Spatial and temporal patterns of throughfall chemistry within a temperate mixed oak–beech stand Frédéric André ⁎ , Mathieu Jonard, Quentin Ponette Université catholique de Louvain, Faculté d'Ingénierie Biologique, Agronomique et Environnementale, Unité des Eaux et Forêts, Croix du Sud 2/009, 1348 Louvain-la-Neuve, Belgium ARTICLE INFO ABSTRACT Article history: Received 27 August 2007 Received in revised form 22 February 2008 Accepted 25 February 2008 Available online 10 April 2008 The effects of meteorological variables and local canopy characteristics on throughfall chemistry were investigated within a mixed oak–beech stand during the leafed and the leafless seasons. Throughfall was collected after each rain event in 12 structural units delimited by three neighbouring trees each. For each investigated ion (H + , Mg 2+ , Ca 2+ ,K + , NH 4 + , Na + , Cl - , NO 3 - and SO 4 2- ), mixed linear models were used to analyse the effects of the rain volume (R) and of the length of the preceding dry period (ADP) on net throughfall ion fluxes and to evaluate the influence of canopy density and tree species composition on these relationships. The models explained more than 70% of the total variability. Canopy characteristics accounted for most of the spatial variability while a large part of the temporal variability was not explained by R and ADP, suggesting an influence of other variables such as wind force and direction. For each season, net throughfall ion fluxes generally increased with increasing R and ADP, whose coefficients were interpreted as leaching capacity and dry deposition rate, respectively; H + is an exception with negative exchange capacity (i.e. absorption) during the leafed season. Dry deposition rate and exchange capacity estimates were generally lower for the leafless canopies compared with the leafed season. For a given density level, exchange capacities were either higher for oak than for beech or similar for both species while dry deposition tended to increase with increasing beech proportion. The enhancing effect of canopy density on dry deposition was particularly marked for the mixed leafed canopies. For the pure canopies, the effect of canopy density on dry deposition rate and exchange capacity tended to be more pronounced during the leafless period compared with the leafed season, while it was generally limited compared with the species effect. © 2008 Elsevier B.V. All rights reserved. Keywords: Throughfall Deposition Quercus petraea Fagus sylvatica Mixed-species stand 1. Introduction As rain passes through the canopy, its chemical composition is affected by two main processes: (i) wash-off of particles and gases deposited on plant surfaces and (ii) ion exchanges with tree organs and their communities (micro-organisms, epiphytes). The distinction between (i) external inputs of elements entering the ecosystem as wet and dry depositions and (ii) internal cycling of nutrients previously absorbed by the roots is of prime importance for studies focusing on forest nutrient cycles. Several approaches have been developed to separate dry deposition from canopy exchange: estimation of dry deposition on artificial surfaces (Dambrine et al., 1998; Rodrigo and Avila, 2002) or from inferential modelling (Sickles et al., 1983; Wesely and Hicks, 2000), isotopic techniques (Lindberg and Garten, 1988) and application of canopy budget or regression models on throughfall measurements (Ulrich, 1983; Lovett and Lindberg, 1984, 1986; Draaijers and Erisman, 1995). SCIENCE OF THE TOTAL ENVIRONMENT 397 (2008) 215 – 228 ⁎ Corresponding author. Tel.: +32 10 47 90 76 or 32 10 47 36 16; fax: +32 10 47 36 97. E-mail addresses: frederic.andre@uclouvain.be (F. André), mathieu.jonard@uclouvain.be (M. Jonard), quentin.ponette@uclouvain.be (Q. Ponette). 0048-9697/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.scitotenv.2008.02.043 available at www.sciencedirect.com www.elsevier.com/locate/scitotenv