Lixin Pei

Lagoons, significant coastal wetlands, stand out for their vital role in the cycles and transformations of phosphorus. However, the relationship between the spatial distributions of various phosphorus forms in the soil and sediments of lagoon areas remains unclear. This study investigated the phosphorus fractions and distribution patterns in the soil and sediments from Shimei Inland Sea, Hainan Province, China, and identified the factors controlling phosphorus distribution and its relationship with lagoon eutrophication. The results revealed significant enrichment of inorganic phosphorus (IP) in the Shimei Inland Sea (64.1–679.0 mg/kg) and offshore areas (56–627.2 mg/kg), while organic phosphorus (OP) was relatively concentrated in land (60–744.3 mg/kg), suggesting that the productivity of the terrestrial ecosystem controlled the OP content and IP formed from the mineralization of OP was more likely to leach into the water and combine with minerals. Total phosphorus (TP) content was negatively affected by pH, and organic matter, cation exchange capacity and iron/aluminum oxides showed significant positive correlations with TP content. These findings highlighted the coupled impact of soil and sediment physicochemical properties on phosphorus enrichment and transformation, providing theoretical support for the ecological restoration of ecosystems in tropical coastal wetlands.

In order to ensure a sustainable water resource for residents of the lower reaches of the Changhua River on Hainan Island, it is crucial to understand the chemical characteristics and formation mechanisms of their shallow groundwater. To achieve this, we collected and analyzed 100 groundwater samples using various methods. Our findings indicate that the groundwater is generally near-neutral to weakly alkaline, suggesting an oxidized environment. We identified 56 chemical types, with Ca•Na-HCO₃ and Ca-HCO₃ being the most common. Water–rock interactions—particularly with silicate rocks—are the primary factor influencing the water’s chemical characteristics, with Na⁺ and K⁺ coming from the leaching of silicate rocks, and Ca²⁺ and Mg²⁺ originating from the dissolution of carbonate rocks. Unfortunately, human activities such as agricultural practices and domestic sewage have had a significant impact on the groundwater, with NO₃⁻ levels surpassing SO₄²⁻ in most samples. These findings provide valuable insights into the development and protection of the shallow groundwater in this area.

The lower reaches of the Changhua River are located in the northwest of Hainan Island, and the shallow groundwater in this area is the main water source for residents living at both sides of the river. In order to sustain the exploitation and use of water resources in this area, it is essential to clarify the chemical characteristics and the formation mechanism of the groundwater. We collected 100 sets of shallow groundwater samples from the lower reaches of the Changhua River, and analyzed the chemical characteristics of the groundwater in shallow aquifers as well as its controlling factors by means of the methods including descriptive statistical analysis, Piper diagram, Gibbs diagram, and ion ratio. The results show that the overall characteristics of groundwater in the study area are near-neutral to weakly alkaline nature, indicating a generally oxidized environment. The groundwater involves in 56 chemical types, and the most predominant types are Ca•Na-HCO3 and Ca-HCO3, respectively. NO- 3 has become a macro component exceeding SO2- 4in most of the sampling groundwater, suggesting a significant impact of human activities in this area. At the same time, the chemical characteristics of groundwater in the study area are mainly affected by the water-rock interaction, while the water-rock interaction is mostly affected by the dissolution of silicate rocks and less by the dissolution of carbonate rocks and evaporite rocks. According to the ion ratio results, Na+ and K+ in the study area are mainly from the leaching of silicate rocks, Ca2+ and Mg2+ are mainly from the dissolution of carbonate rocks, in addition to a certain degree of cationic exchange. NO- 3 is mainly related to human activities, and the human activities are more affected by agricultural activities and domestic sewage than by industrial and mining activities. This study can provide a reference for the development and protection of shallow groundwater in the lower reaches of the Changhua River.

The scarcity of water resources caused by the unique topography and uneven rainfall distribution in Hainan Island has become a major factor restricting local development. In order to provide effective and scientific reference basis for the overall water resource utilization status and solving this problem, this study calculated the water resource utilization situation of Hainan Island from 2017 to 2021 in detail using methods including water resource ecological footprint analysis. Furthermore, a spatial correlation analysis was conducted to examine the island’s water resource utilization characteristics, and the driving factors behind the changes in water resource utilization over the past five years were analyzed using the LMDI model. The results show that: (1) During the study period, the water resource ecological footprint in Hainan Island exhibited a slow growth trend, while the ecological carrying capacity showed a downward tendency. The per capita ecological deficit of water resources remains relatively high, and the water consumption per 10 000 yuan GDP in the whole land continues to decrease, indicating that the overall pressure on water resource demand remains high with significant regional differences accompanied by the efficiency of water resource utilization steadily improving at the same time; (2) Agricultural water use accounts for the highest proportion in the entire water use structure, while ecological water use represents the smallest share, with a year-on-year increase, indicating that Hainan Island highlights the agricultural development and is increasingly conscious of the ecological environment; (3) Significant spatial differentiation in water resource utilization characteristics exists in Hainan Island, with the western region being a hot spot aggregation area for per capita water resource ecological footprint, per capita ecological carrying capacity of water resources, water consumption per 10 000 yuan GDP, while it is a cold spot cluster area for per capita ecological deficit of water resources. The opposite holds true for the eastern region of Hainan Island; (4) Economic and technological factors have a major impact on the changes in water resource ecological footprint within the designated area. Among them, economic factors drive the growth of the water resource ecological footprint in Hainan Island, and exacerbate local water resource consumption, while technological factors negatively contribute to the amount of water resource utilization in Hainan Island, indicating that advanced technology has improved water resource utilization efficiency and significantly reduced water resource consumption.

Assessing natural background levels (NBLs) in groundwater is crucial for evaluating groundwater pollution and the use of groundwater resources in coastal areas. This study assessed NBLs of iodide and ammonium in the shallow groundwater of the Pearl River Delta (PRD) by using a preselection method with Grubbs’ test, and discussed factors controlling NBLs in various groundwater units. Here, the preselection method consists of Cl/Br mass ratios versus Cl concentrations and the oxidation capacity, and the PRD is divided into four groundwater units. Results showed that NBL-iodide in groundwater unit A was 0.14 mg/L and >2 times greater than that in other groundwater units. Similarly, NBL-ammonium in groundwater unit A was 0.32 mg/L and also >2 times greater than that in other groundwater units. The release of iodide from both of organic-iodine in the vadose zone and iodine-rich minerals in aquifer sediments were the two main sources for the higher NBL-iodide in groundwater unit A compared to other units. By contrast, the occurrence of ammonium from organic-nitrogen in the vadose zone was the major source for the higher NBL-ammonium in groundwater unit A compared with the other units. Soluble iodide resulted from the mineralization of organic-iodine in Quaternary marine formation, and the release of iodide accompanied with reductive dissolution of iodide-loaded Fe (oxyhydr) oxides in aquifer sediments was the main driving force controlling the higher NBL-iodide in groundwater unit A compared with the other units. By contrast, the release of soluble ammonium from the mineralization of organic-nitrogen in marine formation entering into groundwater was the main driving force controlling the higher NBL-ammonium in groundwater unit A relative to the other units. These results enhance the knowledge on groundwater NBLs in coastal areas and improve groundwater resources management in coastal areas such as the PRD.

Cadmium (Cd)-contaminated paddy soils are a big concern. However, the effect of irrigation with acid water on the migration and transformation of Cd and the effect of alternating redox conditions caused by intermittent irrigation on Cd aging processes in different depths of paddy soils are unclear. This study revealed Cd fractionation and aging in a Cd-contaminated paddy soil under four irrigation periods with acid water and four drainage periods, by applying a soil columns experiment and a sequential extraction procedure. The results showed that the dynamic changes of soil pH, oxidation reduction potential (ORP), iron (Fe) oxides and dissolved organic carbon (DOC) throughout the intermittent irrigation affected the transformation of Cd fractions. After 32 days, the proportion of exchangeable Cd (F1) to the total Cd decreased with a reduction of 24.4% and 20.1% at the topsoil and the subsoil, respectively. The labile fractions of Cd decreased, and the more immobilizable fractions of Cd increased in the different depths of soils due to the aging process. Additionally, the redistribution of the Fe and Mn oxide-bound Cd (F3) and organic matter and secondary-sulfide-bound Cd (F4) occurred at different depths of soils during the incubation time. Overall, the bioaccessibility of Cd in the subsoil was higher than that in the topsoil, which was likely due to the leaching and accumulation of soluble Cd in the deep soil. In addition, the aging processes in different depths of soils were divided into three stages, which can be mainly described as the transformation of F1 into F3 and F4.

Efficient identification of groundwater contamination is a major issue in the context of groundwater use and protection. This study used a new approach of multi-hydrochemical indicators, including the Cl-Br mass ratio, the hydrochemical facies, and the concentrations of nitrate, phosphate, organic contaminants, and Pb in groundwater to identify groundwater contamination in the Pearl River Delta (PRD) where there is large scale urbanization. In addition, the main factors resulting in groundwater contamination in the PRD were also discussed by using socioeconomic data and principal component analysis. Approximately 60% of groundwater sites in the PRD were identified to be contaminated according to the above six indicators. Contaminated groundwaters commonly occur in porous and fissured aquifers but rarely in karst aquifers. Groundwater contamination in porous aquifers is positively correlated with the urbanization level. Similarly, in fissured aquifers, the proportions of contaminated groundwater in urbanized and peri-urban areas were approximately two times that in non-urbanized areas. Groundwater contamination in the PRD was mainly attributed to the infiltration of wastewater from township-village enterprises on a regional scale. In addition, livestock waste was also an important source of groundwater contamination in the PRD. Therefore, in the future, the supervision of the wastewater discharge of township-village enterprises and the waste discharge of livestock should be strengthened to protect against groundwater contamination in the PRD.