Study On Degradation Characteirstics And Ecological Thresholds Of Wetland Ecosystem In Yellow River Delta

The Yellow River Delta wetland is the most integrated, broadest, youngestwetland ecological system in warm temperate zone in China. It’s known as the “GoldenTriangle” region. However, owing to unreasonable utilization and natural causes, thereare many ecological crises in degradation characteristics for the wetland in YellowRiver Delta. The wetland have changed a great deal in area. Landscape structure andthe ecological function had been seriously influenced and menaced. In order to realizethe sound progress of wetland ecosystem， sustainable development of ecosystemdegradation of that region，we must get down doing something for the protection andwetland health.Consequently, based on the previous research, the paper relies on the project of“The Research of Natural Wetland Ecosystem Stability in Yellow River Delta byNational Natural Foundation of China”. Through compared each succession stage ofthe wetland which to be disturbed by human beings and natural protection wetland areawhich to be interference of the Yellow River Delta, the changes before and after thedegradation of wetland of vegetation and soil respectively were studied. We studied theecological threshold in the degradation of wetland by Analytic Hierarchy Process. Wehope that this research cans provide the basic research and information support forecosystem stability assessment of wetland in Yellow River Delta and establishscientific base for restoration and reconstruction of degraded wetland. The resultsshow:1. The important value of dominant species of each succession stage decreasedbecause of the wetland degradation. The species richness index descended in Imperatacylindrical community and Tamarix chinensis community. The trend ofShannon-Wiener index, Pielou and Simpson indexes in each succession stage weredecreasing. Similarly, biomass also decreased.2. Soil physical structure was poor and soil nutrients degenerated by degenerationof the wetland. Community of wetlands of reverse succession showed that volumeweight increased, total porosity, capillary porosity and non-capillary porosity wentdown gradually while soil salinity increased. The content of the organic matter, total nitrogen, hydrolysable nitrogen, hydrolysable potassium and total phosphorus droppedin different degree, but content of hydrolysable phosphorus have no obvious change.The content of total potassium increased.3. With the degradation of wetland, the activity of urease, protease, alkalinephosphates and catalase went down gradually, and the activity of urease firstlyincreased then decreased. The decreased range of the vitality of alkaline phosphatesactivity was the largest.The microbial quantity has significant differences in a degraded wetland of theyellow river delta. In soil microbial community, bacteria occupy the most proportion,which takes absolute advantage in the amount. Secondly is actinomyces, and amount offungi is the least. With the degradation of wetland, the quantities of microbe weredecreased in some tendency.4. The soil analysis of the relevance and principal component was informed that thevitality of soil urease, alkaline phosphates activity, catalase had closely related withsoil nutrients and microbes. The correlation of protease activity and soil nutrient is notsignificant. There is close relationship between soil nutrients and microbes. Thespecies richness index, Simpson index and Pielou index had remarkable correlationwith soil physical and chemical properties except Shannon-Wiener index. There isinteraction and close relationship between plants and soil. From the analysis of therelevance between the soil and plant diversity, it can be seen that destruction ofvegetation has affected soil physical and chemical properties greatly, and soildegradation has caused the decline in species diversity.5. There are two key stages in the degradation process of wetland in Yellow RiverDelta, which are respectively degenerated from Suaeda salsa community to bare landand from Suaeda salsa-Tamarix chinensis community to Suaeda salsa community.6. The index system of ecological degradation in Yellow River Delta wetland wereestablished to identify the ecological threshold. If ecological degradation index ofwetland is greater than0.70, it will be degraded into bare land; If ecologicaldegradation index of wetland is between0.55and070, it will be degraded into Suaedasalsa community; If ecological degradation index of wetland is between0.42and0.55,it will be degraded into Suaeda salsa-Tamarix chinensis community; If ecologicaldegradation index of wetland is between0.27and0.42, it will be Comm. Tamarixchinensis; If ecological degradation index of wetland is less than0.27, it will beComm. Miscanthus sacchariflorus.