RUI:Erosion in Madagascar: Investigating background and modern rates using 10Be and stream sediment gauging data

传统观点认为，马达加斯加的沉积物产量异常高，是人类活动导致了侵蚀。根据世界银行的数据，这个国家的“世界纪录侵蚀率”为每年每平方公里2 -4万吨，而被称为lavaka的广泛山坡沟壑在每本旅游指南中都被列为该国景观灾难性剥蚀的例子。然而，这种观点是基于少数和局部的测量，并且在许多方面代表了“公认的智慧”，而不是严格确定的解释。因此，测量马达加斯加的侵蚀速率需要系统的分析。宇宙成因10Be是一种由宇宙射线轰击在地球表面产生的短寿命同位素，它可以决定景观侵蚀率。未受干扰的地表物质积累了大量的10Be，但在侵蚀程度高的地方，地表物质的这种同位素含量就低。对马达加斯加河流沉积物的初步分析表明，每年的侵蚀率仅为每平方公里32吨左右，这表明马达加斯加的景观在数千年到数十万年的时间尺度上相当稳定。另一方面，对河流产沙量的直接测量可以提供较短时间尺度（年到世纪）的侵蚀速率。由于人类到达马达加斯加的时间不到2000年，收集和比较10Be和沉积物测量数据将记录人类出现之前到现代的侵蚀速率。该项目将对马达加斯加广大地区的排水网络进行采样，将10Be数据与最近的河流-沉积物测量和水库沉积记录的沉积物数据进行比较。为了量化背景和现代的侵蚀速率。GIS分析将研究流域内侵蚀速率与拉瓦卡沟强度之间的关系。该项目有助于量化人类作为全球地貌因素的影响。马达加斯加作为生物多样性热点地区和受到威胁的环境的地位使这项工作具有更大的意义，因为这些问题在有关保护和国际援助政策的讨论中显得尤为突出。该项目将涉及马达加斯加和美国的学生和工作人员。这个项目的科学成果将与马达加斯加的环境规划和减缓侵蚀战略直接相关。了解侵蚀速率、熔岩在沉积物生成中的作用以及人类在这一过程中的作用，将有助于确定马达加斯加是自然地具有高侵蚀速率的特征，还是它们是最近的和人为的起源。该奖项由美国国家科学基金会国际科学与工程办公室共同资助。

Conventional wisdom holds that sediment yields in Madagascar are uncommonly high, and that human activities drive the erosion. The country has a "world-record erosion rate" of 20,000-40,000 tons per square km per year according to the World Bank, and the widespread hillslope gullies called lavaka are featured in every guidebook as examples of the catastrophic denudation of the country's landscape. This viewpoint is based, however, on measurements that are few and local, and in many respects represents "received wisdom" rather than rigorously determined interpretation. Systematic analysis is therefore necessary to measure the erosion rate of Madagascar. Cosmogenic 10Be, a short-lived isotope created at the Earth's surface by cosmic-ray bombardment, can determine landscape erosion rates. Undisturbed surface materials accumulate substantial amounts of 10Be, but where erosion is high then surface materials are low in this isotope. Preliminary 10Be analyses of sediment from Madagascar rivers indicate erosion rates of only about 32 tons per square km per year, suggesting that the Madagascar landscape has been quite stable on timescales of thousands to hundreds of thousands of years. On the other hand, direct measurements of sediment yield in rivers can provide erosion rates on shorter timescales (years to centuries). Because humans arrived in Madagascar less than 2000 years ago, collecting and comparing 10Be and sediment gauge data will document erosion rates in the pre-human to modern time span. This project will sample drainage networks from broad swaths of Madagascar, omparing 10Be data with recent sediment data from stream-sediment gauging and reservoir sedimentation records.in order to quantify both background and modern erosion rates. GIS analysis will investigate the relationship between erosion rate and the intensity of lavaka gullying in the watersheds. This project contributes to ongoing efforts to quantify the effects of humans as geomorphic agents world-wide. Madagascar's status as a biodiversity hotspot and a threatened environment lend added significance to the work, as these questions loom large in discussions of conservation and international aid policy. The project will involve both Malagasy and U.S. students and personnel. The scientific results of this project will have direct relevance for environmental planning and erosion mitigation strategies for Madagascar. Understanding rates of erosion, the role of lavakas in sediment generation, and the role of humans in the process will help determine whether Madagascar is naturally characterized by high erosion rates or whether they are of recent and anthropogenic origin. This award is co-funded by NSF's Office of International Science and Engineering.