Modelling and managing critical zone relationships between soil, water and ecosystem processes across the Loess Plateau

中国黄土高原位于黄河中上游，面积是英国的2.5倍（约64万平方公里），是世界上水土流失最严重的地区。森林砍伐、过度放牧和不良的农业做法导致了该地区生态系统退化、荒漠化和非生产性农业。为了控制黄土高原严重的水土流失，中国政府实施了一系列针对脆弱生态系统的政策，如1999年国家资助的“退耕还林”工程，该工程导致了重大的土地利用变化。有关方案对土壤侵蚀和水循环产生了有益的影响。然而，这些土壤和水过程的变化对相关生态系统服务的影响尚不清楚，需要进一步研究。研究将集中在三个空间尺度上：坡度、流域和区域。它结合使用a)实验来收集环境、生物和农艺数据；B)遥感数据和C)建模方法。A)数据采集：选取位于青藏高原4个主要地形区的4个实验站作为案例研究：1)安塞水土保持综合实验站；2)长武农业生态实验站；3)固原生态站；4)神木侵蚀与环境监测站。在每个站点建立了20世纪80年代不同植被覆盖、坡度和样地尺度水土保持措施的处理方法，数据收集包括：土壤水分、冠层大小、径流、土壤流失和气象记录。这个项目的大多数中国成员都参与了以前在这些站点的研究。在坡度尺度上，将在一个地块的子集中监测额外的环境、生物和农艺数据。在流域尺度上，监测站所在的四个流域将被监测。将测量以下变量的空间分布：降水、土壤性质、植被类型、冠层大小、径流和土壤流失。B)遥感数据采集：在区域尺度上，将遥感与地面真实数据相结合，研究植被类型、土地覆盖、生产力、水分平衡成分、土壤流失、土壤类型等的空间变异性。c)建模方法：采用级联方法，构建适用于不同空间尺度的改进模型框架。机械土壤-水-植物模型将应用于边坡尺度。然后，它们的产出将用作流域一级模型的输入。将在区域一级使用空间经验/统计模型。从A)和B)中观察和收集的数据将用于进一步开发、校准和验证我们的模型。在坡面进行模型模拟，揭示不同区域土壤和水分的动态机制，分析植被类型、土壤类型、坡度、气候因素和管理措施的影响。流域模型将估算不同植被类型的土壤和水分承载能力，预测土地利用/覆盖变化对土壤流失、水循环和生态系统服务的影响，并评估水土保持、植被变化和生态系统服务实践中的管理方案。在区域尺度上研究不同植被类型的水土承载能力和最优生态系统服务。外联讲习班和示范将向农民和决策者传播知识。该研究将在不同尺度上阐明水土过程与农业生态系统服务之间的耦合关系，并评估黄土高原植被覆盖和土地利用变化对水循环、土壤侵蚀和生态系统服务的影响。

The Loess Plateau of China covers an area 2.5x the size of the UK (some 640,000 square km) in the upper and middle reaches of China's Yellow River and is renowned for having the most severe soil erosion in the world; deforestation, over-grazing and poor agricultural practice have resulted in degenerated ecosystems, desertification and unproductive agriculture in the region. To control severe soil erosion on the Loess Plateau, the Chinese government imposed a series of policies for fragile ecosystems, such as the 1999 state-funded "Grain-for-Green" project, which has resulted in significant land use changes. Related programmes have produced beneficial effects on soil erosion and water cycles. However, the impact of these changes in soil and water processes on related ecosystem services is unknown and demands further study. The proposed research will focus on three spatial scales: slope, watershed, and region. It uses a combination of A) experiments to collect environmental, biological and agronomic data; B) remote sensing data and C) modelling approaches. A) Data collection: Four experimental stations located in four main topographical regions of the Plateau are chosen as case studies: 1) Ansai Comprehensive Experimental Station of Soil and Water Conservation; 2) Changwu Agro-ecology Experiment Station; 3) Guyuan Ecological Station; 4) Shenmu Erosion and Environment Station. At each station, treatments of different vegetative covers, slopes, and the practices of soil and water conservation at the plot scale were set up in the 1980s and data collections include: soil water, canopy size, runoff, soil losses and meteorological records. Most of the Chinese members of this project have been involved in prior studies at the stations.At the slope scale, additional environmental, biological and agronomic data will be monitored in a sub-set of the plots. At watershed scale, four watersheds where the stations are located will be monitored. The spatial distribution of the following variables will be measured: precipitation, soil properties, vegetative types, canopy size, runoff and soil loss.B) Remote sensing data collection: At the regional scale, remote sensing combined with ground-truthing data will be used to investigate the spatial variability of vegetation type, land cover, productivity, the components of water balance, soil losses, soil type, etc.C) Modelling approaches: a cascade approach will be used to build an improved model framework applied to different spatial scales. Mechanistic soil-water-plant models will be applied to the slope scale. Their outputs will then be used as inputs for models at watershed level. Spatial empirical/statistical models will be used at the regional level. Observed and collected data from A) and B) will be used to further develop, calibrate and validate our models.Model simulations at the slope level will be used to reveal the dynamic mechanisms in soil and water in different regions and analyse the effects of vegetation type, soil type, slope degree, climatic factors and management practice. Watershed models will estimate soil and water carrying capacity for different vegetation types, predict the effect of land use/cover changes on soil losses, water cycle and ecosystem services and evaluate management scenarios in the practices of soil and water conservation, vegetative changes, and ecosystem services. The soil and water carrying capacity for different vegetation types and the optimal ecosystem services will be addressed at the regional scale. Outreach workshops and demonstrations will disseminate knowledge to farmers and policy makers.The proposed research will elucidate the coupled relationships between soil and water processes and agro-ecosystem services at various scales, and evaluate the effects of vegetation cover and changes in land use on water cycle, soil erosion, and ecosystem services across the Loess Plateau.