Monitoring nutrient and beneficial elements in the topsoil: the function of weathered background and later surficial...

Monitoring the distribution of nutrient and beneficial elements (NBEs) in topsoils is important for assessing agricultural and ecological risks and for promoting human health. In order to understand their distribution effectively, it is critical to clarify their sources and main influence factors. In this study, a total of 272 topsoils and 46 soil parent material samples and some samples along 4 vertical profiles were collected in the Mentougou area of Beijing. Then, 12 NBEs were determined for each sample, including elements of N, P, S, Se, Zn, Mn, V, Ge, K, F, Ca, Mg. The mean content of 12 NBEs was statistically calculated and their spatial distributions were mapped. NBEs in topsoils were mainly influenced by the background of parent materials and the subsequent surficial processes. To address the weathered background, the study area was divided into 4 units, including igneous rocks, clastic rocks, carbonate, and loess units. For each unit, cluster analysis was performed to identify the relationship between 12 NBEs in topsoils. Furthermore, the changes in characteristics of 12 NBEs along vertical soil profiles of 4 units were individually analyzed by comparison with the weathered background. Therefore, the main factors influencing the distribution of 12 NBEs in topsoils were identified respectively. According to each element's main influencing factors, 12 NBEs were divided into 5 groups. The main influencing factors were same for elements in each group but different each other for 5 groups. Besides the weathered background, the distribution of NBEs in topsoils was significantly influenced by subsequent surficial processes, such as organic enrichment, leaching, and calcification. In addition to these natural surficial processes, the influence of human activities, a special surficial process, was also observed on the distribution of N, P, S, and Zn in topsoils in farming areas by interpreting normalized difference vegetation index (NDVI). This study provides a semi-quantitative method to determine the role of weathered background and subsequent surficial processes in the distribution of NBEs in topsoils, which helps to understand the current situation and evolution trend.