Accumulation of trace metals in grey mangrove Avicennia marina fine nutritive roots: the role of rhizosphere processes.

Mangrove sediment has long been recognized as being important in restricting the mobility of contaminants in estuarine environments. To investigate the role of rhizosphere processes in the accumulation of trace metals in mangrove fine nutritive roots, the mangrove sediments and associated fine nutritive roots are collected from five major embayments of Sydney estuary (Australia) for geochemical studies. In this estuary Avicennia marina sediments are accumulating large quantities of trace metals due to presence of abundant fine sediment (<62.5 μm) and organic matter as well as anthropogenic input. Accumulation of trace metals in fine nutritive roots responds to total sediment chemistry mainly due to rhizosphere sediment geochemical processes resulting in a strong linear correlation between metal concentrations in fine nutritive roots vs. total and bio-available contents in sediments. Accumulation of trace metals in fine nutritive roots is almost always exceeds rhizosphere total sediment metal concentrations.