Role of different salt marsh plants on metal retention in an urban estuary (Lima estuary, NW Portugal) C.M.R. Almeida a, * , Ana P. Mucha a , M. Teresa Vasconcelos a, b a CIMAR/CIIMAR e Centro Interdisciplinar de Investigação Marinha e Ambiental, Universidade do Porto, Rua dos Bragas, 289, 4050-123 Porto, Portugal b Departamento de Química e Bioquímica, Faculdade de Ciências, Universidade do Porto, Rua do Campo Alegre, 687, 4169-007 Porto, Portugal article info Article history: Received 5 August 2010 Accepted 29 October 2010 Available online 10 November 2010 Keywords: metals salt marsh plants native plants invasive plants abstract The aim of the present work was to understand the role different salt marsh plants on metal distribution and retention in the Lima River estuary (NW Portugal), which to our knowledge have not been ascer- tained in this area yet. The knowledge of these differences is an important requirement for the devel- opment of appropriate management strategies, and is poorly described for Eurosiberian estuaries, like the one selected. In addition it is important to understand the difference among introduced and native salt marsh plants. In this work, metal levels (Cd, Cr, Cu, Fe, Mn, Ni, Pb and Zn) were surveyed (by atomic absorption spectrometry) in sediments from sites vegetated with Juncus maritimus, Spartina patens, Phragmites australis and Triglochin striata (rhizo-sediments), in non-vegetated sediments and in the different tissues of the plants (roots, rhizomes and aerial shoots). In general, rhizo-sediments had higher metal concentrations than non-vegetated sediments, a feature that seems common to sediments colo- nized by salt marsh plants of different estuarine areas. All plants concentrated metals, at least Cd, Cu and Zn (and Pb for T. striata) in their belowground structures ([M] belowground tissues /[M] non-vegetated sediment > 1). However, when considered per unit of salt marsh area, the different selected plants played a different role on sediment metal distribution and retention. Triglochin striata retained a significant metal burden in it belowground structures (root plus rhizomes) acting like a possible phyto-stabilizer, whereas P. australis had an higher metal burden in aboveground tissues acting as a possible phyto-extractor. As for J. maritimus and S. patens, metal burden distribution between above and belowground structures depen- ded on the metal, with J. maritimus retaining, for instance, much more Cd and Cu in the aboveground than in the belowground structures. Therefore, the presence of invasive and exotic plants in some areas of the salt marsh may considerably affect metal distribution and retention in the estuarine region. Ó 2010 Elsevier Ltd. All rights reserved. 1. Introduction Estuaries are often considered sinks for pollutants (namely, metals) receiving important anthropogenic inputs from the upstream catchments and from metropolitan areas and industries located on or near those areas. Most estuaries present large salt marsh areas colonized by different plants. Plants are known to be able of oxidizing the sediment through the movement of oxygen towards the roots (Weis and Weis, 2004) or acidifying its rhizo- sphere through the release of root exudates (Jones, 1998; Mucha et al., 2008). Plants can also alter metal speciation in the sediment surrounding its roots (Almeida et al., 2004; Reboreda and Caçador, 2007a; Koretsky et al., 2008). If salt marsh plants are able to immobilize metals in their belowground structures, they may act as phyto-stabilizers, reducing metals bioavailability. On the other hand, plants that accumulate metals in their aboveground tissues can act as phyto-extractors, although, if these tissues are not removed, metals may return into the salt marsh system, increasing their bioavailability. (Reboreda and Caçador, 2007b). Nevertheless, the role of a plant depends on multiple factors, including environ- mental characteristics and plant species. The aim of the present work was to understand the role different salt marsh plants on metal distribution and retention in an urban-industrialized estuary. The knowledge of these differences is an important requirement for the development of appropriate management strategies, and is poorly described for Eurosiberian salt marshes. Lima River estuary (NW Portugal) is an urban-industrialized estuary, which suffers from several sources of disturbance, such as navigation activity in the lower estuary and a cellulose factory in the upper estuary. In addi- tion, this system is impacted by input of agricultural run off and * Corresponding author. E-mail address: calmeida@ciimar.up.pt (C.M.R. Almeida). Contents lists available at ScienceDirect Estuarine, Coastal and Shelf Science journal homepage: www.elsevier.com/locate/ecss 0272-7714/$ e see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.ecss.2010.10.037 Estuarine, Coastal and Shelf Science 91 (2011) 243e249