Heavy metal concentrations in lagoonal saltmarsh species, Illawarra region, southeastern Australia

Abstract

The importance of saltmarsh environments and their floral communities lies in their ability to act as a buffer between land and aquatic systems. Runoff from rural and urban areas, the generation of power and heavy industry all contribute pollutants to the Wollongong coastal Zone, where heavy metal contents in saltmarsh substrates are found to be up to 200 times greater than at localities on the south coast of NSW. The saltmarsh species Sarcocornia quinqueflora, Suaeda australis and Triglochin striata show enhanced levels of Cu, Zn, Pb, Cd, Cr and Mn in the Wollongong area relative to sites at Callala Bay and Burrill Lake. This trend reflects, but is much lower than, levels of these metals in the substrate. Cu, Zn and Pb are concentrated in the horizontal stems of Sarcocornia and the leaves of Suaeda, but both are lower than levels in Triglochin. The elevated Cu and Zn levels in plants at Bellambi Lagoon are probably derived from urban runoff as there is no current industrial source of pollution within the catchment. The type of pollutant affects the bioavailability of the heavy metals. Industrial airborne particulate pollutants generally require considerable acidic leaching before the metals become available to the biological community. These processes only occur to a limited extent in a natural ecosystem and hence account for low uptake of heavy metals by plants in the anoxic environment at Griffins Bay. Saltmarshes act as low energy coastal sediment traps and, together with the plants, effectively reduce the amount of bioavailable pollutants being transferred into the aquatic environment. Analysis of saltmarsh species can rapidly provide very important information about the bioavailability of metal pollutants in marginal marine environments and they have considerable potential as monitors of diverse sources of pollution.