Study On Degradation Characteristics Of Typical Ecosystem In Yellow River Delta

Healthy development of ecosystem of Yellow River Delta was the basic guarantee for realizing sustainable utilization of resource and sustainable development of economy. Because of the double interactions of nature and human activity, ecosystem of Yellow River Delta showed deteriorated and caused unfavorable influences for sustainable development of Yellow River Delta. In this paper, the degradation of forest and wetland ecosystem were studied .The degraded locusts were studied in degradation of forest ecosystem, while soil and vegetation characteristics were studied on various wetland types of different succession stages in wetland ecosystem.Results showed that with degradation degree increasing,the volume's current annual increment and the DBH's annual increment declined, especially moderate-degraded and heavy-degraded locust.Volume weight increased,while total porosity and capillary porosity declined. The soil became compacting, soil water holding declined and hindered outspread of root in soil.Organic matter,available N ,total N ,available K and available P showed the same declined trend. Organic matter content of light-degraded, moderate- degraded, heavy degraded locust decreased by 27.1%,48.7%,56.6% respectively compared to non-degraded locust, total N decreased by 9.9%,17.9%,32.1% and available N decreased by 29.3%,36.7%,43.6%. There were small differences of volume weight and porosity between surface layer and subsurface layer and the two layers tended to homogenization. A comparative study of different degraded degree locust and non-degraded locust , soil nutrients of 40-60cm soil layer decreased more than 0-20cm .The activity of urease, catalase and peroxidase declined with increasing of degradation degree. Bacteria and microbial quantities declined among non-degraded locust,light-degraded and moderate degraded. Relations was related between soil physical and chemical characteristic, soil enzyme, soil nutrients and soil microbes. Main factor analysis showed that: total porosity , capillary porosity soil salt content and pH value were main factor soil quantity of degraded locust.Comparison on different tree species Robinia pseudoaca L., Fraxinnus chinensis Roxb. and Sophora japonica L., soil main nutrients, soil enzyme activity and microbial quantities showed that Robinia pseudoaca L. stand > Fraxinnus chinensis Roxb. stand > Sophora japonica L. stand. Studying of vertical distribution of root of Robinia pseudoaca L., Fraxinnus chinensis Roxb. and Sophora japonica L.. Robinia pseudoaca L. represented the shallow root , main root distributed in soil layer above 0-30cm. Sophora japonica L.was a deep root tree, main distribution of root was below 30cm, Fraxinnus chinensis Roxb. was a shallow tree, whereas a high density was distributed below 30cm.Reverse succession of wetland communities, generally, from Imperata cylindrical community, Tamarix chinensis community Suaeda salsa community to bare land. If the ground was perennial water and abundance of seasonal water , the reed community replaced Imperata cylindrical community Tamarix chinensis community and Suaeda salsa community.From Imperata cylindrical community to bare land,species of plants changed greatly, the importance value of annual herbaceous plants increased gradually and the importance value of perennial herbaceous plants went down gradually. The number of companion species went down gradually, the species richness and plant diversity index reduced. Community structure was from complex to simple.Community of wetlands of reverse succession showed that volume weight increased, total porosity, capillary porosity and non-capillary porosity went down gradually. From Imperata cylindrical community to bare land, main soil nutrients ,organic matter ,total N and available N obviously declined.In successional process of wetlands, bare land Suaeda salsa community, Tamarix chinensis community organic matter content decreased by 81.0%,67.4% and 59.5% separately compared to Imperata cylindrical community,total N decreased 61.1%,59.6%,41.2%,available N decreased 69.2%,60.1%,46.8%,available P decreased 19.5%,7.9%,4.7%.With reverse succession of wetlands, the activity of urease and catalase went down gradually. The number of soil microbes, bacteria and fungi showed declined law. Actinomyces showed the order of Tamarix chinensis community > Suaeda salsa community > Imperata cylindrical community > bare land. The total number of nematodes followed the order of Imperata cylindrical community > Tamaix chinensis community > Suaeda salsa community > bare land, Imperata cylindrical community had maximum value on plant-parasite, bacterivores and pedators-omnivores. Individual density of predators-omnivores was too low to be counted. The magnitude of the diversity of soil nematodes was Imperata cylindrical > Tamarix chinensis > Suaeda salsaï¹¥bare land.The biomass of reed community in bank of yellow river was greater than that in flood control dam, while the later is greater than that in shoal.Organic matter, total N, available N et al main nutrients had a little change. Soil enzyme activity and the number of soil microbes did not show regular pattern.