Characteristic And Water Level Influence On Surface Soil Physical And Chemical Properties In Danjiangkou Reservoir Hydro-fluctuation Belt

Hydro-fluctuation belt of reservoir, whose land is periodically flooded and exposed because of seasonal water level alteration, is a special periodic alternately waterlogged and drained area and also is an important ecotone transition zone in reservoir ecosystem. Soil does not only play non-substitute role in maintaining ecosystem stability, but also is an important component of hydro-fluctuation ecosystem. Characteristic and quantity of soil physical and chemical properties directly reflect soil quality in hydro-fluctuation belt. Cyclical changes of water level, which have great influence on topography, climate and spatial and temporal distribution of water resources in hydro-fluctuation belt change soil biogeochemical cycling characteristic and may be dangerous for ecological adjustment, environmental services, buffer and filtration function. Study on characteristic and water level influence on surface soil physical and chemical properties in Danjiangkou reservoir hydro-fluctuation belt has a significant impact on non-point source pollution control and ecosystem construction.Combining with laboratory analysis of physical and chemical properties, field survey of soil and its environment factors, such as vegetation was conducted in hydro-fluctuation belt to demonstrate characteristics of surface soil. Based on the theoretical basis and research methods of soil science, landscape ecology, hydrology and statistics, relationships between changes of soil physical and chemical properties and environmental factor (water level change, distribution of vegetation et al) were explored in Danjiangkou reservoir hydro-fluctuation belt. The main conclusions are as follows:The surface soil bulk density, total porosity, capillary porosity, non-capillary porosity and aeration porosity did not show a significant difference in three regions (Hanjiang reservoir area, AH, Danjiang reservoir area, AD, Corridor area, AC) of Dangjiangkou reservoir area, while all the chemical properties content in addition to pH and available phosphorus exhibited significant divergence in three regions. Among all the physical properties, non-capillary porosity whose coefficient of variation reached85.99%had the highest variation degree in study area. Organic mater and available phosphorus had a relatively higher degree of variability and variation coefficient of them was more than75%in all chemical index of the surface soil in hydro-fluctuation belt.There existed significant correlation between surface soil bulk density and other physical and chemical properties. Soil bulk density had strong correlation with total porosity and capillary porosity and correlation coefficient was-0.877and-0.709, respectively. Organic matter content showed a negative correlation with soil bulk density and a positive correlation with total porosity. Soil organic carbon directly affects the level of soil nutrient supply, so significant positive correlations between soil organic matter and total nitrogen, available nitrogen, total phosphorus were found. Correlation coefficient between organic matter and total nitrogen, available nitrogen were above0.8. Surface soil total phosphorus was significantly correlated with organic matter, but with low correlation coefficient (0.236).Water level elevation was significantly (p<0.01) correlated with all surface soil physical and chemical properties except non-capillary porosity, aeration porosity, total nitrogen, total phosphorus. There existed significant positive correlations between water level elevation and soil bulk density, organic matter, available nitrogen and correlation coefficient were0.279,0.222,0.201, separately. Water level elevation had a negative correlation with total porosity, capillary porosity, pH, available phosphorus and correlation coefficient were-0.279,-0.307,-0.407,-0.396, respectively. Significant correlations between Water level elevation and surface soil physical and chemical properties such as soil bulk density, organic matter were showed with low correlation coefficient, because influence factors on soil physical and chemical properties were complex.Five different water level gradients(≤140m、140-145m、145-150m、150-155m and≥155m) exhibited significant divergence in surface soil physical properties (excluding non-capillary porosity and aeration porosity),while only total nitrogen and total phosphorus between different water level elevation gradients didn’t show significant differences. Significant differences of surface soil physical and chemical properties variation degree were found under the same water level gradients, and variation degree of the same soil physical and chemical properties in different water level gradients displayed identical discipline. Variation degree of soil physical and chemical properties had a sudden change under water level gradients of150-155m. In contrast, variability of soil physical properties within the same level elevation gradients was lower than the chemical properties.