Predicting the size distribution of sediments on hillslopes and rivers at the landscape scale

地球90%以上的陆地表面被风化层覆盖，风化层是从巨石到粘土大小不等的颗粒的毯子。这些颗粒的大小分布是对地球表面环境的根本控制。在河道中，上游提供的沉积物的粒度分布影响侵蚀速率、河道几何形状和水生生物可利用的栖息地类型。在河流沉积物发源地的山坡上，岩石和土壤的大小分布会影响水文响应、化学风化速率和植被类型。尽管它很重要，但我们几乎没有数据和有限的理论来预测山坡和河流沉积物颗粒的尺寸分布在不同景观中是如何变化的。我的目标是建立一个全面的框架，从岩性、气候和地貌因素方面了解地球表面颗粒尺寸分布的演变，这些因素控制着它们的生产、运输和从源到汇的转化。我把重点放在构造活跃的侵蚀地貌上，在那里，将河流沉积物与其山坡来源联系起来的路径最容易被识别出来。这项研究计划的第一个长期目标是量化控制在山坡上产生并供应给河流的颗粒物的尺寸分布的因素。为此，我将：在三个关键控制因素--侵蚀速度、气候和岩石类型--中沿坡度测量野外场地的山坡颗粒尺寸；检验基岩中裂缝的间距决定进入山坡风化引擎的颗粒的初始尺寸分布的假设；以及从土壤数据库中挖掘山坡颗粒尺寸分布的景观尺度趋势数据。我的第二个长期目标是开发一个基于过程的预测模型，用于预测泥沙在河流网络中传输时颗粒分布的演变。为此，我将量化磨损导致的颗粒尺寸减小过程如何依赖于岩石强度，以及沉积物混合物中颗粒大小和形状的分布。我还将根据实验室结果建立预测现场环境中颗粒尺寸减小率的方法。这些结果将使检验假说成为可能，通过山坡风化和河流切割之间的反馈，确定景观如何随着构造和气候压力而演变。预测景观中沉积物大小的能力也有助于解决许多实际问题，包括：恢复鲑鱼和其他水生生物的栖息地，其生活周期阶段取决于特定粒度分布的可用性；预测和管理向水库和其他水资源基础设施的沉积物输入；以及诊断和减轻伐木、道路建设和其他土地利用与沉积物相关的影响。

Over 90% of Earth's land surface is covered by regolith, a blanket of particles ranging in size from boulders to clay. The size distribution of these particles is a fundamental control on Earth's surface environments. In a river channel, the size distribution of sediments supplied from upstream influences rates of erosion, channel geometry, and the type of habitats available to aquatic organisms. On hillslopes, where river sediments originate, the size distribution of rocks and soil influences hydrologic response, rates of chemical weathering and types of vegetation. Despite its importance, we have few data and limited theory to inform predictions of how the size distribution of hillslope and river sediment particles varies across landscapes. My goal is to develop a comprehensive framework for understanding the evolution of the size distributions of earth surface particles, in terms of the lithologic, climatic and geomorphic factors that control their production, transport and transformation from source to sink. I focus on tectonically active, erosional landscapes, where the pathways linking river sediments to their hillslope sources are most readily identified. The first long-term objective of this research program is to quantify the factors that control the size distributions of particles produced on hillslopes and supplied to rivers. To do this I will: measure hillslope particle size at field sites along gradients in three key controlling factors - erosion rate, climate, and rock type; test the hypothesis that the spacing of fractures in bedrock sets the initial size distribution of particles entering the hillslope weathering engine; and mine data from soils databases for landscape-scale trends in hillslope particle size distributions. My second long-term objective is to develop a process-based, predictive model for how particle size distributions evolve as sediments are transported through river networks. To do this I will quantify how the process of particle size reduction by abrasion depends on rock strength, and on the distributions of particle sizes and shapes in sediment mixtures. I will also establish methods for predicting rates of particle size reduction in field settings by scaling-up from laboratory results. These results will make it possible to test hypotheses for how hillslopes, channels and landscapes are linked by feedbacks between hillslope weathering and river incision, which determine how landscapes evolve in response to tectonic and climatic forcing. The ability to predict sediment size across landscapes can also help solve many practical problems, including: restoring habitat of salmonids and other aquatic organisms with life cycle stages that depend on availability of specific particle size distributions; predicting and managing sediment inputs to reservoirs and other water resources infrastructure; and diagnosing and mitigating sediment-related impacts of logging, road building and other land uses.