The Characteristics Of The Plant Communities And Sediments In The Typical Wetland Recovery Area In The Tai Lake

Zhushan Bay wetland was the first estuary designed as restoration wetland in Taihu lake. It was located adjacent to Taihu lake and close to estuary of Taige canal thus can be influenced by Taihu lake, Gehu lake and Taige canal. The area receive high levels of human the disturbances and destructions. A case study on the wetland plant restoring area of Zhushan Bay was conducted to reveal the characteristics of the wetland plant community, grain size of the sediments, spatial distribution of C, N, P and the pollution condition of heavy metals in the sediments. The results showed:(1) The restored wetland plant community was in early succession stage. The overall plant biomass was low. Ecosystem productivity was positioned to increase. Water depth showed great influence on the species diversity. Plant species richness index reduced, Shannon-wiener diversity index and Pielou evenness index first decreased then increased, while Simpson dominance index first increased then decreased along increase with water depth.(2) In the studied area, the sediments was primarily consisted of silt. Dominant sediments were mainly silt and sandy silt. The clay, silt and sand all had moderate variability and were well-distributed in the space. Deposition of the clay and sand was the highest in Phragmites australis community.(3) SOC was very high with a mean value of 19.59g·kg-1. TN was relatively low with a mean vaule of 1.25g·kg-1. The means of TP, AP were 5.32g·kg-1 and 420mg·kg-1 respectively. The mean of TP greatly exceed levels of toxic tolerance standards issued by Environment and Energy Ministry of Ontario, Canada. From the different community, Phragmites australis community intercepted the highest levels of sediment and C, N, P. Sediment C/N was greater than 20 in most submerged plant community and Phragmites australis community, which showed exogenous input of organic matters.(4) Seasonal changes of SOC, TN, TP and AP all were autumn-winter spring>summer mainly influenced by change of the temperature, water environment, the wetland plants, animals and microbes. In the same area TN of Phragmites australis was 6.65 times that of Typha angustifolia. TP of Phragmites australis was 4.41 times that of Nelumbo nucifera. Phragmites australis community was most effective in intercepting sediments and elements.(5) The average contents of As, Cd, Cr, Cu, Ni, Pb and Zn were all higher than their background values. Results from Geo-accumulation index method indicated that As and Cd reached the serious pollution level, that Zn was the moderate pollution level, that Cr and Pb reached the lower pollution level, that Cu and Ni pollution had different pollution levels in the studied area. Results from ecological risk index method indicated that about 80% of the studied area reached severe and very severe harm degree and Cd and As were the main elements of potential harm.