Groundwater is a vital source of fresh water for drinking and agricultural purposes in the region of Hatiya Island, Bangladesh, yet it is subject to contamination by natural and anthropogenic activities. Over time, the contamination has resulted in a variety of negative effects on human health. This research aims to examine groundwater hydrogeochemical characterization and suitability for irrigation and drinking purposes on different indices utilizing a combined geochemical method, multivariate statistical approaches, and geospatial analysis. Results of hydrogeochemical analyses of 15 groundwater samples from the intermediate aquifer (60–90 m depth) represent the order of cations, anions, and metal concentrations as Na⁺ > Mg²⁺ > Ca²⁺ > K⁺, Cl⁻ > SO₄²⁻ > HCO₃⁻ > NO₃⁻, and Fe > I > Br > Mn > As, respectively. Saltwater intrusion has been determined to be the most important hydrogeochemical process influencing the chemistry of groundwater. Principal component analysis, Pearson’s correlation matrix, and hierarchical cluster analysis indicate that groundwater quality is highly governed by geogenic influences. This information has been evaluated using a drinking water quality index map, which found that six (40%) of the groundwater samples are suitable for human consumption, whereas the other nine (60%) are unfit for drinking. The analysis of irrigation quality parameters revealed that eight (54%) of the groundwater samples are in excellent or good condition for agricultural uses; however, the other seven (46%) samples are unsuitable.

This study aimed to develop a geochemical database by thoroughly analyzing groundwater and sediments from coastal aquifers of southwest Bangladesh. Moreover, we investigated the source of sediment deposition and the mechanisms behind the presence of arsenic and salinity in groundwater. The seasonal distribution patterns of arsenic among the shallow and deep coastal aquifers were found to be 45.12 µg/l and 20.65 µg/l during dry and wet seasons, respectively. Moreover, the groundwater salinity distribution ranged from 3262.88 mg/l to 1930.88 mg/l during the dry and wet seasons. Cored sediment samples showed fine to medium sands of 92%, with silt and clay particles. The petrographic study of authigenic and heavy minerals revealed that the mineral grains were subangular to angular, indicating their textural immaturity of coastal sediments. The reactivity of goethite (FeOOH) and siderite (FeCO₃) minerals suggests that the aquifers were subjected to slightly oxidized to moderately reducing conditions, with ORP values ranging from +50.40 mv to −149.5 mv. Such redox conditions could potentially result in the enrichment and mobility of arsenic in the groundwater. Although arsenic concentrations in deep aquifers are relatively low, higher salinity values are found in both shallow and intermediate coastal aquifers.

Measures of abundance of extraformational conglomerates and clast composition, taken together, can be used to unravel the unroofing history of an orogenic belt. This study develops a new approach in quantifying coarse detritus as a provenance indicator. Known as the “conglomerate measures” in the Cahaba synclinorium, the uppermost Pottsville Formation consists of conglomerates and subordinate sandstone, shale, and coal. These siliciclastic sediments were deposited during the Alleghenian orogeny primarily in braidplain-anastomosis environments in Alabama and Mississippi. The abundance of extraformational conglomerate suggests unroofing of active thrust sheets in the Alleghenian foreland basin, which can be used in deciphering the source of Alleghenian sediments in the southeastern United States. Conglomerate clasts in the upper Pottsville Formation consist mainly of sedimentary lithics (chert, sandstone, and mudstone) and metamorphic lithics (phyllite, schist, and quartzite), with minor volcanic and plutonic lithics. Compositional similarities among clasts in the upper part of the Pottsville Formation in the Cahaba basin and the lithologies of the Valley and Ridge, Piedmont, and Blue Ridge provinces suggest that the sediments were derived from proximal sources in the southern Appalachian provinces. Ternary plots of the sandstone matrix within the conglomerates indicate mostly a recycled orogenic provenance. The textures of the metamorphic clasts suggest a medium- to high-grade metamorphic source terrane. The chemical compositions of garnets (Sp-Alm-Py), including the dominance of almandine-type garnets, also indicate an amphibolite facies provenance. Finally, a whole-rock ⁴⁰Ar/³⁹Ar age of an andesite clast (∼323 Ma) suggests that andesitic volcanism occurred during the Alleghenian orogeny, and a minimum age of a metatonalite clast (∼295 Ma) suggests the minimum possible depositional age of the Pottsville Formation in the Cahaba synclinorium, indicating that the Cahaba section continued to receive Alleghenian metamorphic detritus later than previously thought.

Salinity intrusion in the coastal regions of Bangladesh is particularly challenging for communities living near mangrove forests, which have salinity-dependent ecosystems. The salinity levels within groundwater aquifer systems here vary seasonally, and vegetation has the potential to serve as a mitigation strategy to reduce salinity intrusion. In this study, we focused on the southwest coastal region of Bangladesh, an area characterized by high salinity intrusion. We analyzed groundwater samples collected from monitoring wells during both dry and wet seasons. Additionally, we recorded the necessary physical and chemical parameters to support the analysis. We explored several GIS interpolation methods, including Inverse Distance Weight (IDW), Empirical Bayesian Kriging (EBK), and Kernel interpolation to map salinity while employing remote sensing techniques to map vegetation dynamics. We used spatial regression and bivariate clustering methods to identify and map the seasonal spatial dependence variation of salinity and vegetation. Our analysis indicates a negative linear relationship between salinity and vegetation dynamics, with the correlation being notably stronger in the dry season (Pearson correlation − 0.540) compared to the wet season (Pearson correlation − 0.149). The spatial regression model indicated spatial dependence between these two variables only during the dry season, with an R-squared value of 0.972. Bivariate clustering results identified approximately 20% of the area during the dry season with high average salinity and low average vegetation index values. The spatial context of this study is crucial for developing mitigation strategies for salinity intrusion, considering the vegetation dynamics of coastal regions of Bangladesh.

Naturally occurring biogenic pyrite has been found in Holocene fluvial aquifers in the Uphapee watershed, Macon County, Alabama. The electron microprobe (EMP) analysis showed that the pyrite grains contain 0.20–0.92 weight% of arsenic (As). The scanning electron microscope and energy dispersive spectroscopy (SEM-EDS) analysis confirmed a similar concentration of As in the pyrite that was consistent with the EMP analysis. The SEM analysis also confirmed the presence of additional trace elements such as cobalt (0.19 wt.%), and nickel (0.15 wt.%), indicative of pyrite’s capacity to sequester As and other trace elements. Pyrite grains were naturally formed and developed as large (20–200 μm) euhedral (i.e., cube, octahedron) crystals and non-framboid aggregates. However, the inductively coupled plasma mass spectrometry (ICP-MS) analysis showed that the As concentration in the groundwater was not high, and it was within the EPA drinking water standard for As (10 µg/L). These results indicate that dissolved As is sequestered in naturally formed pyrite found in the fluvial sediments. The groundwater was moderately reducing to slightly oxidizing (Eh = 46 to173 mV), and nearly neutral to slightly acidic (pH = 5.53 to 6.51). Groundwater geochemistry data indicated a redox sequence of oxidation, denitrification, Mn(IV) reduction, Fe(III) reduction, and sulfate reduction along the flow path in the fluvial aquifer. The downgradient increases in dissolved Mn and then Fe concentrations reflect increased Mn(II) and Fe(II) production via microbial competition as the aquifer becomes progressively more reduced. Bacterial sulfate reduction seems to dominate near the end of the groundwater flow path, as the availability of Mn- and Fe-oxyhydroxides becomes limited in sediments rich in lignitic wood where increasing sulfate reduction leads to the formation of biogenic pyrite. The groundwater is a Ca-SO₄ type and is not SO₄ limited; thus, sulfate may serve as an electron acceptor for the bacterial sulfate-reducing reactions that sequester As into pyrite, which in turn results in very low groundwater As concentration (<2 µg/L).