The long-term impacts of anthropogenic and natural processes on groundwater deterioration in a multilayered aquifer

Hydrochemical and microbial community characteristics and the sources of inorganic nitrogen in groundwater from different aquifers in Zhanjiang, Guangdong Province, China

Groundwater from different aquifers in the Zhanjiang area suffers from different degrees of nitrogen pollution, which poses a serious threat to the health of urban and rural residents as well as the surrounding aquatic ecological environment. However, neither the water chemistry and microbial community characteristics in different aquifer media nor the sources of inorganic nitrogen pollution have been extensively studied. This study integrated water quality parameters, dual isotopes (δ15N-NO3- and δ18O-NO3-), and 16S rRNA data to clarify the hydrochemical and microbial characteristics of loose rock pore water (LRPW), layered bedrock fissure water (LBFW), and volcanic rock pore fissure water (VRPFW) in the Zhanjiang area and to determine inorganic nitrogen pollution and sources. The results show that the hydrochemistry of groundwater in different aquifers is complex and diverse, which is mainly affected by rock weathering and atmospheric precipitation, and the cation exchange is strong. High NO3- concentration reduces the richness of the microbial community (VRPFW). There are a large number of bacteria related to nitrogen (N) cycle in groundwater and nitrification dominated the N transformation. A quarter of the samples exceeded the relevant inorganic nitrogen index limits specified in the drinking water standard for China. The NO3- content is highest in VRPFW and the NH4+ content is highest in shallow loose rock pore water (SLRPW). In general, NO3-/Cl-, dual isotope (δ15N-NO3- and δ18O-NO3-) data and MixSIAR quantitative results indicate manure and sewage (M&S) and soil organic nitrogen (SON) are the main sources of NO3-. In LRPW, as the depth increases, the contribution rate of M&S gradually decreases, and the contribution rate of SON gradually increases. The results of uncertainty analysis show that the UI90 values of SON and M&S are higher. This study provides a scientific basis for local relevant departments to address inorganic nitrogen pollution in groundwater.

Interaction between the hydrochemical environment, dissolved organic matter, and microbial communities in groundwater: A case study of a vegetable cultivation area in Huaibei Plain, China

Intensive vegetable planting has a profound impact on the surrounding aquatic environment. The self-purification ability of groundwater is poor, and it is difficult to return groundwater to its original state once polluted. Therefore, it is necessary to clarify the impact of intensive vegetable planting on groundwater. This study selected the groundwater of a typical intensive vegetable planting base in the Huaibei Plain of China as the research object. This work analyzed the content of major ions, the dissolved organic matter (DOM) composition, and the bacterial community structure in groundwater. Redundancy analysis was used to explore the interactions between the major ions, the DOM composition, and the microbial community. The results showed that under the influence of intensive vegetable planting, the F- and NO3--N contents in groundwater were significantly increased; the excitation-emission matrix combined with parallel factor analysis identified four fluorescent components (C1 and C2 were humus-like components, while C3 and C4 were protein-like components), which mainly consisted of protein-like components. Proteobacteria was the dominant phylum (mean = 69.27 %), followed by Actinobacteriota (mean = 7.25 %) and Firmicutes (mean = 4.02 %), which together explained over 80 % of the total abundance; and TDS, pH, K+, and C3 were the main influencing factors affecting the microbial community structure. This study provides a better understanding of the impact of intensive vegetable cultivation on groundwater.

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.

Aquifer system and depth specific chemical patterns in fractured-rock groundwater from the Critical Zone revealed by untargeted LC-MS-based metabolomics

In the Earth's Critical Zone, water plays an essential role as a collector and transporter of metabolites and their transformation products. It is generally believed that the chemical profiles of groundwater are strongly impacted by land use. However, predictors for the effects of above-ground natural and anthropogenic activities on below-ground chemistry are rare. We reasoned that comparing groundwater metabolomes from different land-use sites and depths can give insight into this coupling of above and below-ground processes in the Critical Zone. This study used an LC-MS-based untargeted metabolomic approach to identify links between groundwater metabolomes from monitoring wells in fractured carbonate-/siliciclastic alternations along a hillslope of the Hainich Critical Zone Exploratory (CZE) in Thuringia, Germany. Our results identify the land-use type, aquifer system, and sampling depth as critical factors determining the differences among groundwater metabolomes. We established five groundwater metabolic clusters and correlated these to the aquifer systems, hydrogeochemistry, and microbial community composition. Our untargeted metabolomic approach reveals the limited connectivity of groundwater chemical profiles with above-ground activities and illustrates how deep the input signals can travel.

Hydrochemical characteristics and identification of groundwater pollution sources in tropical savanna

Groundwater pollution of the watershed is mainly influenced by the multifaceted interactions of natural and anthropogenic processes. In this study, classic chemical and multivariate statistical methods were utilized to assess the groundwater quality and ascertain the potential contamination sources affecting the groundwater quality of Galma sub-watershed in a tropical savanna. For this purpose, the data set of 18 groundwater quality variables covering 57 different sampling boreholes (BH) was used. The groundwater samples essentially contained the cations in the following order of dominance: Ca²⁺  > Na⁺  > Mg²⁺  > K⁺. However, the anions had HCO₃^- > Cl^- > SO₄^-2 > NO₃^- respectively. The hydrochemical facies classified the groundwater types of the sub-watershed into mixed Ca-Mg-Cl type of water, which means no cations and anions exceeds 50%. The second dominant water type was Ca-Cl. The Mg-HCO₃ water type was found in BH 9, and Na-Cl water type in BH 29 of the studied area. The weathering of the basement rocks was responsible for the concentrations of these ions in the groundwater chemistry of the sub-watershed. Hierarchical cluster analysis (HCA) grouped the groundwater samples (boreholes) into five clusters that are statistically significant regarding the similarities of groundwater quality characteristics. The principal component analysis (PCA) extracted two major principal components explained around 65% of the variance and suggested the natural and anthropogenic processes especially the agricultural pollutants including synthetic fertilizers, and leaching of agricultural waste as the main factors affecting the groundwater quality. The integrated method proved to be efficient and robust for groundwater quality evaluation, as it guaranteed the precise assessment of groundwater chemistry in the sub-watershed of the tropical savanna. The findings of this investigation could be useful to the policy makers for developing effective groundwater management plans for the groundwater resources and protection of the sub-watershed.

Impact of Malaysian palm oil on sustainable development goals: co-benefits and trade-offs across mitigation strategies

Palm oil (PO) is an important source of livelihood, but unsustainable practices and widespread consumption may threaten human and planetary health. We reviewed 234 articles and summarized evidence on the impact of PO on health, social and economic aspects, environment, and biodiversity in the Malaysian context, and discuss mitigation strategies based on the sustainable development goals (SDGs). The evidence on health impact of PO is equivocal, with knowledge gaps on whether moderate consumption elevates risk for chronic diseases, but the benefits of phytonutrients (SDG2) and sensory characteristics of PO seem offset by its high proportion of saturated fat (SDG3). While PO contributes to economic growth (SDG9, 12), poverty alleviation (SDG1, 8, 10), enhanced food security (SDG2), alternative energy (SDG9), and long-term employment opportunities (SDG1), human rights issues and inequities attributed to PO production persist (SDG8). Environmental impacts arise through large-scale expansion of monoculture plantations associated with increased greenhouse gas emissions (SDG13), especially from converted carbon-rich peat lands, which can cause forest fires and annual trans-boundary haze; changes in microclimate properties and soil nutrient content (SDG6, 13); increased sedimentation and change of hydrological properties of streams near slopes (SDG6); and increased human wildlife conflicts, increase of invasive species occurrence, and reduced biodiversity (SDG14, 15). Practices such as biological pest control, circular waste management, multi-cropping and certification may mitigate negative impacts on environmental SDGs, without hampering progress of socioeconomic SDGs. While strategies focusing on improving practices within and surrounding plantations offer co-benefits for socioeconomic, environment and biodiversity-related SDGs, several challenges in achieving scalable solutions must be addressed to ensure holistic sustainability of PO in Malaysia for various stakeholders.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s11625-021-01052-4.

Evaluating the nitrogen-contaminated groundwater treatment by a denitrifying granular sludge bioreactor: effect of organic matter loading

A sequential bed granular bioreactor was adapted to treat nitrate-polluted synthetic groundwater under anaerobic conditions and agitation with denitrification gas, achieving very efficient performance in total nitrogen removal at influent organic carbon concentrations of 1 g L^-1 (80-90%) and 0.5 g L^-1 (70-80%) sodium acetate, but concentrations below 0.5 g L^-1 caused accumulation of nitrite and nitrate and led to system failure (30-40% removal). Biomass size and settling velocity were higher above 0.5 g L^-1 sodium acetate. Trichosporonaceae dominated the fungal populations at all times, while a dominance of terrestrial group Thaumarchaeota and Acidovorax at 1 and 0.5 g L^-1 passed to a domination of Methanobrevibacter and an unclassified Comamonadaceae clone for NaAc lower than 0.5 g L^-1. The results obtained pointed out that the denitrifying granular sludge technology is a feasible solution for the treatment of nitrogen-contaminated groundwater, and that influent organic matter plays an important role on the conformation of microbial communities within it and, therefore, on the overall efficiency of the system.

Numerical and experimental analyses of the use of double vertical barrier walls for groundwater protection

The groundwater contamination and its impacts on the hydrologic systems and society are critical environmental concerns in the world. This research presents insights from the numerical (SEEP/W and CTRAN/W) and the experimental (sandbox model) analyses of the use of double vertical barrier walls for groundwater protection. The main objective was to evaluate contaminant transport under the effect of several variables. The arrival time increases with increasing the distance between the pollutant source and the first wall, first wall depth of penetration, the distance between the two walls and also increases at smaller hydraulic head differences, and lower conductivities. Furthermore, using double barrier walls would significantly reduce contaminant concentration at the downstream area. This control is most significant when the depth of first wall penetration is larger than that of the second wall. Results proved consistent with several similar studies and advantageous over many of them by the integrated use of both techniques with more variable parameters evaluated. PRACTITIONER POINTS: The research will introduce insights from the effect of using double barrier walls on the hydraulic control of contaminant transport. The effect of several variables on the contaminant arrival time and concentration is investigated. Using double barrier walls has a significant impact on contamination transport through the soil. This control is most significant when the penetration depth of the first wall is larger than that of the second.

Evaluation of groundwater hardness removal using activated clinoptilolite

Current study aimed to investigate modified natural clinoptilolite for removal of calcium and magnesium from the groundwater. Feasibility of clinoptilolite for groundwater hardness removal in production and operation was verified by static adsorption experiment and the experiment of fixed bed and degasification column. Subsequently, the main parameters for groundwater treatment using clinoptilolite were also explored. Results show that in the process of clinoptilolite in adsorption is dominant reaction process. The adsorption equilibrium time was unchanged when the hardness of raw water changes from 450 to 550 mg/L. With respect to comparative analysis of price and performance, NaCl found to be the most suitable clinoptilolite regenerated agent. The adsorption efficiency was high when the residence time was 20-25 min in the pilot experiments. The reaction mechanism was mainly substitution reaction according to ion equilibrium, and the treatment capacity of the degasifier combined with the fixed bed was 20% higher than that of with only fixed bed.

Phreatic Water Quality Assessment and Associated Hydrogeochemical Processes in an Irrigated Region Along the Upper Yellow River, Northwestern China

Groundwater resources are playing an increasingly vital role in water supply for domestic and irrigation purposes in the Yinchuan Plain, along with the reduction in water transfer from the Yellow River. This study aimed to identify the current status of phreatic water quality and associated hydrogeochemical processes in an irrigated region along the upper Yellow River. A total of 78 water samples were collected in September 2018 for chemical analysis. Results showed that the phreatic water was excellent or good in most areas west of the Yellow River, while it was poor or very poor quality in some places east of the Yellow River. The nitrate contamination is particularly severe in the pluvial-alluvial plain, relating to the localized fine-grained zone with low permeability. Most samples had no sodium hazard but had magnesium hazard. Additionally, the overall evolutionary trend of the phreatic water showed the transformation of Ca-Mg-HCO3 into Na-Cl-SO4 type. Rock weathering and evaporation jointly predominate the evolution of phreatic water chemistry. The main geochemical processes involve the dissolution/precipitation of gypsum, halite, dolomite. and calcite, along with the cation exchange. Insights from this work have important implications for groundwater sustainable management in such irrigated regions along the upper Yellow River.

Hydrogeochemical characteristics of a multi-layered coastal aquifer system in the Mekong Delta, Vietnam

Groundwater is a primary freshwater source for various domestic, industrial and agricultural purposes, especially in coastal regions where there are lacking surface water supply. However, groundwater quality in coastal regions is often threatened by seawater intrusion and contamination due to both anthropogenic activities and natural processes. Therefore, insights into groundwater geochemistry and occurrences are necessary for sustainable groundwater management in coastal regions. The main aim of this study is to investigate the hydrogeochemical characteristics and their influencing factors in a coastal area of the Mekong Delta, Vietnam (MD). A total of 286 groundwater samples were taken from shallow and deep aquifers for analyzing major ions and stable isotopes. The results show that deep groundwater is dominated by Ca-HCO[Formula: see text], Ca-Na-HCO[Formula: see text], Ca-Mg-Cl, and Na-HCO[Formula: see text] while shallow groundwater is dominated by the Na-Cl water type. In this region, the main geochemical processes controlling groundwater chemistry are ion exchanges, mineralization and evaporation. Groundwater salinization in coastal aquifers of the Mekong Delta is caused by (1) paleo-seawater intrusion and evaporation occurring in the Holocene and Pleistocene aquifers, (2) dissolution of salt sediment/rock and leakage of saline from upper to lower aquifers due to excessive groundwater exploitation and hydraulic connection. High nitrate concentrations in both shallow and deep aquifers are related to human activities. These results imply that groundwater extraction may exacerbate groundwater quality-related problems and suitable solutions for sustainable groundwater management in the coastal area of the Mekong Delta are needed.

Towards understanding groundwater quality using hydrochemical and statistical approaches: case of shallow aquifer of Mahdia-Ksour Essaf (Sahel of Tunisia)

Understanding the controlling factor of groundwater quality could certainly enhance the promotion of the sustainable development of groundwater resources. In fact, during the last decades, the coastal aquifer of Mahdia-Ksour Essef that belongs to the semi-arid region of Tunisia has been marked by an increase of groundwater extraction for irrigation and water for drinking. Moreover, the water quality shows deterioration due to the septic tanks and intensive agricultural activities especially in the coastal side of the aquifer. This study aimed to (1) assess the water quality using Piper Diagram, Box Plot, ions scatter diagrams, (2) understand the processes of mineralization acquisition in the aquifer, and (3) identify the chemical processes and their spatial distribution in the study area. To solve these objectives, the multivariate statistical analysis such as multiple correspondence analysis and hydrochemical analysis was performed. Accordingly, two types of groundwater are identified through the hydrochemical analysis as Na-Cl and Ca-SO₄. According to multiple correspondence analysis, three water groups are determined (G1, G2, and G3). Indeed, the groundwater quality is controlled by the water-rock interactions and affected by the seawater intrusion and agricultural activities. The generated results would be helpful to provide a managing model highlighting the threatened locations. It could be considered as a basis for future monitoring programs that aspire to protect water resources.

Anthropogenic Effects on Hydrogeochemical Characterization of the Shallow Groundwater in an Arid Irrigated Plain in Northwestern China

Many irrigated plains in arid and semi-arid regions have groundwater quality issues due to both intensive human activity and natural processes. Comprehensive studies are urgently needed to explore hydrogeochemical evolutions, investigate possible pollution sources, and understand the controls on groundwater compositions in such regions. Here, we combine geostatistical techniques and hydrogeochemical assessments to characterize groundwater quality over time in the Yinchuan Plain (a typical irrigated plain in China), using 12 physicochemical variables derived from sampling in 600 and 602 wells in 2004 and 2014, respectively. Our results show that groundwater-rock interactions and evaporation are the key natural factors controlling groundwater compositions. Hydrogeochemical water types in both 2004 and 2014 were Ca-HCO3, Na-Cl, and mixed Ca·Mg-Cl. Along with the hydrogeochemical compositions, we used ionic ratios and the saturation index to delineate mineral solution reactions and weathering processes. Dissolution of gypsum, halite, fluorite, and mirabilite, along with silicate weathering and cation exchange, were identified in the study area. Our results indicated rising ion concentrations in groundwater, which could be the result of anthropogenic influences. Increasing total hardness and nitrates over the study period were most likely caused by agricultural activity and the discharge of waste water from human residential areas.