Q-mode Hierarchical Cluster Analysis Research Articles

HERisk and statistical clustering integrated for health risk modelling of PTEs in natural water resources for drinking and sanitary uses

Potentially toxic elements (PTEs) are well-known for exposing living organisms and humans to different levels of risk. The present study aimed to evaluate the extent of exposure to health risks sustained by the inhabitants of different suburbs across Southeastern Nigeria as a result of contaminated water sources. There are existing literatures on human health risk assessment in the study region. However, this is the first study to report a detailed breakdown of the risks faced by nine age groups in the study area. This was achieved by integrating a novel code (HERisk), statistical clustering, and water quality data. Laboratory analysis showed that the levels of PTEs (Fe2+, Ni2+, Cr3+, and Pb2+) in 53.6%, 17.8%, 3.5%, and 46% of the samples were found to be above the recommended limits. Aggregated human health risk scores for ingestion and dermal routes revealed that children aged 1 to 2 years are the most vulnerable to health hazards. According to cumulative carcinogenic health risk values (0.00E+00 to 2.41E-04), samples proximal to regions with significant human activities expose the locals to a high risk of developing cancer via ingestion. Q-mode hierarchical cluster analysis successfully validated the classification schemes used for the interpretation of the HERisk code values, captured the patterns in the dataset, and brought forth new perspectives. The comprehensive approach detailed in this study can be adopted as a framework for ongoing monitoring and assessment of water quality.

Hydrogeochemical characterization and natural background level determination of selected inorganic substances in groundwater from a semi-confined aquifer in Midwestern Burkina Faso, West Africa.

Hydrogeochemical processes that govern selected inorganic substances distribution in a semi-confined aquifer were characterized using traditional hydrogeochemical approaches and natural background levels (NBLs). Saturation indices and bivariate plots were used to investigate the effects of water-rock interactions on natural evolution of the groundwater chemistry, whereas Q-mode hierarchical cluster analysis and one-way analysis of variance classified the groundwater samples into three distinct groups. To highlight the groundwater status, NBLs and threshold values (TVs) of the substances were calculated using pre-selection method. Piper's diagram showed that the Ca-Mg-HCO3 water type was the only hydrochemical facies of the groundwaters. Although all samples, except a borewell with a high NO3- concentration, had major ion and transition metal concentrations within the World Health Organization's recommended guideline values for drinking water, Cl-, NO3- and PO43- exhibited scattered distribution patterns, reflecting their nonpoint anthropogenic sources in the groundwater system. The bivariate and saturation indices revealed that silicate weathering and possible gypsum and anhydrite dissolution contributed to the groundwater chemistry. In contrast, NH4+, FeT and Mn abundance appeared to be influenced by redox conditions. Strong positive spatial correlations between pH, FeT, Mn and Zn suggested that mobility of these metals was controlled by pH. The relative high F- concentrations in lowland areas may imply the impact of evaporation on this ion's abundance. Contrary to TVs of HCO3-, those of Cl-, NO3-, SO42-, F- and NH4+ were below the guideline values, confirming the influence of chemical weathering on the groundwater chemistry. Based on the present findings, further studies that take into account more inorganic substances are required for NBLs and TVs determination in the area, thereby setting up a robust sustainable management plan for the regional groundwater resources.

Evaluation of Hydrogeochemical Processes in Groundwater Using Geochemical and Geostatistical Approaches in the Upper Bengal Basin

Overexploitation of groundwater for irrigation and radical changes of river morphology in the Bengal basin has posed difficulties to sustainable management of this resource. Forty groundwater samples were collected from tube wells of the pre-monsoon and postmonsoon seasons in 2020, and the water parameters were analyzed. The hydrogeochemical studies, bivariate plots, and multivariate techniques were used to evaluate the rock-water interactions, influencing factors, and contamination pathways. The principal component analysis (PCA) was used to extract several directions in the data space and understand the different geochemical processes. Q-mode hierarchical cluster analysis coupled with the post hoc ANOVA test of variance was also used to divide the sampling sites based on the geochemical water facies. The PHREEQC-3v software was used to measure the partial pressure of CO2 in groundwater and elucidate the chemical reactions controlling the water chemistry. Near-neutral pH (7.4) and high EC (813.2 μS/cm), TDS (507.35 mg/L), and total hardness (383.45 mg/L) characterize the groundwaters of the study area. The research revealed that the order of abundance of cations was Ca2+>Mg2+>Na+>K+ and of anions was HCO3−>>Cl->SO42−>NO3->PO43-. The PCA revealed that the chemical properties of the groundwater are derived from rock-water interactions. Hierarchical cluster analysis showed that two distinct groundwater zones were affected by neighboring river flow and irrigation return flow. Several diagrams suggested that the water was mainly of Ca-HCO3 type originating from chemical weathering of rock-forming minerals with advanced water-rock interaction. The analyzed groundwater was supersaturated with calcite and partially saturated with dolomite. As a result, the chemical features of groundwater in the study area were largely dependent on the water-rock interaction, local lithological conditions, and neighboring river morphology. This study can be helpful for the improvement of water resource management, especially for drinking and irrigation purposes.

Characterization of groundwater in the 'Tamnean' Plutonic Suite aquifers using hydrogeochemical and multivariate statistical evidence: a study in the Garu-Tempane District, Upper East Region of Ghana

The 'Tamnean' Plutonic Suite aquifer is the main public water supply for the Garu-Tempane District. Thus, hydrogeochemical characterization is essential to provide valuable insights into pollution sources and the main controls on groundwater chemistry. In this regard, multivariate statistical methods, conventional hydrochemical graphical methods, and various ionic ratios complemented with PHREEQC geochemical modelling were carried out using 38 groundwater samples collected from the Tamnean Plutonic Suite aquifers, Ghana. The ionic ratio plots, the chloro-alkaline indices, and the graphical diagrams indicate that the major sources of groundwater chemistry are silicate mineral dissolution and cation exchange coupled with the leaching of domestic solid waste and nitrogen-based fertilizers. The Q-mode hierarchical cluster analysis reveals three spatial groundwater zones. Groundwater from recharge areas consists of Ca–Na–HCO3 water types in cluster 1. The intermediate zone is characterized by Ca–Mg–Na–HCO3 water types of moderate ionic compositions in cluster 2, and this evolves into a discharge zone in cluster 3 mainly of Ca–Mg–Na–HCO3–NO3 water types. The principal component analysis (PCA) reveals three factors, which account for 81% of the total variance, and this suggests most of the groundwater chemistry had longer interaction with the lithological materials. The PHREEQC geochemical modelling consisting of mineral saturation index indicates that groundwater is mostly supersaturated with respect to dolomite and undersaturated with respect to calcite, anhydrite, fluorite, gypsum, and halite. Based on the water quality index, the groundwater in the district is generally suitable for drinking water purposes. All the samples are within the World Health Organization acceptable limits for drinking water except for lower pH, elevated nitrate and bromide concentrations in some of the wells. About 10.5% of the groundwater samples are contaminated with nitrate, which may pose a health danger to the inhabitants in the communities. The finding of this study will not only contribute to solving the research paucity regarding the Tamnean Plutonic Suite aquifers in the Garu-Tempane District but will serve as a valuable document for water managers and decision-makers in Ghana.

Water quality assessment and geochemical processes in the unconfined coastal Boa Viagem Aquifer, Recife, NE Brazil

A hydrochemical study was conducted on the Quaternary Aquifer, in Recife, Brazil. Groundwater samples were collected in March–April 2015, at the beginning of the rainy season. Conventional graphics, ionic ratios, saturation indices, GIS mapping, and geostatistical and multivariate statistical analyses were used to water quality assessment and to characterize the main hydrochemical processes controlling groundwater’s chemistry. Q-mode hierarchical cluster analysis separated the samples into three clusters and five sub-clusters according to their hydrochemical similarities and facies. Principal Component Analysis (PCA) was employed to the studied groundwater samples where a three-factor model explains 80% of the total variation within the dataset. The PCA results revealed the influence of seawater intrusion, water-rock interaction, and nitrate contamination. The physico-chemical parameters of ~30% groundwaters exceed the World Health Organization (WHO) guidelines for drinking water quality. Nitrate was found at a concentration >10 mg NO3−/L in ~21% of the wells and exceeded WHO reference values in one. The integrated approach indicates the occurrence of the main major hydrogeochemical processes occurring in the shallow marine to alluvial aquifer as follow: 1) progressive freshening of remaining paleo-seawater accompanying cation exchange on fine sediments, 2) water-rock interaction (i.e., dissolution of silicates), and 3) point and diffuse wastewater contamination, and sulfate dissolution. This study successfully highlights the use of classical geochemical methods, GIS techniques, and multivariate statistical analyses (hierarchical cluster and principal component analyses) as complementary tools to understand hydrogeochemical processes and their influence on groundwater quality status to management actions, which could be used in similar alluvial coastal aquifers.

The geological and hydrogeological framework of the Panabako, Kodjari, and Bimbilla formations of the Voltaian supergroup – Revelations from groundwater hydrochemical data

This research demonstrates the utility of groundwater hydrochemical data for facilitating lithological mapping in a sedimentary terrain. Factor analysis and Q-mode Hierarchical Cluster Analysis (HCA) were applied to groundwater hydrochemical data from the Nasia Basin in Northern Ghana to determine the major sources of hydrochemical variation and the main spatial groundwater associations (groups). These analyses were complemented by mass balance hydrochemical modeling from PHREEQC and petrographical analysis of rock samples from the area. Rock samples from the study area were subjected to petrographical and geochemical analyses from a petrographic microscope and Scanning Electron Microscope (SEM) respectively. Four principal factors were distinguished from the factor analysis, highlighting four principal processes responsible for the observed hydrochemistry in the area. These four factors cumulatively account for over 79% of the total variance in the dataset. Factor scores were computed from the factor loadings matrix through a regression process, to highlight the spatial variations in the significance of each of the factors in the terrain. On the basis of the parameter loadings, the first factor, which has been noted to be pervasive throughout the terrain, has been interpreted to represent silicate mineral weathering. Both the geochemical data and petrographical analysis indicate the presence of silicate minerals indicating the plausibility of silicate mineral weathering. The process of silicate mineral weathering appears to be highly pervasive throughout the basin, indicating high factor scores in places. The trend of spatial variations in the scores of factor 1 clearly mimics the known geology of the terrain, indicating that the geology is the main controlling factor in the hydrochemistry of groundwater in the basin. This pattern, exhibited by the factor scores indicates that where adequate groundwater hydrochemical data is available, factor analysis would prove useful in mapping out lithological variations in an area. Two of the remaining factors have been observed to represent other specific geogenic processes. Mass balance hydrochemical modeling suggests that albite may be in active dissolution, presenting pervasively negative saturation indices (undersaturation), while kaolinite is extensively supersaturated. Five groundwater associations distinguished from the Q-mode HCA display a spatial pattern which identifies with the underlying geology.

Geochemical evolution of groundwater in hard-rock aquifers of South India using statistical and modelling techniques

ABSTRACTMultivariate statistical analysis and inverse geochemical modelling techniques were employed to deduce the mechanism of groundwater evolution in the hard-rock terrain of Telangana, South India. Q-mode hierarchical cluster analysis (HCA) and principal component analysis (PCA) were used to extract the hydrogeochemical characteristics and classify the groundwater samples into three principal groups. Use of thermodynamic stability diagrams and inverse geochemical modelling in PHREEQC identified the chemical reactions controlling hydrogeochemistry of each of the groups obtained from statistical analysis. The model output showed that a few phases are governing the water chemistry in this area and the geochemical reactions responsible for evolution of groundwater chemistry along the flow path are (i) dissolution of evaporite minerals (dolomite, halite); (ii) dissolution of primary silicate minerals (albite, anorthite, K-feldspar, biotite); (iii) precipitation of secondary silicate minerals (kaolinite, quartz, gibbsite, Ca-montmorillonite) along with anhydrite and calcite; and (iv) reverse ion exchange processes.

Assessment of groundwater quality and the main controls on its hydrochemistry in some Voltaian and basement aquifers, northern Ghana

Groundwater resources play the single most important role in the delivery of potable water to rural communities in northern Ghana, especially during the long dry season and where surface water sources are polluted or non-existent. This study sought to assess the quality and main controls on groundwater chemistry in parts of Sawla-Tuna-Kalba District in the Savannah Region of Ghana. Multivariate statistical analysis and conventional hydrochemical plots were employed in the analysis of 112 groundwater samples from the study area. Conventional graphical methods, R-mode Hierarchical Cluster Analysis (HCA) and Principal Component Analysis (PCA) identified dissolution of silicates and the influence of agrochemicals and domestic wastewaters as the main sources of variations in the hydrochemistry in the study area. Q-mode HCA coupled with Stiff diagrams identified Ca–HCO3 water type in recharge areas, and Mg–Ca–HCO3 water type, which evolves into a Ca–Na–K–HCO3 water type in discharge areas in the groundwater flow regime. Mineral stability diagrams indicate the groundwater is stable in kaolinite, which suggests little or no restricted groundwater flow conditions. Groundwater quality for domestic purposes was assessed using the weighted arithmetic index approach. The computed water quality indices (WQIs) from the data suggest that 94% of the sampled boreholes provide groundwater of “excellent” quality for drinking purposes, whereas 5% and 1% present water of “good” and “poor” quality respectively. Spatial interpolation of the estimated WQIs suggests the quality of the groundwater in the study area is suitable for domestic purposes. The assessment of the groundwater quality for irrigation purposes suggests the water is of “excellent” to “permissible” quality and may be used for irrigation without prior treatment.

Hydrochemical Characterization of Benin Formation in Benin-city and Environs, Nigeria using Multivariate Analyses

Multivariate statistics was applied to some hydrochemical data from Benin Formation in Benin-city metropolis, Southern Nigeria with a view to characterizing and determining the main structures underlying groundwater chemistry in the area. Laboratory chemical analysis followed standard laboratory analytical procedures stipulated by American Society for Testing and Materials (ASTM). Hydrochemical data were standardized to z-scores and screened for outliers, normality and linearity prior to statistical analysis at significant level of 5%. Q-mode Hierarchical Cluster Analysis (HCA) grouped the groundwater samples into distinct clusters to represent different hydrochemical facies. R-mode Principal Component analysis (PCA) reduced bulk hydrochemical data to discrete principal components indicating possible dominant processes responsible for groundwater chemistry. Results of PCA revealed six principal components (PCs) which together explain 86.84 % of the total variance in the dataset. The results of PCA implied that Ca, total hardness, Mg, total dissolved solids, chloride, electrical conductivity and Na are the most significant parameters controlling groundwater chemistry in the area. The extracted components also indicated that atmospheric controls and silicate mineral weathering processes are the main factors responsible for variation in groundwater chemical variations in the area. Results of HCA which identified six significant clusters indicated high degree of spatial, statistical and chemical coherence, and validated grouping of groundwater into chemical clusters in the study area. Results from this study showed PCA and HCA are useful tools for analyzing dominant processes responsible for variation in groundwater chemistry in the study area. Keywords : Principal component analysis, cluster analysis, groundwater chemistry, coefficient of variation. DOI : 10.7176/JSTR/5-7-02

Provenance studies of Kalabsha kaolin deposits, Egypt: a petrographical and geochemical approach

The present study focuses on the kaolin deposit in Kalabsha area south Western Desert of Egypt in an attempt to determine its possible source, tectonic setting, and weathering history by means of integrated petrographical and geochemical approaches. The petrographical study was worked by microscopic investigation and supported by X-ray diffraction analysis. X-ray fluorescence and inductively coupled plasma-mass spectrophotometry methods were used for the determination of the bulk elemental composition. Mineralogical analysis revealed that kaolinite is the main clay mineral component indicating a severe chemical weathering of Al-rich source rocks and complete leaching under warm, semiarid climatic conditions. The nonclay minerals are represented by quartz, iron oxides and hydroxides, Ti-bearing minerals, and zircon. Geochemical data show a prevalence of SiO2 and Al2O3 and enrichment of Hf, Nb, Ta, Th, U, and Zr that support the kaolinitic nature of the deposits and their derivation from a felsic granitic terrain. The high values of the chemical index of alteration and the lower values of the index of compositional variability also suggest an intensive weathered source area and the geochemical maturity of the sediments. Other relevant geochemical discriminant functions and plots reveal felsic igneous parent rock for the kaolin deposits. Q-mode hierarchical cluster analysis combined with the normalized rare earth element patterns played a crucial role in unraveling the origin of the studied deposits. The results show that the most probable source rock of the Kalabsha kaolin deposits is the intense weathering of relatively proximal Adara Adatalob granites and their similar rock types in the Arabian-Nubian Shield from the south Eastern Desert of Egypt.

Evolutionary analysis of groundwater flow: Application of multivariate statistical analysis to hydrochemical data in the Densu Basin, Ghana

An evolutionary trend has been postulated through the analysis of hydrochemical data of a crystalline rock aquifer system in the Densu Basin, Southern Ghana. Hydrochemcial data from 63 groundwater samples, taken from two main groundwater outlets (Boreholes and hand dug wells) were used to postulate an evolutionary theory for the basin. Sequential factor and hierarchical cluster analysis were used to disintegrate the data into three factors and five clusters (spatial associations). These were used to characterize the controls on groundwater hydrochemistry and its evolution in the terrain. The dissolution of soluble salts and cation exchange processes are the dominant processes controlling groundwater hydrochemistry in the terrain. The trend of evolution of this set of processes follows the pattern of groundwater flow predicted by a calibrated transient groundwater model in the area. The data suggest that anthropogenic activities represent the second most important process in the hydrochemistry. Silicate mineral weathering is the third most important set of processes. Groundwater associations resulting from Q-mode hierarchical cluster analysis indicate an evolutionary pattern consistent with the general groundwater flow pattern in the basin. These key findings are at variance with results of previous investigations and indicate that when carefully done, groundwater hydrochemical data can be very useful for conceptualizing groundwater flow in basins.

Hydrogeochemistry and geothermometry of thermal springs from the Guelma region, Algeria

This paper reports the results of our studies, the chemical analysis of thermal spring’s waters and their geological settings, the use of different statistical methods to evaluate the origin of the dissolved constituents of spring waters and the estimation of the reservoir temperature of the associated geothermal fields of the Guelma region, Algeria. A major component in 13 spring water samples was analyzed using various techniques. The waters of the thermal springs at Guelma basin vary in temperature between 20 and 94oC. Q-mode hierarchical cluster analysis suggests three groups. The water springs were classified as low, moderate and high salinity. Mineral saturation indices (SI) calculated from major ions indicate the spring waters are supersaturated with the most of the carbonate minerals, and all of the spring water samples are under-saturated with evaporite minerals. The thermal spring waters have a meteoric origin, and all samples are immature with strong mixing between warm and shallow waters, where the temperatures of reservoirs to which the thermal waters are related ranged between 64° and 124°C. The deep circulation of meteoric waters in the study area is supplied by the high geothermal gradient around 4.5°C per 100 m and reaches a high temperature before rising to the surface. The estimated circulation depths ranged from 1425 and 3542 m.

Multivariate indications between environment and ground water recharge in a sedimentary drainage basin in northwestern China

A paucity of studies on the interaction between environment and ground water recharge severely restricts the ability of people to assess future water resources under changing environment. In this study, an effort to explore the relationship between the arid environment and ground water recharge was carried out using multivariate statistical techniques in a sedimentary drainage basin (the Jungar) in northwestern China. Hierarchical cluster analysis (HCA) and principal components analysis (PCA) were performed based on hydrogeochemical data to assess the ground water recharge and its governing factors. Observation of the HCA and PCA analytical results revealed a division of seven clusters (C1 to C7) and three principal components (PC1 to PC3), which explained 59.6%, 16.6% and 10.9% of the variance, respectively, and thus, accounted for the majority of the total variance in the original dataset. Based on these Q-mode HCA clusters and R-mode PAC scores, dominant environmental processes influencing recharge regimes were identified, i.e., geogenic, geomorphoclimatic, and anthropogenic, which separated the recharge regimes into four zones (Zone I to Zone IV). Zones I and II (C4+C1) were associated to “elevated hydroclimate degree” coupled to “low salinity”. Zone III (C2+C3) was associated to “moderately elevated salinity” and evidently “elevated contamination” but coupled to “low hydroclimate degree”. Zone IV (C5+C6+C7) was associated mainly to “elevated salinity” coupled to “low or inverse hydroclimate degree”. It revealed that the geogenic processes are more significant (60%) than the geomorphoclimatic (17%) and anthropogenic (11%) processes. As a result, the overall recharge process is rather heterogeneous and is strongly environment dominated in the Jungar drainage system. Compared with other watersheds in arid environment, a distinctive feature of the Jungar waters is that they are affected by a combination of natural and non-natural events, rather than following a steady and continuous geological evolution. These will continue to influence the recharge regime of the Jungar for a long time due to its steady tectonics and arid climate. However, changing rainfall, but not snow, is becoming the key factor driving changes in ground water resources in this drainage system, as results of the decades of warming and humidification in northwestern China.

Influence of ligands on metal speciation, transport and toxicity in a tropical river during wet (monsoon) period

Metal speciation and transport are seldom assessed in densely populated Tropical River. An evaluation of the phase distribution for Copper (Cu), Lead (Pb) and Zinc (Zn) along with chemical speciation, variance with different water quality parameters and toxicity were conducted in the Brahmaputra River of India from upstream to downstream during wet (monsoon) periods in July 2014. Results indicated that metal free ions and carbonates were dominant in the inorganic fractions whereas metal concentrations were negligible in the anionic inorganic fractions. Due to high sediment load in the river during monsoon, metals were substantially higher in the particulate fractions than in the aqueous phase. Partition coefficient for Cu (3.1–6.1), Pb (3.4–6.5) and Zn (3.5–6.9), demonstrated strong adsorption of the metals on suspended matter. Q-mode hierarchical cluster analysis (HCA) illustrated groupings mainly governed by quality parameters rather than by the river course. R-mode results imply selectivity of the affinities of metals for different ligands. Health risk index (HRI) values were less than 1 for dissolved metal for Cu, Pb and Zn while it was greater than 1 for total metal for Pb and Cu indicating potential human health risk. The study demonstrated that binding of metals with naturally occurring dissolved organic matter or suspended particulate matter affects metal bioavailability in river during wet periods when sediment load is particularly high. A combination of empirical, computational and statistical relationships between ionic species and fractions of metals provided greater certitude in identifying the resemblance among the different locations of the river.

Hydrogeochemistry and quality of surface water and groundwater in the vicinity of Lake Monoun, West Cameroon: approach from multivariate statistical analysis and stable isotopic characterization.

With the use of conventional hydrogeochemical techniques, multivariate statistical analysis, and stable isotope approaches, this paper investigates for the first time surface water and groundwater from the surrounding areas of Lake Monoun (LM), West Cameroon. The results reveal that waters are generally slightly acidic to neutral. The relative abundance of major dissolved species are Ca(2+)>Mg(2+)>Na(+)>K(+) for cations and HCO3 (-)≫NO3 (-)>Cl(-)>SO4 (2-) for anions. The main water type is Ca-Mg-HCO3. Observed salinity is related to water-rock interaction, ion exchange process, and anthropogenic activities. Nitrate and chloride have been identified as the most common pollutants. These pollutants are attributed to the chlorination of wells and leaching from pit latrines and refuse dumps. The stable isotopic compositions in the investigated water sources suggest evidence of evaporation before recharge. Four major groups of waters were identified by salinity and NO3 concentrations using the Q-mode hierarchical cluster analysis (HCA). Consistent with the isotopic results, group 1 represents fresh unpolluted water occurring near the recharge zone in the general flow regime; groups 2 and 3 are mixed water whose composition is controlled by both weathering of rock-forming minerals and anthropogenic activities; group 4 represents water under high vulnerability of anthropogenic pollution. Moreover, the isotopic results and the HCA showed that the CO2-rich bottom water of LM belongs to an isolated hydrological system within the Foumbot plain. Except for some springs, groundwater water in the area is inappropriate for drinking and domestic purposes but good to excellent for irrigation.

Using inverse modeling and hierarchical cluster analysis for hydrochemical characterization of springs and Talkhab River in Tang-Bijar oilfield, Iran

Hierarchical cluster analysis (HCA) and inverse modeling (PH REdox EQuilibrium (in C language) (PHREEQC)) were simultaneously useful approaches in interpreting surface water hydrochemistry within Talkhab River in the Tang-Bijar oilfield, Iran, where large uncertainties exist in the understanding of the water quality system. Q-mode HCA applied to the data revealed three major surface water associations distinguished on the basis of the major causes of variation in the hydrochemistry. The three water groups were classified as upstream waters (group 1: Ca–SO4), intermediate waters (group 2: Ca–SO4–Cl), and downstream waters (group 3: Na–Cl). Geochemical reaction models were constructed using PHREEQC to establish the reactions associated with the different mineral phases through inverse modeling. The hydrochemical compositions of the water groups and the mass balance calculations indicate that the dominant processes and reactions responsible for the hydrochemical evolution in the system are (1) dissolution of evaporites, (2) precipitation of carbonate minerals, (3) silicate weathering reactions, (4) limited mixing with saline water, and (5) ion exchange.

Statistical study to identify the key factors governing ground water recharge in the watersheds of the arid Central Asia

Understanding the source and recharge of ground waters is of great significance to our knowledge in hydrological cycles in arid environments over the world. Northern Xinjiang in northwestern China is a significant repository of information relating to the hydrological evolution and climatic changes in central Asia. In this study, two multivariate statistical techniques, hierarchical cluster analysis (HCA) and principal component analysis (PCA), were used to assess the ground water recharge and its governing factors, with the principal idea of exploring the above techniques to utilize all available hydrogeochemical variables in the quality assessment, which are not considered in the conventional techniques like Stiff and Piper diagrams. Q-mode HCA and R-mode PCA were combined to partition the water samples into seven major water clusters (C1-C7) and three principal components (PC1-PC3, PC1 salinity, PC2 hydroclimate, PC3 contaminant). The water samples C1 + C4 were classified as recharge area waters (Ca-HCO3 water), C2 + C3 as transitional zone waters (Ca-Mg-HCO3-SO4 water), and C5 + C6 + C7 as discharge area waters (Na-SO4 water). Based on the Q-mode PCA scores, three groups of geochemical processes influencing recharge regimes were identified: geogenic (i.e., caused by natural geochemical processes), geomorphoclimatic (caused by topography and climate), and anthropogenic (caused by ground water contamination). It is proposed that differences in recharge mechanism and ground water evolution, and possible bedrock composition difference, are responsible for the chemical genesis of these waters. These will continue to influence the geochemistry of the northern Xinjiang drainage system for a long time due to its steady tectonics and arid climate. This study proved that the chemistry differentiation of ground water can effectively support the identification of ground water recharge and evolution patterns.

Physical and isotopic characteristics in peri-urban landscapes: a case study at the lower Volta River Basin, Ghana

The study presents the application of selected multivariate techniques: display methods (principal component analysis) and unsupervised pattern recognition (cluster analysis) in an attempt to discriminate sources of variation of water quality. PCA has allowed the identification of a reduced number of latent factors with a hydrochemical meaning: natural and anthropogenic (domestic and agricultural activities) factors, which also agrees with the R-mode hierarchical cluster analysis (HCA). Q-mode HCA also corroborates the results of the correlation analysis in relation to sampling sites established on hydrochemical parameters, indicating that there are no spatial and temporal characteristics among the sampling sites in the study area. The suitability of river water for irrigation use was assessed in the study area. A plot of the sodium adsorption ratio (SAR) and salinity data on a semilog axis suggests that river water provides good irrigation quality in the area. According to the SAR values plotted in the USSL Staff diagram, 100 % of the river water samples fall in C1–S1 (low salinity–low sodium type) group, which provides good irrigation quality to river water from this area. Also, all the data points showed permeability index values in Class II category which is suitable for irrigation purposes. Recorded magnesium ratio and Kelly’s ratio showed that <50 % of the river water samples were suitable for irrigation purposes. Stable isotope data of water (δ18O and δ2H) obtained revealed that stream waters joining the Volta River were depleted and possibly recharged by rain and waters from the Akwapim Mountains (located at the western part of the Volta River) than the isotopically heavy evaporated waters found within the Lower Volta River. These results would therefore be useful for water balance studies in the study area.

Evaluation of groundwater quality and assessment of scaling potential and corrosiveness of water samples in Kadkan aquifer, Khorasan-e-Razavi Province, Iran.

The chemical analysis of 129 groundwater samples in the Kadkan area, Khorasan-e-Razavi Province, NE of Iran was evaluated to determine the hydrochemical processes, assessment of groundwater quality for irrigation purposes, corrosiveness, and scaling potential of the groundwater. Accordingly, the suitability of groundwater for irrigation was evaluated based on the sodium adsorption ratio, residual sodium carbonate, sodium percent, salinity hazard, and US Salinity Laboratory hazard diagram. Based on the electrical conductivity and sodium adsorption ratio, the dominant classes are C3-S1, C3-S2, C2-S1, and C4-S2. According to the Wilcox plot, about 50 % of the samples fall in the "Excellent to Good" and "Good to Permissible" classes. Besides, the Langelier saturation index, Ryznar stability index (RSI), Larson-Skold index, and Puckorius scaling index were evaluated for assessing the corrosiveness and scaling potential of the groundwater. Corrosiveness and scaling indices stated that the majority of samples are classified into "Aggressive" and "Very Aggressive" category. In addition, chloride and sulfate interfere in 90 % of the samples. Assessment of hydrochemical characteristics indicates Na-Mg-Cl as the predominant hydrochemical type. Spatial distribution of hydrochemical parameters indicates that hydrochemical processes are influenced by geology and hydrogeology of Kadkan aquifer. The Gibbs plots gave an indication that groundwater chemistry in this area may have acquired the chemistry mainly from evaporation and mineral precipitation. Grouping the samples based on Q-mode hierarchical cluster analysis helped to more separation of similar samples. The R-mode HCA grouped analyzed parameters into two groups based on similarity of hydrochemical characteristics. As a result, the samples collected in northern and southern parts of the study area show the best quality (i.e., lowest salinity) for some purposes such as irrigation and drinking.

Assessment of the quality of water by hierarchical cluster and variance analyses of the Koudiat Medouar Watershed, East Algeria

The assessment of surface water in Koudiat Medouar watershed is very important especially when it comes to pollution of the dam waters by discharges of wastewater from neighboring towns in Oued Timgad, who poured into the basin of the dam, and agricultural lands located along the Oued Reboa. To this end, the multivariable method was used to evaluate the spatial and temporal variation of the water surface quality of the Koudiat Medouar dam, eastern Algeria. The stiff diagram has identified two main hydrochemical facies. The first facies Mg-HCO3 is reflected in the first sampling station (Oued Reboa) and in the second one (Oued Timgad), while the second facies Mg-SO4 is reflected in the third station (Basin Dam). The results obtained by the analysis of variance show that in the three stations all parameters are significant, except for Na, K and HCO3 in the first station (Oued Reboa) and the EC in the second station (Oued Timgad) and at the end NO3 and pH in the third station (Basin Dam). Q-mode hierarchical cluster analysis showed that two main groups in each sampling station. The chemistry of major ions (Mg, Ca, HCO3 and SO4) within the three stations results from anthropogenic impacts and water–rock interaction sources.