Background values for Selenium (Se) in German soils 1:1,000,000

New, nationwide background values for 16 heavy metals and trace elements were published by the LABO in 2017. They are based on profile descriptions and measurements of aqua regia extracts, which were combined and homogenized by the BGR. Measurements with high quantification limits were excluded from further evaluation according to certain criteria in order to avoid their influence on the derivation of background values. To prevent the background values from being disproportionately influenced by regions with high sample densities, spatial thinning was partially performed. The values of several horizons of a site were combined to one value by depth-weighted averages. For evaluation, the available measured values were assigned to different groups of soil parent materials. In addition, a distinction was made whether the samples were taken in the topsoil, in the subsoil or in the underground. In the case of topsoil, the different land use (arable land, grassland, forest) was also taken into account for the evaluation. Unconsolidated rocks were evaluated separately for northern and southern Germany due to their different composition. By dividing the data into sub-collectives, reliable case numbers were not achieved in all cases. Consequently, only background values with case numbers ?20 are presented. The exact derivation procedure can be found in the report of the LABO-Bund/Länder-Arbeitsgemeinschaft Bodenschutz (2017): 'Hintergrundwerte für anorganische und organische Stoffe in Böden', 4th revised and supplemented edition.德国土壤保护联邦与州工作组（LABO）于2017年发布了针对16种重金属与微量元素的全新全国性土壤背景值数据集。该数据集基于土壤剖面描述与王水（aqua regia）提取液测试分析数据，相关数据由德国联邦地质科学与自然资源研究所（BGR）完成整合与均质化处理。为避免高定量限的测试数据对背景值推导造成干扰，研究团队依据特定标准将此类数据排除在后续评估之外。为防止高采样密度区域对背景值产生过度影响，研究人员对数据集进行了部分空间稀疏化处理。研究人员采用深度加权平均法，将同一采样点多个土壤发生层的测试值整合为单一数值。评估阶段，所有有效测试数据被划分为不同的土壤母质类别。此外，还依据采样深度将样本区分为表土、底土与地下层三类。针对表土样本，评估过程还需考虑其土地利用类型（耕地、草地、林地）的差异。鉴于松散沉积岩的组成存在显著区域差异，德国北部与南部的松散沉积岩数据被分开评估。若将数据划分为多个子数据集，并非所有类别都能获得足够的有效样本量。因此，本次仅公布有效样本量≥20的背景值数据。完整的背景值推导流程可参阅LABO-Bund/Länder-Arbeitsgemeinschaft Bodenschutz（2017）发布的《土壤中无机与有机物质背景值》（第4次修订增补版）报告。