title: Topological data analysis (TDA) applied to reveal pedogenetic principles of European topsoil system.
abstract: Recent developments in applied mathematics are bringing new tools that are capable to synthesize knowledge in various disciplines, and help in finding hidden relationships between variables. One such technique is topological data analysis (TDA), a fusion of classical exploration techniques such as principal component analysis (PCA), and a topological point of view applied to clustering of results. Various phenomena have already received new interpretations thanks to TDA, from the proper choice of sport teams to cancer treatments. For the first time, this technique has been applied in soil science, to show the interaction between physical and chemical soil attributes and main soil-forming factors, such as climate and land use. The topsoil data set of the Land Use/Land Cover Area Frame survey (LUCAS) was used as a comprehensive database that consists of approximately 20,000 samples, each described by 12 physical and chemical parameters. After the application of TDA, results obtained were cross-checked against known grouping parameters including five types of land cover, nine types of climate and the organic carbon content of soil. Some of the grouping characteristics observed using standard approaches were confirmed by TDA (e.g., organic carbon content) but novel subtle relationships (e.g., magnitude of anthropogenic effect in soil formation), were discovered as well. The importance of this finding is that TDA is a unique mathematical technique capable of extracting complex relations hidden in soil science data sets, giving the opportunity to see the influence of physicochemical, biotic and abiotic factors on topsoil formation through fresh eyes.
authors.affiliation: Laboratoire de Spectrochimie Infrarouge et Raman (LASIR), UMR 8516, Université Lille 1, Sciences et Technologies, Bâtiment C5, 59655 Villeneuve d'Ascq Cedex, France. Electronic address: asavic@imsi.rs.
authors.forename: Aleksandar
authors.initials: A
authors.lastname: Savic
authors.affiliation: European Commission, Joint Research Centre (JRC), Directorate D - Sustainable Resources, Via Enrico Fermi 2749, 21027 Ispra, VA, Italy. Electronic address: gergely.toth@jrc.ec.europa.eu.
authors.forename: Gergely
authors.initials: G
authors.lastname: Toth
authors.affiliation: Laboratoire de Spectrochimie Infrarouge et Raman (LASIR), UMR 8516, Université de Lille, Sciences et Technologies, Bâtiment C5, 59655 Villeneuve d'Ascq Cedex, France. Electronic address: ludovic.duponchel@univ-lille1.fr.
authors.forename: Ludovic
authors.initials: L
authors.lastname: Duponchel
keywords: Ecology; Land Use/Land Cover Area Frame Survey (LUCAS); Pedology; Soil geography; Soil typology; Topological data analysis (TDA)