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To comprehensively explore the research hotpots and trends in soil salinization in China, CiteSpace software (version 6.3.R1) was used to visualize the knowledge graph and bibliometric analysis of relevant literature from 2000 to 2024 in the China Knowledge Network (CNKI) database and Web of Science (WoS) database. Analysis of 1963 CNKI documents and 2134 WoS documents published by 249 units for annual publications, research institutions, authors, and keyword graph revealed that the annual publication volume of the literature in the field of salinization shows an upward trend and the volume of quality English publications is higher than that of Chinese. The cooperation network of authors and institutions had already been formed in the field. The cooperation among research institutes was stable, and a core group of authors had already been formed. Since 2020, “spectral index”, “machine learning”, “remote sensing inversion”, “spatial and temporal changes”, “inter-root”, “simulation”, “oasis”, “ rainy season”, and “soil water content” have become hot words in research. The visualization of spatial and temporal distribution of soil salts based on big data and artificial intelligence has become the focus of attention of the academic community. Therefore, the challenges of salinization should be better addressed through scientific and technological innovation and comprehensive measures. The results of the study are expected to provide scientific references for the field of salinization in China.

The muddy coastal region of North Shandong, China, including Laizhou Bay and the Huanghe River (Yellow River) Delta, is a complex depositional environment where land and sea intersect, creating diverse water types and intricate coastal groundwater formation and evolution. This study focuses on the shallow Holocene aquifer (SHA) and the deep Pleistocene aquifer (DPA) groundwater, using hydrogeochemical, isotope analysis and numerical simulation methods to infer the source of water and salt and hydrogeological chemical processes. The results reveal that the groundwater is a mix of seawater, freshwater, and brine, with significant differences in hydrochemical types and isotopic signatures between the SHA and DPA aquifers. The SHA groundwater is dominated by low salinity (TDS ≈ 8 g/L), with the freshwater dominated by Cl-Na and Cl-Na·Mg hydrochemical types. In contrast, the DPA groundwater is characterised primarily by high salinity (TDS ≈ 72 g/L) and the Cl-Na type. δ 18 O-δ 2 H deviates from the precipitation line and is close to the seawater evaporation line, indicating stronger seawater intrusion and salt accumulation processes. Interestingly, δ 18 O and δ 2 H stable isotopes' relative abundance in the DPA brine samples from the Huanghe River Delta (at a burial depth of ~260 m) and Huanghe River water samples bear a resemblance, suggesting a strong correlation between the river water and the subsurface brine water source in the EPA. The Hydrochemical Facies Evolution Diagram (HFE–Diagram) analysis shows 63.77% of SHA samples underwent desalination, while 79.31% of DPA samples experienced seawater intrusion, this was restricted by structural constraints and rock salt dissolution. This study provides new insights into the hydrogeochemical evolution of coastal aquifers.

Sea (salt) water intrusion is a significant and ongoing geological disaster, and in recent years, it has become a notable concern for Laizhou City, Shandong Province. To identify the characteristics and mechanism of sea (salt) water intrusion in Laizhou City, samples of different types of water bodies (such as seawater, freshwater, slightly brackish water, brackish water, saline water, and brine) were systematically collected from the coastal zone area. The hydrochemical composition and evolution characteristics of the water bodies and the current situation, trends, and causes of sea (salt) water intrusion were analyzed. In 2020, the sea (salt) water intrusion reached 645.76 km 2 (including 151.64 km 2 of serious intrusion area), which is the largest ever recorded. The sea (salt) water intrusion had a strip-sheet distribution. From land to sea, groundwater gradually transitioned from the HCO 3 ·SO 4 ·Cl-Ca type to SO 4 ·Cl-Na·Ca and SO 4 ·Cl-Na types and then evolved to the Cl-Na type. Furthermore, from land to sea, the dominant cations and anions shifted from Ca 2+ and HCO 3 - to Na + and Cl - . The influence of seawater or brine gradually increased, that of Ca 2+ and HCO 3 - gradually decreased; whereas that of Cl - and Na + gradually increased, showing a division zone of freshwater → slightly brackish water → brackish water → saline water → seawater (brine) in the macroscopic territory. The freshwater, slightly brackish water, and brackish water bodies in the study area were controlled by evaporation and concentration processes and rock weathering leaching, whereas the saline water and brine were primarily controlled by evaporation and concentration processes. Groundwater salinity in the study area mainly originates from sea (salt) water intrusion, and locally groundwater salinity mainly originates from mineral dissolution or human activities. In addition, significant cation exchange adsorption occurred in slightly brackish and brackish water. Overall, these results will help to prevent and control seawater intrusions and improve disaster management.

In situ remediation of ammonium-contaminated groundwater is possible through a zeolite permeable reactive barrier (PRB); however, zeolite's finite sorption capacity limits the long-term field application of PRBs. In this paper, a pilot-scale PRB was designed to achieve sustainable use of zeolite in removing ammonium (NH4+-N) through sequential nitrification, adsorption, and denitrification. An oxygen-releasing compound was added to ensure aerobic conditions in the upper layers of the PRB where NH4+-N was microbially oxidized to nitrate. Any remaining NH4+-N was removed abiotically in the zeolite layer. Under lower redox conditions, nitrate formed during nitrification was removed by denitrifying bacteria colonizing the zeolite. During the long-term operation (328 days), more than 90% of NH4+-N was consistently removed, and approximately 40% of the influent NH4+-N was oxidized to nitrate. As much as 60% of the nitrate formed in the PRB was reduced in the zeolite layer after 300 days of operation. Removal of NH4+-N from groundwater using a zeolite PRB through bacterial nitrification and abiotic adsorption is a promising approach. The zeolite PRB has the advantage of achieving sustainable use of zeolite and immediate NH4+-N removal.

The hydrogeochemical analysis and numerical simulation were conducted to explore the impact of land reclamation on submarine groundwater discharge and groundwater evolution in the seawater intrusion-retreat processes in eastern Jiangsu, China. The hydrogeochemical results indicated that the origin of salt in most groundwater is saltwater mixing, and weathering-dissolution of minerals enriches the salt in fresh groundwater. The evolution path of coastal groundwater in Jiangsu is Ca-Na-HCO3-Cl → Ca-Na-Cl-HCO3 → Na-Ca-Cl-HCO3 → Na-Mg-HCO3 → Na-Mg-HCO3-Cl → Na-Cl-HCO3 → Na-Cl, and the difference in groundwater evolution in different regions is obvious. The numerical simulation revealed that the land reclamation has blocked groundwater exchange and restrained the seawater intrusion. The sensitive analysis indicated that the permeability and the slope of the land reclamation have dominated the salinity distribution. And the aquifer heterogeneity promotes groundwater evolution and leads to the irregular salinity distribution of the groundwater. Moreover, the groundwater evolution in the shallow aquifer with the land reclamation shows that the residual seawater is gradually desalinating and discharged into the sea. The land reclamation is salinized by saltwater discharge and seawater intrusion together and then subsides into a stable saltwater wedge. The groundwater salinity distribution in Jiangsu is not fit seawater intrusion, which is caused by the coastline changes due to anthropogenic land reclamation and natural activities.

Nitrogen as ammonium (NH4+-N) is one of the most common nitrogen contaminants in groundwater; this is particularly true in the industrial and agricultural regions of northern China, where rapid population growth and economic development have stressed public water supplies and reduced groundwater quality. In this study, we report the performance of a zeolite permeable reactive barrier (PRB) designed to remove ammonium from contaminated river water that infiltrates to a groundwater aquifer that serves as a drinking water supply for the city of Shenyang. Groundwater monitoring data obtained over 5 months of operation indicate that ammonium concentrations in the groundwater decreased from 2–10 mg/L to <0.5 mg/L after the PRB was installed in the vicinity. Data suggest that ammonium removal was mainly due to sorption and ion exchange, with NH4+ exchanged with Na+ and K+ in the zeolite. After more than 1 year of continuous operation, there is no evidence of microbial ammonium oxidation. To our knowledge, this was the first field-scale demonstration of a PRB in China.

Liu, S.; Gao, M.; Hou, G., and Jia, C., 2021. Groundwater characteristics and mixing processes during the development of a modern estuarine delta (Luanhe River Delta, China). Journal of Coastal Research, 37(2), 349–363. Coconut Creek (Florida), ISSN 0749-0208. The Luanhe River Delta (LRD) is divided into two parts, the ancient LRD and the modern LRD (MLRD), and has formed since 7000 calibrated years before present (cal yr BP). The MLRD developed from 2500 cal yr BP. Influenced by paleoclimatic changes and human activity, its groundwater environment is complex. In this study, groundwater monitoring methods, hydrochemistry, and isotopes are used to determine the groundwater characteristics and mixing processes during MLRD development. The groundwater dynamics show seasonal variations. The groundwater salinity distribution features vertical zones and is the same as the stratal distribution. The saline groundwater formation involves evaporation, condensation, hydrolysis, dissolution of evaporated salts, and mixing of groundwater with different qualities and hydrochemical compositions. Brackish water and saline water are the result of mixing between fresh and highly saline waters in deep groundwater based on the hydraulic conditions and the dispersion effect. The formation of the MLRD, which can be described as natural reclamation, provides good groundwater flow and mixing channels. Based on hydrochemical data, the mixing model, and the hydrochemical facies evolution diagram, salinity in shallow groundwater is influenced by seawater intrusion and saline water intrusion. The concentrations of sodium and chloride can indicate the intrusion degree. Precipitation and other freshwater inputs provide the main recharge sources that lead to freshening of the shallow groundwater. Close to the sea, the water exchange between groundwater and seawater is intense, which can lead to similar hydrochemical characteristics of groundwater and local seawater. Saline water intrusion in deep groundwater is more serious than that in shallow groundwater because there is no other freshwater recharge to deep groundwater.

Gao, M. S.; Hou, G. H., and Guo, F., 2016. Conceptual model of underground brine formation in the silty coast of Laizhou Bay, Bohai Sea, China. There were three major transgression-regression events since the late Pleistocene in the southern coast of Laizhou Bay, Bohai Sea, China. The three marine facies were correspondingly formed. Large amount of underground brine has been found in the late Pleistocene aquifers. A multi-source fluvial delta sedimentary system where the processes of replenishment, migration, filtration, storage, capping condition act together may be more dominant for the formation of underground brine. The dissolved salinity in the liquid of surface microtopography such as lagoon, paleochannel and tidal creek was originated from marine sediment and influenced partly by normal seawater over the time interval, which ran across the bar during the process of storm surge sometimes, but the water body in the sediment only came from fresh groundwater in the fluvial delta. In order to better understand and utilize the underground brine resources, we proposed a conceptual model about the formation of underground brine. Underground brine evolution can be categorized into two stages with six processes. The first stage could be the early regression period. Taking microrelief as a control condition of brine generated reactor, dissolved components were fractionated under the effect of pump evaporation combined with ion exchange between sediment and pore water, leading to the mineral composition changes in groundwater. As a result, underground brine was generated in the tidal flat and delta front under the effect of backflow-infiltration. The saline brine flushed into the tidal flat and the delta front under the effect of backflow-infiltration and remained stable with high degree of mineralization for a long time. The second stage would be the end period of regression. Brine-producing reservoir was formed by a combined effect of both long-term evaporation and seasonal fluvial material input. When lateral terrestrial deposit covered the early brine layer, the underground brine was then formed. Therefore, the three underground brine layers were results of three large scale sea-land changes.

Exopolysaccharide of Lachnum YM130 (LEP) was purified by diethylaminoethyl cellulose 52 and Sepharose CL-6B column chromatography. LEP-2a was identified to be a homogeneous component with an average molecular weight of 1.31 × 106 Da, which was consisted of mannose and galactose in a molar ratio of 3.8:1.0. The structure of LEP-2a was characterized by methylation analysis, FT-IR analysis, and NMR analysis. Results indicated that LEP-2a was a galactomannan with a backbone, composed of 1,2-linked-α-D-Manp, 1,2,6-linked-α-D-Manp, 1,3,4-linked-α-D-Manp, and 1,3-linked-β-D-Galp, which was substituted at O-2, O-3, O-4, and O-6 by branches. In vitro antitumor activity assay proved that LEP-2a could significantly enhance the inhibitory effectiveness of 5-FU on Hela cells at the concentrations of 100, 200, 300, and 400 μg/mL. The above results suggested that LEP-2a could be seen as a potential source for developing novel antineoplastic agents.

Since the Quaternary Period, paleo-seawater intrusions have been suggested to explain the observed saline groundwater that extends far inland in coastal zones. The Luanhe River delta (northwest coast of the Bohai Sea, China) is characterized by the distribution of saline, brine, brackish, and fresh groundwater from the coastline inland. The groundwater in this region exhibits a wide range of total dissolved solids (TDS): 0.38–125.9 g L−1. Meanwhile, previous studies have revealed that this area was significantly affected by Holocene marine transgression. This study used hydrochemical, isotopic, and sedimentological methods to investigate groundwater salinization processes in the Luanhe River delta and its links to paleo-environmental settings. Isotopic results (2H, 18O, 14C) allowed old groundwater recharge to be distinguished from new groundwater recharge. Hydrochemical analysis using the PHREEQC code indicated that the salt in saline and brine groundwater originates from a marine source. The 18O–Cl relationship diagram yields three-end-member groundwater mixing, and two mixing scenarios are suggested to explain the freshening and salinization processes in the study area. When this was interpreted along with data from paleo-environmental sediments, we found that groundwater salinization may have occurred since the Holocene marine transgression. The brine is characterized by radiocarbon activities of ∼ 50–85 pMC and relatively depleted stable isotopes, which are associated with seawater evaporation in the ancient lagoon during delta progradation and mixing with deeper fresh groundwater, which was probably recharged in the cold Late Pleistocene. The brackish and fresh groundwaters are characterized by river-like stable isotope values, where high radiocarbon activities (74.3–105.9 pMC) were formed after the washing out of the salinized aquifer by surface water in the delta plain. This study presents an approach that utilizes geochemical indicator analysis with paleo-geographic reconstruction to better assess groundwater evolutionary patterns in coastal aquifers.