Multi-dimensional Soil Erosion and Associated Chemical Transport: Experiments, Mathematical Modelling and Field Evaluation

《欧盟水框架指令》包括控制扩散污染的具体要求，并要求各国政府根据良好的生态状况制定水质目标。欧盟栖息地指令和英国政府的生活质量指标设定了在保护区实现有利条件的目标，英国生物多样性行动计划旨在扭转和恢复关键物种和栖息地的种群数量。考虑到磷、硝酸盐和沉积物在影响水质和生物多样性方面发挥的关键作用，以及农业被认为对地表水的投入负有50%的责任，预测这些扩散污染物从陆地到水中的运动变得越来越重要。被侵蚀的农业土壤是农药、除草剂、肥料和微生物等污染物的载体。被侵蚀的农业土壤和相关污染物从农田的运输导致地表水富营养化，破坏淡水生态系统和地表水源的微生物污染。它现在也被视为英国海滩和沿海环境水质下降的主要污染源。污染物要么以溶解形式在径流水中携带，要么通过附着在土壤颗粒上携带。由于污染物优先与不同大小的土壤颗粒结合，因此确定污染物对水道的负荷需要预测或计算侵蚀沉积物的泥沙大小分布。我们提出，这可以通过求解Hairsine和Rose的多粒径类、多维土壤侵蚀模型以及溶解污染物的输运方程来实现。模型的验证和校准将通过一个分级程序来完成，从控制良好的实验室实验，到自然山坡，最后是一个小的集水区。在每个尺度下，我们将确定模型在出口和空间上的性能。对于水槽（1.5米x 4米），测量的流出数据将包括随时间变化的粒径和污染物分布，作为土壤类型、表面几何形状、降雨量和初始土壤湿度条件的函数。此外，将通过使用数字摄影测量获得高分辨率空间数据，其中可以测量水槽表面地形的局部方向和局部坡度，以便与侵蚀模型的预测进行比较。在山坡尺度上，我们将与Defra资助的磷和沉积物缓解项目联系起来，使用从52个仪器山坡上收集的三种不同土壤类型的补充数据。我们还将在这个尺度上利用稀土元素氧化物作为示踪剂来确定沉积物的来源，并将这些空间数据与我们的模型预测进行比较。在流域尺度上，我们将使用从俄亥俄州Coschocton获得的现有稀土流域数据来测试模型的空间预测。这项研究为从土壤到水的扩散污染物转移的物理理解方面取得重大进展提供了巨大的潜力，为目前由Defra资助的更多应用研究以及诸如水框架指令和集水区敏感农业等政策措施的实施提供了科学基础。

The EU Water Framework Directive includes specific requirements to control diffuse pollution and also places requirements on national governments to set water quality objectives based on good ecological status. The EU Habitats Directive and the UK government's Quality of Life indicators set targets for achieving favourable conditions on conservation sites, and the UK Biodiversity Action Plan aims to reverse and restore populations for key species and habitats. Given the pivotal role phosphorous, nitrate and sediment play in influencing water quality and biodiversity, and that agriculture is thought to be responsible for 50% of the inputs to surface waters, predicting the movement of these diffuse pollutants from land to water is becoming increasingly important. Eroded agricultural soil is carrier of pollutants such as pesticides, herbicides, fertilizers and microbes. The transport of eroded agricultural soil and associated pollutants from farmlands, results in the eutrophication of surface waters, damage to freshwater ecosystems and the microbial contamination of surface water sources. It is now also seen as a major pollutant source responsible for the reduction of water quality in UK beaches and coastal environments. Pollutants are either carried in dissolved form in the runoff water, or through attachment to the soil particles. Since pollutants bind preferentially to different sized soil particles, determining the pollutant loading to waterways requires predicting or calculating the sediment size distribution of the eroded sediment. We propose that this can be achieved by solving the multi-particle size class, multi-dimensional soil erosion model of Hairsine and Rose in conjunction with a transport equation for the dissolved pollutants. Validation and calibration of the model will be done through a hierachical programme, moving from well controlled laboratory experiments, to natural hillslopes and finally a small catchment. T each scale we will determine model performance both at the outlet and spatially. For the flume (1.5 m x 4 m) measured outflow data will include time varying particle size and pollutant distributions as a function of soil type, surface geometry, rainfall rate and initial soil moisture conditions. Addition high resolution spatial data will be obtained through the use of digital photogrammetry where local aspect and local slope measurements of the surface topography in the flume can be measured for comparison against predictions from the erosion model. At the hillslope scale we will link with the Defra funded Mitigation of Phosphorus and Sediment Project, using a supplementing data collection from 52 instrumented hillsides on three contrasting soil types. We will also utilise rare earth element oxides as tracers at this scale to determine where the sources of sediment are and compare this spatial data with our model predictions. At the catchment scale we will use existing rare earth catchment data obtained from Coschocton, Ohio to test the spatial predictions of the model. This research offers significant potential for achieving major advances in the physical understanding of the transfer of diffuse pollutants from soils to waters, providing scientific underpinning for the more applied research currently being funded by Defra and for the implementation of policy measures such as the Water framework directive and Catchment Sensitive Farming.