SEGH Articles

# Sedimentary geochemistry of platinum in intertidal salt marsh sediments of the Tagus River Estuary, Lisbon, Portugal

03 December 2012
Studies of platinum in intertidal sediments have highlighted a number of features of Pt dynamics in saltmarsh environments.

Clara Almécija-Pereda was joint oral presentation winner at the 9th ISEG meeting held in Aveiro Portugal in July 2012. Her studies of platinum in intertidal sediments have highlighted a number of features of Pt dynamics in saltmarsh environments, an element which has rarely been studied in the estuarine environment. In December 2010 she started a PhD in Marine Biogeochemistry Group in Marine Research Institute IIM-CSIC (Spanish Research Council) in Vigo, under the supervision of Dr. Antonio Cobelo-García and Dr. Juan Santos-Echeandía and in collaboration with IPMA (Portuguese Institute of Sea and Atmosphere).

In order to better understand the role of salt mash plants in the cycle of this element, sediment cores from vegetated and non-vegetated intertidal sediments of the Tagus Estuary (Lisbon, Portugal, SW Europe), which are subject to strong anthropogenic inputs, were studied. Sediments cores, leaves, stems and roots of Sarcocornia fruticosa were collected in two salt marsh areas and analysed for their Pt concentration. Pore-water was separated from the sediments and analysed for dissolved Pt. Auxiliary parameters – dissolved oxygen, redox potential, total dissolved Mn and Fe – were also determined. Depth profiles of Pt in non-vegetated sediments showed low concentrations ranging from 0.5 to 1.0 ng g-1. Since oxygen penetration depth in these sediments is restricted to a few millimetres the observed slight enhancement with depth suggests its retention as sulphides or associated with sulphide phases. In vegetated sediments, higher levels of Pt were found in the uppermost layers (up to 3ng.g-1). This increase was found in sediment layers containing higher root biomass, suggesting that Pt retention may derived from plant activity. The atmospheric – traffic-borne – input of Pt may also contribute to the higher values in the topmost sediment layer.

Plant roots exhibited lower Pt concentrations (0.2-0.9 ng g-1) than sediments indicating that Pt is not significantly sequestered in root tissues. The oxic condition of vegetated sediments due to the plant activity may stabilize Pt in the dissolved fraction, aided by its association with dissolved organic matter derived from root exudates. Levels in the leaves and stems (0.015-0.12ng.g-1) were up to one order of magnitude lower than in roots, indicating that small amounts of Pt was translocated upward and not retained in the above ground tissues. Our results point that either S. fruticosa has low Pt phytoextraction capacity of and/or Pt is mostly present as non-bioavailable forms.

The results presented in this study were discussed in Aveiro in terms of their implications on (i) the status of Pt contamination in the Tagus Estuarine/Salt Marsh sediments due to traffic-borne emissions; (ii) the influence of redox conditions and vegetation on the geochemical sedimentary behaviour of Pt; and (iii) the uptake of Pt by vegetation.

Carla is currently (Autumn 2012) working at Dartmouth College (Hanover NH USA) as a visiting researcher and hopes to complete her PhD in Autumn 2014.

Clara Almécija-Pereda

Marine Research Institute IIM-CSIC, Vigo, Spain

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