Qian Zhang

Soil Fe cycling is co‐regulated by texture and land use intensity (LUI), but their synergistic mechanism and depth‐dependent effects remain unclear. We analyzed 68 samples (0–200 cm) from one cultivated (CL, high LUI, silty loam, clay = 11%–18%) and three non‐cultivated (AC1–AC3, low LUI, sandy loam, clay = 2.65%–9.00%) profiles in Thailand's Mun River Basin, using hierarchical regression, slope difference tests, and CV decomposition. Results showed: (1) Soil texture best explains Fe content variation—silty loam maintains stable high Fe (25.4–39.7 g kg ⁻¹ ) via clay adsorption, while sandy loam has variable Fe (1.1–118.5 g kg ⁻¹ ) with severe depletion in topsoil. (2) The top 1.2 m is a δ ⁵⁶ Fe‐sensitive zone (CV = 35.7%), more variable than deep soil (CV = 21.8%). (3) Texture ×LUI synergy is statistically significant (Fe: Δ R ² = 0.09, p < 0.01; δ ⁵⁶ Fe: Δ R ² = 0.13, p < 0.001). (4) Fe content (static pool) and δ ⁵⁶ Fe (dynamic tracer) are complementary, with LUI acting as a “switch” for texture‐Fe relationships. This study clarifies the vertical differentiation and synergistic controls of Fe biogeochemistry in tropical soils, and strengthens the mechanistic basis for land degradation assessment and restoration in tropical agroecosystems.

Arsenic (As) contamination poses substantial ecological and human health concerns in karst regions due to high geochemical background levels and enhanced mobility associated with carbonate weathering and thin soil cover. To investigate the vertical distribution, sources, and environmental risks of soil As under different anthropogenic land uses, we analyzed soil profiles from three representative ecosystems—secondary forest, abandoned cropland, and grazing shrubland—in a typical karst area of Southwest China. The As contents were identified between secondary forest (19.00 ∼ 41.17 mg/kg), abandoned cropland (22.55 ∼ 34.47 mg/kg), and shrubland (14.19 ∼ 34.46 mg/kg), with no significant differences, indicating a predominantly geogenic origin from carbonate bedrock weathering. Long-term cultivation homogenized surface soil As through plowing and crop uptake, whereas grazing introduced additional organic-bound As via livestock excreta, promoting downward migration and accumulation in deeper soil layers. Ecological risk assessment, using contamination and enrichment indices, revealed low to moderate potential risks (contamination factor: 0.71 ∼ 2.06; enrichment factor: 0.76 ∼ 2.34). Health risk assessment indicated that non-carcinogenic risks (hazard index, HI: 0.09 ∼ 0.21) were within acceptable limits for all exposure pathways, while carcinogenic risks for children (carcinogenic risk (CR): 0.11 ∼ 0.21) approached the threshold of concern. Despite overall low risk levels, the high mobility of As and its potential co-mobilization with other toxic elements underscore the need for continued monitoring. These findings highlight the importance of sustainable land-use practices to mitigate As mobilization and safeguard soil quality in vulnerable karst ecosystems.

With the ongoing changes in the global climate system and the continuous intensification of human activities, aquatic ecosystems face unprecedented stresses from multiple sources

As emerging contaminants, rare earth elements (REEs) have undergone significant anthropogenic enrichment in aquatic systems. This study investigates the REE concentrations, major metal elements, and grain size in surface sediments from the East Tiaoxi (ETX) River in eastern China, a small urban river subjected to substantial anthropogenic influences. Total REE concentrations of surface sediments ranged from 133.62 to 222.92 mg/kg with MREE enrichment and HREE depletion. REE concentration and fractionation were strongly correlated with Ca, Fe, Mg, and Mn, which may reflect the control of clay minerals, Fe-Mn oxides, and specific heavy minerals, and differences in REE behavior between riparian sediments and riverbed sediments highlighted the impact of hydrodynamic sorting and chemical weathering on REE distribution. Anthropogenic activities, particularly urbanization, were found to increase REE concentrations, especially at urban-adjacent sites (e.g., RBS2 and RS2), while natural processes such as soil transport and chemical weathering primarily contributed to REE variation at other sites. The enrichment factor and ecological risk assessment revealed that the enrichment and moderate risks associated with REEs occurred in river sediments adjacent to urbanized areas, though agricultural impacts were less pronounced. The findings emphasize the combined influence of urbanization and natural processes on REE distribution and ecological risks in the ETX River basin and underscore the need to prioritize urban-derived REE contamination in environmental management strategies.