Distribution and accumulation of nutrients and heavy metals in Dongtan wetlands on Chongming Island, China

The rapid growing estuary wetlands resulted from Yangtze River sedimentations on Chongming Island of eastern Shanghai, China is accompanied with invasion of spartina (Spartina alterniflora), which collective shape the overall function of the coastal ecosystems. The objective of this study is to quantify the distribution and accumulation of nutrients and heavy metals in the salt marsh plants and their sediments in Dongtan wetlands. The total nitrogen (TN), total phosphorus (TP) and heavy metals (Cu、Zn、Pb and Cd) were measured from the sediments and the plant tissues of Phragmites australis, S. alterniflora, and Scirpus mariqueter. It was found that TN、Cu、Pb and Cd in the aboveground part of S. mariqueter were significantly higher than those of P. australis and S. alterniflora (p0.01), while TP and Zn in the aboveground part of P. australis were significantly lower than those of S. mariqueter and S. alterniflora (p0.01). We also found that the distribution of TN and heavy metals in the sediments had similar levels in an order of P. australis zone S. alterniflora zone S. mariqueter zone mudflat zone. With increasing in elevation, TN and heavy metals also increased but TP in the sediment remained at about 0.06%. Measured by aboveground standing stock, it appeared that all nutrients and heavy metals of invasive S. alterniflora had higher levels than those of native P. australis and S. mariqueter. The TN stock of S. alterniflora was about 1.5 and 2.6 times higher than those of P. australis and S. mariqueter, respectively. The aboveground standing TP stock was about 3.8 and 5.2 times higher than those of P. australis and S. mariqueter, respectively. Clearly, removals of S. alterniflora through harvesting can be an effective management protocols to reduce nutrients and toxic heavy metals from the site.