Genetic Types and Ecological Potential of Selenium-Enriched Land in the Northern Margin of the Qinghai—Xizang Plateau

The study of the genesis type of selenium (Se)-enriched land found in the Qinghai—Xizang Plateau can provide a scientific basis for the construction of the research, development and utilization system of Se resources on the Qinghai—Xizang Plateau and has practical significance for improving the risk of low Se intake on the Qinghai—Xizang Plateau. On the basis of summarizing the characteristics and genesis types of the main natural Se-enriched lands in China, the distribution characteristics of Se and related elements are analyzed through the coordinated monitoring of soil and rock, and the conclusion is that there are three types of Se-enriched lands in the northern margin of the Qinghai—Xizang Plateau, namely, arid saline lake sedimentary type, sulfide mineralization type and organic matter adsorption type. (1) In the sedimentary Se-enriched land of the arid saline lake, the Se content ranges from 0.30 to 1.16mg/kg, and the contents of heavy metals are below the risk control screening values. Spatially, Se overlaps and co-enriches with beneficial elements such as Sr, Mg, Fe, Ca, and Mo. Se is derived from the red mudstone weathering of the Xining Group, which has the advantages of stable Se source sedimentation, moderate total amount of Se, low heavy metals, and composite of a variety of beneficial elements. It is a type of Se with greater ecological potential in the northern margin of the Qinghai—Xizang Plateau and even the entire northwest region. (2) In sulfide mineralized Se-enriched land, Se content ranges from 0.30 to 2.22mg/kg; Ni, Cd, Cr and As exceed screening values in 0.2%−2.4% of the samples; As exceeds control values in 0.1% of the samples. The land has high natural heavy metal backgrounds, posing ecological risks and limitations of high-altitude and cold climate, which can be used to develop the forest-based economy and wild Chinese herbal medicine industry under monitoring. (3) In the organic matter adsorption type Se-enriched land, Se content ranges from 0.30 to 0.59mg/kg, and Ni, Cd, Cr and As do not exceed the standard. Se has the dual effects of increasing forage nutrition and resisting heavy metal absorption, so the maximum ecological effect of Se can be regulated by further exploring the equilibrium conditions of organic matter in the process of adsorption-release of Se.