Ecological Indicators 14 (2012) 170–177 Contents lists available at ScienceDirect Ecological Indicators jo ur n al homep ag e: www.elsevier.com/locate/ecolind Atmospheric element deposit on tree barks: The opposite effects of rain and transpiration Mickaël Catinon a,∗ , Sophie Ayrault b , Omar Boudouma c , Juliette Asta a , Michel Tissut a , Patrick Ravanel a a Laboratoire LECA, UMR 5553, Equipe Perturbations Environnementales et Xénobiotiques, Univ. J. Fourier, 38041 Grenoble, France b Laboratoire des Sciences du Climat et de l’Environnement, UMR 1572, CEA-CNRS-UVSQ/IPSL, 91198 Gif-sur-Yvette, France c Service du MEB, UFR928, Université Pierre et Marie Curie, 75252 Paris VI, France a r t i c l e i n f o Article history: Received 16 February 2011 Received in revised form 1 July 2011 Accepted 10 July 2011 Keywords: Bark Air pollution Stemflow Transpiration SEM-EDX ICP-MS a b s t r a c t The elemental composition of the deposit formed on the bark of ash-trees was studied over several months on stems ranging from 3 months to 10 years. For this purpose (1) the total elemental composition of the deposit, (2) the structure and composition of the solid particles and (3) the deposit dry weight per dm 2 were studied. Concurrently the part of this superficial deposit washed out by rain during 3.5 months was sampled at each rain event and its elemental composition analyzed. This study shows that the deposit was submitted to an intense turnover, with an average leaching-out flux reaching approximately 27 mg dm -2 month -1 and a very low increase of the deposit weight per dm 2 during the first five years and almost null afterwards. The origin of this superficial deposit was investigated. The main part (78 ± 10%) was organic matter originating from the atmospheric deposition or from the tree. The inorganic content originated partly from the atmosphere, with geogenic and anthropogenic particles, and also from the tree, in which it was demonstrated by scanning electron microscopy – energy dispersive X-ray that a non-negligible part was obtained from bark transpiration, inducing a superficial deposit, mainly of Ca or K in the area surrounding the lenticels. All those results demonstrate that this bark superficial deposit is a complex matrix which must not be considered as a simple cumulative archive but which seems to be the source of interesting information targeting mostly recent atmospheric pollution pressures, when compared to the bulk of suber integrated particles. © 2011 Elsevier Ltd. All rights reserved. 1. Introduction The deposition of atmospheric components on tree barks has been supposed for a long time to be representative of the atmo- spheric content and of its changes over long periods of time (Ballach et al., 2002; Purvis et al., 2007; Schulz et al., 1999). As trees are very common in countries with a temperate climate, they were chosen by numerous scientific teams for several decades to study the nature of atmospheric deposition on their barks, its changes as a function of time and to carry out quantitative mea- surements of deposition rate (Al-Shayeb et al., 1995; Askoy and Öztürk, 1997; Böhm et al., 1998; El-Hasan et al., 2002; Freitas et al., 1997). Concurrently, the numerous direct measurements of the ele- mental composition of atmospheric gazes and particles suspended ∗ Corresponding author. Tel.: +33 4 76 51 46 54. E-mail addresses: mickael.catinon@gmail.com (M. Catinon), Sophie.Ayrault@lsce.cnrs-gif.fr (S. Ayrault), boudouma@ccr.jussieu.fr (O. Boudouma), juliette.asta@ujf-grenoble.fr (J. Asta), michel.tissut@ujf-grenoble.fr (M. Tissut), patrick.ravanel@ujf-grenoble.fr (P. Ravanel). in the air column (Freitas et al., 2004; Geagea et al., 2008; Salma and Maenhaut, 2006) allowed to understand that the deposits found on tree barks (1) were far more complex than a simple representation of the atmospheric mixture (Catinon et al., 2009a) and (2) were therefore not a true faithful record of the atmospheric composition changes over periods of time corresponding to the tree’s age. However, the numerous interesting results previously obtained on tree bark, especially in typical situations (heavily polluted areas, surroundings of mines or large towns (Ballach et al., 2002; Bellis et al., 2001; Kuang et al., 2007; Palma et al., 2003)) suggested that fruitful information about air contaminations was registered in such deposits but there was yet no way of reading and under- standing it, as was the case for hieroglyphs before Champollion’s discovery. For a better use, it was consequently necessary to know the numerous events and mechanisms involved in the formation and fate of this superficial deposit. For this purpose, in a first attempt we measured the bark deposit accumulation kinetics from year to year through a comparison of the deposits per dm 2 bark area coming from the stem segments corresponding to each year (Catinon et al., 2008). In a second attempt, the deposit on bark was compared to the part integrated inside suber (Catinon et al., 2009b). It showed that solid particles integrated inside the suber tissue 1470-160X/$ – see front matter © 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.ecolind.2011.07.013