Clay mineral inventory in soils of Europe based on LUCAS survey soil samples

Clay minerals are a key factor in mineral soils as they are controlling physic, chemical and biological soil properties. The X-ray diffraction (XRD) analysis has been widely used to identify and quantify minerals in earth science The aim of this research is to describe the clay minerals in soils of Europe and United Kingdom by using soil samples from the Land Use/Cover Area Frame Survey (LUCAS) topsoil database sampled in 2015. A subset of 388 soil samples were selected from LUCAS 2015 topsoil survey. The clay fraction (<2 μm) was separated by sedimentation in distilled water. X-ray powder diffraction (XRPD) measurements have been carried out with a Siemens D5000 diffractometer with a graphite monochromator, using CuKα radiation at 40 kV and 40 mA. Clay mineralogy has been studied by measurement of basal spacing parameters on the clay fraction oriented in glass slides: 3 to 13 °2θ range 0.02 °2θ step size. The study involved the measurement of the 1. air-dried sample, 2. ethylene glycol solvated sample, 3. heat treatment at 110, 350 and 550 °C. Identification of clay minerals were based on the d-spacing value of their 00l (mainly 001) reflections after different diagnostic treatment. The semiquantitative composition of <2 μm fractions was estimated by using integrated areas of 00l reflections. Brief description of the clay mineralogy of all samples and semi quantitative mineral composition was performed at country level. The X-ray diffractograms after the different treatment (black = untreated, blue = ethylene glycol solvated, green = 110 °C, dark red = 350 °C, red = 550 °C) for each soil sample were analyzed. Majority clay minerals were compared to soils properties such as CEC, soil pH, soil organic carbon (SOC), and clay and sand content. Current descriptive analysis can be used to identify the most relevant clay minerals in soils of Europe. Monitoring over time can be used as soil health indicator to establish potential correlations between clay minerals and relevant threats as soil degradation, soil erosion, and soil pollution.