In this study, the regional spatial-temporal variability of cadmium (Cd) in the topsoil of Guangxi, China from 2010 to 2016 was studied from data obtained from the China Geochemical Baseline Project (CGB Ⅰ and CGB Ⅱ). The driving forces of natural and anthropogenic variables were quantitatively analyzed using a geographically and temporally weighted regression model. The results showed that 1) soil Cd was highly enriched in 2010 and in soils of Hechi city in northwest Guangxi, a non-ferrous metal mining and metallurgy area, ~17% of the samples exceeded the soil contamination risk limit. In contrast, in 2016, the topsoil Cd content decreased significantly, with 7% of sites exceeding the soil risk limit. 2) Multiple factors jointly influenced the regional spatial variability of Cd. pH and organic carbon were found to be the main factors influencing Cd content and were strongly spatially correlated with Cd. Anthropogenic activities, including mining and industrial emissions, resulted in significant Cd enrichment in local areas, whereas agricultural and domestic pollutants were relatively weakly correlated with Cd. The weathering products of carbonates were significantly enriched in Cd; thus, the geological background played a significant role in the spatial variability of Cd. Soil-forming factors, including temperature, precipitation, and elevation influenced the spatial distribution of Cd, especially in the Cd background area. 3) Anthropogenic activities were the key factors influencing temporal changes in Cd. Mining caused significant enrichment of Cd in CGB Ⅰ, while industrial emissions were the primary factor for Cd enrichment in CGB Ⅱ. In addition, natural factors also played an important role; the increased Normalized Difference Vegetation Index suggested reduced desertification and reduction of soil erosion in the watershed and in pollutants transported from upstream.

Ion-adsorption rare-earth deposits supply over 90% of the global market’s heavy rare-earth elements (HREEs). The genesis of these deposits, particularly HREE deposits, has garnered significant attention. To elucidate the metallogenic mechanisms of HREE deposits, a comprehensive study of the weathering profile of granite was conducted in Jiangxi Province, South China. This study focuses on the following two aspects: the petrogeochemistry of HREE-rich granite and the enrichment and fractionation of rare-earth elements (REEs) during the weathering process. The results suggest that the Dabu granites are a typical peraluminous, high-K, calc-alkaline granite series with high silica content (SiO₂: 74.5%–76.4%), relatively low phosphorus content (P₂O₅: <0.05%), and high HREE content (ΣLREE/ΣHREE: 0.16–0.66). Weathering advances the decomposition of minerals and the release of elements. REEs are mainly fixed in the regolith by scavengers, mainly clays, Fe–Mn oxides, and carbonates, and ΣREE can reach 799 ppm in the B horizon. However, HREEs tend to migrate further and preferentially combine with Fe–Mn oxides and carbonates as compared to LREEs, leading to a significant fractionation of REEs in the regolith (ΣLREE/ΣHREE = 0.2–1.1). Additionally, the differential weathering of REE-bearing minerals and the precipitation of secondary REE-bearing minerals are also vital for REE fractionation.

Spatial–temporal variation in soil organic carbon is an important factor for national targets to mitigate climate change and land degradation impacts. In this research, we took Guangdong Province of China as the study area, evaluated the spatial–temporal distributions of soil organic carbon using data from three China Geochemical Baseline projects (conducted in 2009, 2016, and 2023, respectively), and quantified the main driving factors of spatial–temporal variations in soil organic carbon using the random forest algorithm, further predicting the density and inventories of soil organic carbon. The results demonstrate that the mean value of SOC in Guangdong in 2009 was 0.81%; in 2016 it was 1.13%; and in 2023 it was 1.02%. The inventories of soil organic carbon (0–30 cm) in Guangdong Province were 0.61 Pg in 2009, 0.74 Pg in 2016, and 0.62 Pg in 2023. Soil in Guangdong acted as a carbon sink from 2009 to 2023 as a whole, and the most important driving force behind spatial–temporal variations in soil organic carbon was temperature, followed by precipitation and vegetation cover.