Study On The Nutritional Characteristics Of Hangzhou Xixi Wetland Ecosystem

Wetland ecosystem is the most important basis for protecting the ecological security and developing the social-economic-environmental system in reginal zone due to its huge ecosystem sevice value. Norwadys wetland ecosystems in the most places are being disturbed seriously, especially with the fast urbanization during the last decades in China. Wetlands in cities imply a high level of disturbance and degradation stemming from human stronger activities. So researchers paid much attention to urban wetland protection, restoration and management.Hangzhou Xixi wetland, a history of1800years, has successed the secondary wetland under the dense and stronge disturbance. The vegetation, water and soil in Xixi wetland, which are basic components for wetland, changed completely during the process. Because Hangzhou city government realized that Xixi wetland function to support biodiversity, protect water quality, store floodwaters, provide natural areas for passive recreation, education, and esthetic appreciation for both human populations and city development, Hangzhou city government began to conduct Xixi Wetland Comprehensive Protection Engineering in August2003. Because the temporal and spatial structures of Xixi wetland changed obviously, we studied (1) the temporal and spatial distribution of the soil nutrient elements in Xixi wetland, and compared these results with Xiasha riverside beach;(2) studied the temporal and spatial distribution of the nutrient elements in plants in Xixi wetland;(3)analysied the changes of nutrient elements in water in Xixi wetland, meanwhile compared these results with the other water bodied in Hangzhou and (4) analysied the relationship of the nutrient elements between soil, plant and water.The main research results are as follows:(1) The contents of organic carbon, total nitrogen and phosphorus in Xixi wetland sampling zone soil are respectively similar to those in the same latitude wetlands in China and are less than those in other wetlands in China. The storages of organic carbon, total nitrogen and phosphorus in Xixi wetland are far less than those in other wetlands, but the storage of carbon in Xixi wetland is over seven times than that in natural soil in China and is over ten times than that in rice soil respectively. The results also show that the contents of organic carbon in plant is less than that in wetland plants in plateau and the contens of nitrogen in plant is also less than that in wetland plant in lower latitudinal zone, meanwhile, the contens of phosphorus is no remarked difference between Xixi wetland plant and others. The storage of carbon and nitrogen in Phragmites australi are higher than those in Typha orientalis, contrarily, the storage of phosphorus in Typha orientalis is higher than that in other plant communities.(2) The comparative results show the contents of organic carbon, ammonium nitrogen, effective phosphorus in Xiasha riverside beaches are significantly lower than those in the Xixi wetland, contrarily, the contents of soil total nitrogen and soil total phosphorus are higher than those in Xixi wetland. The contents of the soil organic carbon in tree zone is higher than that in Phragmites australi and in Typha orientalis zone, respectively; Also, the contents of the soil organic carbon in Phragmites australi is higher than that in Typha orientalis. The contens of the soil nitrogen content in tree zone is more than that in Phragmites australi and in Typha orientalis zone, respectively; meanwhile, the contents of soil total nitrogen in Phragmites australi is higer than that in Typha orientalis zone and in Phragmites australi mixed zone respectively. The results also show the contents of ammonium nitrogen is similar tendency to the contents of the soil total nitrogen, but the contents of NO3-in Typha orientalis zone is the highest among plant communities. At the same time, the total phosphorus in tree zone and in Typha orientalis zone are higher than those in other communities.And, the contents of soil effective phosphorus in tree zone is higher than thaose in Typha orientalis zone and in Phragmites australi zone respectively. The contents of organic nitrogen, the ammonium nitrate and NO3-of the sampling zone in Xixi wetland account for94.56%-98.28%,1.61%-5.35%and0.04%-0.2%of the soil total nitrogen, respectively. The contents of organic carbon and the total phosphorus show a decreasing tendency in soil vertical layers, especially in the tree zone and in Phragmites australi mixed zone. On the other hand, there is an accumulative peak of the total nitrogen in sludge in Typha orientalis zone and in Phragmites australi zone respectively. The distribuation of Ammonium nitrate nitrogen, NO3-and the effectve phosphorus are similar with the soil total nitrogen. The soil organic carbon reaches the peaks in January and July, total phosphorus in April and October, effective phoshprous in April and NO3-in July.(3) The result show the stem and leaf of plants in Xixi wetland account for64.10%-80.24%and14.97%-21.12%of biomass, and the spike and fruit occupy relatively lower proportion of biomass. The biomasses of plant reach the peak in October. The results also show the absolute growth rates of Typha orientalis and Phragmites australi in April to July are more than those in July to October respectively, meanwhile, the absolute growth rates of Phragmites australi mixed zone in April to July are less than those in July to October. There are obvious differences among the different plant biomass; there are also differences among plants in different habitats. The biomass in Phragmites australi zone is higer than that in Phragmites australi mixed zone. The contents of organic carbon show different in the different plant organs, which are higher in stem, leaf, spike and flower compared to those in other parts. The content of organic carbon in Phragmites australi zone is more than that in Typha orientalis zone, and the conten of Phragmites australi mixed zone is higher than that in Phragmites australi zone. The results suggest that the contents of organic carbon in plant show an increasing tendeny in April to October. The contents of nitrogen and phosphorus in plants can be ranked in decreasing order as leaf> stem> root. The contents of nitrogen and phosphorus in Typha orientalis zone are higher than those in Phragmites australi zone and the contents of nitrogen and phosphorus in Phragmites australi mixed zone are lowest among communities. The contents of nitrogen and phosphorus reach the peak in April and the lowest in summer and fall respectively.(4) According to Environmental quality standards for surface water (GB3838,2002). the nitrogen in Hangzhou water system show more serious situation; In sampling zone. NO3-concentration in water account for about38.91%-64%of the total nitrogen concentration and is a component of the most important inorganic nitrogen. The total nitrogen, ammonium nitrate nitrogen, phosphorus and phosphate contents in Typha orientalis zone were higher than those in other zones. The contents of water TIN and TIP in internal Xixi wetland are less than those in external Xixi wetland, the results show there is a stronger retention and enrichment in Xixi wetland. The content of inorganic salt in external Xixi wetland is far higher than that in internal Xixi wetland. The content of inorganic salt in Maojiapu, a palce near Weat Lake, is also slightly higher than that in internal Xixi wetland. The content of inorganic salt in Dasha canal, a part of the Hangzhou Canal, is the highest among the sampling canal. There are different inorganic salt contents in different parts in Xiasha district. There is phosphorus surplus situation in most water bodies in Hangzhou based on C/P(5) The comparative results show the soil C:N in Xixi wetland is better than that in Xiasha riverside beach and the C:N in Phragmites australi mixed zone is the best among all the sampling zone. The ammonium nitrogen nutrient coefficient and effective phosphorus nutrients coefficient in Phragmites australi mixed zone are also the highest among all the sampling zone. The C:N and C:P of the aboveground parts in plant are higher than other parts.Both the growth of Typha orientalis and stem and leaf growth of Phragmites australi are limited by nitrogen based on N:P analysis. The growth of plants in Xiasha show similar tendency. The phosphorus transport coefficient in Phragmites australi mixed zone is more than the nitrogen transport coefficient, contrarily, the phosphorus transport coefficient in Typha orientalis is less than the nitrogen transport coefficient.(6) There are positive correlation between soil nutrition elements in different layers and the different organs in plants.Further more, there are negative correlation between water and soil, and correlation between water and plant also show negative. The nutrient element among soil, plant and water in sampling data do not exist correlation.