Vegetation morphology and phytobiology intervene in heavy metal contamination of surface sediments in Yangtze River Estuary

Accumulation of heavy metals in estuaries can represent potential risks to the aquatic environment and public health. Estuarine coastal vegetation's physical form and biological function have important effects on dynamic processes and migration of pollutants in estuaries. Field observations were conducted at sites SJG and LHK in the Yangtze River Estuary (YRE) from September 2021 to February 2022 and September 2022 to December 2022. Site LHK (Liuhekou) represents a typical natural environment, whereas Site SJG (Sanjiagang) is more significantly influenced by anthropogenic activities. At both sites, samples of unvegetated sediments, vegetated sediment, and vegetation were collected and analyzed for six heavy metals (As, Cd, Cr, Pb, Cu, Zn). The sequence of heavy metal concentrations in both sediments and vegetation was as follows: Zn > Cr > As > Pb > Cu > Cd. The results of the contamination assessment indicated that the risk of heavy metal contamination was higher at SJG than at LHK. Cr, As, and Cd were identified as pollutants, with Cd posing the main potential ecological risk. Correlation and principal component analyses indicated that anthropogenic emissions and atmospheric deposition were the main sources of heavy metal contamination, with vegetation exhibiting elemental variability in heavy metal interception. Phytobiological analyses of the pollutant elements Cr, As, and Cd indicated that phytobiology's attenuation of sediment heavy metal contamination was significant based on metabolic processes. However, the hyper-enrichment of Cd was independent of metabolism, with its concentration stabilizing around biotoxic levels. The results in this paper promote a deeper understanding of heavy metal mitigation under the biological effectiveness of vegetation in coastal areas of the Yangtze River Estuary. The proposed analytical method provides ideas for the study of contaminant partitioning under the influence of vegetation in estuaries and coastal water environments.