Submarine groundwater discharge as sources for dissolved nutrient fluxes in Coleroon river estuary, Bay of Bengal, India

Hydrogeochemical assessment of aquifer salinization in north-eastern Morocco's Gueroaou coastal plain using statistical methods

The Guerouaou aquifer investigation spanning 280 km2 in Ain Zohra yields promising outcomes, instilling optimism for regional water quality. These analyses were applied to 45 sampling instances from 43 wells, enabling a comprehensive water quality assessment. Groundwater conductivity ranged from medium to high, peaking at 18360 ms/cm2. The conductivity reveals insights about the groundwater's mineralization. Key physiochemical parameters fell within desirable thresholds, bolstering the positive perspective. HCO3- levels spanned 82-420 mg/L, while chloride content ranged from 38 to 5316 mg/L, benefiting water quality. NO3- ions, vital for gauging pollution, ranged from 0 to 260 mg/L, indicating favorable results. Cation concentrations exhibited encouraging variations: Ca2+- 24 to 647 mg/L, Mg2+- 12 to 440 mg/L, Na+- 18 to 2722 mg/L, K+- 1.75 to 28.65 mg/L. These collectively favor water quality. Halite breakdown dominated mineralization, as evidenced by the prevalence of Na-Cl-Na-SO4 facies. Water resource management and local communities need effective management and mitigation strategies to prevent saltwater intrusion.

Fresh and recirculated submarine groundwater discharge zones along the central west coast of India

The study area receives an average of 2840.0 mm of rainfall within four months every year. A portion of the rainwater is flown to the sea as surface water, and the other part is percolated into the bottom as groundwater. In coastal aquifers, the groundwater is transported to the sea due to a hydraulic gradient, and it contains a significant quantity of dissolved materials and nutrients. SGD processes impact the ocean productivity, mangrove and coral growth, local acidification and many. To isolate the SGD on the central west coast of India, different data was referred. The GWL concerning MSL contributed significantly to demarcating the SGD zones by considering the positive (>0 m) and negative (<0 m) values of GWL concerning above MSL. Thermal images for SST of pre-monsoon and post-monsoon periods of 2020 exhibit cooler surrounded by warmer, which might be the SGD buffering zones in the off-central west coast of India. By considering the results from GWL and SST, 8 SGD beach sites were identified for the further particularized study. The water samples were collected in March 2022, and analyzed using standard procedures and instruments. Fresh and mixing (recirculated) zones have been isolated by piper, hydrochemical facies evolution, and Ca2++Mg2+/K++Na + Vs log Cl- ionic ratio plots. The aquifer water chemical elements are converting possibly due to ionic exchange processes. The decrease in salinity and conductivity observed in the pore water just below the seawater might be due to the influence of freshwater inputs, helping to isolate the fresh SGD and recirculated SGD zones in the study area. Among 8 sites, 3 were found to be fresh SGD sites and 5 were noticed to be mixing/recirculated SGD sites. Most of these Beaches are bounded by hills, which helps to lead the SGD along the central west coast of India.

A review on global status of fresh and saline groundwater discharge into the ocean

Submarine groundwater discharge (SGD) is the groundwater flow from land to the sea across the seabed, and it includes both terrane freshwater and recirculated seawater in the sub-surface. This review (i) systematically evaluates findings of various quantification methodologies, (ii) examines the estimated SGD in scientific publications between 2000 and 2020, and (iii) quantitatively evaluates current situation of coastal zone management through the bibliometric analysis of research papers. Apart from enhancing the shortage of groundwater resources in coastal area, the SGD brings nutrients (nitrate and phosphate), toxic heavy metals, and organic compounds, and thus contaminate the seawater. Therefore, the improved understanding about location and quantity of global SGD is essential to conserve the coastal and ocean ecosystems.

Hydrogeochemical evolution and assessment of groundwater quality in the Togo and Dahomeyan aquifers, Greater Accra Region, Ghana

Groundwater quality is generally better than surface water quality but this is not sacrosanct because during recharge and abstraction, groundwater may be subjected to variations due to influence from natural and anthropogenic processes. The Togo and Dahomeyan aquifers are threatened by several anthropogenic activities like dumping of domestic and industrial wastes in open landfill sites. These activities can be sources of groundwater constituents and can pose adverse health effects on humans and the ecosystem but little is known about the hydrogeochemical characteristics of groundwater and its quality in the area. Therefore, the present study is aimed at unravelling the hydrogeochemical characteristics and quality of groundwater in the Togo and Dahomeyan aquifers in the Greater Accra Region of Ghana. A total of 37 groundwater samples were collected and analysed for the concentrations of major ions, minor ions, and trace elements. The results were used to compute water quality parameters like electrical conductivity, sodium adsorption ratio, sodium percent, and magnesium ratio to assess the quality of the water for irrigation purposes. Groundwater shows acidic to slightly alkaline pH and evolved from Mg-Na-HCO₃, Ca-Na-Mg-HCO₃, Na-Ca-Mg-HCO₃-Cl to Na-Mg-Ca-HCO₃ with other mixed water types, which reflect the local geology. Geochemical modelling indicates that groundwater is supersaturated with respect to goethite and hematite and saturated with respect to calcite, aragonite, and dolomite in some samples. Hydrochemical graphing and multivariate statistical analysis indicate that the chemistry of groundwater in the area is primarily controlled by an interplay of chemical weathering, mineral dissolution, ion exchange reactions, agricultural activities, and sewage disposal. The groundwater is not entirely suitable for drinking purposes because of high concentrations of EC, TDS, Na⁺, Cl^-, F^-, Fe, Mn, Pb, Cr, and Ni, which exceed their maximum permissible limits provided by the World Health Organization. The computed parameters for assessing the quality of the water for irrigation reveal that 64.9% of the samples are suitable for irrigation purposes. However, 35.1% of the samples show very high salinity and sodium hazard and thus, are unsuitable for irrigation purposes. Therefore, it is recommended that mixing of the high salinity and sodium water with low salinity and sodium water can improve crop yields.

Integrating magnetic susceptibility, hydrogeochemical, and isotopic data to assess the seawater invasion in coastal aquifers of Digha, West Bengal, India

Seawater intrusion in coastal aquifers is a major concern due to geogenic and anthropogenic activities leading to declining groundwater quality. The present study focuses on deciphering the sea water intruded zones and its extent in the Quaternary alluvial aquifer system in the coastal belt of Digha, West Bengal, India. In this study, 36 groundwater samples were collected during pre-monsoon (2020). Subsequently, an integrated approach of hydrogeological, hydrogeochemistry, bulk magnetic susceptibility, isotopic, multivariate statistical, and geochemical modeling is adopted. Spatial distribution maps of hydrological parameters (salinity, conductivity, TDS) and major ion concentration (Na+, K+, Ca2+, Mg2+, Cl-, SO42-, F-, and Br-) suggest that the northern, south-west, and eastern parts of the study area are largely affected by saltwater intrusion and are corroborated with seawater mixing index (SMI). Based on sodium adsorption ratio (SAR), sodium percentage (Na%), and Permeability index (PI) distribution maps, the same locations are identified under critical condition for the suitability of groundwater for irrigation. The order of concentration of cations and anions in the water samples are Na+  > Ca2+  > Mg2+  > K+ and HCO3-  > SO4-  > Cl-  > Br-  > F- respectively. Piper diagram shows three principal hydrochemical water types with water composition changes from fresh (86%) to saline water mix (14%). The hydrochemical facies evolution diagram depicts 81% of water samples are in the freshening phase, and 19% are in the intrusion phase. The various bivariate plots revealed that ion exchange, reverse ion exchange, silicate weathering, seawater mixing, and anthropogenic inputs are the governing factors that control groundwater evolution. R-mode factor analysis, principal component analysis (PCA), and agglomerative hierarchical cluster (AHC) also indicate the influence on groundwater from seawater mixing and/or seawater intrusion. The superlativeness of bulk magnetic susceptibility (χ) analysis of water samples in delineating seawater intruded zones is elaborated. Saturation index (SI) shows that groundwater is saturated (> 0) with calcite, dolomite, and aragonite, plausibly due to seawater ingression. Stable isotopic analysis of δ2H (- 53.979 to - 16.9578‰) and δ18O (- 7.00183 to - 1.37 ‰) suggests precipitation recharge/paleo-water at some locations and evaporation enrichment of groundwater. It is recommended to increase groundwater recharge, reduce groundwater extraction at critically affected locations, and have regular monitoring and management to control seawater intrusion.

Hydrogeochemical investigations to assess groundwater and saline water interaction in coastal aquifers of the southeast coast, Tamil Nadu, India

Groundwater and saline water interaction is the most common processes in the coastal aquifers that alters the quality of aquifer waters. The quaternary alluvium aquifer system is a significant water resource of southeast coastal Tamil Nadu that provides water supplies for industrial, agriculture, and domestic utilities. Hydrogeochemical investigations were attempted to analyze groundwater-saline water interactions for which a total of three hundred and sixty samples representing surface water, pore water, and groundwater samples collected from three significant locations (location A, B, and C) and analyzed for major ion concentrations. Piper plot infers surface and pore water samples representing saline water type (Na-Cl) in all the three locations due to tidal variation and sand dominant surface layer. Groundwater samples represent (Ca-HCO₃) type at location A due to fresh groundwater discharge, mixed or subterranean estuary (Ca, Mg-Cl, HCO₃) at location B due to conversion of freshwater (Ca-HCO₃) at low tide to saline water (Na-Cl) at high tide, and saline (Na-Cl) water at location C due to proximity and influence of tides. The Cl^-/HCO₃^- vs. Cl^- plot represents two water types, such as fresh groundwater (0.5) and strongly affected by seawater intrusion (6.6). The plot (Ca²⁺+Mg²⁺)/(K⁺+Na⁺) vs. log Cl^- represents freshwater in location A, mixing in location B, and saline water in location C. Groundwater samples observed to be fresh in location A (20.0 km away from the coast), recirculated in location B (9.0 km away from the coast), and saline in location C (0.5 km away from the coast).

Submarine Groundwater Discharge from an Urban Estuary to Southeastern Bay of Bengal, India: Revealed by Trace Element Fluxes

Submarine groundwater discharge and associated trace element fluxes from the Coleroon River estuary to south bay, India, has been attempted, because increasing trace elements could result in harmful algal blooms and eutrophication. Trace elements (Al, Cr, Mn, Fe, Ni, Cu, Zn, Sr, Mo, Ba, Pb, Th, and U) in surface water, pore, and groundwater samples were monitored for 10 days in three locations (A, B, and C) by considering tidal fluctuations. The trace elements Al, Cr, Fe, Ni, Zn, Sr, Mo, Pb, Th, and U were greater and found to be influenced by processes, such as fresh groundwater discharge and seawater intrusion. Lower Mn, Cu, and Ba signifies impact due to sediment adsorption, mixing, and elemental exchange during fresh groundwater and seawater mixing. Salinity versus trace element plot infers greater trace element mobility with cumulative salinity influenced by the conformist behavior of freshwater, seawater, and mixing. The calculated submarine groundwater discharge supported dissolved trace elements fluxes were 107,047.8 n mol d^-1 m^-1 for location A, 183,520.2 n mol d^-1 m^-1 for location B, and 181,474.4 n mol d^-1 m^-1 for location C, respectively. Variations in dissolved trace elements fluxes are attributed to variations in pH, free redox environment in the aquifer, adsorption or desorption by sediments, and the environmental cycle of marine organisms.