Studies On The Changes Of Soil And Vegetation In Floodplain Wetland And Its Degradation Succession In The Yellow River Souce Zone

The soil and vegetation evolutional characteristics of floodplain wetlands in the Yellow River Source Zone, were studied and analyzed, and the climate impacts on the wetland degradation as weel. The study is useful for namaging the wetland and preventing from its degradation across the Yellow River Source Zone.Through the changes of geograp Hic, soil and plant community in the floodplain wetland, the degradation successions of the wetland were studied. Meteorological factors such as temperature, precipitation, evaporation, sunshine and geothermal were analyzed to explore the influences of the climate to the wetland change. The stages of the degradation succession in the floodplain wetland were divided by non-degraded, lightly degraded, moderately degraded, severely degradedand extremely degraded wetlands which are also considered as stage 1, stage 2, stage 3, stage 4 and stage 5.The main research conclusions are as following: 1. Floodplain wetland soil in the Yellow River Source Zone is alkaline. The ratio value between plant roots and soil in the wetland decreased as increasing the soil depth levels. The ratio reached the highest value at the degree of depth0-7.5cm.The soil mainly presents sandy soil. Water content in the soil decreased as the increase of soil depth. 2. Soil organic matter and total nitrogen(TN) appeared a decreased trend with increasing wetland degradation. This showed that the soil fertility descended as the degradadtion of wetlands. The contents of TN, total potassium(TK) and organic matter of the stage 5 had significant deference(p<0.05), compearing with those of the stages 1, 2, 3 and 4. The contents of TN, TK and organic matter between the stages 1, 2, 3 and 4 had not significant difference, but TN of stage 2 and 5 is different(p<0.05). The TN of stages 1, 3 4 is not significantly different.The contents of total p Hosp Horus(TP), available P and available K didn’t reach to be significantly different, but the available P appeared decreasing trend, and the TP and available K appeared increasing trend as the degradations of wetlands. 3. In different depths of the soil the distribution of the actinomycetes is not significantly different. The actinomycetes quantity decreased as increasing soil depth. This is mainly reasons that the plant roots are concentrated in the soil depth of 0-7.5cm which could provide suitable environment for the bacterial. The water content of the wetland gradually decreased as the continued succession in the wetland, but those of stages 1, 2 and 3 are not significantly different. The water contents of stages 1, 2, 3, 4 and 5 are significantly different(P<0.05). 4. In the beginning of the succession the floodplain wetland was dominated by Kobresia tibetica, with the continued succession, the Kobresia tibetica gradually decreased, and those of weeds and poisonous weeds gradually increased. The plant diversity was going to increase, and the plant community constructs tended to be complexed and the richness of the wetland was being higher. 5. Many meteorological factors produce negative impacts on the wetland for water balance, but less is positive. Negative factors include the increased annual average temperature, the increased annual average geothermal, the annual sunshine days and evaporation of the wetland.