Effect of Topography on the Spatial Distribution of Selenium in Soil Within a County Level

<p indent="0mm">In this study, Wuhua County, Meizhou City, Guangdong Province, was selected as the research area to investigate the spatial distribution of selenium content in topsoil. Eight topographic factors, including elevation, slope, aspect, the relief degree of land surface, surface cutting depth, terrain roughness, plane curvature, profile curvature, topographic wetness index and vegetation cover index was used to quantitatively analyze the mechanism of regional topography affecting the spatial differentiation of selenium content in topsoil. The results indicate that the study area belongs to a typical subtropical monsoon climate, the humid and hot conditions lead to strong weathering in the region. During the weathering process of parent rock, selenium is released and deposited in the soil, resulting in selenium enrichment in the soil in the study area, which belongs to natural selenium rich soil. The spatial distribution of selenium content in topsoil was significantly correlated with topographic factors. The selenium content was higher in mountainous and hilly areas with higher elevations, while lower in plain areas with lower elevations in central and northern regions. On the one hand, selenium in soil is greatly affected by human activities in the low altitude areas, such as the absorption of crops, which can easily lead to the loss of soil selenium. On the other hand, topography affects the redistribution of substance and the physical and chemical properties of soil through surface runoff and soil erosion, which have a primary or secondary affect on the migration and enrichment of selenium in soil. Among them, soil moisture index, altitude, terrain roughness and slope had more significant impact on the surface soil selenium. In contrast, aspect and curvature had no significant effect on the migration and accumulation of selenium in topsoil. The results showed that the higher the altitude, the more complex and steeper the terrain, the stronger the soil erosion, the lower the soil moisture, the lower the pH value, and the higher the content of available phosphorus, and finally lead to selenium enriched in the topsoil. But when the steepness and complexity reach a certain level, the trend of selenium enrichment in the soil slightly changes.