Jianyao Chen

Analysis of groundwater-level fluctuation in a coastal confined aquifer induced by sea-level variation

Groundwater responses to tide fluctuations in different hydrogeological situations have been investigated for many years. Various solutions have been derived using the assumption that tides are composed of sinusoidal components, neglecting non-periodic variables. This approach has resulted in the introduction of some inaccuracy in predictions of groundwater responses to sea-level variation. To resolve this problem, this study used the Fourier sine transform method to derive an analytical solution based on the measured sea-level boundary. Compared with an analytical solution based on a sinusoidal assumption and a numerical solution generated by MODFLOW, this solution provided better performance in groundwater-level prediction in a coastal confined aquifer in Zhuhai City, China. The hydrogeological parameters estimated by the three aforementioned methods fitted well with those estimated by field surveys and pumping tests. The introduced analytical solution not only reflects the physical mechanisms of tide-induced groundwater-level fluctuation, but also reveals the non-periodic fluctuation of groundwater level caused by sea-level variation. This solution may also be used to evaluate groundwater responses to random mechanical stresses.RésuméLes réponses piézométriques aux fluctuations du niveau marin dues à la marée dans différents contextes hydrogéologiques ont été étudiées depuis de nombreuses années. Différentes solutions ont été décrites à partir de l’hypothèse que les marées étaient constituées de composantes sinusoïdales, négligeant les variables non périodiques. L’utilisation de cette approche a conduit à introduire certaines incertitudes dans les prévisions des réponses piézométriques vis-à-vis des variations du niveau marin. Afin de résoudre ce problème, l’étude a eu recours à la méthode de la transformée de Fourier afin de définir une solution analytique intégrant la limite mesurée du niveau marin. Cette solution comparée à une solution analytique construite avec l’hypothèse de la sinusoïdale et à une solution numérique générée à l’aide de MODFLOW a permis de montrer qu’elle fournit une meilleure performance pour la prévision des niveaux piézométriques d’un aquifère côtier captif, l’aquifère de la ville de Zhuhai en Chine. Les paramètres hydrogéologiques estimés à l’aide des trois méthodes indiquées précédemment sont cohérents avec ceux estimés par des reconnaissances de terrain et des essais de pompage. La solution analytique introduite ne reflète pas seulement les mécanismes physiques des fluctuations piézométriques induites par les marées, mais met aussi en évidence la variation non périodique des niveaux d’eau souterraine causée par les fluctuations du niveau marin. La solution peut également être utilisée pour évaluer les réponses piézométriques à des contraintes mécaniques aléatoires.ResumenLas respuestas del agua subterránea a las fluctuaciones de la marea en diferentes situaciones hidrogeológicas han sido investigadas por muchos años. Varias soluciones se han desarrollado usando el supuesto que las mareas están compuestas por componentes sinusoidales, dejando de lado variables no periódicas. Este enfoque ha dado lugar a la introducción de ciertas inexactitudes en las predicciones de las respuestas de las aguas subterráneas a la variación del nivel del mar. Para resolver este problema, este estudio usó el método de la transformada del seno de Fourier para desarrollar una solución analítica basada en el límite del nivel del mar medido. Comparado con una solución analítica basada en un supuesto sinusoidal y una solución numérica generada por MODFLOW, esta solución provee un mejor desempeño en la predicción del nivel de agua subterránea en un acuífero confinado costero en Zhuhai City, China. Los parámetros hidrogeológicos estimados por los tres métodos arriba mencionados ajustan bien con aquellos estimados por relevamientos de campo y ensayos de bombeo. La solución analítica introducida no solo refleja los mecanismos físicos de la fluctuación del nivel de agua subterránea inducida por la marea, sino también revela las fluctuaciones no periódicas del agua subterránea causada por la variación del nivel del mar. Esta solución también puede ser usada para evaluar las respuestas del agua subterránea a tensiones mecánicas aleatorias.摘要关于在不同水文地质条件下潮汐变化引起地下水位波动的研究已进行多年。针对这个问题的不同解析解都是建立在潮汐水位是由正弦成分组成的假设上,这个假设忽略了海水位中的非周期变化成分。因此,建立在这个假设上的解析解可能会引起对地下水位预测的不准确性。为了解决这个问题,本文的研究使用傅里叶正弦变换的方法,推导出一个以实测海水位为边界条件的解析解。将这个解析解与建立在正弦边界假定的解析解以及建立在MODFLOW基础上的数值解应用于中国珠海沿海承压含水层地下水位波动情况的预测上,结果表明本文推导出的解析解预测效果较好。上述三种方法在模拟过程中率定的水文地质参数与实地调研和抽水试验得到的结果比较符合。新的解析解不仅可以很好的反应潮汐水位波动影响下地下水位波动现象的物理机制,还可以揭示地下水位中由海水波动引起的非周期变化。这个解析解可能用于将来对随机动力引起下的地下水水位波动的研究中。ResumoA análise da influência das marés na variação dos níveis piezométricos em aquíferos costeiros com diferentes características hidrogeológicas tem sido objeto de estudo por vários investigadores. As várias soluções apresentadas assumem que as marés são constituídas por componentes sinusoidais, negligenciando as variáveis não periódicas. Os resultados obtidos através desta aproximação introduziram alguns erros na previsão da variação dos níveis piezométricos induzidos pela variação das marés. No sentido de dar um contributo para a resolução deste problema, este estudo utilizou o método da derivada do seno da Transformada de Fourier para encontrar uma solução analítica que melhor represente a variação do nível do mar medido junto à costa. Comparando esta solução analítica baseada na hipótese da sinusoidal com a solução numérica gerada pelo modelo MODFLOW, obtiveram-se melhores resultados com esta solução na previsão dos níveis de águas subterrâneas no aquífero costeiro da Cidade de Zhuhai, na China. Os parâmetros hidrogeológicos obtidos através dos três métodos acima mencionados ajustaram-se bem aos estimados em medições de campo e ensaios de bombagem. A solução analítica introduzida reflete não só os mecanismos físicos da variação da piezometria induzida pelas marés, como revela também a flutuação não-periódica das águas subterrâneas, causada pelas variações do nível do mar. Esta solução também pode ser utilizada para avaliação da resposta das águas subterrâneas a pressões mecânicas aleatórias.

Assessment of major ions and heavy metals in groundwater: a case study from Guangzhou and Zhuhai of the Pearl River Delta, China

Anthropogenic activities in the Pearl River Delta (PRD) have caused a deterioration of groundwater quality over the past twenty years as a result of rapid urbanization and industrial development. In this study, the hydrochemical characteristics, quality, and sources of heavy metals in the groundwater of the PRD were investigated. Twenty-five groundwater samples were collected and analyzed for pH, electrical conductivity (EC), total dissolved solids (TDS), δ18O, δ2H, major ions, and heavy metals. The groundwater was slightly acidic and presented TDS values that ranged from 35.5 to 8,779.3 mg·L−1. The concentrations of the major ions followed the order Cl−>HCO3−>Na+>SO42−>NO3−>NH4+>Ca2+>K+>Mg2+>Fe2+/3+>Al3+. Ca-Mg-HCO3 and Na-K-HCO3 were the predominant types of facies, and the chemical composition of the groundwater was primarily controlled by chemical weathering of the basement rocks, by mixing of freshwater and seawater and by anthropogenic activities. The heavy metal pollution index (HPI) indicated that 64% of the samples were in the low category, 16% were in the medium category and 20% were in the high category, providing further evidence that this groundwater is unsuitable for drinking. Lead, arsenic, and manganese were mainly sourced from landfill leachate; cadmium from landfill leachate and agricultural wastes; mercury from the discharge of leachate associated with mining activities and agricultural wastes; and chromium primarily from industrial wastes. According to the irrigation water quality indicators, the groundwater in the PRD can be used for irrigation in most farmland without strong negative impacts. However, approximately 9 million people in the Guangdong Province are at risk due to the consumption of untreated water. Therefore, we suggest that treating the groundwater to achieve safer levels is necessary.

Vertical microbiological variation of a coastal aquifer in southern China.

Microbial communities in a coastal aquifer in the Zhuhai region of southern China were investigated by culture-independent molecular approaches. Four 16S rRNA gene libraries of three groundwater samples from varied depths and one seawater sample were constructed and analysed by the amplified ribosomal DNA restriction analysis technique (ARDRA). The phylogenetic analysis indicated that the 16S rDNA of clones presenting dominant ARDRA patterns were most similar to Proteobacteria, Bacteroidetes, Actinobacteria, Planctomycetes, and candidate divisions OPx (such as OP3, OP8, and OP11). In samples extracted from wells of 5-, 20-, and 35-m depth (i.e., D1, D5, and D6) Proteobacteria made up 32.3, 34.3, and 46.7% of the microbial communities, respectively. The same samples from D1, D5, and D6 also consisted of 5.0, 11.2, and 6.5% Bacteroidetes and 5.4, 6.6, and 7.8% Actinobacteria, respectively. In contrast, the seawater clone library had a predominant number of Proteobacteria (32.8%), while Bacteroidetes and Planctomycetes both accounted for 9.3%. Total microbial diversity remained relatively constant over the top layer to a depth of approximately 35 m, significant community vertical and horizontal (seawater-groundwater) shifts were observed for certain bacterial populations.

Groundwater Recharge and Hydrogeochemical Evolution in Leizhou Peninsula, China

An analysis of the stable isotopes and the major ions in the surface water and groundwater in the Leizhou Peninsula was performed to identify the sources and recharge mechanisms of the groundwater. In this study, 70 water samples were collected from rivers, a lake, and pumping wells. The surface water was considered to have a lower salinity than the groundwater in the region of study. The regression equations for δD and δ18O for the surface water and the groundwater are similar to those for precipitation, indicating meteoric origins. The δD and δ18O levels in the groundwater ranged from −60; to −25; and −8.6; to −2.5, respectively, and were lower than the stable isotope levels from the winter and spring precipitation. The groundwater in the southern area was classified as the Ca2