Influence of regional hydrogeological systems at a local scale: Analyzing the coupled effects of hydrochemistry and biological activity in a Fe and CO2 rich spring

Analysis of hydrochemical characteristics and assessment of organic pollutants (PAH and PCB) in El Fahs plain aquifer, northeast of Tunisia

The availability of good quality groundwater constitutes a major concern in many developing countries. The El Fahs shallow aquifer, northeastern Tunisia, is an important source of water supply for various economic sectors in the agricultural region. The intensive exploitation of this groundwater has led to its quality degradation. In fact, assessment of water quality degradation is very useful in planning the conservation and management practices of water resources in this watershed. This research aims to evaluate the groundwater quality and its suitability for irrigation uses, identify the main processes to assess their chemical composition, and investigate the potential sources of persistent organic pollutants (POPs). The hydrogeochemical investigation is thus conducted by collecting groundwater samples and analyzing their physicochemical characteristics. Polycyclic aromatic hydrocarbons (16 PAHs) and polychlorinated biphenyls (7 PCBs) were determined in groundwaters from nine stations. The sampling took place in July 2020. The relative abundance of ions was Na > Mg > Ca > K for cations and Cl > SO4 > HCO3 for anions. The groundwater exhibits two predominant hydrochemical facies: Ca-Mg-Cl/SO4 and Na-Cl. The relevant recorded pollutant is nitrate, which was generally far above values of pollution thresholds indicating the influence by the intensive agricultural activity. The suitability for irrigation purposes was assessed using several parameters (EC, SAR, %Na, TH, PI, Mh, and Kr). As a matter of fact, the results mentioned that the majority of the samples are unsuitable for irrigation uses. An analysis of the organic pollutants indicates that the total PAH and PCB concentrations are above the permissible values. Therefore, a considerable predominance of naphthalene and PCB28 was observed in order to discriminate between pyrolitic and petrogenic PAH sources; low-molecular-weight (LPAH)/high-molecular-weight (HPAH) ratio was calculated. Results showed that PAHs were mainly of petrogenic origin. The results revealed also that the chemical composition of groundwater is influenced by evaporation process, ion exchange, and water-rock interaction during the flow. A high risk of organic contamination has been highlighted linked to anthropogenic activities which have exerted increasing pressure on groundwater quality. The presence of organic pollutants in groundwater is becoming a serious threat to the environment and human health.

Coupled controls of the infiltration of rivers, urban activities and carbonate on trace elements in a karst groundwater system from Guiyang, Southwest China

Hydrogeochemical processes of trace elements (TEs) are of considerable significance to river water and groundwater resource assessment and utilization in the karst region. Therefore, seven TEs were analyzed to investigate their contents, spatial variations, sources, and controlling factors in Guiyang, a typical karst urban area in southwest China. The results showed that the average content of TEs in river water (e.g., As = 1.44 ± 0.47 μg/L andCo = 0.15 ± 0.06 μg/L) was higher than that of groundwater (e.g., As = 0.51 ± 0.42 μg/L andCo = 0.09 ± 0.05 μg/L). The types of groundwater samples were dominated by Ca/Mg-HCO₃ and Ca/Mg-Cl types, while those of the river water samples were Ca-Cl and Ca/Mg-Cl types. Principal component analysis (PCA) and correlation analysis (CA) analyses indicated that As and Mn in the groundwater of the study area were related to river infiltration. The end-member analysis further revealed that river infiltration (As = 0.86-1.81 μg/L, Cl/SO₄^2- = 0.62-0.89) and urban activities (As = 0.21-0.32 μg/L, Cl/SO₄^2- = 0.51-0.89) were two main controlling factors of TEs (e.g., As, Co, and Mn) in the study area. In addition, the ion ratios in river and groundwater samples indicated that the weathering of carbonates was also an important control on the hydrogeochemistry of TEs (e.g., Fe and Mn) in Guiyang waters. This study showed that the trace element (TE) contents of groundwater in the Guiyang area were greatly associated with urban input and river recharge, and provided a new perspective for understanding the geochemical behavior of TEs in urban surface and groundwater bodies, which will help the protection of groundwater in the karst areas of southwest China.

Hydrochemical Parameters to Assess the Evolutionary Process of CO2-Rich Spring Water: A Suggestion for Evaluating CO2 Leakage Stages in Silicate Rocks

Eighteen water samples collected from eight CO2-rich springs in the northern part of the Gyeongsang sedimentary basin (GSB), South Korea showed distinct hydrochemistry, in particular, pH, total dissolved solids (TDS), and Na contents, and they were classified into four groups: (1) Group I with low pH (average of 5.14) and TDS (269.8 mg/L), (2) Group II with high TDS (2681.0 mg/L) and Na-enriched (202.9 mg/L), (3) Group III with intermediate Na content (97.5 mg/L), and (4) Group IV with Na-depleted (42.3 mg/L). However, they showed the similar partial pressure of CO2 (0.47 to 2.19 atm) and stable carbon isotope ratios of dissolved inorganic carbon (−6.3 to −0.6‰), indicating the inflow of deep-seated CO2 into aquifers along faults. In order to elucidate the evolutionary process for each group of CO2-rich springs, a multidisciplinary approach was used combining stable hydrogen (δD), oxygen (δ18O) and carbon (δ13C), and radioactive carbon (14C) isotopic, geophysical, and hydrochemical data. The highest δD and δ18O ratios of water and the relatively young 14C ages in Group I and the lowest δD and δ18O in Group II indicated the short and long residence time in Group I and II, respectively. The electrical resistivity tomography (ERT) survey results also supported the fast rising through open fractures in Group I, while a relatively deep CO2-rich aquifer for Group III. Group II had high contents of Mg, K, F, Cl, SO4, HCO3, Li, and As, while Group I showed low contents for all elements analyzed in this study except for Al, which exceeded the World Health Organization (WHO) guideline for drinking-water quality probably due to the low pH. Meanwhile Group IV showed the highest Ca/Na as well as Ca, Fe, Mn, Sr, Zn, U, and Ba, probably due to the low-temperature dissolution of plagioclase based on the geology and the ERT result. The levels of Fe, Mn, and U exceeded the WHO guidelines in Group IV, while As in Group II. The different hydrochemistry suggests a distinct evolutionary process for each group. Group I seems to represent a fast discharge from the CO2-rich aquifer to a discharge point, experiencing a low degree of water-rock interaction, while Group II seems to represent a slow discharge with a high degree of water-rock interaction. GSB is a potential site for geological carbon storage (GCS), and injected CO2 may leak through various evolutionary processes given heterogenous geology as CO2-rich springs. The study result suggests that the combined use of pH, Na, K, Li, and Ca/Na are effective hydrochemical monitoring parameters to assess the leakage stage in silicate rocks in GCS projects. Besides, aluminum (Al) can be risky at the early stage of CO2 leakage, while Fe, Mn, U, and As at the later stage of CO2 leakage.

The improvement on total nitrogen removal in nitrate reduction by using a prepared CuO-Co3O4/Ti cathode

In this work, a CuO-Co₃O₄/Ti composite was prepared via the coating-calcination method and employed as a cathode for the NO₃^--N reduction to increase the removal efficiency of total nitrogen (TN). SEM, EDS, and XRD characterization results indicated that CuO and Co₃O₄ were successfully introduced to the surface of Ti. The CuO-Co₃O₄/Ti electrode eventually removed NO₃^--N with the main products of N₂, NH₄⁺-N and NO₂^--N. In comparison to the Co₃O₄/Ti electrode, the better hydrogen evolution properties of the CuO-Co₃O₄/Ti electrode resulted in pH increase and NH₃ gas release, so the TN removal for CuO-Co₃O₄/Ti electrode was improved approximately 20%. The presence of Cl^- with the concentration up to 1000 mg L^-1 greatly promoted the removal of TN from 40.1% to 94.0%, as a result of NH₄⁺-N oxidation with free chlorine produced from the anode. Furthermore, the CuO-Co₃O₄/Ti electrode was applied to conduct three types of actual wastewater (biological effluent of municipal wastewater and industrial wastewater, and a regeneration concentrate from an anion exchange process) for nitrate removal. The highest TN removal efficiency (78.5%) and current efficiency (54.5%), and the lowest energy consumption (2 × 10^-4 kWh mg^-1 TN) were obtained for the regeneration concentrate, suggesting the feasibility of the CuO-Co₃O₄/Ti electrode to the water with high conductivity and high Cl^- concentration for removing TN by the reduction of nitrate.

Evaluation of Long-Term Impacts of CO2 Leakage on Groundwater Quality Using Hydrochemical Data from a Natural Analogue Site in South Korea

Three hydrochemical types of CO2-rich water (i.e., Na-HCO3, Ca-Na-HCO3 and Ca-HCO3) occur together in the silicate bedrock (granite and gneiss) of Gangwon Province in South Korea. As a natural analogue of geological carbon storage (GCS), this can provide implications for the environmental impacts of the leakage of CO2 from deep GCS sites. By using hydrochemical and isotopic datasets that were collected for previous and current studies, this study aimed to carefully scrutinize the hydrochemical differences in the three water types with an emphasis on providing a better understanding of the impacts of long-term CO2 leakage on groundwater quality (especially the enrichments of minor and trace metals). As a result, the Na-HCO3 type CO2-rich water contained higher Li, Rb and Cs than the Ca-HCO3 type, whereas Fe, Mn and Sr were higher in the Ca-HCO3 type than in the Na-HCO3 type despite the similar geological setting, which indicate that the hydrochemical differences were caused during different geochemical evolutionary processes. The δ18O and δD values and tritium concentrations indicated that the Na-HCO3 type was circulated through a deep and long pathway for a relatively long residence time in the subsurface, while the Ca-HCO3 type was strongly influenced by mixing with recently recharged water. These results were supported by the results of principal component analysis (PCA), whose second component showed that the Na-HCO3 type had a significant relation with alkali metals such as Li, Rb and Cs as well as Na and K and also had a strong relationship with Al, F and U, indicating an extensive water-rock interaction, while the Ca-HCO3 type was highly correlated with Ca, Mg, Sr, Fe and Mn, indicating mixing and reverse cation exchange during its ascent with hydrogeochemical evolution. In particular, the concentrations of Fe, Mn, U and Al in the CO2-rich water, the result of long-term water-rock interaction and cation exchange that was enhanced by CO2 leakage into silicate bedrock, exceeded drinking water standards. The study results show that the leakage of CO2 gas and CO2-rich fluid into aquifers and the subsequent hydrogeochemical processes can degrade groundwater quality by mobilizing trace elements in rocks and consequently may pose a health risk.

Biotic and Abiotic Factors Influencing Arsenic Biogeochemistry and Toxicity in Fluvial Ecosystems: A Review

This review is focused on the biogeochemistry of arsenic in freshwaters and, especially, on the key role that benthic microalgae and prokaryotic communities from biofilms play together in through speciation, distribution, and cycling. These microorganisms incorporate the dominant iAs (inorganic arsenic) form and may transform it to other arsenic forms through metabolic or detoxifying processes. These transformations have a big impact on the environmental behavior of arsenic because different chemical forms exhibit differences in mobility and toxicity. Moreover, exposure to toxicants may alter the physiology and structure of biofilms, leading to changes in ecosystem function and trophic relations. In this review we also explain how microorganisms (i.e., biofilms) can influence the effects of arsenic exposure on other key constituents of aquatic ecosystems such as fish. At the end, we present two real cases of fluvial systems with different origins of arsenic exposure (natural vs. anthropogenic) that have improved our comprehension of arsenic biogeochemistry and toxicity in freshwaters, the Pampean streams (Argentina) and the Anllóns River (Galicia, Spain). We finish with a briefly discussion of what we consider as future research needs on this topic. This work especially contributes to the general understanding of biofilms influencing arsenic biogeochemistry and highlights the strong impact of nutrient availability on arsenic toxicity for freshwater (micro) organisms.

Hydrogeochemistry and quality of surface water and groundwater in the drinking water source area of an urbanizing region

The water quality in drinking water source area is essential for human health. Due to rapid urbanization and industrialization, the pollutants, especially trace elements, are continuously discharged into aquatic environment and pose a risk to human health. An extensive investigation was carried out in drinking water source area in highly urbanized Tianjin of China. Long-term monitoring data of the water body was collected on conventional physical and chemical parameters (pH, ions, TOC etc.) and metallic elements (Hg, As Cd, Pb, Co, U etc.) from 2005 to 2017. Our results showed that CaMg-Cl-SO₄ and CaMg-HCO₃ were the two prominent hydrochemical materials, implying that the pollution of aquatic system was mainly caused by anthropogenic activities and mineral dissolution within terms of drinking water guidelines (national and international standards), the concentrations of arsenic (As) and iron (Fe) were beyond the quality standards. Multivariate statistical approaches were applied to assess the origins of the elements. The results showed that human activities, as well as endogenous release, contributed significantly to appearance of trace elements. A transformation from low-trophic state to high-trophic state was in progress from 2005 to 2017 in Yuqiao reservoir, and most of the water was not heavily polluted by trace elements. The health risk assessment suggested that As had the potential to cause carcinogenic harm to the local residents, with daily dietary ingestion as the most predominant pathway.

Water quality assessment in the Bétaré-Oya gold mining area (East-Cameroon): Multivariate Statistical Analysis approach

The influence of gold mining activities on the water quality in the Mari catchment in Bétaré-Oya (East Cameroon) was assessed in this study. Sampling was performed within the period of one hydrological year (2015 to 2016), with 22 sampling sites consisting of groundwater (06) and surface water (16). In addition to measuring the physicochemical parameters, such as pH, electrical conductivity, alkalinity, turbidity, suspended solids and CN^-, eleven major elements (Na⁺, K⁺, Ca²⁺, Mg²⁺, NH₄⁺, Cl^-, NO₃^-, HCO₃^-, SO₄^2-, PO₄^3- and F^-) and eight heavy metals (Pb, Zn, Cd, Fe, Cu, As, Mn and Cr) were also analyzed using conventional hydrochemical methods, Multivariate Statistical Analysis and the Heavy metal Pollution Index (HPI). The results showed that the water from Mari catchment and Lom River was acidic to basic (5.40<pH<8.84), weakly mineralized (6.3<EC<160.8μS/cm) and had a high concentration of total suspended solids (TSS) (2<TSS<8996.00mg/L). The major elements were all within the World Health Organization (WHO) guidelines for drinking water quality, except for nitrates in some wells, which was found at a concentration >50mg NO₃^-/L. This water was found as two main types: calcium magnesium bicarbonate (CaMg-HCO₃), which was the most represented, and sodium bicarbonate potassium (NaK-HCO₃). As for trace elements in surface water, the contents of Pb, Cd, Mn, Cr and Fe were higher than recommended by the WHO guidelines, and therefore, the surface water was unsuitable for human consumption. Three phenomena were responsible for controlling the quality of the water in the study area: hydrolysis of silicate minerals of plutono-metamorphic rocks, which constitute the geological basement of this area; vegetation and soil leaching; and mining activities. The high concentrations of TSS and trace elements found in this basin were mainly due to gold mining activities (exploration and exploitation) as well as digging of rivers beds, excavation and gold amalgamation.