Halophytes as sources of metals in estuarine systems with low levels of contamination

Heavy metal concentrations present in the above- and beowground tissues of Scirpus maritimus L., Spartina maritima (Curtis) Fernald and Zostera noltii Hornem were analysed seasonally in the Mondego Estuary, Portugal. The sediments of the estuary were confirmed to contain only low concentrations of heavy metals. The belowground tissues of all three species showed higher heavy metal concentrations than the aboveground tissues. Although the sediments only contained low levels of contamination, because the area occupied by S. maritimus and Z. noltii was large, significant quantities of heavy metals were accumulated and exported to the surrounding water bodies. In contrast with observations of highly contaminated estuaries, it was found that in spite of the low level of contaminants in the sediments of the Mondego Estuary, aquatic vegetation functioned as a source of metals for nearby systems.