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.

Due to the growth of tourism, mining and manufacturing, economy of the Hainan Island, southern China has swiftly expanded, but also poses a risk of soil pollution by mercury (Hg) due to the traffic and mineral processing. In order to investigate the characteristics of soil Hg pollution in the Hainan Island and assess the health risk, a total of 239 samples were gathered from five representative regions across the island. A vehicle-mounted potable mercury analyzer was used to measure the atmospheric Hg and soil Hg concentrations in the collected samples. The results indicate that the soil Hg concentration of the five sub-study areas exhibits notable fluctuations, which was found to be influenced by various factors, including wind direction, mining activities, and economic development conditions. The degree of Hg pollution was assessed using both the Single Pollution Index Method and the Geoaccumulation Index Method. The results showed that although nearly half of the sampling points were contaminated, the current soil Hg level does not pose a non-carcinogenic risk to human health.

Carbonaceous material (CM) is common in meta-sediments and is generally interpreted to be intimately associated with gold mineralization. For the Bumo deposit in Hainan Province, South China, CM is mainly hosted by greenschist facies- to amphibolite-facies metamophic rocks of the Paleo- to Mesoproterozoic Baoban Group and by auriferous veins and is used as an important gold prospecting indicator. However, the genesis of CM and the relationship with gold mineralization are still not clear. Field work and thin section observation indicates that two types of CM occur, i.e., layered and veinlet. Layered CM, up to meters thick, prevails in the deposit. More importantly, Au-bearing sulfides are commonly distributed along the boundary between the quartz veins and layered CM. In contrast, veinlet CM, co-precipitated with gold and sulfides, has the thickness of micro- to centi- meters, and these thin veins occur in quartz veins and hydrothermally altered rocks. Scanning Electron Microscope (SEM) analysis indicates that layered CM has a stringy shape and laminate structure, while veinlet CM occurs as isometric particles. Raman carbonaceous material geothermometer indicates that layered CM with high maturity is formed at elevated temperatures of 400 – 550°C, consistent with X-ray diffraction (XRD) analysis. In contrast, veinlet CM with low maturity is formed at 200 – 350°C, generally consistent with gold mineralization. In addition, layered CM has δ13C values ranging from -30 to -20%, demonstrating a biogenic origin. Consequently, it is interpreted that layered CM is formed by a pre-ore metamorphic event during Caledonian, and its reducing nature promotes gold precipitation via destabilization of aqueous Au bisulfide complexes or facilitating sulfidation. Veinlet CM is hydrothermal origin, and its precipitation modified the chemical conditions of ore fluids, leading to the destabilization of Au complexes and thus favorable for mineralization.

Banana plantation is an important type of agro-ecosystem in the tropics, and it is important to carry out a quantitative assessment of the carbon footprint of the banana growing process for the development of low-carbon agriculture to cope with global warming. The carbon footprint of two banana cultivation processes was assessed using the life cycle assessment method through field trials and farmer surveys in Chengmai County, Hainan Province, China. The results showed that: (1) N2O emissions caused by the application of nitrogen fertilizers and compound nitrogen fertilizers were the largest source of carbon emissions from banana plantation farmland, and the production and transportation of common compound fertilizer were the second largest source of carbon emissions. Banana fruits and plants were the main contributors to carbon fixation in banana plantation ecosystems, with about 24.72 t CO2 eq hm-2 for Musa paradisiaca AA, and 34.66 t CO2 eq hm-2 for M. AAA Cavendish var. Brazil. (2) The annual carbon emissions of Musa paradisiaca AA and M. AAA Cavendish var. Brazil farmland systems were 35.40 t CO2 eq·hm-2 and 43.83 t CO2 eq·hm-2, respectively, and the annual carbon fixation was 38.23 CO2 eq·hm-2 and 48.17 CO2 eq·hm-2, respectively. The banana plantations had a negative carbon footprint per unit area, showing a net carbon sink function. (3) Banana is a plant with high carbon emission and strong carbon fixation capacity. Scientific management in the field can achieve the decrease of agricultural inputs, high quality and abundant agricultural products, and the reduction of carbon footprint of farmland.

The study concentrated on Myzostomida, which are microscopic polychaetes that live in symbiosis with feather stars, within the coastal waters of Hainan Island. Specimens were collected by researchers using SCUBA diving techniques, leading to the identification of a new species, as well as the documentation of four species that had not been previously recorded in Chinese waters. This discovery stands apart from the seven known Myzostomida species found near Hong Kong and the Dapeng Peninsula in Shenzhen. It underscores significant gaps in our comprehension of marine life in the South China Sea, suggesting the existence of unexplored biodiversity within the region.