Review The natural rehabilitation of an anthropogenically acidified tropical Lake: Two decades of monitoring Cristiano V.M. Araújo a,b,⇑ , Salomão J. Cohin-de-Pinho a , Carla B.A. Chastinet c , Sandro L. Machado d , Eduardo M. da Silva a a Instituto de Biologia, Federal University of Bahia, Campus de Ondina, 40170-115 Salvador, BA, Brazil b IMAR – Instituto do MAR, Department of Life Sciences, University of Coimbra, Apartado 3046, 3001-401 Coimbra, Portugal c Instituto do Meio Ambiente e Recursos Hídricos, Rua São Francisco, No. 1, 40245-060 Salvador, BA, Brazil d Departamento de Ciência e Tecnologia dos Materiais, Escola Politécnica, Federal University of Bahia, 40210-630 Salvador, BA, Brazil highlights " Natural rehabilitation of an acidified Lake was monitored during two decades. " pH, conductivity, sulphate, iron and toxicity of the water were monthly recorded. " Toxicity levels were related to Lake pH values which ranged with rain and dry regime. " Moving average approach using pH data showed clearly the Lake recovery process. " Recent data highlight Lake rehabilitation and the efficiency of the containment plan. article info Article history: Received 7 November 2011 Received in revised form 21 May 2012 Accepted 23 June 2012 Available online 21 July 2012 Keywords: Acidification Monitoring pH Rehabilitation Toxicity abstract The rehabilitation of a pond after approximately 20 years of strong acidified conditions due to industrial and domestic waste deposition in its catchment basin is reviewed. We describe in this study the acidifi- cation process that occurred in a tropical pond in Northeast Brazil (Dunas Lake), the rehabilitation plan for the pond and the subsequent monitoring conducted over two decades. After the contamination assessment by the late 80s, a rehabilitation plan was carried out in the early 90s, in which the contam- inated soil and water have been removed and reduced, respectively. No further attempt to neutralize the water or any remediation has been carried out. A toxicity monitoring plan based on toxicity assays with the fish Poecilia reticulata was employed to verify the natural rehabilitation of the pond. The data on tox- icity, pH, conductivity, sulphate and dissolved iron recorded from 1994 to 2010 were also compiled and discussed. The collected data in 2003 and 2004 indicated changes in water quality and from them com- plementary management actions, namely improvement in the containment plant, were conducted in 2005. Results for toxicity assays and pH results indicated interannual changes in the water quality similar to rainy-dry periods. Moving average approach using pH data clearly showed the recovery process of Dunas Lake as well as the importance of the containment plan to reduce the contamination. Finally, a summary of the recent situation after two decades of rehabilitation is provided. Ó 2012 Elsevier Ltd. All rights reserved. Contents 1. Introduction ......................................................................................................... 888 2. Material and methods ................................................................................................. 888 2.1. Dunas Lake: general description and origin of contamination ............................................................ 888 2.2. Rehabilitation plan and monitoring ................................................................................. 888 2.3. Physical–chemical analysis ........................................................................................ 889 0045-6535/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.chemosphere.2012.06.029 ⇑ Corresponding author at: Instituto de Biologia, Federal University of Bahia, Campus de Ondina, 40170-115 Salvador, BA, Brazil. Tel.: +55 71 3263 6525; fax: +55 71 3263 6511. E-mail address: cristiano.araujo@icman.csic.es (C.V.M. Araújo). Chemosphere 90 (2013) 887–894 Contents lists available at SciVerse ScienceDirect Chemosphere journal homepage: www.elsevier.com/locate/chemosphere