Contributions of Wetland Plants on Metal Accumulation in Sediment

Wetlands, and especially salt marshes, are well-known sinks of metals, which limit toxic amounts of metals from entering the food chain. This study investigated metal concentrations (Cr, Cu, Fe, Mn, Ni, Pb, Zn) in a highly urbanised estuary, and compared vegetated rhizosediment (Salicornia tegetaria, Spartina maritima, and Zostera capensis) with bare sediment, in a depositional and non-depositional site, in the intertidal zone of the Swartkops Estuary. The samples were collected at two sites along the middle and lower reaches of the estuary and analysed using a Total X-ray Fluorescence (TXRF) spectrometer. It was found that the rhizosediment contained more metals and that metal concentrations in the sediment decreased as follows: S. tegetaria > S. maritima > Z. capensis > bare sediment. Although metal accumulation was similar in bare sediment for the depositional (Site B) and the non-depositional site (Site A), the rhizosediment displayed higher metal accumulation in the depositional site (Site B). However, regardless of site-specific depositional tendencies, rhizosediment displayed higher metal accumulation than bare sediment. These results indicate that vegetated sites and vegetated depositional sites should be the focus of monitoring metals in estuaries around the world.

Automated summary

Wetlands, especially salt marshes, are important sinks of metals and should be focused on for monitoring metal accumulation in estuaries worldwide. This study found that vegetated depositional sites exhibited higher metal accumulation compared to bare sediment, with rhizosediment containing higher metal concentrations. The results suggest that vegetation plays a significant role in limiting the amount of metals entering the food chain.