黄土高原径流泥沙过程对土地利用变化和植被演替的响应及其区域差异

The streamflow and sediment load reduced significantly for past 50 years on the Loess Plateau due to land use remarkable change and land cover great improvement. To rationally regulate the resources of water, sediment and vegetation in watershed, and high efficiently integrated management, it is necessary to fully understand and exactly identify the impact from land use and vegetation succession on runoff and sediment processes. However, the previouse research mainly focused on the contribution estimation from the land use change in the amount reduction of streamflow and sediemnt load, lack of consideration of the processes of runoff and sediment, also the response mechanism from land use and land cover change is not very clear, so it couldn’t meet the scientific requirement of the sustainable use of water and sediment resources. In this proposal, it is planned to take the Beiluo River as study area because it has clear vegetation differentiation and landform pattern which could stand for the characteristics on the Loess Plateau. Firstly, the multiple source of data from RS, census, literature, and investigation are used to analyze the transformation of land use types, and the change of vegetation succession and associated soil features. Then, the hydrological statistical methods were used to investigate the trend of the quantitative composition, proportioning structure, flood hydrography, and the coupling relationship of runoff and sediment load. The data fitting method and mathematical statistics will be applied and comparison will be strengthened among regions with different vegetation and landforms to reveal the dominant factor and process during land use change and vegetation succession in influencing streamflow generation and sediment yield. In the mean time, it is expected to deduce the steady state and their regional differentiation after long term vegetation restoration. It is supposed to provide the theoretical support in the macro decision-making for the implementation of soil and water conservation and ecological restoration, and at the same time, it will enrich the content of watershed eco-hydrology subject.

黄土高原50多年来径流和输沙量急剧减少，长期水土流失治理、土地利用变化和大规模植被恢复是其主要原因。准确辨识土地利用变化和植被演替对径流泥沙过程的影响，是合理调控流域水-土-植被资源和有效综合管理的前提。受资料限制，以往研究多关注土地利用变化对水沙总量的影响和统计归因，较少对径流泥沙的过程和机理进行研究，不能满足对水土资源持续利用的科技需求。本项目拟选择对黄土高原植被和地貌类型极有代表性的北洛河流域，基于野外调查、试验测定、统计资料、遥感解译等方法采集数据，综合径流泥沙水文统计、数理统计、综合对比等方法，系统研究土地利用、植被演替和相应土壤性质的变化规律；探明径流泥沙的数量组成、配比结构、过程线特征、水沙关系的演变规律；揭示径流泥沙对土地利用和植被演替的响应机理及其区域差异；推演长期植被恢复后的径流泥沙稳定状态，为黄土高原水土保持和生态环境建设宏观决策提供理论依据，丰富流域生态水文学内容。

黄土高原近50多年来径流和输沙量急剧减少，而长期以来，对水土流失治理、土地利用变化和大规模植被恢复对其影响的深刻程度认识还不够。选择北洛河流域（2.69万km2），开展植被恢复和演替对土壤水文物理性质影响、不同区间径流泥沙过程及归因识别、径流泥沙过程对土地利用变化和植被演替响应机制、植被盖度与径流组分比例结构的协同性以及不同区间的趋同性等研究，为合理调控区域水-土-植被资源和有效综合管理提供科学支持。重要结果和关键数据如下：..（1）明确了近50年来流域土地利用结构变化和植被覆盖增长的贡献来源地..流域耕、林、草地的数量结构，从2000年前的1：1.1：0.6变化到2000年后的1：2.7：0.7，以上游丘陵沟壑区土地利用结构变化最显著。.2001—2017年流域植被盖度上升面积占比90.9%，其中显著上升占比44.3%。主要贡献地区为上游黄土丘陵沟壑区，贡献率为46.3%。..（2）辨识了影响区域生态水文过程的土壤学指标..对上游丘陵区不同植被类型37个标准地、中游子午岭林区8个演替阶段26个标准地的土壤剖面采样调查和室内分析认为，植被恢复显著影响了剖面土壤水文物理性质，长期自然恢复对土壤的改善效果更明显。土壤容重、总孔隙度、>0.25mm水稳性团聚体含量、土壤有机质、饱和导水率等5个指标，是影响区域水沙演变的重要土壤学指标。..（3）比较精准地估算了近60年来影响不同区间径流泥沙通量变化的因素和驱动程度，揭示了土壤性质在这一过程中的关键作用..对比1960s，上、中、下游2010s径流减少主导因素分别是人类活动、气候变化、人类活动，其贡献率分别为66.3%、97.2%、64.3%。而上、中、下游2010s输沙量减少的主导因素均为人类活动，其贡献率分别是80.7%、59.2%、92.7%。..相对于土地利用和植被盖度等宏观因素，土壤性质的改善对这一地区生态水文过程的影响更关键。..（4）流域尺度上植被恢复与长序列径流量及其组分比例结构的协同变化及其阈值辨识..上游丘陵区，20年的植被恢复结果，植被盖度趋近至60-70%，同时其径流组分比例已经逐渐趋同于类似林区的稳定态势，即基流指数65%。