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Cui, G., Lu, Y., Zheng, C., Liu, Z., & Sai, J. (2019). Relationship between soil salinization and groundwater hydration in Yaoba Oasis, Northwest China. Water, 11(1), 175.
Abstract: Precipitation is scarce and evaporation is intense in desert areas. Groundwater is used as the main water source to develop agriculture in the oases. However, the effects of using groundwater on the ecological environment elicit widespread public concern. This study investigated the relationship between soil salinity and groundwater characteristics in Yaoba Oasis through in situ experiments. The relationship of the mineral content, pH, and main ion content of groundwater with soil salt was quantitatively evaluated through a gray relational analysis. Four main results were obtained. First, the fresh water area with low total dissolved solid (TDS) was usually HCO3− or SO42− type water, and salt water was mostly Cl− and SO42−. The spatial distribution of main ions in groundwater during winter irrigation in November was basically consistent with that during spring irrigation in June. However, the spatial distribution of TDS differed in the two seasons. Second, soil salinization in the study area was severe, and the salinization rate reached 72.7%. In this work, the spatial variability of soil salinization had a relatively large value, and the values in spring were greater than those in autumn. Third, the soil in the irrigated area had a high salt content, and the salt ion content of surface soil was higher than that of subsoil. A piper trilinear diagram revealed that Ca2+ and K+ + Na+ were the main cations. SO42−, Cl−, and HCO3− were the main anions, and salinization soil mainly contained SO42−. Fourth, the changes in soil salt and ion contents in the 0–10 cm soil layer were approximately similar to those of irrigation water quality, both of which showed an increasing trend. The correlation of surface soil salinity with the salinity of groundwater and its chemical components was high. In summary, this study identified the progress of irrigation water quality in soil salinization and provided a scientific basis for improving the oasis ecosystem, maintaining the healthy development of agriculture, managing oasis water resources, and policy development. Our
findings can serve as a reference for other, similar oasis research.
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Naranjo-Fernández, N., Guardiola-Albert, C., & Montero-González, E. (2019). Applying 3D geostatistical simulation to improve the groundwater management modelling of sedimentary aquifers: The case of Doñana (Southwest Spain). Water, 11, 39.
Abstract: Mathematical groundwater modelling with homogeneous permeability zones has been used for decades to manage water resources in the Almonte-Marismas aquifer (southwest Spain). This is a highly heterogeneous detrital aquifer which supports valuable ecological systems in the Doñana National Park. The present study demonstrates that it is possible to better characterize this heterogeneity by numerical discretization of the geophysical and lithological data available. We identified six hydrofacies whose spatial characteristics were quantified with indicator variogram modelling. Sequential Indicator Simulation then made it possible to construct a 3D geological model. Finally, this detailed model was included in MODFLOW through the Model Muse interface. This final process is still a challenge due to the difficulty of downscaling to a handy numerical modelling scale. New piezometric surfaces and water budgets were obtained. The classical model with zones and the model with 3D simulation were compared to confirm that, for management purposes, the effort of improving the geological heterogeneities is worthwhile. This paper also highlights the relevance of including subsurface heterogeneities within a real groundwater management model in the present global change scenario.
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Qi, H., Ma, C., He, Z., Hu, X., & Gao, L. (2019). Lithium and its isotopes as tracers of groundwater salinization: A study in the southern coastal plain of Laizhou Bay, China. Sci Total Environ, 650(Pt 1), 878–890.
Abstract: In the southern coastal plain of Laizhou Bay, due to intensive exploitation of groundwater since the early 1970s, the shallow aquifer has been severely influenced by saltwater intrusion, which causes the extraction to shift from shallow to deeper aquifer changing the hydrogeological condition greatly. This study was conducted to investigate the groundwater salinization using hydrochemistry and H, O and Li isotope data. Dissolved Li shows a linear correlation with Cl and Br in seawater, brine and saline groundwater indicating the marine Li source, whereas the enrichment of Li in surface water, brackish and fresh groundwater is impacted by dissolution of silicate minerals. The analyses of hydrochemistry and isotopes (H, O and Li) indicate that brine originated from seawater evaporation, followed by mixing processes and some water-rock interactions; shallow saline groundwater originated from brine diluted with seawater and fresh groundwater; deep saline groundwater originated from seawater intrusion. The negative correlation of δ(7)Li and Li/Na in surface water, brackish and fresh groundwater is contrary to the general conclusion, indicating the slow weathering of silicate minerals and hydraulic interaction between surface water and shallow groundwater in this area. The analyses of hydrochemistry and isotopes (Li, H and O) can well identify the salinity sources and isotope fractionation in groundwater flow and mixing, especially groundwater with high TDS. As both mixing with saltwater and isotope fractionation can explain the combination of high δ(7)Li and low TDS in brackish groundwater, isotope fractionation may limit their use in recognizing salinity sources of groundwater with low TDS.
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Nogueira, G., Stigter, T. Y., Zhou, Y., Mussa, F., & Juizo, D. (2019). Understanding groundwater salinization mechanisms to secure freshwater resources in the water-scarce city of Maputo, Mozambique. Science of The Total Environment, 661, 723–736.
Abstract: In this study hydrochemical, isotopic and multivariate statistical tools are combined with a recharge analysis and existing geophysical data to improve understanding of major factors controlling freshwater occurrence and the origins of high salinities in the multi-layered coastal aquifer system of the Great Maputo area in Mozambique. Access to freshwater in this semi-arid area is limited by an inefficient public supply network, scarce surface waters, long droughts and an increasing population growth. Groundwater has a large potential to enhance water security, but its exploitation is threatened by both coastal and inland salinization mechanisms that are poorly understood. A GIS approach is utilized to classify potential recharge zones based on hydrogeological properties and land use/cover, whereas potential recharge rates are estimated through a root zone water balance method. In combination with water stable isotope data results reveal that extreme rainfall events provide the most relevant contributions to recharge, and interception and evaporation play an important role in the low recharge areas. Hierarchical clustering of hydrochemical and isotopic data allows the classification of six water groups, varying from fresh to brackish/salt waters. Corresponding scatter plots and PHREEQC modelling show evaporation and mixing with seawater (up to 5%) as major processes affecting salinity in the area. The co-occurrence of high alkalinity and Cl concentrations, in combination with piezometric and geo-electrical data, suggests that: 1) inland brackish/salt groundwater is caused by mixing with seawater trapped within clay layers; and 2) brackish/salt surface waters result from seepage of brackish groundwater into rivers and wetlands, followed by evaporation, hence increasing salinity and δ18O values. Mixing with small fractions of trapped seawater as main salinity source, rather than halite dissolution, is further corroborated by Br/Cl ratios of brackish/salt water samples near the ocean ratio. Cation exchange upon salinization is mainly observed in the semi-confined aquifer, while freshening takes place in the phreatic aquifer, particularly in areas presenting high recharge rates.
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Liu, F., Wang, S., Wang, L., Shi, L., Song, X., Yeh, T. - C. J., et al. (2019). Coupling hydrochemistry and stable isotopes to identify the major factors affecting groundwater geochemical evolution in the Heilongdong Spring Basin, North China. Journal of Geochemical Exploration, 205.
Abstract: Understanding the interference of natural processes and anthropogenic activities in geochemical evolution of groundwater is vital for groundwater sustainable management in water-stressed regions. This study is devoted to the identification of the main factors controlling the evolution of groundwater chemistry by the combined use of hydrogeochemical indicators along with isotope tracers in the Heilongdong Spring Basin, North China. Thirty-nine groundwater samples and twelve surface water samples were collected, and major ions and stable isotopes were measured during the two campaigns (December 2017 and August 2018). The isotope approach indicates that the groundwater is recharged by precipitation infiltration after evaporation, and interacts with surface water along preferential flow paths in fault zones and karst conduits. Currently, the main chemical facies of groundwater evolve from Ca-HCO3 and Ca-Mg-HCO3 types with low TDS, through Ca-Mg-HCO3-SO4 and Ca-HCO3-SO4 types with moderate TDS, to Ca-SO4, Ca-SO4-Cl and CaCl types with high TDS. Apart from natural processes (involving dissolution/precipitation of minerals, cation exchange, and evaporation) regulating the groundwater quality, the stagnant zones also play a crucial role in the formation of severe localized nitrate contamination. The deterioration in groundwater quality can be attributed to anthropogenic factors (including the change in groundwater exploitation, the leaching of solid waste, and the overuse of agricultural fertilizers). The high loads of agricultural fertilizers in irrigation return flows are likely to be the main contributor of the dissolved nitrate in groundwater. The findings of this work not only have important implications for groundwater sustainable utilization, but also could serve as a template for other rapidly industrialized and water-stressed regions.
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