Geochemical Characteristics and Spatial-Distribution Controls of Soil Selenium in Ninghua, Fujian Province

Selenium (Se), an essential trace element for humans, animals, and plants, plays a critical role in ecosystem health and human nutrition. China exhibits significant regional variations in soil selenium content, making systematic research on its spatial distribution and controlling factors vital for agricultural biofortification, endemic disease prevention, and land resource management. However, the enrichment-depletion patterns and influencing factors of selenium in soil profiles within geological high-background areas remain insufficiently studied. The geochemical characteristics and spatial distribution of soil selenium in Ninghua County, Fujian Province are investigated in this study, by analyzing multi-target geochemical data and eight soil profiles of varying parent materials. Results indicate that Ninghua’s deep soil selenium content (0.24mg/kg) exceeds the national average (0.17mg/kg), classifying it as a geological high-background area. Surface selenium distribution exhibits notable heterogeneity, with high concentrations primarily in Cambrian metamorphic rock zones, confirming parent rock dominance. Profile analysis reveals distinct controlling factors: in granite/basalt profiles, selenium correlates strongly with organic matter; in metamorphic rock profiles, clay minerals and iron oxides are key selenium carriers, though surface depletion occurs due to phosphorus antagonism; in limestone profiles, soil pH primarily governs selenium content. Additionally, soil particle size selectively adsorbs selenium-clay particles (<0.002mm) adsorb 15–20 times more selenium than coarse sand in granite/basalt profiles, while alkaline conditions in limestone mask this effect. The spatial differentiation and multi-factor control mechanisms of soil selenium is explained, offering a scientific foundation for leveraging selenium-enriched land resources in Ninghua.