Effect Of River-flooding On Desert Riparian Plant Community And Soil

This paper relies on the projection of the water conveyance of the lower reaches of Tarim River, mainly researches the ecological variation after water conveyance through comparing with the vegetation characteristics under the different coming-water fashion, the causes of difference vegetation phenomena were analyze, the effect of flooding for vegetation restoration were discussed. We analyze the influence of the river flooding disturbance on soil physical-chemical properties, the characteristic of dissolve organic matter (DOM) and the vegetation. The influence of the river-flooding on the vegetation restoration was discussed.The species richness, individual density and cover degree of flooded sites are more than non-flooded sites. The comparison results of soil salinity on surface soil during fore-and-aft flooding in the lower reaches of the Tarim River were analyzed, and the effect of different flooding fashion on soil salinity were discussed, this research try to explain the reason of nature vegetation increased after Ecology Water Transferring. The results were showed as follows: (1) The total soil salt contents in the lower reaches of Tarim River are generally high, which affected the distribution and growth of nature vegetation. (2) The soil salinity of soil surface have changed obviously after flooding disturbance, the soil salinity decreased in different flooding area, for example, the total salt contents of Daxihai and Alagan flooding area are reduced 60%. (3) The results of ANOVA analysis about soil salinity of surface soil under different flooding fashion showed, the effect of more flooding frequency for the total soil salt contents are distinctive than less-flooding frequency and flooding scour, long-term submerge is disadvantage for soil desalination, so the effect of flooding fashion for soil salinity are significant. (4) The discussion about flooding fashion, the flooding frequency and standing time for soil salinity and species diversity index showed the moderate disturbance are beneficial for the ecology restoration in the lower Reaches of the Tarim River.The influence of the river-flooding on the vegetation restoration was discussed though the changes of soil physic-chemical properties and vegetation fore-and-aft river-flooding. The results show as follows: The contents of clay grain in river-flooding area is higher than non-flooding area, the contents of clay grain in less-flooding area is lower than in several times of river-flooding area in the same observed sites. With the times of flooding increasing, the contents of medium, fine and very fine sands decreased significantly, but the contents of medium and coarse silts increased, these phenomena may be aroused by water washing out and the deposits of soil sediment. Soil moisture contents and bulk density are increasing with the river-flooding, so the river-flooding made the soil compaction. The process of eluviation and sedimentation on soil nutrient are evident, which aroused the distribution of soil nutrient changed in the surface of soil-layer after flooding. From these changes of soil physical-chemical properties, it can be explained the obvious changes of vegetation coverage and species diversity in the river-flooding area.The results show that fluorescence characteristics of DOM from soil of different land using have the good correlation with dissolved organic carbon (DOC), the soil with different land using have the good correlation between the fluorescence intensity of DOM and DOC, so the change of fluorescence characteristics of DOM can reflect the changed DOC. The EEM spectra of DOM would drift when the soil in high temperature and UVB processing.The fluorescence intensity of DOM is higher under different temperature of 15℃except farmland. When the pH arrived 7, the EEM spectra of DOM show the turning point.We selected the 26 Km both sides of the 218 national highway at tail continental river of central Asia as the study area , where located in the lower reaches of Tarim River. Through comparing with the vegetation characteristics under the different coming-water fashion, the causes of difference vegetation phenomena were analyze ,the effect of flooding for vegetation restoration were discussed. The aim of this study are not only to emphasis the effect of flooding for vegetation restoration, but also to raise the direction of large-scale vegetation restoration. Restoration of the river natural ecology function and the river-flooding condition by artificial measure are important. The results showed: (1) the salinity of surface soil is an important factor for the spatial distribution of vegetation, the effect of salinity is stand out than the effect of water in particular environment. (2) The seed bank density was affected evidently than the plant species by river-flooding. (3) The comparison results of soil characteristics on surface soil during fore-and-aft flooding showed that soil salinity of soil surface have changed obviously after flooding disturbance, the soil salinity decreased from 50.2 g/kg to 25.0 g/kg, but the soil salinity increased to 116.4 g/kg in the elevation area of groundwater, which make the different vegetation in these area, therefore, the flooding have the important effect for soil salinity in vegetation restoration. The appeared frequency of Populus euphratica has the negative correlation with the salinity of surface soil, the seed of Populus euphratica can not germinate when the soil conductance arrived 7 ms/cm from the experiment, and these causes formed the particular distribution characters of Populus euphratica in such area. Therefore, the salinity of surface soil is an important factor for the spatial distribution of Populus euphratica populations.Restoration of the river natural ecology function and the river-flooding condition by artificial measure are important technology for improving of local environment and implementing of the large-scale ecology restoration in the lower reaches of Tarim River. For the riparian forest restoration, such as Populus euphratica, the time of ecological water conveyance must consider the date of seed fall down from Populus euphratica. The date of water conveyance from July to October is best time for the arbor and shrub restoration. But for the appropriate flooding frequency , flooding intensity and flooding duration are still waiting to affirm.