Abstract
Sediment cores from two salt marshes, Rosário (Tagus estuary) and Laranjo (Ria de Aveiro), were analyzed for total Hg and Al, and for Fe and Mn extracted with a hydroxylamine-acetic acid solution. Both areas have been contaminated by industrial discharges during the last decades. Vertical distributions of Hg in sediments colonized by Arthrocnemum fruticosum and Halimione portulacoides were compared to profiles in non-vegetated sediments. The same vertical distribution pattern was observed in all situations: Hg enriched in sediment layers with high root density. Mercury concentrations reached 9.3 and 29.1 nmol g–1 in Rosário, and 149.0 and 196.0 nmol g–1 in Laranjo. At both marshes, higher concentrations were found in sediments colonized by H. portulacoides. These values are one order of magnitude above the levels found in nonvegetated sediments. Mercury was enriched in sediment layers containing high concentrations of Fe extracted with a hydroxylamine-acetic acid solution, indicating the importance of Fe (and Mn) oxides formed in the rooting sediments for the retention of anthropogenic Hg.
Highlights
IntroducciónMany estuarine salt marshes in the proximity of industrialized areas receive substantial quantities of anthropogenic material transported by the tidal currents, both in dissolved and particulate forms
This paper reports the depth distribution of mercury concentration in salt marsh sediments of Ria de Aveiro and the Tagus estuary with different degree of contamination, and relates these profiles to below-ground biomass and reactive iron and manganese concentration in sediments
Sediment cores were collected in two salt marshes of the Tagus estuary (Rosário) and Ria de Aveiro (Laranjo) from pure areas colonized by A. fruticosum and H. portulacoides and non-vegetated sites
Summary
IntroducciónMany estuarine salt marshes in the proximity of industrialized areas receive substantial quantities of anthropogenic material transported by the tidal currents, both in dissolved and particulate forms. Contaminants associated with the suspended particulate matter are trapped by vegetation (Chenhall et al, 1992) and eventually incorporated into the surface sediment of salt marshes (Orson et al, 1992). The amount taken up by the plants is dependent on the metal availability in the sediment, and this is modified by the root activity (Alloway et al, 1988). Post-depositional redistribution of the anthropogenic mercury in contaminated sediment is considered small with respect to the mercury in solids, and the toxicity of the buried mercury is limited. Because the sediment environment in salt marshes is exceedingly complicated, with the presence of exudates and intense microbial activity in the interfacial zone between the root and the sediment (Alloway, 1990), it is pertinent to investigate the behaviour of mercury in these peculiar environments
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