三峡库区草地土壤分离能力动态变化及其驱动机制

Soil detachment is the initial stage of soil erosion. It is a dynamic and complicated process as influenced by many factors. Accurate simulation on soil detachment is the base of process-based soil erosion model development. The current researches mainly focused on the hydrodynamic mechanism of soil detachment and its static quantitative relations with soil properties, plant roots et al. However, both soil properties and root growth show obvious temporal variations, whether these variations could in turn affect soil detachment capacity and its mechanism is still unclear. Furthermore, plant roots of different root architecture or morphological characteristics may behave differently in impacting soil detachment capacity, studies concerning to this aspect were rarely reported yet. Thus, in this study a series of runoff scouring experiments by a hydraulic flume will be carried out for two grasslands of different root architecture (fibrous root system of perennial ryegrass versus tap root system of alfalfa) and one fallow land as control in the Three Gorges Reservoir Area. The potential effects of root architecture on the hydrodynamic mechanism of soil detachment process will be systemically researched. The dynamics of soil detachment capacity, soil properties, and root morphological characteristics as well as their coupling relations will be thoroughly analyzed, aiming at exploring the central driving factor that inducing the dynamic variations of soil detachment capacity and further identifying its driving mechanism. The results will provide scientific basis for establishing a deep understanding of runoff detachment process and developing or improving process-based erosion models. It also has very important theoretical significance and practical value for soil and water conservation and ecological environment construction in the Three Gorges Reservoir Area.

土壤分离是土壤侵蚀的起始阶段，受诸多因素影响，是一个动态的、复杂的过程，准确模拟土壤分离是建立土壤侵蚀过程模型的基础。当前研究主要集中在土壤分离过程的水动力学机理及其与土壤特性、植物根系等的静态关系，而土壤特性、根系生长均呈现明显的时间变化，这些变化是否对土壤分离能力造成影响及其机制尚不清楚；且不同根型对土壤分离能力的影响可能存在差异，对此目前鲜有报道。本项目以三峡库区两种根型（多年生黑麦草的须根系和紫花苜蓿的直根系）草地为研究对象，通过变坡水槽冲刷试验，系统研究草地土壤分离过程的水动力学机理，比较分析根型对土壤分离能力的潜在影响，深入探索土壤分离能力、土壤特性、根系形态特征的动态变化规律及其耦合关系，揭示土壤分离能力动态变化的主要驱动因子及其机制。研究结果为理解径流分离土壤过程及建立或完善土壤侵蚀过程模型提供科学依据，对于三峡库区水土流失治理、生态环境建设具有重要理论意义和实践价值。

土壤分离是土壤侵蚀的起始阶段，受诸多因素影响，是一个动态的、复杂的过程，准确模拟土壤分离是建立土壤侵蚀过程模型的基础。本项目以三峡库区不同土地利用方式（包括建植不同根型的草地和典型农耕地）为研究对象，通过变坡水槽冲刷试验，系统研究土壤分离过程的水动力学机理，比较分析根型对土壤分离能力的潜在影响，探索土壤分离能力、土壤特性、根系形态特征的动态变化规律及其耦合关系，揭示土壤分离能力动态变化的主要驱动因子及其机制。主要结论如下：（1）不同土地利用下土壤分离速率表现为农地＞草地＞灌木地＞撂荒地＞林地；土壤表层粘结力对各类土地利用土壤分离速率的季节变化具有重要影响；团聚体稳定性特征参数与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呈显著的线性关系。（2）植物生长不同时期，土壤分离过程、土壤理化性质、根系形态特征参数以及植物地上、地下部分对土壤分离的影响具有明显差异。播种期，人为扰动大大提高土壤分离，这一时期植物增强土壤抗侵蚀性能并未体现。但在植物生长初期，由于根系细弱，固土能力有限，以地上部分对土壤分离的影响为主。根平均直径、根长密度、根重密度随着植物生长是增大的，土壤分离速率、土壤可蚀性与根长密度、根重密度分别成负指数关系。草根或侧根明显的根系比直根系减蚀作用强，无论是须根系还是直根系，相对土壤分离速率与直径＜5 mm的根重密度呈负指数关系，且随着根径增大，根系减蚀作用降低。（3）随水流剪切力增大，土壤分离能力呈线性增大；随土壤粘结力、水稳性团聚体和作物根系密度增大，土壤分离能力呈指数下降。农地土壤分离速率的季节变化主要由农事活动导致；农耕地的土壤分离能力在整个实验期先升高再降低，细沟可蚀性先增加再降低，临界剪切力大致呈增加的季节变化趋势。. 研究结果为理解径流分离土壤过程及建立或完善土壤侵蚀过程模型提供科学依据，对于三峡库区水土流失治理、生态环境建设具有重要理论意义和实践价值。