Guanxing Huang

Impact of anthropogenic and natural processes on the evolution of groundwater chemistry in a rapidly urbanized coastal area, South China.

The moving of manufacturing industry from developed countries to Dongguan, China, promoted the semi-urbanization and rural industrialization in this area. It is urgent to acquire the impact of the enhanced anthropogenic pressure on the evolution of groundwater chemistry in this area. The objectives, in this study, were to understand the evolution of groundwater chemistry in Dongguan area based on the comparison of hydrochemical data variations and land use changes during the urbanization, to distinguish the impact of natural processes and anthropogenic activities on the groundwater chemistry by using principal components analysis (PCA) and hierarchical cluster analysis (HCA), and to discuss the origins of trace elements in groundwater. Eighteen physico-chemical parameters were investigated at 73 groundwater sites during July 2006. By analyzing the hydrochemical data, it shows that lateral flow from rivers and agricultural irrigation are the mechanisms controlling the groundwater chemistry in the river network area where the cation exchange of Na(+) in sediments taken up by the exchanger Ca(2+) occurs. Seawater intrusion is the mechanism controlling the groundwater chemistry in the coast area where the cation exchange of Ca(2+) in sediments taken up by the exchanger Na(+) occurs. The ion exchange reaction for fissured aquifer is weak in the study area. In addition, the comparison of hydrochemical data between in 2006 and in 1980 shows that anthropogenic activities such as excessive application of agricultural fertilizers, inappropriate emissions of domestic sewage and excessive emissions of SO2 are responsible for the occurrences of groundwater with NO3(-), SO4(2-) and Mg(2+) types. Four principal components (PCs) were extracted from PCA, which explain 80.86% of the total parameters in water chemistry: PC1, the seawater intrusion and As contamination; PC2, the water-rock interaction, surface water recharge and acidic precipitation; PC3, heavy metal pollution from industry; and PC4, agricultural pollution and sewage intrusion. Four clusters were generated from HCA: cluster 1 is mainly influenced by the industrialization; cluster 2 is mainly affected by the water-rock interaction and the irrigation and lateral flow of river water; cluster 3 is mainly influenced by the seawater intrusion; and cluster 4 is mainly influenced by the sewage intrusion and agricultural pollution. The results show that both natural processes such as seawater intrusion, water-rock interaction and lateral flow of river water and anthropogenic activities such as industrialization, sewage intrusion and agricultural pollution are the two major factors for the evolution of groundwater chemistry in Dongguan area.

Effect of sample pretreatment on the fractionation of arsenic in anoxic soils

Using by sequential extraction procedures to obtain the chemical forms of arsenic in soils can provide useful information for the assessment of arsenic mobility and bioavailability in soils. However, sample pretreatments before the extraction probably have some effects on the fractionation of arsenic in soils. Impact of sample pretreatments (freeze-drying, oven-drying, air-drying, and the fresh soil) on the fractionation of arsenic in anoxic soils was investigated in this study. The results show that there are some differences for arsenic fractions in soils between by drying pretreatments and by the fresh soil, indicating that the redistribution among arsenic fractions in anoxic soils occurs after drying pretreatments. The redistribution of arsenic fractions in anoxic soils is ascribed to the oxidation of organic matter and sulfides, the crystallization of iron (hydr)oxides, the ageing process, and the diffusion of arsenic into micropores. The freeze-drying is the best drying method to minimize the effect on the fractionation of arsenic in anoxic soils, while air-drying is the worst one. Drying pretreatments are not recommended for the fractionation of arsenic in anoxic soils with high concentration of iron.

Driving mechanism and sources of groundwater nitrate contamination in the rapidly urbanized region of south China

Nitrate contamination of groundwater has become an environmental problem of widespread concern in China. We collected 899 groundwater samples from a rapidly urbanized area, in order to identify the main sources and driving mechanisms of groundwater nitrate contamination. The results showed that the land use has a significant effect on groundwater nitrate concentration (P<0.001). Landfill leakage was an important source of nitrate in groundwater in the PRD (Pearl River Delta) region, since landfill yielded the highest nitrate concentration (38.14 mg/L) and the highest ratio of exceeded standard (42.50%). In this study, the driving mechanism of groundwater nitrate contamination was determined to be urban construction and the secondary and tertiary industrial development, and population growth. This study revealed that domestic wastewater and industrial wastewater were the main sources of groundwater nitrate pollution. Therefore, the priority method for relieving groundwater nitrate contamination is to control the random discharge of domestic and industrial wastewater in regions undergoing rapid urbanization. Capsule abstract. The main driving mechanism of groundwater nitrate contamination was determined to be urban construction and the secondary and tertiary industrial development, and population growth.

Water quality assessment and hydrochemical characteristics of groundwater on the aspect of metals in an old town, Foshan, south China

The present study is aimed at assessing the water quality and discussing the hydrochemical characteristics and seasonal variation of shallow groundwater on the aspect of metals in the eastern Chancheng district of Foshan city, south China. Multivariate analytical methods such as principal components analysis (PCA) and hierarchical cluster analysis (HCA) were used in this study. The results show that 45% of groundwater in the east-central of study area is not suitable for drinking purpose due to high concentrations of Fe, Pb and Mn. The mean concentrations of Fe, Hg, Cu, Pb, and Mn in dry season are higher than that in wet season. On the contrary, the mean concentrations of Cd, Co, Zn, Ba, Cr, Mo, Ni and Al in wet season are higher than that in dry season. PCA results show that four PCs are responsible for the 78.6% of the total hydrochemical variables in groundwater. Three groups were generated from HCA method. Group 1 reflects the characteristic of wet season and the low ion exchange capacity; group 2 is mainly influenced by the dry season. Reducing environment and high ion exchange capacity are responsible for group 3. The results are useful in addressing future measures in groundwater resource management for local government.

A regional scale investigation on factors controlling the groundwater chemistry of various aquifers in a rapidly urbanized area: A case study of the Pearl River Delta

A growing population accompanied by urbanization has increased groundwater resource demands in the Pearl River Delta (PRD) area, southern China, and a comprehensive understanding of the groundwater chemistry in the PRD is necessary. The aims of this study were to investigate the groundwater chemistry in various aquifers in the PRD on a regional scale and to discuss the factors that control the groundwater chemistries of different types of aquifers. In addition, the effect of the expansion of construction land on the groundwater chemistry was also taken into consideration in this study. Nearly 400 groundwater samples were collected and fourteen chemical parameters were investigated. The results show that natural factors, such as seawater intrusions, are mainly responsible for the higher concentrations of total dissolved solids, Na+, Mg2+, K+, and Cl-, in granular aquifers than those in fissured and karst aquifers. Similarly, higher concentrations of NH4+, Fe and Mn in granular aquifers than those in the other two types of aquifers are mainly ascribed to natural reduction. In contrast, human activities, such as the continuous irrigation of river water, upon granular aquifer are mainly responsible for the higher concentrations of Ca2+ and HCO3- in granular aquifers than those in other two types of aquifers. Urbanization and industrialization are the main driving forces for the frequently occurrences of NO3 and SO4 water types, respectively. Moreover, the number of water types in the PRD increased to 89 after the decades of urbanization. Factors that control groundwater chemistries in various aquifers were extracted. A four-factor model controlled the groundwater chemistry of granular aquifers, while two three-factor models controlled the groundwater chemistries of fissured and karst aquifers, respectively. The results of this study show that the expansion of construction land is a powerful driving force for the change of groundwater chemistry in the PRD.

Water Quality Assessment and Hydrochemical Characteristics of Shallow Groundwater in Eastern Chancheng District, Foshan, China

Groundwater quality is the critical factor that affects human health and the quality of industrial products in Foshan City, South China. Multivariate statistical techniques, including hierarchical cluster analysis (HCA) and principal component analysis (PCA), were applied to evaluate and interpret the complex groundwater quality in eastern Chancheng district, Foshan City. During the dry and wet seasons, 60% and 11% of the total groundwater samples (respectively) are suitable for drinking purposes; other samples can be used for drinking after being treated for pH, Fe, Mn, Al, NH4, and NO3. Similarly, during the dry and wet seasons, 75% and 33% of the total groundwater samples (respectively) are suitable for industrial purposes; other samples can be used for industrial purposes after being treated for NH4 and NO3. Five principal components are extracted from PCA and used to explain 81.78% of the variance in groundwater. The indicators to groundwater quality assessment are EC, Na, Cl, Fe, Mn, NH4, pH, Eh, PO4, HCO3, and K from PCA. HCA reveals that groundwater samples in the study area can be classified into three groups: one reflecting the interaction of groundwater and sediment medium along with the role of cation exchange; another reflecting the role of anion exchange between phosphate and carbonate; and the final reflecting the reducing environment.

Groundwater quality in aquifers affected by the anthropogenic and natural processes in an urbanized area, south China

ABSTRACT The objective of this study is to investigate the impacts of anthropogenic and natural processes on the granular aquifer (GA) and the fractured rock aquifer (FRA) in the central region of Guangzhou city. Results indicate that 47.8% and 30.4% of samples in GA are not suitable for drinking and industrial purposes respectively, mainly due to the high concentrations of Fe and NH4+. In contrast, 48.3% and 41.4% of samples in FRA are not suitable for drinking and industrial purposes respectively, mainly due to the high concentrations of Al, NO3−, NH4+, Fe, and Pb. The contributions of Pb, Al, and NO3− to groundwater quality in GA are lower than those in FRA, while the contributions of Na+, Cl−, SO42−, and TDS to groundwater quality in GA and FRA are similar. High concentrations of Pb, Al, Na+, Cl−, SO42−, TDS, and NO3− in groundwater of both GA and FRA are mainly ascribed to human activities such as urbanization and industrialization, while high concentrations of Fe and NH4+ in groundwater of GA are mainly ascribed to natural processes such as reducing environment. More attention should be paid to the protection of groundwater quality in FRA than in GA due to the greater utilization of the groundwater resource in FRA than that in GA.

Distribution and Mobility of Heavy Metals in Soil of Sewage Irrigation Area in Pearl River Delta, China

The research reveals the mobility and distribution of heavy metals (Cd, Cu, Zn, Mn, Ni, and Cr) in soil of sewage irrigation area in Pearl River Delta. Samples were collected from topsoil (0-10cm) and subsoil (30-40cm), and the total concentration and available concentration of heavy metals were extracted by HNO3–HF–HClO4 and DTPA respectively. The mean total concentrations for all of the heavy metals in topsoil are higher than that in subsoil in study area. Cd has the best mobility in soil of study area due to soil has lower retention for Cd than for other metals, while Ni has the poorest mobility in soil of study area. The total concentrations of Zn, Cu and Cd decrease with the depth of soil profile, while the total concentrations of Cr and Ni have little change with the depth of soil profile, only the total concentration of Mn has a little decrease at first and then increased rapidly with the depth of soil profile.

Heavy Metal Contamination and Potential Ecological Risk Assessment of Sediments in Yangzonghai Lake

The contents and characteristics of ten heavy metals in surface sediments from Yangzonghai Lake in Yunnan, China were analyzed. Ecological risk index presented by Håkanson to assess the potential ecological risk of Yangzonghai Lake was utilized. The results showed that the average concentrations of titanium(Ti), manganese(Mn), zinc(Zn), vanadium(V), chromium(Cr), copper(Cu), nickel(Ni), cobalt(Co), lead(Pb) and arsenic(As) in surface sediments of Yangzonghai Lake were up to 9413.1, 617.9, 149.2, 189.6, 145.8, 97.6, 55.1, 27.4, 40.3 and 31.4mg/kg, respectively, which are higher than their natural background values. Pearson’s correlation analysis indicated that Zn, Cr, Pb and As were highly correlated, and the similar distributions in sediment indicated that they might originate from activities. Ti, Mn, V, Cu, Ni, and Co were also well correlated, and the distributions indicated that they were mainly from natural factors. The evaluation of pollution index revealed a clear accumulation of the 10 heavy metals, all reaching the level of moderate pollution. As, Cu and Cr were the most important environmental contaminants in Yangzonghai Lake. As a whole, heavy metals reached the level of low ecological risks, and in some parts, they reached the moderate level. Heavy metals in Yangzonghai Lake in the descending order of their ecological risks were As, Cu, Co, Ni, Pb, Cr, V, Zn, Mn and Ti. As was more prominent than other heavy metals in terms of the ecological risk and thus the most important factor of potential ecological risk in surface sediment of Yangzonghai Lake.

Natural Background Levels of Fe and Mn in Groundwater of Pearl River Delta

As scientific references of evaluation on the groundwater contamination, natural background levels about chemical indexes TFe and Mn of shallow groundwater in Pearl River Delta was derived with SPSS statistical software, and its spatial distribution regularities and the controlling factor were discussed. The results show that the regularity in Pearl River Delta is primarily controlled by topography, redox environment, property of the cover, and groundwater flow conditions.