/year for deep aquifers, respectively. The overall contribution of Sr from old groundwater of deep aquifers is 1.43 % (115 m bgl) and 0.66 % (333 m bgl), whereas shallow aquifers show a higher contribution, ranging from 6.18 to 9.57 % of BoB Sr budget. This study suggests that the discharge of recirculated brackish water to the BoB from the shallow aquifers contributes more than 5 times higher Sr to the oceanic budget than the deep aquifer, contributing as an essential component of the global oceanic budget of Sr.

Aquifers adjoining tropical oceans, such as the Ganges-Brahmaputra-Meghna river fluvio-deltaic system, host > 30% of the global population, highlighting the importance of understanding their geochemical signatures and the processes governing them. Here, Sr signature has been used as a conservative geochemical tracer together with some other major ions to delineate the hydrological processes and salinisation of groundwater by exchange with surface water (sea, river, and tidal creeks) and multi-depth groundwater in and around the Ganga River mega-delta. Our study results revealed that there are significant differences between the studied hydrological reservoirs and a change in lithological and hydrogeochemical conditions reflects changes in sediment source and dominant geochemical processes. An increasing rate of chemical weathering is observed within the delta system for river water. Similarly, Sr values are indicative of higher interaction of groundwater with aquifer sediment, which suggests a longer residence time observed in inland parts of the basin. Silicate weathering with minor carbonate weathering is the dominant process regulating the Sr cycling between lithologic and hydrologic reservoirs within the basin. In contrast, the groundwater Sr in coastal, delta-front aquifer systems is dominantly influenced by exchanges with seawater. The intruded brackish water mixes with resident fresh groundwater and is discharged into the coastal ocean as submarine groundwater discharge.

Coastal aquifers, a critical component of the land-ocean continuum, act as hotspots of fresh groundwater and seawater mixing while reactive processes further govern the elemental flux to the ocean in form of groundwater discharge. Here we report stable Sr (δ88/86Sr) and Ca isotope (δ44/40Ca) data for groundwater samples collected from multiple depths (14–333 mbgl) from two coastal aquifers in the Ganges River delta (Sundarbans). Significant variability is observed in δ88/86Sr values (range 0.542 ‰) with shallow (up to 42 mbgl) aquifer samples showing high δ88/86Sr values (up to 0.666 ‰ relative to NIST SRM987), which indicates pronounced interaction with seawater and fractionation induced by Sr removal during carbonate precipitation. The δ44/40Ca values of these samples also show large variability (range 0.76 ‰) which loosely follows the δ88/86Sr trend. The δ88/86Sr-δ44/40Ca correlation is relatively poor for shallow groundwater samples and reflects differences in fractionation mechanisms during carbonate precipitation for Sr and Ca isotopes. In contrast to the shallow aquifer samples, the deep aquifer samples display limited seawater influence. The depth-bound variability of molar Sr/Ca, δ88/86Sr, and δ44/40Ca suggests considerable removal of solute Sr and Ca due to secondary mineral formation, dominated by carbonates at shallower depths consistent with saturation index (SI) calculations. This study highlights that formation of secondary minerals in coastal aquifers, as inferred from stable Sr and Ca isotopes, can affect the transport of highly soluble elements like Sr and Ca from the continents to the oceans and has implications for solute geochemistry in coastal aquifers.

Rooftop Rainwater Harvesting (RRWH) offers a viable solution to the pressing issue of saline groundwater in regions like Ainavolu, a village in Andhra Pradesh, India. This study examines the potential of RRWH systems to provide a sustainable alternative water source in rural settings faced with water scarcity due to saline groundwater. Firstly, in view of the limitation in terms of spatial resolution associated with satellite imagery, a UAV-based survey is conducted to create a high-resolution orthomosaic of the study region, enabling precise delineation and classification of rooftop materials to estimate harvestable rainwater. Findings of this study suggest that RRWH could significantly alleviate water shortages by potentially collecting approximately 20.16 million litres of rainwater annually. However, despite this substantial capacity, the adoption of RRWH remains limited due to financial, technical, behavioural, and institutional factors. Through comprehensive fieldwork, including focus group discussions and one-on-one interactions, we identified 17 critical factors hindering RRWH adoption. Based on these insights, we propose a tailored roadmap to promote RRWH implementation, incorporating strategies such as partnerships with local vendors, specialized training programs, subsidies, and targeted awareness campaigns. This study not only underscores the practicality of RRWH in offsetting the challenges posed by unsuitable groundwater but also provides a scalable model for enhancing water security through community-based initiatives and technological integration. Since the scenario of water scarcity and responses of residents change with the cultural and economic characteristics, it is suggested to update the factors while adopting the proposed framework.

Sustainable development goals (SDGs), notably SDG 6, emphasize the need to preserve clean and sustainable water resources for the well-being of current and future generations. Natural water resources, such as lakes, rivers, oceans, and groundwater, play a vital role in sustaining the delicate ecosystems that facilitate life on our planet. Since the presence of contaminants such as heavy metals, agricultural runoff, emergent organic compounds, microplastics (MPs), and microbiological pollutants in the aquatic environment deteriorate the quality of the natural water systems, the progress toward the achievement of SDGs gets challenging and complex. These above stated contaminants follow diverse pathways, including stormwater runoff, agricultural runoff, effluent discharges, and the natural weathering of sediments and solid wastes. The concentration of these contaminants detected in the environment varies largely depending on various factors, such as land use or season, which further add to the difficulties and hence requires proper detection and management strategies. Certain pollutants, such as MPs, are at a very preliminary stage of investigation and their proper detection techniques and classification is the need of the hour. Various mitigation techniques have been explored till date among which many techniques have proved to be beneficial. However, to ensure proper mitigation of contaminants and protection of our valuable natural water resources, integrated efforts of researchers, policy makers, and the community is necessary. Hence, further reinvestigations are required to come up with scalable and economically viable mitigation techniques that will not only focus on contaminant removal but also on reusability of wastewater or resources, which is consistent with the larger goal of promoting sustainability in water resource management.

There has been a growing concern over the occurrence of fluoride (F−) in groundwater and the impact of F− exposure on human health issues over the past decades. So, this study conducted a regional–scale assessment of the occurrence and trend of groundwater F− distribution [2014–2018] integrated with locally field–based investigations on F− exposure to a few selected families (10 households and 35 respondents) and reason behind their consumption of F− containing water (n = 18). In the local study, water samples were collected from multiple sources around the selected households by dividing them into consumptive and non–consumptive use. Results revealed that across the state of Andhra Pradesh, the occurrence of F− is more than the permissible limit in groundwater, and it has been increasing over the years (2014–2018) (average SD is 0.55), and the local study showed that the groundwater had an average of 1.5 mg/L F−, while other sourced water had an average of <1 mg/L F−. Most interestingly, nine families are consuming non–F− containing water (<0.52 mg F−/day) which is commercially available, while only one family is consuming F− containing groundwater and being exposed to >3 mg F−/day. This disparity in fluoride exposure is dependent on economic stability and health exposure policies.

Microplastics, small sized plastic particles having size <5 mm are formed through primary process including production of beauty products, microbeads and microfibres as well as secondary process including mechanical weathering, friction, aberration and fragmentation of large plastics. The major sources of microplastics are land-based and ocean-based sources. Microplastic pollution is a serious concern due to the persistent, low biodegradability and bio-accumulative behaviour. Microplastics can bioaccumulate in the food chain and can cause ecological and human health risk. Hence, it is important to remove from the aquatic ecosystems. Microplastics are removed from aquatic systems and wastewater through a series of processes such as physical, chemical and biological treatments. In the present articles, >250 articles are reviewed to collect the information regarding the various physical, chemical and biological methods for the removal of microplastics. Also, the probable control strategies to combat with plastic pollution were assessed. It was concluded that recent water treatment methods are efficient in removing microplastic pollution. The efficiencies to remove microplastic from the water ranged between 74 %-99.2 %, 65 %-99.20 % and 77 %-100 % for physical, chemical and biological treatment methods, respectively. Among the three treatment methods, physical methods especially the filtration of water from biochar is the most efficient way (efficiency up to 100 %) to remove microplastics. It was also concluded that creating public awareness, promoting reusing, recycling and reducing, and application of bioplastics can control the production of microplastics from plastic wastes. This review will be useful to add current knowledge regarding the abatement of microplastic pollution, and finding novel solution to control microplastics. This review will also help the policymakers to implement most effective and cost-efficient method to remove microplastics, and to find out new methods to reduce, reuse and recycle plastic wastes.

Drinking water sources with groundwater arsenic (As) contamination face multifaceted challenges in the removal and supply of fresh drinking water resources. To eradicate this problem, bioremediation has evolved to become more effective than other chemical and physical removal processes in its cost-effectiveness, high removal efficiency, and lesser production of secondary by-products or waste. Thus, this study aimed to treat As from aqueous media and to detoxify highly toxic forms of As by the isolated bacteria from As-affected areas. We isolated two new Gram-positive bacteria, which are reported here (Bacillus sp. and Bacillus cereus), with As5+ minimum inhibitory concentrations (MICs) of 4500 mg/L for the Bacillus sp. and 1000 mg/L for Bacillus cereus; meanwhile, for As3+, the MICs are 600 mg/L for both isolates. Bacillus sp. and Bacillus cereus can also effectively convert the highly toxic and easily mobile As3+ to As5+ in aqueous media. This study also demonstrates that these bacteria can remove a significant proportion of As3+ and As5+ (averaging 50% for both) from aqueous media. These As-resistant bacteria from the As-affected area can be used and upscaled for the treatment of As for a safer drinking water supply.

Groundwater of coastal aquifers have strong hy-draulic connections with the coastal hydrodynamics in a various spatiotemporal scale. But the along with the sub daily tidal influence the Tropical cyclone dependent acute groundwater level response has rarely been studied. These acute and instantaneous groundwater level (GWL) fluctuations during tropical cyclones (atmospheric depression) have a direct impact on groundwater flow dynamics and have an impact on instantaneous solute and contaminant mobilization. These groundwater dynamics include influx of sweater and submarine groundwater discharge over the period each atmospheric low-pressure events simultaneously. The dynamic state of GWL fluctuations get stabilized along with decay of atmospheric low-pressure events but the change in solute concentration may stay for a month to seasonal recharge of groundwater and is proportional to the level of acute GWL fluctuations. Thus, this monitoring and prediction of atmospheric low- pressure event dependent GWL fluctuations is a possible indicator of groundwater vulnerability, especially in coastal aquifers. This study conducts a comparative analysis of machine learning and deep learning models to predict groundwater level fluctuations. The models include a Fully Connected Neural Network (FCNN), Artificial Neural Network (ANN), MLPRe-gressor, Support Vector Regressor (SVR), and Random Forest Regressor (RFR). Each model is evaluated using metrics such as Mean Squared Error (MSE), R2 score, Normalized Root Mean Squared Error (NRMSE), Root Mean Squared Error (RMSE), and standard deviation. The results underscore the capability of deep learning techniques to capture nonlinear features in hydrological data, thereby enhancing the understanding and prediction of groundwater levels. Such predictions are crucial for assessing seawater infiltration, which is a potential threat to the available drinking water sources and nutrient and contaminant fluxes within coastal aquifers. Submarine groundwater discharge, facilitated by these aquifers, plays a pivotal role in nutrient transfer from terrestrial to marine ecosystems, thereby influencing marine health and primary productivity.

Biogeochemical transformations within highly saline subterranean estuaries (STE) dramatically affect solute cycling, resulting in submarine groundwater discharge (SGD) with distinct chemical signatures. The study hypothesizes that biogeochemical processes within hypersaline bay porewaters (PW) simultaneously affect nitrogen, carbon, and radium cycling. We measured radium isotopes (226Ra, 224Ra, and 223Ra), nutrients (dissolved inorganic nitrogen [DIN: NH4+ + NO2− + NO3−], HPO42− [DIP], HSiO3− [DSi], dissolved organic carbon [DOC]), total alkalinity (TA), dissolved inorganic carbon (DIC), stable isotopes, and major cations in PW and surface water (SW) of Baffin Bay, a well-mixed, semi-enclosed estuary along the semiarid northwestern Gulf of Mexico coast, over three seasons in a characteristically dry year. This study's findings show a concurrent increase in NH4+, DIP, DSi, and TA/DIC with reduced metal species (e.g., Mn and Fe) and Ra during the hot and dry seasons, particularly in PW, under increasingly reducing conditions. Principal component analyses (PCA) suggest these increases are primarily driven by dissimilatory nitrate/nitrite reduction to ammonium (DNRA) and dissolution of lithogenic particles and biogenic CaCO3, modulated by organic matter degradation or remineralization. While more significant terrestrial groundwater inputs may contribute to solutes and Ra supply in the STE, the biogeochemically induced variability in solute concentrations in PW primarily drives larger SGD-derived fluxes, particularly notable in hot months. During a typically dry year, these fluxes, estimated as the average of 226Ra and 223Ra mass balance models (e.g., July/November fluxes in Mmol∙d−1: 0.093/0.092 of NO3−; 0.2/0.02 of NO2−; 72/16 of NH4+; 72.2/18 of DIN; 1.5/0.2 of HPO42−; 20/9 of HSiO3−; 42/37 of DOC; 503/399 of TA; 582/431 of DIC) are orders of magnitude (∼4 for DIN and DIC, ∼3 for DIP, DSi, and DOC, and ∼2 for TA) greater than surface runoff inputs. These substantial SGD inputs likely sustain phytoplankton growth and potentially fuel harmful algal blooms while countering estuarine acidification.

Freshwater is a finite resource, especially in the coastal zones around the world. Managing this precious resource becomes even more important in developing countries with severe water pollution and poor governance, such as those in Asia and Africa. Submarine groundwater discharge (SGD) brings the hydraulic connection between terrestrial groundwater and marine water along the coast and has control over the supply of nutrients and pollutants in the coastal ecosystems. The hydraulic connection of SGD often depends on the local hydrogeological conditions and sociocultural activities, which eventually depend on the awareness of local communities. So, this study explains SGD from different scientific, cultural, and religious points of view, in addition to listing its benefits and marine ecosystem services. It also highlights the role of submarine springs (listed under SGD) in nutrient transport and cycling in the coastal ecosystem. Study results revealed that SGD-mediated discharge of nutrients contains nitrate (NO3), sulfate (SO4), phosphate (PO4), and ammonium (NH4 +) and is also involved in ocean acidification as well if not monitored and maintained diligently. SGD is not important at the continental level, but it is locally significant as it is related to local terrestrial activity along the topography, hydraulic conductivity, and tidal forcing. Thus, this study would allow attention to be directed toward alternative ideas and ways of optimal societal and scientific investment, focusing on their strategies not to harm or pollute the marine ecosystem because of the inadequate sociocultural and scientific understanding of terrestrial freshwater pollution.

Elevated groundwater salinity is unsuitable for drinking and harmful to crop production. Thus, it is crucial to determine groundwater salinity distribution, especially where drinking and agricultural water requirements are largely supported by groundwater. This study used field observation (n = 20,994)-based machine learning models to determine the probabilistic distribution of elevated groundwater salinity (electrical conductivity as a proxy, >2000 μS/cm) at 1 km2 across parts of India for near groundwater-table conditions. The final predictions were made by using the best-performing random forest model. The validation performance also demonstrated the robustness of the model (with 77% accuracy). About 29% of the study area (including 25% of entire cropland areas) was estimated to have elevated salinity, dominantly in northwestern and peninsular India. Also, parts of the northwestern and southeastern coasts, adjoining the Arabian Sea and the Bay of Bengal, were assessed with elevated salinity. The climate was delineated as the dominant factor influencing groundwater salinity occurrence, followed by distance from the coast, geology (lithology), and depth of groundwater. Consequently, ∼330 million people, including ∼109 million coastal populations, were estimated to be potentially exposed to elevated groundwater salinity through groundwater-sourced drinking water, thus substantially limiting clean water access.

Coastal aquifers are hydraulically connected to the sea and a storm (cyclone/hurricane) can disrupt the surface water-groundwater (SW-GW) interaction process which is largely unexplored. Thus, this study aims to explore the impact of storm surges (both positive and negative) on coastal aquifers, focusing on pollutant mobilization, groundwater level (GWL) fluctuations, and solute concentration (Salinity, Cl-) and subsequent re-stabilization based on pre-existing studies from the coast of USA and India through a systematic review process. The outcome of this study revealed that there is a positive relationship between cyclonic speed, rainfall, storm surge height and GWL in lithologically conductive aquifers. Positive surge raises GWL, salinity and transportation of surface contaminants into groundwater while negative surge induces fall in salinity, and accelerates submarine groundwater discharge and exports contaminants/nutrients to sea. The restabilization of SW-GW interaction dynamics is case dependent, which takes a week to month to years, and is dependent on local hydrogeology and intensity of storm. So, the study recommends prioritizing to safeguard the coastal groundwater otherwise increasing storms will lead to questions on freshwater sustainability and coastal ecosystems in present climate change scenario.

Groundwater salinization of coastal aquifers as a result of climate change and anthropogenic activities is a widely acknowledged phenomenon. Sundarbans, in India is one such area where this phenomenon is noticed at an unprecedented rate making drinking water unpotable for consumption. Studies identifying the prime drivers causing this detrimental phenomenon are limited as the existing studies explicitly lack analyzing the holistic view. Building on this gap, this study aims to conduct a systematic literature review and identify the list of drivers that are promoting groundwater salinization. The influence of wide range of parameters depicting the climate change i.e., varying rainfall pattern, sea level rise (SLR), El Nino-Southern Oscillation (ENSO) and tropical cyclones (TC) on qualitative and quantitative variations in the groundwater at various temporal scales is studied with the help attributes collected from literature. The study reveals a significant drop in groundwater levels (GWL) between 1996 and 2017. This depletion is noted to be primarily attributed to variations in the Indian Ocean Dipole (IOD) and El Niño Southern Oscillation (ENSO), affecting rainfall patterns and recharge rates. During tropical cyclones, GWL rapidly raised, while it is noted that the groundwater quality is sensitive to ENSO. Sea-level rise, changing rainfall patterns, and increasing population density exacerbate groundwater salinization. Existing sources of water, i.e., shallow aquifers exhibit high salinity, and deep aquifers exceed permissible limits. The study evidences the needs to address drinking water scarcity and potential migration resulting from these complex interactions between climate, population, and groundwater management.

The Sundarbans represent the largest mangrove system on Earth, covering >10,000 km2. These mangroves can export a vast amount of aquatic carbon that can be potentially sequestered for millennia. However, the mechanisms that drive these processes remain poorly constrained. Here, we estimate porewater-driven carbon exchange between the Sundarbans and the Bay of Bengal using high-resolution time series and a radon groundwater mass balance approach spanning a neap-spring tidal cycle. Submarine groundwater discharge (SGD) increased from neap to spring tides by 352 % up to a maximum of 65.6 cm d−1 largely driven by creek bank overtopping after the mid-tide. Exports of dissolved organic and inorganic carbon and alkalinity doubled between neap and spring, likely due to the ‘first flush’ of older porewater in the mangrove flats. Groundwater discharge was a significant driver of the net carbon export, contributing up to 86.7 % of DIC and 74.0 % of alkalinity during the spring tide while contributing a lower proportion of DOC (4 %–23 %). If these results are representative of the Sundarbans more broadly, carbon fluxes from the Sundarbans would be more than an order of magnitude higher than some of the world's largest rivers on an areal basis, highlighting the importance of Sundarbans mangroves to global oceanic carbon budgets.

Microplastics (MPs) have already been detected in various environmental matrices like soil, sediment, and surface water, and recently in groundwater also. The occurrence of MPs in groundwater depends up on the transportation through recharge and may controlled by source and local hydrogeology, and partly on the process of surface water-groundwater interaction (SW-GW). Based on the available studies, we intended to establish a hypothetical overview on the source and process-dependent occurrence of MPs in groundwater across terrestrial and coastal aquifers. Groundwater recharge from agricultural stagnant water, losing streams near dumping sites and agricultural fields, effluents from wastewater treatment plants, septic system failure etc. are the potential sources of MPs in groundwater. The factors like sea level rise and tidal pumping are among the major factors which may control the migration of MPs in coastal aquifer along with the physical and chemical properties of the aquifer media. These MPs have another ecological concern as they can adsorb persistent organic pollutants as well as heavy metals and transfer them to animal tissues through food chain. Studies are being conducted mainly focusing the MP contamination in surface water, marine environment and soil, and very limited studies are available to address the source of MPs in groundwater. However, no such study has been done on the existence, profusion, or environmental factors that contribute to MP pollution in the groundwater in relation to the present climate change scenario. Understanding the extent of MP contamination in groundwater systems is necessary for developing effective management strategies and minimizing their impact on the environment and human health. This study focusses on the source along with the controlling factors of the migration of MPs towards groundwater including the effect of climate change.

The role of submarine groundwater discharge (SGD) in transporting terrestrial-sourced arsenic (As) to the global oceans is not well documented. In the present study, executed on a coast adjoining the extensive groundwater As-contaminated Ganges river delta, we hypothesize that As-enriched groundwater discharges to the adjoining Bay of Bengal (BoB) through SGD flow paths. We conducted high-resolution, field-based investigations and thermodynamic modeling to understand the SGD-sourced As discharge and geochemical cycling of As and other redox-sensitive solutes along the discharge path under varying redox conditions and water sediment interactions. The As distribution and other solutes were measured in a series of multi-depth observation wells and sediment cores, extending from the high tide line (HTL) to 100 m toward the sea, for pre- and post-monsoon seasons. Results reveal the presence of a plume carrying up to 30 μg/L dissolved load of As toward the sea. Arsenic is associated with a plume of Fe and exhibits similar shore-perpendicular variability. Arsenic distribution and transport is controlled by the Fe-Mn redox cycle and influenced by terrestrial groundwater discharge. Field-observations and geochemical modeling demonstrate that Fe-hydroxide precipitates in the subterranean estuary and acts as an interim sink for As, which is eventually mobilized on alteration of geochemical conditions with the season. Fluctuating plume size can be attributed to seasonal variation in fresh groundwater input to the site. Estimates indicate up to 55mg/m2/d As is released to BoB from the site. Based on physicochemical observations this study demonstrates the yet to be studied SGD derived As cycles and the role of SGD dynamics in controlling the fate of redox-sensitive contaminants and their discharge into global oceans.

The conversion of CO2 to a sole carbonaceous product using photocatalysis is a sustainable solution for alleviating the increasing levels of CO2 emissions and reducing our dependence on nonrenewable resources such as fossil fuels. However, developing a photoactive, metal-free catalyst that is highly selective and efficient in the CO2 reduction reaction (CO2RR) without the need for sacrificial agents, cocatalysts, and photosensitizers is challenging. Furthermore, due to the poor solubility of CO2 in water and the kinetically and thermodynamically favored hydrogen evolution reaction (HER), designing a highly selective photocatalyst is challenging. Here, we propose a molecular engineering approach to design a photoactive polymer with high CO2 permeability and low water diffusivity, promoting the mass transfer of CO2 while suppressing HER. We have incorporated a contorted triptycene scaffold with “internal molecular free volume (IMFV)” to enhance gas permeability to the active site by creating molecular channels through the inefficient packing of polymer chains. Additionally, we introduced a pyrene moiety to promote visible-light harvesting capability and charge separation. By leveraging these qualities, the polymer exhibited a high CO generation rate of 77.8 μmol g−1 h−1, with a high selectivity of ∼98% and good recyclability. The importance of IMFV was highlighted by replacing the contorted triptycene unit with a planar scaffold, which led to a selectivity reversal favoring HER over CO2RR in water. In situ electron paramagnetic resonance (EPR), time-resolved photoluminescence spectroscopy (TRPL), and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) techniques, further supported by theoretical calculations, were employed to enlighten the mechanistic insight for metal-free CO2 reduction to exclusively CO in water.

Access to clean water has been identified as one of the primary Sustainable Development Goals. Rapid urbanization is going on in developing nations creating additional pressure on water resources in most of these places which in turn also affects individuals which is largely reliant on proper sanitation and drinking water quality. In addition, open sanitation practice is becoming major public health problem in rural and in some urban areas in India. Groundwater contamination by pathogenic bacteria sourced from both sanitation system and surface water is becoming one of the major concerns now-a-days. The residents of the Ganges river basin in India are already stressed with natural arsenic pollution as well as other various types of water pollution, and microbial pollution from sanitation is a new addition to it. A field-based hydrogeological investigation with the identification of sanitation sites (surface and subsurface) was conducted in some parts of the Ganges basin, in and around a lower order distributary river, River Churni in West Bengal state, to identify the natural and human influences on sanitation drinking water pollution in a highly populated part of South Asia. Groundwater was found to be contaminated severely with total (TC) and fecal (FC) coliform bacteria. The abundance of TC was found to be the highest in monsoon season (78%) than in pre-monsoon (48%) and post-monsoon (29%) seasons. The results revealed that the groundwater samples from shallow depths and close to sanitation sites were highly contaminated with coliform bacteria than the deeper and higher distant (>30 m distance) ones. Shallow groundwater samples near to surface water (River Churni) source, other than sanitation sites, showed elevated TC levels. The occurrence of coliform bacteria in studied groundwater samples was observed to be positively correlated with conductivity, TDS, TOC, chloride, and sulfate, while the abundance was restricted by pH and temperature of groundwater. Thus, improper sanitation systems and contaminated surface water were identified as one of the major sources of pathogenic contamination of groundwater-sourced drinking water in the studied area, whereas improper human practices further complicate the scenario which needs to be managed properly.

The groundwater of the coastal aquifers, the primary source of drinking water for the community around it, is under stress due to changing climatic conditions, extreme climate events, over-exploitation, and natural/anthropogenic interferences. To sustain coastal groundwater, it is essential to understand the hydrogeological control on the distribution of salinity and submarine groundwater discharge (SGD) in various spatial and temporal scales at different depths. This study is focused to delineate the SGD and salinity distribution for shallow surficial and deep aquifers by application of the hydrogeochemical and geophysical approach in an intertidal zone. The resistivity [Electrical Resistivity Tomography (ERT), Vertical Electrical Sounding (VES)] and Ground Penetrating Radar (GPR) data show surficial aquifers have (up to 1.5 m below ground level (m bgl)) have higher freshwater discharge at the post-monsoon season and recirculation of infiltrated brackish water with increasing offshore distances. The re-circulated seawater in distant offshore was also predominant for intermediate (>1.5 up to 100 m bgl) (brackish water-saturated) and deeper depths (>100 m bgl) (fresh groundwater), which is observed from the distinct resistivity contrasts from VES. The interaction process for all the depths with seawater has been induced by the coastal hydrodynamics, meteoric recharge, and fluctuation of groundwater levels. However, variations of resistivity and sounding data delineate that the groundwater resources underneath the shallow depth brackish water are physically vertically disconnected from the surficial aquifer, but spatial variation in sounding data shows the hydraulic connectivity, which would lead to a serious concern for fresh groundwater resources, where density-dependent transportation of solute is plausible, both vertically and horizontally.

Extreme weather events, such as tropical storms and hurricanes, are known to deliver large amounts of freshwater (surface runoff) and associated inorganic and organic nutrients to estuaries and the coastal ocean, affecting water quality and nutrient budgets. However, while Hurricane Harvey produced an unprecedented 1,000-year flood event in 2017 that inundated areas north of the landfall, like the Houston/Galveston region (Texas, United States), the impact on the Corpus Christi area, south of the landfall, was an intermittent negative surge (∼0.5 m below mean sea level (MSL)), caused by the southerly direction of winds and limited freshwater inflows. With the use of pre- and post-landfall surface-water, porewater, and groundwater nutrient measurements and dissolved organic matter (DOM) molecular characterization analyses, this study assessed the influence of negative storm surge on groundwater–surface water interactions and nutrient composition. Within 2 weeks following the first landfall, the forms and inputs of inorganic and organic nutrients fluctuated significantly nearshore Corpus Christi Bay. Sudden drops in sea level were correlated with pulses of NH4+ and disproportionately more dissolved organic carbon (DOC) than dissolved organic nitrogen (DON), likely from a carbon-rich groundwater or benthic source with slightly lower labile characteristics. Recovery to MSL drove higher proportions of nitrogenous DOM and lower dissolved inorganic nitrogen (DIN) inputs. An increased presence of sulfurized DOM derived from anaerobic microbial processing of organic matter mineralization in marine sediments post-landfall was facilitated by enhanced groundwater inputs and flushing of porewater due to considerable drops in sea level and steepening hydraulic gradients toward the coast. The induced pulses of higher groundwater advective fluxes are also hypothesized to have intermittently enhanced flushing of anoxic DIN and biodegraded DOM from porewater and groundwater and suggested that dynamic hurricane-induced negative surge events affect net nutrient budgets in estuarine and coastal seas.

The global climate patterns like El Niño Southern Oscillation (ENSO) cycle and Indian Ocean Dipole (IOD) have impacts on surface water quality and groundwater recharge patterns. But the ENSO and IOD impacts on surface water-groundwater (SW-GW) interaction in terms of quality have not been studied. Therefore, the present study was conducted to delineate the impacts of ENSO and IOD on the SW-GW interaction process-induced groundwater quality of coastal aquifers of Sundarbans, by the application of isotopic signature, salinity content of groundwater and seawater in relation to rainfall variability. Study results revealed that the declining trend of rainfall potentially increases the seawater salinity. The rainfall pattern also positively correlates with the groundwater level (GWL) at a 5% level of significance observed from the wavelet analysis. The deficit in rainfall due to the El Niño is the possible reason for the declining GWL, which is giving rise to groundwater salinity. El Niño also affected the nearshore seawater salinity which was increased from 19 to 24 ppT. The study provides a surrogate understanding of the potential impact of El Niño in one of the most climatically vulnerable parts of the planet, while IOD impacts are not conclusive. In the scenario of depleted rainfall amount, groundwater abstraction practices need to be managed, otherwise, it could create a potential threat to the available drinking water resources in the present and future climate change scenarios.

Groundwater depletion has been an emerging crisis in recent years, especially in highly urbanized areas as a result of unregulated exploitation, thus leaving behind an insufficient volume of usable freshwater. Presently Ganges river basin, the sixth largest prolific fluvial system and sustaining a huge population in South Asia, is witnessed to face (i) aquifer vulnerability through surface waterborne pollutant and (ii) groundwater stress due to summer drying of river as a result of indiscriminate groundwater abstraction. The present study focuses on a detailed sub-hourly to seasonally varying interaction study and flux quantification between river Ganges and groundwater in the Indian subcontinent which is one of the first documentations done on a drying perennial river system that feeds an enormous population. Contributing parameters to the total discharge of a river at its middle course on both temporal and spatial scale is estimated through three-component hydrograph separation and end-member mixing analysis using high-resolution water isotope (δ18O and δ2H) and electrical conductivity data. Results from this model report groundwater discharge in river to be the highest in pre-monsoon, that is, 30%, whereas, during post-monsoon the contribution lowers to 25%; on the contrary, during peak monsoon, the flow direction reverses thus recharging the groundwater which is also justified using annual piezometric hydrographs of both river water and groundwater. River water-groundwater interaction also shows quantitative variability depending on river morphometry. The current study also provides insight on aquifer vulnerability as a result of pollutant mixing through interaction and plausible attempts towards groundwater management. The present study is one of the first in South Asian countries that provides temporally and spatially variable detailed quantification of baseflow and estimates contributing parameters to the river for a drying mega fluvial system.

The coastal aquifers of Sundarbans, an UNESCO world biodiversity heritage site, are highly vulnerable due to changing climatic conditions, intensification and increasing frequency of extreme climate events and uncontrolled abstraction of groundwater. The exchange of solutes between hydraulically connective shallow and deep aquifers, the seawater intrusion and the role of growing population are poorly understood in the Sundarbans. This study aims to address the solute exchange (Cl−, Sr2+, and salinity) process between surface water and groundwater (SW-GW) at local to regional scale under variable hydraulic head conditions, where annual rainfall is declining and population density is increasing [population 573 (1991) to 819 (2011)/Km2]. Electrical resistivity tomography (ERT) in combination with salinity and δ18O data was used to address the exchange of solutes between SW-GW in a hydraulic continuation. The results revealed that regionally, the Cl− concentration of Sundarbans shows an increasing trend (average 329–351 mg/L) with declining groundwater levels (⁓3 m). Local, depth-dependent study depicting there is a predominant exchange of Sr2+ between shallow depth [D1: 14–25 and D2: 30–50 m below ground level (m bgl)] with seawater (Sr2+: 30–85 μM), which is possibly absent at greater depths (D3:115 and D4: 333 m bgl). The recorded Sr2+ content ranged from 25 to 102 and 16 to 78 μM for shallow depth D1 and D2, respectively, whereas, the Sr2+ concentrations ranged from 1.4 to 6.8 and 1.2 to 5.7 μM for D3 and D4, respectively. The ERT data showed progressively increasing resistivity with increasing depth, similar to high salinity and enriched δ18O at shallow depths and depleted δ18O with low salinity at higher depth reflects the continuous distribution of solutes, which is possibly a result of local downward migration of contaminated shallow brackish water within this physically disconnected zone. The lateral and vertical transportation of solutes in variable hydraulic head conditions would be a measure of drinking water threat in present-day and in imminent future for millions of inhabitants near the coastal area.

Groundwater resources in South Asian cities are facing immense stress due to over-extraction leading to environmental, social and economic instabilities. The perennial mega rivers of Himalayas form the lifeline for South Asia, underpinning food and water security for a large population both directly and indirectly through exchange with groundwater systems. The present study delineates the spatio-temporal variation in patterns and processes of sub-hourly to annual-scale hydrological exchanges between the Ganges and its adjoining highly exploited aquifer in a urban-peri urban reach. Multivariate statistical analyses established river water-groundwater interaction in this region with ~40% loading of first principal component, i.e river water during monsoon on the shallow aquifer. The part of the aquifer detached from the main confined aquifer show an influence of precipitation (the second principal component) with loading of ~90%. Again the part of the aquifer suffering infiltration of local surface water bodies show effect of precipitation with a second principal loading of ~80%. Fourier transformation is used in the hydrograph to remove influence of heavy urbanization on the hydrographs. This study proves that the phenomenon of infiltrating river water during monsoon plays a primary role in controlling aquifer storage although contaminating the aquifer simultaneously. However, during pre and post-monsoon the flow path reversal helps in maintaining river baseflow. Cross-correlation between the river and piezometric series show increased delay of pressure head propagation of the infiltrating river waterfront, with increasing distance. These observations are also substantiated by stable isotope signatures. The present study provides an understanding of potential groundwater vulnerability resulting from waste water and irrigational contamination through river water intrusion which would eventually lead the government to implement proper water and environmental management policies towards availability of long-term sustainable water resources for the residents.

Coastal regions are the residence of an enormously growing population. In spite of rich biodiversity, coastal ecosystems are extremely vulnerable due to hydroclimatic factors with probable impact on socio-economy. Since the last few decades, researchers and policymakers were attracted towards the existing water demand–resource relationship to predict its future trends and prioritize better water resource management options. Water Evaluation And Planning (WEAP) serves the wholesome purpose of modeling diverse aspects of decision analysis using water algorithm equations for proper planning of water resource management. In this study, future groundwater demand (domestic, agricultural, and livestock sector) in the fragile Sundarbans ecosystem was estimated considering different human population growth rates (high, low, and current) for 2011–2050. The results showed that the sustainability of coastal aquifer-dependent rural livelihood is expected to face great danger in the near future. The total groundwater demand is expected to rise by approximately 17% at the current growth rate in the study area to fulfill the domestic and agricultural requirement, while this value goes up to around 35% for a higher growth rate and around 4% for a lower growth rate. The impact of increasing groundwater demand was analyzed further to identify any socio-economic shifts in this region.

Groundwater level (GWL) of coastal aquifers are strongly influenced by the ocean tide at sub-daily to seasonal scale. Similarly, GWL are influenced by storm induced ocean wave surge lasting few hours to a day. There has not been a detailed study on the conjunctive impact of such tidal and storm waves on coastal groundwater and its vulnerability. Through our coastal and field-laboratory observations at one of the world's most extreme climate affected regions, the Ganges river mega-delta, we delineate the influence of ocean wave surge impacts on the shallow (<24 m below ground level [m bgl]) and deep (115 m bgl) aquifers GWL. Our study on the multi-layered delta-front aquifers, adjoining the tropical BoB shows that the high-temporal resolution GWL fluctuation due to wave surges are instantaneous, rapid and synchronous at all depths of the aquifers. The potential rise of ocean waves caused by tropical cyclone Bulbul (November 2019) significantly increases the GWL, both in shallow and deeper aquifer. Using multivariate statistics and machine learning techniques, we have attempted to quantify the rise of GWL during each of the ocean wave surge event. The model shows good predictability for deeper groundwater, however it is unable to quantify the shallower GWL of each of the ocean wave surge during storm events. Such phenomenon indicates aquifer vulnerability, thereby posing an emerging threat to drinking water availability to millions of groundwater-dependent inhabitants in coastal areas, globally, which may rapidly intensify with increasing rates of tropical cyclones and sea level rise in recent times and impending future.

The present study is undertaken in the eastern coast of India, along the coastal tract of Bay of Bengal (BoB), to delineate the submarine groundwater discharge (SGD)-borne nutrient flux at temporal scale and their impact to coastal ecology and biogeochemical processes. Solutes chemistry, seepage meter study, stable-isotopic signature, and geophysical techniques were used to identify the surface water–groundwater interaction zone, SGD rate and nutrient flux. The estimated rate of major annual discharge of nutrient fluxes were 240 and 224 mM m−2 day−1 for NO3 − and Fetot. The variation of solute and nutrient fluxes was depending on the load of terrestrial water masses, which is triggered by the local monsoonal meteoric recharge. The ecohydrological response to this solute flux results in spatio-temporal patterns of N and P-sensitive algal blooms in the intertidal zones. Most algae were identified as dinoflagellates and some haptophytes, with greenish and brownish hue that provides a distinct look to the coastal landscape. The algal blooms were found to be substantially influenced by the seasonal-nutrients flux and discharge location. Our study is expected to increase the understanding of a rarely reported eco-hydrological response to terrestrial–marine water interactions and their implications in the tropical ocean adjoining the Indian Subcontinent.

Worldwide, >2 billion people (~1/3 world population), mostly living in economically stressed areas of Africa and South Asia, still do not have access to basic sanitation, and ~1 billion still practice open defecation. Water pollution due to open defecation may primarily be linked to economy, and other factors such as social and hygiene practices, land use and hydrogeological parameters could also have sufficient influence. The present study describes the effect of human development index (HDI, 2001–2015) and economic development (NL, 1992–2013) on groundwater microbial pollution (FC, 2002–2017) across India. Economic development pattern suggested discernable inverse relationship with FC in most areas, although areas with inferior water quality, improper human practices were found to outweigh economic development. Vulnerability modelling, using these data, along with measured FC in groundwater-sourced drinking water locations (n = 235) demonstrated the heterogeneity of FC distribution potential in areas of homogenous economy, social practices, and land use. High-resolution numerical modelling of the advective transport of the hypothetical FC particles in the aquifers, suggest up to ~24 times faster movement of pollutants under irrigation-induced pumping regimes. Hence, the results of our study highlight and quantify the potential pitfalls that are possible hindrance for achieving the United Nations sustainable development goal, despite social and economic development, across the spatial scales.

The groundwater of the Western Bengal basin is found to be polluted by various non-point sourced contaminants. A significant increase in anthropogenic activities subsequently affects water quality. This study is the first attempt to evaluate the groundwater vulnerability to pesticide pollution due to anthropogenic activities across the Western Bengal basin. Pesticide concentration of 141 wells for three consecutive years (2012 - 2014) was collected and data were acquired from West Bengal Pollution Control Board (WBPCB). Based on seven hydrogeological parameters groundwater specific vulnerability was assessed. The vulnerability to pesticide pollution across the Western Bengal basin was again validated with analyzed pesticide concentration for 235 wells for 2014–2016. The agricultural prone region of the study area is highly susceptible to pesticide pollution. The spatiotemporal trend of different pesticides suggests the basin is more vulnerable to insecticides such as malathion than that of herbicides. The application of pesticides influences mostly the spatio-temporal variability of pesticide concentration in groundwater of shallow aquifer across Western Bengal basin; however, the natural hydrogeological setting of this area is one of the most influential parameters which impact the pesticide infiltration onto aquifer. Depth to the water table is the most sensitive parameter which showed a significant impact on pesticide concentration in groundwater. Vulnerability assessment across different land-uses helps the decision-makers to improve water quality.

Submarine groundwater discharge (SGD) acts as major pathway to transport solute-laden terrestrial-sourced fresh groundwater, as well as re-circulated marine water to the global oceans. The study area, Bay of Bengal (BoB), a part of the Indian Ocean, receives one of world's highest terrestrial riverine fresh water discharge, sediment and solute flux from the adjacent Himalayan and cratonic South Asia. Thus, together with the monsoon-dominated tropical climate, it forms one of the most complicated, productive and interactive global hydrological systems. However, understanding such topical phenomena needs intricate mechanistic understanding, based on high resolution data, which are barely available from the BoB. Delineation of stable isotopic and chemical signature of hydrologic-sourced components in the SGD to the BoB would help to identify the intra-annual to diurnal-scale impact of seasonality and tidal cycles, as well as interactions with other surface water bodies. This study provides one of the first documentation of such high-resolution, temporally-variable, stable isotope patterns of SGD in coastal systems of the BoB, and possibly of any tropical ocean. During post-monsoon season, the discharging groundwater was observed to have depleted δ 18 O (ranges −2.12‰ to −4.19‰) and low Cl − concentrations (745 to >11,500 ppm) (seepage water), which is closely associated with the groundwater δ 18 O composition (−3.18‰ to −4.05‰) and Cl − content (775 to >5900 ppm) range. In pre-monsoon season depleted δ 18 O values suggests that regional groundwater contributes up to 45 m from high tide line (HTL) (up to 88%), and re-circulated seawater-sourced SGD dominates 45 m to 110 m (extent of study transect) offshore. In post-monsoon season, terrestrial-sourced groundwater predominates the SGD composition (up to 99%) till 110 m. Changes in δ 18 O and Cl − content, in pre-monsoon season indicates enhanced infiltration of seawater in the seepage face, due to lower terrestrial-sourced freshwater discharge, whereas, in post-monsoon terrestrial-sourced, resident freshwater dominates in the seepage face. The study suggests that SGD are sourced to interactions between local-regional hydrological systems, and do reflect their compositional variability. It also provides insight of influencing physico-chemical mechanisms, ranging from seasonal to daily-tidal time-scales. The outcome of this study thus may provide intricate insights in delineating the coastal hydrologic and biogeochemical processes, as well as detecting, carbon sinks, nutrient sources and primary productivity in a tropical ocean.

With increasing population and urbanization in the deltas across global mega-river basins, groundwater stress is increasing due to changing ocean-land disposition, hydroclimatic extremes, over-exploitation and natural/anthropogenic contamination. Such change in coastal hydrodynamic process makes an impact in to the resilience of groundwater-sourced drinking water vulnerability. The groundwater responses studied in this work in the ecologically-vulnerable, UNESCO World Heritage site of the Sundarbans delta-front aquifers at the river Ganges-Brahmaputra mega delta, demonstrate a unique example of such intricacies and complexities. High-resolution, temporal, depth-dependent hydraulic connectivity and hydrochemistry was studied for this complex, climate-driven, tidal-induced hydrological interactions between surface water (seawater of Bay of Bengal [BoB] and Ganges river water) with shallow and deep groundwater by stable isotopic (δ18O and δD) signatures and piezometry. A wide range of salinity content and δ18O composition of groundwater samples for 14–25 (salinity: 3–45 ppT, δ18O: −3.63 to −1.15‰) and 30–50 meter below ground level (mbgl) (salinity: 5–25 ppT, δ18O: −3.41 to −1.34‰) was recorded, while, comparatively, a narrow range of temporal variability was observed for the depths of 115 (salinity: 1–4 ppT, δ18O: −5.04 to −2.15‰) and 333mbgl (salinity: 1 to 3 ppT, δ18O: −4.43 to −2.81‰). Study results revealed that vertical transport of solute has been induced by coastal hydrodynamics. However, human interferences, in terms of groundwater abstraction and land use-land cover change (e.g. brackish aquaculture) do have substantial impact on evolving groundwater response, thereby impacting resilience to drinking water option in this densely populated area. Fluctuations of groundwater level in relation with δ18Ogw composition showed shallow depths (14–50 mbgl) are hydraulically connected by local flow and conducive of chemical exchanges. The deeper groundwater (115–330 mbgl depths) flow suggests regional-scale hydraulic connections along flow paths. In-spite of sub-meter scale seasonal groundwater level changes, salinity variability is observed between 1 and 4 ppT at >100 mbgl depths, suggest mixing between chemically-distinct water reservoirs, conserving hydraulic mass-balance. However, such observation suggests severe implications for groundwater vulnerability, which might aggravate with future intensification of irrigational abstraction, as well as with changing hydroclimatological regime and extreme events. Thus, future planning and management strategies of sustainable supply of safe water in such ecologically-sensitive groundwater systems need to incorporate such dynamic chemical evolution.

Submarine groundwater discharge (SGD) introduces solute and nutrients to the global oceans, resulting in considerable nutrient cycling and dynamics in the coastal areas. We have conducted high-resolution, spatio-temporal, lunar tidal cycle patterns and variability of discharged solute/nutrient assessment to get an overview of seasonal nutrient flux to the Bay of Bengal in eastern parts of the Indian subcontinent. Whereas the premonsoon season SGD was found to be dominant in the marine influence (M-SGD), the postmonsoon season was found to be predominated by the terrestrial component of SGD (T-SGD), extending from coast to near offshore. The solute fluxes and redox transformation were found to be extensively influenced by tidal and diurnal cycles, overlapping on seasonal patterns. We have assessed the possible role of SGD-associated solute/nutrient fluxes and their discharge mechanisms, and their associated temporal distributions have severe implications on the biological productivity of the Bay of Bengal. The estimated annual solute fluxes, using the average end-member concentration of the SGD-associated nutrients, were found to be 240 and 224 mM·m−2·day−1 for NO3 − and Fetot, respectively. Together with huge freshwater flux from the Himalayan and Peninsular Indian rivers, the SGD has considerable influence on the bay water circulation, stratification, and solute cycling. Thus, the observation from this study implies that SGD-associated nutrient flux to the Bay of Bengal may function as a nutrient sink, which might influence the long-term solute/nutrient flux along the eastern coast of India.

Identification of tree species that can biologically monitor air pollution and can endure air pollution is very much important for a sustainable green belt development around any polluted place. To ascertain the species, ten tree species were selected on the basis of some previous study from the campus of the University of Burdwan and were studied in the pre-monsoon and post-monsoon seasons. The study has been designed to investigate biochemical and physiological activities of selected tree species as the campus is presently exposed to primary air pollutants and their impacts on plant community were observed through the changes in several physical and biochemical constituents of plant leaves. As the plant species continuously exchange different gaseous pollutants in and out of the foliar system and are very sensitive to gaseous pollutants, they serve as bioindicators. Due to air pollution, foliar surface undergoes different structural and functional changes. In the selected plant species, it was observed that the concentration of primary air pollutants, proline content, pH, relative water holding capacity, photosynthetic rate, and respiration rate were higher in the pre-monsoon than the post-monsoon season, whereas the total chlorophyll, ascorbic acid, sugar, and conductivity were higher in the post-monsoon season. From the entire study, it was observed that the concentration of sulfur oxide (SOx), nitrogen oxide (NOx), and suspended particulate matter (SPM) all are reduced in the post-monsoon season than the pre-monsoon season. In the pre-monsoon season, SOx, NOx, and SPM do not have any significant correlation with biochemical as well as physiological parameters. SPM shows a negative relationship with chlorophyll ‘a’ (r = −0.288), chlorophyll ‘b’ (r = −0.267), and total chlorophyll (r = −0.238). Similarly, chlorophyll a, chlorophyll b, and the total chlorophyll show negative relations with SOx and NOx (p < 0.005) during the post-monsoon season. Proline shows a positive relationship with SOx in the pre-monsoon season whereas in the post-monsoon season proline content shows a positive relationship with both SOx and NOx. The present study facilitates to screen eight sensitive and two moderately tolerant tree species according to their air pollution tolerance index (APTI) values.

Fluoride contamination and other physicochemical parameters in groundwater of Simlapal block of Bankura district were investigated. A total of 50 deep tube well (DTW) samples were collected from 18 villages of Simlapal. The higher concentration of iron values was recorded, 9.40 mg/L with an average value of 2.11 mg/L. Drastically, 58 % of water samples exceed the permissible limit of 1.5 mg/L (Guidelines for drinking water quality, World Health Organization, Geneva, 2004). Spatial distribution of F− (Guidelines for drinking water quality, World Health Organization, Geneva, 2004) concentration classes is represented by the simple Inverse Distance Weighting (IDW) interpolation method. The affinity between the pH and F− in groundwater suggests the dissolution of fluoride-bearing minerals in groundwater. Furthermore, the pH has a good positive correlation with HCO3− (r = 0.224). This indicates a prevailing condition of alkalinity (caused by HCO3 only here) in the groundwater, which promotes a mineral dissolution. The F− shows a significant positive correlation with pH (r = 0.313, p < 0.05) and HCO3− (r = 0.224), while it has a negative correlation with Ca and Mg ions (r = −0.225 and −0.226). PCA accounts for 74.21 % of the variability for the first four components. F1 values have high loading (32.71 %), second component (F2) exhibits 19.98 %, third component (F3) shows 12.74 %, and fourth component (F4) shows only 8.72 % of the total variability to justify the significant correlation between chemical constituents. In terms of quality of water, sodium adsorption rate (SAR) showed that all the samples are from the group of excellent to good. With respect to permeability, sodium percentages show that 18 % are permissible but doubtful and 2 % are unsuitable for irrigation purposes.

Color is the main attraction of any fabric industry. No matter how excellent its constitution, if unsuitably colored it is bound to be a failure as a commercial fabric. Manufacture and use of synthetic dyes like methylene blue (MB) for fabric dyeing has therefore become a massive industry today. Soil is widely used as adsorbent for removing toxic pollutants from their aqueous solutions due to its wide availability and cost efficiency. In this work, the feasibility of employing calcareous soil to remove MB, a cationic dye from its aqueous solutions was investigated. The entire process has been done through batch operation. Percentage removal was greater for dilute solutions, but the absolute amount of MB adsorbed by the calcareous soil at equilibrium increased with an increase of the initial concentration. The kinetics of the adsorption process was analyzed by pseudo-first-order, pseudo-second-order, intraparticle diffusion, surface mass transfer, and Elovich models. The first four mechanisms seem to be significant in the rate controlling step. Equilibrium adsorption was investigated by Freundlich, Langmuir, Temkin, and D-R isotherms. The Langmuir equation (R2 = 0.982) fitted to equilibrium data better than all the tested isotherm models. The dimensionless separation factor (RL) was low (0.00007) indicating favorable adsorption of MB on to calcareous soil. Thermodynamic activation parameters such as ΔS°, ΔG°, and ΔH° were also calculated and results revealed that the adsorption process is a favorable exothermic and can be spontaneous in nature. Finally, it can be concluded that calcareous soil can be an effective low-cost adsorbent for removal of cationic dye from waste effluents.

There has been growing public concern about intellectual performance of children at high levels of fluoride exposure. A cross-sectional study was conducted in Simlapal Block of Bankura District, West Bengal, to find out the relationship between fluoride (F) exposure as exposure dose (ED) with dental fluorosis (DF), urinary fluoride concentration (UF), intelligence quotient (IQ) and body mass index (BMI). Fifty groundwater samples were collected from the target area. One hundred forty-nine children belonging to age group 6 to 18 years were considered for this study. Experimental results reveal that mean F− concentration of that area is 2.11 mg/L (±SD 1.64). On the basis of F concentration in groundwater and water consumption pattern, ED was calculated to explore the impact of F− on DF, UF, IQ, and BMI. Paired t test results suggest that exposure rate of F does not show any significant differences (<0.05) among the children of 12 different places. As a result of F exposure, DF cases are mostly found in the order of moderate > severe > mild > very mild > questionable > normal conditions. The highest UF concentration was recorded as 17 mg/L, but the status of DF in the affected children was recorded as moderate. The results also reveal that ED has a positive correlation with DF (r = 0.299, P < 0.01) and UF (r = 0.513, P < 0.01) and a negative correlation with IQ (r = −0.343, P < 0.01) along with BMI (r = 0.083, non-significant). Therefore, from this study, it may be concluded that UF and DF concentration could act as a biomarker of fluoride toxicity.

The present study was conducted in some randomly selected area of Malda and South Dinajpur district of West Bengal to find out the level of fluoride in groundwater and its association with other inorganic constituents through statistical modeling and chemical indices. Results revealed that the considerable variation of different parameters, among them 7.90% sample showed F- levels beyond the WHO recommended value. Moreover, F- shows positive correlation with Na+ (p < 0.467*) and negative correlation with Ca2+ (p < -0.289) which is again well supported by factor analysis study. From the results of Multiple linear regression model and piper diagram revealed the significant relationship of F- with Na+, alkaline pH and Ca2+ and dominancy of F- due to high Na-HCO3 enrichment respectively. The higher level of F- in groundwater is the consequence of fluoride containing sedimentary rock weathering.

Soils play a key role in various hydrological and meteorological applications. The objective of this paper is to analyze the spatial variability of very high resolution (3.3 m) RISAT-1 (5.35 GHz) data with surface soil parameters to produce soil moisture retrieval model. The behaviors of the RISAT-1 signal were analyzed for two configurations, RH and RV at high incident angle (48.11°), with regard to several soil conditions: volumetric moisture content (Mv), root mean square surface roughness (r.m.s.) and soil composition (texture). The relationship between the backscattering coefficient (σ°) and the soil parameters (moisture, surface roughness and texture) was examined by means of satellite images, as well as ground truth measurements, of each of the 23 plots, recorded during several field campaigns in the January 2015. RISAT-1 images demonstrate high potential for the identification of local variations of soil dielectric constant (ε), texture and Mv. σ° has a positive relationship with Mv both for σ° (RH) and σ° (RV) with R2 = 0.588 and R2 = 0.525. The roughness component was derived in terms of r.m.s. having a positive correlation with σ° (RH) (R2 = 0.009) and σ° (RV) (R2 = 0.029). Dielectric constant (ε) has a positive relationship with σ° (RH) having R2 = 0.656 and σ° (RV) having R2 = 0.534. By considering all the major influencing factors (σ° (RH), σ° (RV), ε and r.m.s.) a semi-empirical model has been developed, where Mv is a function of σ° (RH), σ° (RV), ε and r.m.s. This model has adjusted R2 = 0.956 and RMSE = 0.010 at 95% confidence level.

Objective: To synthesize and characterize silver nanoparticles from aqueous root extract of Parthenium hysterophorus (P. hysterophorus) and also to evaluate the potentiality of synthesized silver nanoparticles as larvacidal agent against Culex quinquefasciatus (Cx. quinquefasciatus). Methods: The silver nano particles were generated using root extract of P. hysterophorus. The characterization of synthesized nanoparticles was done by visual color change, UV-Vis spectrum, scanning electron micrograph, fluorescent microscope and Fourier transform infrared spectroscopy. Results: It was found that aqueous silver ions can be reduced by aqueous root extract of P. hysterophorus to generate extremely stable silver nanoparticles in aqueous medium. Larvae were exposed to varying concentrations of plant extracts, aqueous silver nitrate solution and synthesized silver nanoparticles for 0, 24 and 48 h separately. Aqueous root extract showed moderate larvicidal effects; however, the maximum efficacy (60.18%) was observed with the synthesized silver nanoparticles against the larvae of Cx. quinquefasciatus. Conclusions: These results suggest that the green synthesis of silver nanoparticles have the potential to be used as an ideal eco-friently approach for the control of the Cx. quinquefasciatus. This is the first report on the mosquito larvicidal activity of the nano particle synthesized by P. hysterophorus. © 2014 Asian Pacific Tropical Medicine Press.

Arsenic in drinking water has been recognized as a serious community health problem because of its toxic nature and therefore, its removal is highly essential. A series of adsorption experiments (batch and column) were performed utilizing iron impregnated sugarcane carbon (Fe-SCC), a composite adsorbent, to remove arsenic from aqueous systems. Under optimized batch conditions, the Fe-SCC could remove up to 94.5% of arsenic from contaminated water. The artificial neural network (ANN) model was developed from batch experimental data sets which provided reasonable predictive performance (R2 = 0.964; 0.963) of arsenic adsorption. In batch operation, the adsorbent dose had the most significant impact on the adsorption process. For column operation, central composite design (CCD) in response surface methodology (RSM) was applied to investigate the influence on the breakthrough time for optimization and evaluation of interacting effects of different operating variables. The perturbation plot depicted that the breakthrough time is more sensitive to initial concentration and adsorbent dose than flow rate. The optimized result obtained from bar plot revealed that the Fe-SCC was an effective and economically feasible adsorbent; whereas more than 93% desorption efficiency showed the reusability of the adsorbent. The high arsenic adsorptive removal ability and regeneration efficiency of this adsorbent suggest its applicability in industrial/household systems and data generated would help in further upscaling of the adsorption process. © 2013 Elsevier Ltd.

A survey was conducted in the remote area of Laxmisagar village of Simlapal Block, Bankura District, West Bengal, India, of the fluoride (F) concentration in ground water and dental fluorosis in children, 66 boys and 83 girls, aged 6 - <8 yr, 8 - 10 yr, and >10 yr. The ground water F concentration range was 0.25-9.30 mg F/L and the mean 2.02 mg F/L. Using Dean's Index, the severity of dental fluorosis tended to increase with age, particularly for girls but the result was not significant (boys: r=0.474, p=0.893; girls: r=0.949, p=0.146). In the >10 yr groups, severe dental fluorosis was present in 15.79% of boys and 35% of girls. Copyright © 2013 The International Society for Fluoride Research Inc.

The objective of the present study was to access the pollutant generated from bio-fuels like bamboo sticks, cow dung, paddy straw, carbon dust cake, gobar gas, jute stick, and mustard stick and synthetic fuel like LPG during cooking in rural villages of Burdwan, West Bengal, India and its fluctuation in living room. The average SO2 released from the fuels was found in the following order: bamboo stick > cow dung > paddy straw > carbon cake >gobar gas > jute stick > LPG > mustard stick; NO2 emission was in the following order : mustard stick > carbon dust cake >paddy straw > cow dung cake > LPG, jute stick > gobar gas > bamboo stick > and SPM was obtained in the following sequence : cow dung cake > bamboo stick > carbon dust cake > gobar gas > LPG > mustard stick > paddy straw > jute stick, respectively. The highest living room to kitchen room (L/K) ratio of SO2, NO2 and SPM was found in LPG, gobar gas, jute stick respectively in 2009 and followed by bamboo stick > paddy straw > jute stick > cow dung cake, respectively in 2010. Results of this study suggest that different fuels released different amount of air pollutants, but more extensive study is needed to confirm the relationship between fuels and released air pollutants. © Triveni Enterprises, Lucknow (India).

High arsenic in natural groundwater in most of the tubewells of the Purbasthali- Block II area of Burdwan district (W.B, India) has recently been focused as a serious environmental concern. This paper is intending to illustrate the statistical modeling of the arsenic contaminated groundwater to identify the interrelation of that arsenic contain with other participating groundwater parameters so that the arsenic contamination level can easily be predicted by analyzing only such parameters. Multivariate data analysis was done with the collected groundwater samples from the 132 tubewells of this contaminated region shows that three variable parameters are significantly related with the arsenic. Based on these relationships, a multiple linear regression model has been developed that estimated the arsenic contamination by measuring such three predictor parameters of the groundwater variables in the contaminated aquifer. This model could also be a suggestive tool while designing the arsenic removal scheme for any affected groundwater. © 2013 Journal of Urban and Environmental Engineering (JUEE). All rights reserved.

Batch and column operations were performed utilizing thioglycolated sugarcane carbon (TSCC), a low-cost adsorbent, to remove As(III) and As(V) from aqueous systems. Under optimized batch conditions, the TSCC could remove up to 92. 7 and 91. 4 % for As(III) and As(V), respectively. An artificial neural network model showed the validity of TSCC as a preferable adsorbent for arsenic [As(III) and As(V)] removal in batch studies. In column operations, removal efficiency increases with increase in influent arsenic concentration and adsorbent dose and decreases with increase in flow rate. At an adsorbent dose of 6. 0 g, flow rate 3. 0 mL min-1, and initial arsenic concentration 1,500 μg L-1, the arsenic uptake capacity of TSCC for As(III) and As(V) was found to be 85. 01 and 83. 82 μg g-1, respectively. The Thomas model was used to analyze the column experimental data. Results from the column operations indicated that the adsorption behavior of arsenic [As(III) and As(V)] fits exceptionally well with the Thomas model with high correlation coefficient and very low standard error. Examinations of scanning electron microscopy and FTIR spectroscopy reveal that high arsenic adsorption favors surface complexation on the adsorbent surface. © 2013 The Author(s).

Adsorption of fluoride (F) by Aspergillus and Ca-pretreated Aspergillus biomass was conducted in an aqueous batch system and the maximum F adsorption capacities were found to be 8.09 mg/g (at pH 10) and 4.80 mg/g (at pH 8) respectively. For both the Aspergillus and Ca-pretreated Aspergillus adsorbents, the equilibrium isotherm fitted with the Freundlich isotherm and the adsorption kinetics obeyed the pseudo-second order equation. Thermodynamic analysis indicated that the adsorption process was exothermic and spontaneous for both adsorbents. Fourier transform infrared analysis of Aspergillus indicated the existence of potential fluoride-capturing functional groups. © 2013 The International Society for Fluoride Research Inc.

The effects of 4.0, 8.0, 10.0, and 20.0 mM aqueous sodium fluoride (NaF) were studied on Bengal gram seedlings, Cicer arietinum L. A significant decrease (p<0.01) in the physiological growth parameters (root and shoot length, fresh root and shoot weight, dry root and shoot weight, number of primary leaves, and number of root branches) was observed with increasing F concentration after seven days of treatment. However, separate addition of aqueous calcium chloride (CaCl2) to the NaF growth media gave little or only minor improvement in the growth physiology of the seedlings. On the other hand, the pigment, protein, and proline content showed good agreement with F stress, and addition of CaCl2 caused improvement in all biochemical parameters. The concentration of F in the plant body increased with increasing NaF concentration, but maximum reduction of plant body F occurred with the addition of 10.0 mM CaCl2 to the 20mM NaF growth medium. © 2012 The International Society for Fluoride Research Inc.