Effects of Municipal Sewage Sludge Application on Soil and Purple Moor-grass (Molinia caerulea) Contamination by Metals in a Maritime Pine Forest Laurence Denaix & Anne-Laure Thomas-Chéry & Julie Balet & Mohammed Benbrahim & Jean-Michel Carnus Received: 23 June 2010 / Accepted: 16 November 2010 / Published online: 3 December 2010 # Springer Science+Business Media B.V. 2010 Abstract The effects of municipal sewage sludge applied on topsoil and understory vegetation (Molinia caerulea (L.) Moench) were studied in a maritime pine forest located in the South West of France (Landes of Gascogne). Understory response to sludge application is important as sludge addition to forest could increase competition with pine and affect herbivorous wildlife through incorporation of heavy metals in the food chain. The experiment was conducted in a young stand of maritime pines. The experimental design consisted of three 0.1-ha plots. One plot received composted sludge, one plot received liquid sludge, and one control plot received no sludge. Liquid sludge and composted sludge were applied on the basis of 3 tons dry matter sludge per hectare and per year. After 2 years of sludge application, we observed the following: (1) a signif- icant increase in total concentrations of the following major and trace elements in the topsoil (layer 0– 20 cm) [organic carbon (+140%), nitrogen (+140%), and lead (+80%)] and (2) no significant accumulation of trace elements in M. caerulea except nickel, which increased moderately (+40%) following application of composted sludge. These initial results need to be completed (1) by the assessment of long-term effects and dynamics of trace elements with additional applications of sludge and (2) by analyzing secondary understory species to determine if understory response to sludge application is more dependant on species than on soil parameters and sludge type. Keywords Sewage sludge . Trace element . Contamination . Pine forest . Podzol 1 Introduction In agriculture, the use of sewage sludge as a fertilizer is a common practice, but its social acceptance is currently being questioned (Renner 2000). The increase in sludge production concomitantly with a decrease in the content of sludge contaminants means that new alternatives for recycling sludge need to be developed. In this context, forest land offers several Water Air Soil Pollut (2011) 219:239–249 DOI 10.1007/s11270-010-0702-8 L. Denaix (*) : A.-L. Thomas-Chéry : J. Balet UMR 1220 TCEM, INRA, Centre de Bordeaux, 33883 Villenave d’Ornon Cedex, France e-mail: denaix@bordeaux.inra.fr M. Benbrahim : J.-M. Carnus Unité de Recherches Forestières, INRA, Route d’Arcachon, 33610 Gazinet-Cestas, France J. Balet INRA, USRAVE, Centre de Bordeaux, 33883 Villenave d’Ornon Cedex, France M. Benbrahim RITTMO, 37, rue d’Herrlisheim, 68000 Colmar, France