NATURAL EROSION RATES AND THEIR PREDICTION IN THE IDAHO BATHOLITH1

ABSTRACT: Natural rates of surface erosion on forested granitic soils in central Idaho were measured in 40 m² bordered erosion plots over a period of four years. In addition, we measured a variety of site variables, soil properties, and summer rainstorm intensities in order to relate erosion rates to site attributes. Median winter erosion rates are approximately twice summer period rates, however mean summer rates are nearly twice winter rates because of infrequent high erosion caused by summer rainstorms. Regression equation models and regression tree models were constructed to explore relationships between erosion and factors that control erosion rates. Ground cover is the single factor that has the greatest influence on erosion rates during both summer and winter periods. Rainstorm intensity (erosivity index) strongly influences summer erosion rates, even on soils with high ground cover percentages. Few summer storms were of sufficient duration and intensity to cause rilling on the plots, and the data set was too small to elucidate differences in rill vs. interrill erosion. The regression tree models are relatively less biased than the regression equations developed, and explained 70 and 84 percent of the variability in summer and winter erosion rates, respectively.     

中国亚热带土壤不同前期含水量对可蚀性K值的影响

采用人工模拟降雨试验的方法,研究我国亚热带７种有代表性土壤在干、湿两种状态下的土壤可蚀性Ｋ值,结果表明、相同类型土壤在干、湿两种状态下的可蚀性Ｋ值存在着明显的差异,耕作土壤的可蚀性Ｋ值高于非耕作土壤。     

Assessment of Soil Erodibility Indices for Conservation Reserve Program Lands in Southwestern Kansas Using Satellite Imagery and GIS Techniques

The soil erodibility index (EI) of Conservation Reserve Program (CRP) lands, which was the major criterion for CRP enrollment, was assessed for six counties in southwestern Kansas using USGS seamless digital elevation model data and Geographical Informational System techniques. The proportion of land areas with EI values of 8 or lower was less than 1% of the entire study area and most of the land areas (72.5%) were concentrated on EI values between 8 and 24. Although land acreage with EI values of 24 or higher decreased dramatically, the proportion of CRP lands to the other land-use types did not change much from low to high EI levels. The soil EI and physical soil characteristics of the CRP lands were compared to those of other land-use types. In general, the mean EI values of the land-use types were strongly correlated with physical soil properties, including organic matter content, clay content, available water capacity, permeability, and texture. CRP lands were compared in detail with cropland in terms of their soil characteristics to infer the pivotal cause of the land transformation. Although there was no significant statistical difference in EI between cropland and CRP soils, soil texture, soil family, and permeability were statistically different between the two. Statistical analyses of these three variables showed that CRP soils had coarser texture and higher permeability on average than cropland soils, indicating that CRP lands in the study area are drier than cropland soils. Therefore, soil moisture characteristics, not necessarily soil erosion potential, might have been the key factor for CRP enrollment in the study area.     

The impacts of Robinia pseudoacacia litter cover and roots on soil erosion in the Loess Plateau,China

The impacts of vegetation on soil erosion are closely associated with the combined effects of above- and below-ground components. In this study, we explore the effects and contributions of Robinia pseudoacacia litter cover and roots on soil erosion. Experiment sites under natural conditions with vegetation cover, plant roots and bare ground plots were investigated for overland flow discharges of 0.5, 1.0 and 2.0?L?s^?1 and slope gradients of 8.7%, 17.6%, 26.8%, 36.4% and 46.6%. Results indicate that litter cover and roots have a significant impact on sediment reduction; soil loss was reduced by about 57% and plant roots had a greater impact on the reduction of soil erosion than litter cover. The combination of litter cover and plant roots had a significant effect on decreasing K_r, increasing τ_c and consequently strengthening soil resistance capacity to erosion. When plants and roots existed on the slopes, K_r decreased by 81% and 66%, and τ_c increased by 319% and 246%, respectively, in comparison with bare slopes. These results illustrate the importance of high-forest in controlling soil erosion by quantifying the specific contributions of litter cover and plant roots in erosion reduction in the Loess Plateau.     

尖山河小流域土壤可蚀性K值空间变异研究

小流域尺度的土壤可蚀性 K 值空间分异特征及其与土地利用、植被类型、土壤理化性质等相关关系的研究,可以为小流域土壤侵蚀定量研究及综合治理决策提供科学依据。以云南省抚仙湖库区尖山河小流域为研究区,在大密度土壤采样和土壤理化性质测试分析的基础上,采用EPIC模型K值计算方法、地统计学方法和Kriging空间插值方法,计算分析了尖山河小流域土壤可蚀性K值的空间变异特征及土地利用/植被覆盖对K值的影响作用。结果表明,（1）研究区K值变化范围为0.1628-0.3836,均值为0.2824,中值为0.2885,均值与中值相近似,表明K值分布较均匀;变异系数为17.98%, K值存在中等程度的空间变异性。（2）不同土壤质地类型的K值存在一定差异,研究区主要土壤质地类型K值从大到小依次为粉壤〉壤土〉粘壤〉砂壤。（3）研究区以中可侵蚀性（0.25-0.30）、中高可侵蚀性（0.30-0.35）和中低可侵蚀性（0.20-0.25）土壤为主,面积分别为1797.88 hm2、1185.51 hm2和542.32 hm2,分别占小流域总面积的50.76%、33.47%和15.31%,而高可侵蚀性（〉0.35）土壤和较低可侵蚀性（0.15-0.20）土壤分布面积较少,无低可侵蚀性（〈0.15）土壤;在空间分布上,北部高山区土壤具有中低可侵蚀性,中、南部的低海拔区土壤具有中高可侵蚀性,中、南部其余区域土壤具有中可侵蚀性,这种空间分布与海拔存在较强的相关关系。（4）土地利用/植被覆盖对K值具有明显的影响作用,研究区主要土地利用/植被覆盖类型 K 值从小到大依次为林地〈灌草地〈荒草地〈旱平地〈园地〈旱坡地〈水田,需频繁松土、除草、耕作和扰动的土地利用/植被覆盖类型（园地、旱坡地、旱平地和水田）其K值较大,而无需耕作、扰动小的土地利用/植被覆盖类型（林地、荒草地和灌草地）其K值较小,这表?     

新疆土壤可蚀性K值空间插值及其分布特征研究

土壤可蚀性是土壤侵蚀预报和土地利用规划的重要参数,本文采用EPIC（Erosion Productivity Impact Caculator）模型中土壤可蚀性因子K值为指标,利用新疆土壤污染状况调查资料,探讨新疆土壤可蚀性K值及分布特征,并采用Kriging插值法进行全疆K值的空间插值。结果表明：新疆各类型土壤表层平均K值为0.238～0.441,主要分布在可侵蚀-易侵蚀-较易侵蚀范围;其中K值最大的土类为石质土和风沙土,均属于岩成土土纲;K值最小的土类为棕钙土;不同的土地利用方式,土壤可蚀性特征也不同,耕地土壤K值最大。从总体上看,土壤经过多年耕种,抗侵蚀能力明显下降。     

土壤可蚀性及其在侵蚀预报中的应用

土壤可蚀性是土壤侵蚀预报和土地利用规划的重要参数,国外已有物理意义明确、可操作性强、应用方便的土壤可蚀性定义和指标。国外的指标在我国不适用,而我国又没有这样的指标。在系统全面查阅和分析６０多年来已有研究成果的基础上,根据我国具体情况,提出我国土壤可蚀性指标的定义和测定方法,即在１５°坡度、２０ｍ坡长、清耕休闲地上,单位降雨侵蚀力所引起的土壤流失量。这一标准的确定对规范土壤可蚀性实验研究,促进我国土壤侵蚀预报模型的建立有重要意义