Hydrogeochemical Processes Affecting Groundwater Chemistry in the Central Part of the Guanzhong Basin, China.

Groundwater is essential for the sustainable development of the Guanzhong Basin, China, and its quality is mainly controlled by hydrogeochemical processes and anthropogenic pollution. This study used statistical and multivariate statistical analysis approaches to recognize the hydrogeochemical processes and affecting factors of groundwater in the central part of the Guanzhong Basin. Correlations among 14 hydrochemical parameters were statistically examined. Principal component analysis (PCA), factor analysis (FA), and hierarchical cluster analysis (HCA) techniques were applied to analyze the physicochemical variables to understand the affecting factors of groundwater quality in the study area. The correlation analysis results indicate that cation exchange is the dominant process affecting the concentration of Na+ and Ca2+ in the groundwater. Both the PCA and FA indicate that minerals dissolution/precipitation and human activities are the key factors that affect groundwater quality. All parameters except CO32- and pH increase from C1 to C4 obtained through the Q mode HCA. C4 has a hydrochemical type of SO4-Na·K, indicating that the sample of this cluster is primarily influenced by anthropogenic processes.

Regional and temporal variation in minor ions in groundwater of a part of a large river delta, southern India.

Impact of agricultural activities on groundwater can be determined from the concentration of nutrients present in groundwater. This study was carried out with the aim to assess the minor ions content of groundwater and to identify its sources, spatial, and seasonal variations in a part of the Cauvery River basin, southern India. Groundwater samples were collected from July 2007 to September 2009 and were analyzed for minor ions. These ions were in the order of dominance of nitrate> phosphate> bromide> fluoride> ammonium= nitrite> lithium. The concentration of ions tends to increase towards the coast except for fluoride. Increased concentration of ions identified in shallow wells than in deep wells with an exception of few locations indicates the impact of human activities. Relatively high concentration of agriculture-sourced nitrate was identified which pose a threat to groundwater suitability for agriculture and domestic usage. Combined influence of use of agrochemicals, improper sewage disposal, aquaculture activities, seawater intrusion due to heavy pumping near the coast, and natural weathering of aquifer materials are the major sources. Also, fine grain sediments of this area aid in poor flushing of the ions towards the sea resulting in accumulation of higher concentration of ions. A sustainable management strategy is essential to control the concentration of these ions, especially nitrate. Reduced use of fertilizers, increasing the rainfall recharge for diluting the pollutants in groundwater and maintaining the river flow for sufficiently longer period to reduce dependence on groundwater for irrigation can help to improve the situation.

Geochemical evolution and the processes controlling groundwater chemistry using ionic ratios, geochemical modelling and chemometric analysis in uMhlathuze catchment, KwaZulu-Natal, South Africa.

The sources of chemical constituents of groundwater and its associated hydrogeochemical processes in the part of Mhlathuze catchment was identified. Groundwater of the area is classified into soft to very hard and the nature is identified as acidic to alkaline. The overall electrical conductivity is < 3000 µS/cm except in three wells. The predominant water type is NaCl (69% of samples) and CaMgCl facies. Gibbs plots, mCa/Mg ratio, mNa/Cl ratio, Ca + Mg vs HCO3+SO4 plot, Na + K vs HCO3 plot, Ca/Na vs HCO3/Na, Chloroalkaline indices (CAI 1, CAI 2) and Ca + Mg-HCO3-SO4 vs Na + K-Cl plots confirm the impact of silicate, carbonate mineral weathering and ion exchange reaction in this aquifer. However, few wells are influenced by the evaporation process. Groundwater is highly undersaturated with sulphate, chloride minerals and saturated with carbonate minerals. CA revealed that Cl and SO4 are derived from anthropogenic sources and a significant positive correlation between HCO3 and Cl reveals that wastewater recharge has most likely simulated the mineral weathering in the vadose zone, which could have further enhanced HCO3 and Cl in the aquifer. PCA resulted in three factors. Factor 1 defines the influence of geogenic and anthropogenic processes while Factors 2 and 3 imply the mineral weathering and nitrification processes. Hierarchical cluster analysis defines that evaporation, anthropogenic input, silicate and carbonate weathering and nitrification process are the sources of chemical constituents of groundwater in this aquifer.

Determination of potential recharge zones and its validation against groundwater quality parameters through the application of GIS and remote sensing techniques in uMhlathuze catchment, KwaZulu-Natal, South Africa.

Urbanization has accelerated changes in the quantity and stability of the water resources in the uMhlathuze watershed of KwaZulu-Natal. This study applied the use of GIS and remote sensing to demarcate groundwater potential recharge zones in the uMhlathuze catchment using AHP approach and Catastrophe theory by assigning weights to 10 parameters with their sub-criteria and the results were validated against groundwater quality data. It was discovered that 22.92% and 26.38% of the catchment is encompassed by 'Low' groundwater potential recharge zones, 0.37% and 0.08% by 'Very low' groundwater potential recharge zones, 9.42% and 10.26% by 'Good' groundwater potential recharge zones, 66.87% and 63.19% by 'Moderate', and 0.42% and 0.09% by 'Very good' for AHP and Catastrophe theory respectively. The resultant map demonstrated that recharge potential of groundwater is lowest in mountainous regions coupled with hard rock geology of low transmissivity, whereas the highest potential prevails in lower slopes and plains with more permeable soil. The findings of the validation revealed that the lowest and highest total dissolved solid, nitrate and groundwater level overlaps with the 'Good and Very good' and 'Low and Very low' groundwater potential recharge zones respectively. From the collective findings of this study, it is inferred that the convergence and use of GIS and remote sensing for delineating the groundwater potential recharge zones are effective. The study further recommends that this method can be applied in research/projects involving the implementation of artificial groundwater recharge structures for better groundwater planning and governance.

Mercury pollution on tourist beaches in Durban, South Africa: A chemometric analysis of exposure and human health.

Mercury (Hg) is a global pollutant that is a major public health concern due to its mobility, stability and toxicity behavior in the environment. In this study Hg concentrations were determined in beach sediment samples (n = 43) collected from the South Durban Coast, South Africa. A human health risk assessment was also carried out to comprehend the potential health effects of incidental ingestion/direct contact with contaminated sediments in a recreational setting. Hg concentrations ranged between 0.62 and 4.88 mg kg-1 dw., exceeding all background and regulatory limits. Numerical values of calculated exposure pathways represented dermal contact with the sediments as one of the potential paths in both adults and children. Hazard Index (HI) values were found to be less than unity signifying no adverse health effects. This study validates the critical need for long-term monitoring of Hg in various scenarios in order to incorporate better public health management strategies.

Adsorption behavior of aged polybutylece terephthalate microplastics coexisting with Cd(II)-tetracycline.

Microplastics (MPs) are one of the emerging classes of pollutants that can be infiltrated into any aqueous solutions from disposed toxic metals and antibiotics, further exacerbating the potential biotoxicity of MPs. However, the research on the interaction between MPs and various pollutants is limited. Therefore, in this study, the changes in toxicity of polybutylece terephthalate (PBT) MPs were assessed following adsorption of heavy metals and antibiotics. The adsorption behavior of Cd(II) and tetracycline (TC) on ultraviolet (UV) light-aged PBT was investigated. The results demonstrated that the Cd(II) adsorption behavior could be described by the pseudo-second-order kinetic and Langmuir isothermal models, while the TC adsorption behavior has well fitted using Elovich and Sips models. The whole adsorption process occurred via either external diffusion or internal diffusion. The interactions between aged PBT and pollutants were evaluated under different environmental conditions, such as solution pH and the concentrations of dissolved organic matter and cations. The amounts of Cd(II) and TC adsorbed were higher in the competitive systems than the single solution, which might attribute to the formation of Cd(II)-TC complexes and aged PBT functional group changes. The results of two-dimensional correlation spectroscopy (2D-COS) describes the sequence of functional group transformation during the uptake of Cd(II)-TC by aged PBT in binary systems. These findings identify a strong interaction between aged PBT and contaminants, establishing the potential fate of aged MPs under natural aquatic environment conditions.

Evaluation of high fluoride contaminated fractured rock aquifer in South Africa - Geochemical and chemometric approaches.

The first systematic study on high fluoride contaminated fractured rock aquifer in South Africa using geochemical and chemometric approach is presented. Groundwater samples were collected from 49 boreholes and analysed for EC, pH, major and minor ions. The groundwater with high fluoride is associated with NaCl water types. The groundwater chemistry is governed by mineral weathering, evaporation and wastewater infiltration. PHREEQC modelling indicates that carbonate mineral saturation is decreasing with increasing salinity due to evaporation whereas fluorite saturation increases with increasing F being one of the prime controlling factors. Silicate minerals namely chalcedony, quartz and talc express saturation and over-saturation while chrysotile and sepiolite are undersaturated in most of the samples. PCA provided four factors and justified the role of mineral weathering, evaporation, ion exchange, longer residence time and anthropogenic impacts on water chemistry. R-mode and Q-mode cluster analysis resulted in four clusters. In cluster 1, (29%) of groundwater is less mineralized due to recent recharge. In cluster 2 (45%), groundwater chemistry is governed by weathering of silicates and fluorite minerals. Cluster 3 (20%) reveals the impact of anthropogenic activities and induced mineral weathering. Cluster 4 shows high EC, TDS, major ions, F and low HCO3 implying that groundwater is affected by evaporation and longer residence time promoting mineral-water interaction and precipitation of carbonate minerals. More than 50% of the study area is degraded due to fluoride contamination which requires proper remedial actions and further investigations on human health risk due to impact of fluoride contamination in groundwater is recommended.

Spatial interpolation methods and geostatistics for mapping groundwater contamination in a coastal area.

Mapping groundwater contaminants and identifying the sources are the initial steps in pollution control and mitigation. Due to the availability of different mapping methods and the large number of emerging pollutants, these methods need to be used together in decision making. The present study aims to map the contaminated areas in Richards Bay, South Africa and compare the results of ordinary kriging (OK) and inverse distance weighted (IDW) interpolation techniques. Statistical methods were also used for identifying contamination sources. Na-Cl groundwater type was dominant followed by Ca-Mg-Cl. Data analysis indicate that silicate weathering, ion exchange and fresh water-seawater mixing are the major geochemical processes controlling the presence of major ions in groundwater. Factor analysis also helped to confirm the results. Overlay analysis by OK and IDW gave different results. Areas where groundwater was unsuitable as a drinking source were 419 and 116 km2 for OK and IDW, respectively. Such diverse results make decision making difficult, if only one method was to be used. Three highly contaminated zones within the study area were more accurately identified by OK. If large areas are identified as being contaminated such as by IDW in this study, the mitigation measures will be expensive. If these areas were underestimated, then even though management measures are taken, it will not be effective for a longer time. Use of multiple techniques like this study will help to avoid taking harsh decisions. Overall, the groundwater quality in this area was poor, and it is essential to identify alternate drinking water source or treat the groundwater before ingestion.

Chemical, microbial and antibiotic susceptibility analyses of groundwater after a major flood event in Chennai.

During floods, human exposure to pathogens through contaminated water leads to the outbreak of epidemic diseases. This research presents the first extensive assessment of surface and groundwater samples collected immediately after a flood (December 2015) and post-flood (April 2016) from the Adyar River of Chennai, a major city in India, for major ions, trace metals, bacterial population, and pathogens. Severe rains in a short period of time resulted in flooding which inundated the wells, allowing the entry of sewage contaminated river water into the groundwater zone. This has led to bacterial counts and chemical ions exceeding Bureau of Indian Standard's recommended limits in most flood affected areas. Pathogens isolated from the groundwater showed resistance to antibiotics, namely ceftriaxone, doxycycline and nalidixic acid. However, they were sensitive to chloramphenicol, ciprofloxacin, norfloxacin, and tetracycline. Determining the antibiotic susceptibility of pathogens will help in the treatment of humans affected by contaminated water through an appropriate selection of prescribed medication.