分类： 农、林、牧、渔 >> 土壤学 提交时间： 2021-03-17
摘要： Purpose Soil structures are the main course of the formation and development of collapsing gullies, which are the most severe type of erosion in south China. However, few studies have focused on the relationship between soil macropores, soil erosion, and local topography. This study aimed to quantify and compare soil properties and macropore characteristics in the collapsing gully region, and explore their influences on the formation and development of the associated erosion. Materials and methods Soil core columns at different positions of a typical collapsing gully were excavated, and then scanned to analyze soil macropores. Moreover, soil properties and saturated hydraulic conductivity were investigated in the laboratory and in the field, respectively. Results and discussion The results indicated that the sand content increased from the ridge to the slope and the valley, while silt and clay contents decreased for the same catena. The mean weight diameter of aggregates was largest at the ridge and lowest at the valley. The infiltrate rates were highest at the valley and lowest at the slope. The valley had the greatest macroporosity (1.09±0.33%), and the highest number (5919±703), volumes (24.7±7.5 cm3) and surface (10.4±2.6 m2) of macropores, as well as the highest conectivity (42.3), while the slope had the smallest macroporosity (0.15±0.14%), and the smallest number (1189±747), volumes (3.4±3.2 cm3) and surface (1.7±1.4 m2) of macropores. The mean pore volume of macropores larger than 1 mm3 was largest at the ridge (16.8±7.4), and smallest at the slope (10.6±2.9). The number of macropores and their macroporosity mainly decreased with increasing depth, but were influenced by the soil macrofauna as well as the erosion and sediment processes. Macropores were mainly vertical, which is affected by the roots of plants and is conducive to the vertical infiltration of water. But, there wer many horizontal macropores at the valley because of the sediment process. The equivalent pore diameter of macropores was mainly smaller than 2 mm (accouting for more than 76.3%), and the macropores larger than 5 mm were less than 1%. Conclusions The macropore characteristics at different sites of the collapsing gullies affected the soil water infiltration and hydraulic conductivity, and further affected the processes of water erosion and mass ersion. The highest macroposities at the valley would result strong subsurface flow erosion and the loss of the base of collapsing wall. Macropores at the ridge would increase rain infiltration and promote soil collapsing. Few macropores and low infiltration abilities at the slope would strengthen the overland flow erosion. Thus, macropore characteristics had significant effects on both the formation and development of collapsing gullies.
分类： 地球科学 >> 水文学 提交时间： 2021-03-17
摘要： The interaction between the surface hydrologic cycle and the shrub-encroached landscape at different slope positions remains poorly investigated. This study aims to explore the interaction between the water infiltration patterns affected by shrub encroachment at different hillslope positions. Soil water content and temperature were continuously measured at 10-min intervals at four or five depths under shrub patches and the grass matrix at four slope positions of a Caragana microphylla encroached hillslope from July 2009 to May 2013. The rainfall and meltwater infiltrations were estimated based on above data. Results showed that the rainfall infiltration ratios (IRs) at the grass matrix were as high as 0.78±0.08, except at the lower site, where it was only 0.47. The IRs of shrub patches increased from 0.38 at the top site to 0.77 at the lower site. The IRs were higher at the grass matrix than that at the shrub downslope edges at the top, upper, and middle sites of the hillslope due to the raised microtopography of the shrub mounds. However, at the lower site, IR was higher at the shrub patch than that at the grass matrix than due to more upper slope runoff input and higher infiltration capacity at the shrub patches. The preferential flow was not an important factor influencing the redistribution of water resources on the slope. Snow and ice were blown up by wind and accumulated in the shrub patches and their lees resulted higher water input to the shrub patches than that in the grass matrix during snowy years. Shrub encroachment changed the microtopography, soil property under different canopy and slope positions, and further affected the surface hydrological processes. The feedbacks between shrub encroachment and water infiltration varied at different sites of the hillslope and affected the development of shrub patches.
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