Modelling and mapping heavy metal and nitrogen concentrations in moss in 2010 throughout Europe by applying Random Forests models

Publication date: May 2017
Source:Atmospheric Environment, Volume 156
Author(s): Stefan Nickel, Winfried Schröder, Werner Wosniok, Harry Harmens, Marina V. Frontasyeva, Renate Alber, Julia Aleksiayenak, Lambe Barandovski, Oleg Blum, Helena Danielsson, Ludwig de Temmermann, Anatoly M. Dunaev, Hilde Fagerli, Barbara Godzik, Ilia Ilyin, Sander Jonkers, Zvonka Jeran, Gunilla Pihl Karlsson, Pranvera Lazo, Sebastien Leblond, Siiri Liiv, Sigurður H. Magnússon, Blanka Mankovska, Javier Martínez-Abaigar, Juha Piispanen, Jarmo Poikolainen, Ion V. Popescu, Flora Qarri, Dragan Radnovic, Jesus Miguel Santamaria, Martijn Schaap, Mitja Skudnik, Zdravko Špirić, Trajce Stafilov, Eiliv Steinnes, Claudia Stihi, Ivan Suchara, Lotti Thöni, Hilde Thelle Uggerud, Harald G. Zechmeister
ObjectiveThis study explores the statistical relations between the concentration of nine heavy metals (HM) (arsenic (As), cadmium (Cd), chromium (Cr), copper (Cu), mercury (Hg), nickel (Ni), lead (Pb), vanadium (V), zinc (Zn)), and nitrogen (N) in moss and potential explanatory variables (predictors) which were then used for mapping spatial patterns across Europe. Based on moss specimens collected in 2010 throughout Europe, the statistical relation between a set of potential predictors (such as the atmospheric deposition calculated by use of two chemical transport models (CTM), distance from emission sources, density of different land uses, population density, elevation, precipitation, clay content of soils) and concentrations of HMs and nitrogen (N) in moss (response variables) were evaluated by the use of Random Forests (RF) and Classification and Regression Trees (CART). Four spatial scales were regarded: Europe as a whole, ecological land classes covering Europe, single countries participating in the European Moss Survey (EMS), and moss species at sampling sites. Spatial patterns were estimated by applying a series of RF models on data on potential predictors covering Europe. Statistical values and resulting maps were used to investigate to what extent the models are specific for countries, units of the Ecological Land Classification of Europe (ELCE), and moss species.ResultsLand use, atmospheric deposition and distance to technical emission sources mainly influence the element concentration in moss. The explanatory power of calculated RF models varies according to elements measured in moss specimens, country, ecological land class, and moss species. Measured and predicted medians of element concentrations agree fairly well while minima and maxima show considerable differences. The European maps derived from the RF models provide smoothed surfaces of element concentrations (As, Cd, Cr, Cu, N, Ni, Pb, Hg, V, Zn), each explained by a multivariate RF model and verified by CART, and thereby more information than the dot maps depicting the spatial patterns of measured values.ConclusionsRF is an eligible method identifying and ranking boundary conditions of element concentrations in moss and related mapping including the influence of the environmental factors.



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