Total contents and mobile fractions of chemical elements within a soil toposequence in the south-east of the Valdai Hills, Russia

Samples were taken from September 2016 to May 2018 in the southern part of the Central Forest Reserve (Russia) within a catena with c Retisols under coniferous-deciduous forest (Tília cordáta, Pícea ábies, Ácer platanoídes) on loess-like loams underlain by carbonate moraine deposits. Soil properties were analysed at the MSU (Lomonosov Moscow State University) Faculty of Geography: - pH value was measured in suspension (static conditions) using a pH-meter "Expert-рН" (Russia); - total organic carbon (TOC) content was determined in 120 samples using titrimetric method with phenylanthranilic acid (Reeuwijk, 2002); - the particle-size distribution was analyzed using laser diffraction technique and an ‘Analizeter 22’ equipment (Germany). Particle-size classes (Russian system): G1 – clay (<1 μm), G2 – very fine silt (5–1), G3 – medium silt (10–5), G4 – сoarse silt (50–10), G5 –fine sand (250–50), G6 – medium sand (500–250). Total content of chemical elements (ChEs) and mobile fractions was measured at the VIMS (N. M. Fedorovskii All-Russia Institute of Mineral Raw Materials) using an Elan-6100 ICP-MS System and an Optima-4300 DV ICP-AES System. The studied fractions of the ChEs: - F1 (exchangeable) was extracted with NH4Ac (ammonium acetate buffer) - F2 (bound within organo-mineral complexes) was extracted with with 1% EDTA (ethylenediaminetetraacetic acid) - F3 (bound with Fe and Mn hydroxides) was extracted with 1M HNO3 - F4 (residual fraction) - the difference between the total content of elements and the content of mobile forms.

本数据集的样本采集于2016年9月至2018年5月，采自俄罗斯中部森林保护区南部的一段土链（catena），该土链上发育针阔混交林（心叶椴*Tília cordáta*、云杉*Pícea ábies*、挪威槭*Ácer platanoídes*），林下为黄土状壤土，下伏碳酸盐冰碛沉积物，且以粘磐土（Retisols）为主要土壤类型。土壤属性分析在莫斯科国立罗蒙诺索夫大学（Lomonosov Moscow State University, MSU）地理学院完成，具体测定项目与方法如下：
1. pH值采用静态悬液法，使用俄罗斯产"Expert-pH"pH计进行测定；
2. 总有机碳（total organic carbon, TOC）含量采用苯基邻氨基苯甲酸滴定法（Reeuwijk, 2002）对120份样本进行测定；
3. 粒度分布采用激光衍射技术，搭配德国产"Analizeter 22"仪器开展分析。
本次研究采用俄罗斯标准土壤粒度分级体系，具体分级标准如下：
G1 – 黏粒（<1 μm），G2 – 极细粉粒（5–1 μm），G3 – 中粉粒（10–5 μm），G4 – 粗粉粒（50–10 μm），G5 – 细砂粒（250–50 μm），G6 – 中砂粒（500–250 μm）。
化学元素（chemical elements, ChEs）总量及有效态组分的测定工作在全俄N. M. 费多罗夫斯基矿物原料研究所（N. M. Fedorovskii All-Russia Institute of Mineral Raw Materials, VIMS）完成，所用仪器为Elan-6100型电感耦合等离子体质谱（ICP-MS）系统与Optima-4300 DV型电感耦合等离子体原子发射光谱（ICP-AES）系统。
本次研究针对以下化学元素组分开展分析：
- F1（可交换态）：采用醋酸铵缓冲液（ammonium acetate buffer, NH₄Ac）进行提取；
- F2（有机-矿质复合体结合态）：采用1%乙二胺四乙酸（ethylenediaminetetraacetic acid, EDTA）溶液进行提取；
- F3（铁锰氢氧化物结合态）：采用1mol/L硝酸（HNO₃）溶液进行提取；
- F4（残渣态）：为化学元素总量与有效态组分含量的差值。