【作者】 王军光；

【导师】 蔡崇法；

【作者基本信息】 华中农业大学 ， 土壤学， 2013， 博士

【摘要】 我国南方红壤丘陵区地处热带、亚热带,水热资源丰富,但由于该区域土壤性能较差,加之不合理的土地利用,土壤侵蚀退化严重。同时,该区域降雨集中且强度大,分散的地表径流由于地形影响逐渐集中,形成的集中水流冲刷地表,在土壤表面有明显的细沟和侵蚀沟出现。因此,研究该区域集中水流内红壤分离机制和红壤结构因子——团聚体在集中水流内的剥蚀特征十分必要。本文以我国南方亚热带丘陵区泥质页岩和第四纪红粘土两种典型母质发育红壤为研究对象,系统分析了水力学特性、红壤结构因子与红壤分离过程间的内在关系,并深刻探讨了水力学特性、运移距离、团聚体粒径大小、稳定性强弱对自身剥蚀程度的定量影响以及团聚体剥蚀后颗粒粒径、粒形、胶结物质的分布规律,从机理层面对红壤坡面集中水流内土壤分离机制和粗颗粒泥沙(团聚体)剥蚀过程进行了详细阐述。取得的主要结论如下：1.在采用传统的湿筛法指标分析红壤团聚体稳定性的基础上,结合可以区分团聚体破碎方式的LB法,从多个角度综合评价了红壤团聚体稳定性。同时,针对红壤独特的成土条件和物质组成,分析了红壤基本理化性质对团聚体稳定性的影响作用机制,重点探讨了粘粒、有机质和铁铝氧化物与团聚体稳定性间的关系。(1)由于预处理、团聚体稳定机制和衡量指标的差异,所有供试红壤团聚体稳定性排序不完全相同。湿筛法研究结果表明,在相似的土地利用状况,泥质页岩发育红壤的团聚体水稳性总是低于第四纪红粘土发育红壤(QJ4土样除外)；忽略成土母质,所供试红壤中茶园、林地、草地的农耕活动相对较少,因此水稳性相对较强。LB法测得的不同处理各红壤间差异显著性趋势不同,但所有供试红壤团聚体平均重量直径排序均为MWDFW(快速湿润)<MWDWS(预湿润振荡)<MWDSW(慢速湿润),可见快速湿润引起的消散作用和外应力引起的机械破碎作用是红壤团聚体的主要破碎机制。(2)团聚体稳定性参数不同,与理化性质问的相关性也明显不同。红壤团聚体稳定性主要与粘粒含量、有机质、游离态铁铝相关性较好,而与阳离子交换量、非晶形铝未有显著性相关。其中,粘粒在快速湿润的条件下所起的作用更强,与团聚体稳定性间相关性更好,而有机质、游离态氧化铁铝在维持土壤团聚体稳定性上起到主导作用。2.通过选取扰动土样和野外原状土样,进行室内模拟集中水流冲刷试验。研究得出了不同水力学参数及水动力学参数对集中水流内红壤分离速率的定量影响。同时,综合团聚体稳定性特征参数(As)、饱和抗剪强度(σs)及根系密度(Rd)相关参数,分析其参数与集中水流内红壤分离速率、可蚀性因子及临界剪切力间定量关系。(1)集中水流内水流流态主要以紊流、急流为主,且坡度对水流流态的影响远小于流量对流态的影响。平均流速、径流水深与坡度、流量的关系均可用幂函数来模拟。红壤分离速率是流量、坡度的幂函数,也是径流水深和坡度的幂函数,此外,红壤分离速率与坡面水流流速关系密切,呈较好的幂函数关系。所选取的水流剪切力、水流功率和单位水流功率三个水动力力参数,它们均与红壤分离速率呈线性关系,水流功率是描述红壤分离速率最为确切的水动力参数。(2)各红壤分离速率与水流剪切力间呈较好的线性关系,但红壤间集中水流内可蚀性系数Kc与临界水流剪切力τc有较大差异。团聚体稳定性特征参数As与不同水流剪切力中红壤分离速率有较好的相关,并且与集中水流内可蚀性系数Kc呈现显著的线性关系(R2=0.70,p<0.01),同时,作物根系密度(Rd)与其呈现较好的负相关幂函数关系(R2=0.40,p=0.09)；红壤饱和抗剪强度(σs)与集中水流内临界水流剪切力(τs)亦呈较好的线性关系(R2=0.64,p=0.02)。利用WEPP细沟侵蚀模型框架,以团聚体稳定性特征参数As、根系密度Rd代替可蚀性因子Kc,饱和抗剪强度σs代替临界水流剪切力τc,通过回归分析,得出新的预测集中水流内红壤分离速率方程。3.通过4个相关的集中水流内团聚体冲刷试验,分析得出运移距离、水力学特性、粒径大小及自身稳定性对团聚体剥蚀破坏的定量影响。首次阐述其在集中水流内剥蚀规律,团聚体剥蚀后粒径、粒形变化及红壤团聚体胶结物质—有机质、铁铝氧化物在其内外的分布特征。(1)团聚体在坡面集中水流中的剥蚀破坏受自身稳定性、粒径大小的影响,稳定性越强、粒径越小,在不同运输距离和流量中破坏程度越小。不同粒径团聚体在坡面运移过程中的剥蚀破坏大致分为两个阶段。团聚体在坡面集中水流中的破坏机制与砾石在河流中的剥蚀破坏机制不同。团聚体剥蚀程度与径流水深、阻力系数水力学参数关系密切。融合坡度和径流水深的多元回归方程亦可准确预测不同坡度和流量条件下团聚体剥蚀破坏程度。初步得出单位水流功率是描述集中水流内红壤团聚体剥蚀破坏程度较好的水动力学参数。(2)研究得出具有一定物理意义的机械破碎指数RMI与不同运移距离中团聚体剥蚀破坏程度Wr/Wi值均达到显著性相关(p<0.05),利用团聚体机械破碎指数RMI和运移距离x相结合,得出了集中水流中不同运移距离红壤团聚体剥蚀程度预测方程。(3)初始对机械破碎敏感较弱的团聚体,一定运移距离内剥蚀破坏程度较低,大颗粒团聚体含量相对较多,剥蚀破坏后的MWD相应较大。剥蚀破坏后供试各红壤间微团聚体粒径粒形变化不大,而形状因子(Cir)的Ds0值均随运移距离的增加呈现对数函数增加的趋势。即对机械破碎程度敏感较弱的团聚体,定运移距离剥蚀破坏后微团聚体颗粒形状愈接近球形。(4)红壤团聚体中主要胶结物质有机质(SOM)、游离态铁铝(Fed和Ald)在团聚体内外并非均匀分布,而是集中于团聚体颗粒内部,且经过一定运移距离剥蚀后的团聚体内部SOM、Fed和Ald含量对其原土中相应含量值贡献最大。更多还原

【Abstract】 Hilly red soil region of southeast China locate in the tropical and subtropical area, and they are abundant in hydrothermal resources. However, many reasons, such as undulating topography, poor soil properties, improper land use and soil management, have caused severe soil erosion in this region. Besides, due to the effects of high intensity rainfalls and topographic, the rills and gullies caused by washing are obvious on the surface of the soil in this area. It is important and essential to understand the red soil detachment mechanism and aggregate (Red soil structure factor) abrasion characteristic in concentrated flow. In this paper, selected soils were derived from Quaternary red clay and Shale, which were main parent materials in this region. The relationship between hydraulic characteristics, red soil structure factor and red soil detachment processes were obtained. In addition, we analyzed the quantitative effects of hydraulic characteristics, transport distance, particle size and stability on aggregate abrasion degree, and the distribution of aggregate size, shape and cementing material after it abrasion in concentrated flow was also studied. The main results were listed as following:1. The red soil aggregate stability and breakdown mechanisms were estimated by traditional wet-sieving and LB method. Moreover, due to the subtropical conditions of the red soil region, the relationship between and aggregate stability and some basic physical and chemical properties were studied. Especially, we focused on analyzing the effects of clay content, organic matter, and different forms of Fe oxides and Al oxides on selected red soil aggregate stability.(1) The trend of the aggregate stability was not always the same because of the difference of pretreatment and selected indexes. In the wet-sieving method, for similar land use of the two parent materials, the water stability of the aggregates from Quaternary red clay was stronger than those from Shale except QJ4sample. Because of the relatively small farming activities, the water stability of the aggregates from tea garden, woodland and weed land was also stronger than cropland. In the LB method, values of these parameters did not always show the same trend in different treatments. In all the soil samples of the three treatments, aggregate stability was the greatest for the slow-wetting treatment (MWDSW), followed by the wet-stirring treatment(MWDws) and the fast-wetting treatment (MWDFW).This result showed that slaking and mechanical breakdown were probably the main mechanisms of aggregate breakdown in these study soils.(2) Because of the difference of the parameters from aggregate stability, the correlation between the red soil physical and chemical properties and the aggregate stability was significantly different. In this study, the aggregate stability was significantly correlated with the contents of soil organic matter, free iron and aluminum oxides, while not significantly related to cation exchange capacity and acid ammonium oxalate extracted aluminum oxides. The clay content played an important role while the aggregate was suffered the fast wetting conditions. Organic matter and free iron and aluminum oxides played a leading role in maintaining the aggregate stability.2. Through selected disturbed and undisturbed soil samples, concentrated flow simulation and measurements of detachment was carried out in this study. The quantitative effects of hydrodynamics on red soil detachment rate in concentrated flow were analyzed. Further, this study was conducted to establish the quantitative relationship between soil detachment rate in concentrated flow with the aggregate stability index (As), root density (Rd) and saturated soil strength (σs).(1) The flow regime was mainly turbulent and torrent in this concentrated flow. The effect of slope was smaller than discharge on flow regime. It could be used the power function to simulate the relationship between velocity or flow deep with slope and discharge. The red soil detachment rate would be predicted by the power function of discharge and slope, or flow deep and slope, or velocity. Among shear stress, stream power and unit stream power, all of them were a linear relation with red soil detachment rate, and stream power was the best related to soil detachment rate.(2) The results showed a linear relationship between the detachment rates and shear stress for different soils. It was clear that erodibilities and critical shear stresses varied among different soil samples. The correlation between the aggregate stability index (As) and the soil detachment rates showed that As was well related with soil detachment rate. The As values had better linear relationship with concentrated flow erodibility factors (R2=0.70, p<0.01), and a significant negative exponential relationship between Kc and root density (Rd) was obtained at the10%level (R2=0.40, p=0.09). A positive linear relationship between saturated soil shear strength and critical flow shear stress could be also observed for study soils (R2=0.64, p=0.02). By introducing As, Rd and σs into the WEPP model frame as a substitute for soil erodibility factor and critical flow shear stress, statistical formulae for estimating red soil detachment rate were established with a good correlation coefficient.3. Fore related test of the aggregate abrasion were conducted in concentrated flow. We analyzed the quantitative effects of transport distance, hydraulic characteristics, particle size and aggregate stability on aggregate abrasion degree. And the abrasion regularities, the distribution of aggregate size, shape and cementing material (organic matter, iron and aluminum oxides) after it abrasion in concentrated flow was also studied.(1) The abrasion of aggregates in concentrated flow was affected by its stability and particle size. Aggregate with higher stability or smaller size suffered less extent of abrasion in different transport distances and discharges. The study revealed that the mechanism of abrasion and destruction of soil aggregates in concentrated flow was different from the mechanism of the abrasion of rock fragments in river flow, and two stages of aggregate breakdown could be identified. These results demonstrated that flow depth and friction factor should be appropriation indicators to reflect aggregate abrasion in concentrated flow. The aggregate abrasion degree under different slopes and discharges could be predicted from the slope and flow deep. Among three hydrodynamic parameters, unit stream power was the best related to aggregate abrasion.(2) In the present study, the Wr/Wi(%) values were highly correlated to RMI from LB method in different transport distances (p<0.05), and therefore it would be logical to include the RMI and transport distance x in the aggregate abrasion prediction equation. A multiple regression equation was then developed, relating Wr/Wi(%) to RMI and x for all the tested samples(3) The aggregate with weaker susceptible to mechanical breakdown, the content of large particles and the value of MWD were higher under them suffered to abrade in a transport distance. There are small changes in the particle size and shape after the aggregate abraded, and the D50of shape factor (Cir) was logarithmic function increasing with the transport distance increasing. The aggregate with weaker susceptible to mechanical breakdown, the micro-aggregate was more nearly spherical under them suffered to abrade in a transport distance.(4) From the preceding study, the dominantly cementing agents of the aggregate were organic matter, free iron and aluminum oxides (SOM, Fed and Ald). The organic matter, free iron and aluminum oxides contents distribute mainly near the inside of the aggregate and in the aggregates inside were higher than the aggregates outside. The SOM, Fed and Ald contents of the aggregates retained on the0.25mm sieve after subjecting to abrade upon72m distances in overland flow (Ag72m>o.25) were larger contributed to the bulk SOM, Fed and Ald contents in the study soils from the high correlation coefficients.更多还原