Study On Succession And Ecological Thresholds Of Natural Ecosystem In Yellow River Delta

Coastal wetlands provide comprehensive eco-environmental and productive services in terms of flood mitigation, climate control, pollution prevention, soil-erosion reduction, environment beautification,biodiversity maintenance, and bio-productivity protection.It is closely and inseparably related to economic and social development. The Yellow River Delta wetlands is the most integrated, broadest, youngest wetland ecological system in warm temperate zone of our country, is one of the biodiversity richest areas in the world, It is vital significance to guaranteed health of the new-born wetlands ecosystem, maintain the biodiversity and protect network of migration birds according to thorough study on the Yellow River wetland.This paper studied on the succession of nature wetlands in the Yellow River Delta by the method of trade space for time. According to the vegetation investigation,We studied the dynamic change of main ecological factor and the ecological threshold in the succession of wetland,The main results were showed as follows:1. Community structure and biodiversity in Yellow River wetland.23 taxa,belonged to 9 families and 19 genus,were found in wetland according to the vegetation investigation. As the succession going,species number increased significantly,species diversity and richness increased too,but evenness hold comparatively firm,and community biomass was found same trends with diversity index.The niche overlaps between species was comparatively high,there were 56.12% have been found which were larger than 0.7,this showed that there was keen competition between species.2.Changes in the physics and chemistry character of soil in the succession of wetland.The soil structural and nutrient status was ameliorated with the succession of wetland.Soil bulk density and salinity decreased and total soil porosity increased.Total nitrogen and hydrolysable nitrogen was ascend,content of available phosphorus and quick acting potassium was downtrend,but content of total phosphorus and potassium have no obvious change.3. Changes in soil enzymes and microbes in the succession of wetland.The activity of soil urease enzyme,catalase enzyme and alkaline phosphate enzyme had an increasing tendency in different degree with the succession of wetland,except the activity of soil protease enzyme no significant difference. Among soil microbes, bacteria were predominant, actinomyces were the next, and fungi were the least. Bacteria and fungi increase gradually, actinomyces increased first,but decreased then with the succession,reached the maximum at Comm. Suaeda salsa—Tamarix chinensis. 4.The soil salinity is the primary drivers in the succession of Yellow River Delta wetland.All factors effecting the soil salinity had an indirect effect on the succession. Comm. Suaeda salsa and Comm. Suaeda salsa—Tamarix chinensis were both key stage in the succession of Yellow River Delta wetland.5.The index system of ecological success in Yellow River Delta wetland were established to identify the ecological threshold. If succession index of wetland is less than 0.11,it will be Comm.beaches;If succession index of wetland is between 0.11 and 0.31,it will be Comm. Suaeda salsa;If succession index of wetland is between 0.31 and 0.50,it will be Comm. Suaeda salsa—Tamarix chinensis;If succession index of wetland is between 0.50 and 0.64,it will be Comm. Tamarix chinensis;If succession index of wetland is greater than 0.64,it will be Comm. Miscanthus sacchariflorus.