Mercury and flooding cycles in the Tapajós river basin, Brazilian Amazon: The role of periphyton of a floating macrophyte (Paspalum repens) Sérgio A. Coelho-Souza a, ⁎, Jean R.D. Guimarães a , Márcio R. Miranda a , Hugo Poirier b , Jane B.N. Mauro a , Marc Lucotte b , Donna Mergler c a Lab. Traçadores Wolfgang C. Pfeiffer, SL 049, Instituto de Biofísica Carlos Chagas Filho/UFRJ, Bloco G, Centro de Ciências e Saúde, Ilha do Fundão, Rio de Janeiro, RJ, CEP 21949–902, Brazil b Chaire de Reserche en Environment, Université du Québec à Montréal (UQaM), CP 8888, Montreal, Canada H3C 3P8 c CINBIOSE, UQaM, CP 8888, succ. Centre-ville, Montreal, Canada H3C 3P8 abstract article info Article history: Received 22 October 2010 Received in revised form 22 March 2011 Accepted 23 March 2011 Available online 4 May 2011 Keywords: 203 Hg Floodplain lakes 13 C/ 15 N stable isotopes 3 H-leucine incorporation Bacterial activity Clear-water river Methylmercury (MeHg) increases mercury (Hg) toxicity and is biomagnified in the trophic chain contaminating riverine Amazon populations. Freshwater macrophyte roots are a main site of Hg methylation in different Brazilian environments. Paspalum repens periphyton was sampled in four floodplain lakes during the dry, rainy and wet seasons for measurement of total Hg (THg), MeHg, Hg methylation potentials, %C, %N, δ 13 C, δ 15 N and bacterial heterotrophic production as 3 H-leucine incorporation rate. THg concentration varied from 67 to 198 ng/g and the potential of Me 203 Hg formation was expressive (1–23%) showing that periphyton is an important matrix both in the accumulation of Hg and in MeHg production. The concentration of MeHg varied from 1 to 6 ng/g DW and was positively correlated with Me 203 Hg formation. Though methylmercury formation is mainly a bacterial process, no significant correlation was observed between the methylation potentials and bacterial production. The multiple regressions analyses suggested a negative correlation between THg and %C and %N and between methylation potential and δ 13 C. The discriminant analysis showed a significant difference in periphyton δ 15 N, δ 13 C and THg between seasons, where the rainy season presented higher δ 15 N and the wet period lighter δ 13 C, lower THg values and higher Me 203 Hg formation. This exploratory study indicates that the flooding cycle could influence the periphyton composition, mercury accumulation and methylmercury production. © 2011 Published by Elsevier B.V. 1. Introduction The first data on mercury (Hg) contamination in the Brazilian Amazon were reported in the 1980s, following a decade of gold rush (Martinelli et al., 1988). Gold production resulted in atmospheric and aquatic mercury contamination since metallic Hg was directly dis- charged in the river during the amalgamation process and thereafter, this amalgam burned to recover gold (Pfeiffer et al., 1993). Currently, artisanal gold mining has lost intensity and it was suggested that soil podzolization and erosion are responsible for losses of accumulated natural mercury complexed with Al and Fe oxy-hydroxides (Roulet and Lucotte, 1995). Mercury in different systems seems to be from natural origin and accumulated by dry and wet deposition on Amazon soils (Roulet et al., 1999, 2000b). Fine particulate matter (FPM), richer in Hg and oxy-hydroxides is easily carried to aquatic systems by runoff and soil erosion (Farella et al., 2001; Sampaio da Silva et al., 2009). In water, Hg can undergo different transformations, of which methylation is an important one, due to the irreversible human neurotoxic effects of its product, methylmercury (Brigham et al., 2009). Methylmercury (MeHg) formation increases Hg availability and dispersion along the environ- ment since it has little affinity with mineral surfaces (Melamed et al., 1997) and is biomagnified along the trophic chain (Bastos et al., 2008; Molina et al., 2010). In Brazilian Amazon, Hg can reach high concentrations in hair of riverine communities (Malm et al., 1997, 2010; Harada et al., 2001). The roots of floating aquatic macrophytes are an important site of periphyton, detritus and FPM accumulation and are considered a main Hg methylation site in tropical aquatic systems (Guimarães et al., 1998, 2000b; Mauro et al., 2002). In addition to the favorable conditions they offer to heterotrophic microorganism activity (Guimarães et al., 2006; Miranda et al., 2007a), aquatic macrophyte roots act as a trap for inorganic and organic contaminants (Guasch et al., 2003), including mercurial species (King et al., 2002; Göthberg and Greger, 2006). Also, MeHg production by biofilms in floodplain environments is poorly studied (Hughett et al., 2010; Acha et al., 2011). Molina et al. (2010) showed the importance of periphyton as a main food source to macroinvertebrates in a floodplain lake of Beni river basin (Bolivia), and that the biomagnifica- tion of MeHg was very effective in the periphyton-based chain. The hydrological cycle of the Amazon system is dominated by annual flooding events. This phenomenon is known as Flood Pulse. Large areas are inundated for long periods and some authors (e.g., Roulet et al., Science of the Total Environment 409 (2011) 2746–2753 ⁎ Corresponding author. Tel.: + 55 2125626651; fax: + 55 2122808193. E-mail address: sacs@biof.ufrj.br (S.A. Coelho-Souza). 0048-9697/$ – see front matter © 2011 Published by Elsevier B.V. doi:10.1016/j.scitotenv.2011.03.028 Contents lists available at ScienceDirect Science of the Total Environment journal homepage: www.elsevier.com/locate/scitotenv