A compound-specific isotopic approach to quantifying the source of terrestrial organic matter transported by a large river

一种化合物特异性同位素方法，用于量化大河输送的陆地有机物的来源

• 批准号: 1227192
• 负责人: A Joshua West
• 金额: $ 27.31万
• 依托单位: University of Southern California
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2012
• 资助国家: 美国
• 起止时间: 2012-10-01 至 2015-09-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1227192&HistoricalAwards=false
• 关键词: compound; specific; isotopic; approach; quantifying

The erosion of organic matter from the land surface and its transport by rivers reflects a central link between Earth's biological and geological systems. Pinpointing the sources of organic material within large river systems has been difficult but is crucial for understanding and quantifying the carbon cycle, which is an important aspect of the climate system. The goal of this project is to contribute valuable new information about the sources of organic matter in rivers by identifying the isotopic composition of specific organic molecules, namely the waxy molecules from plant leaves, and by tracing these molecules through their transport downstream. These same molecules are also used for past climate reconstruction, and this work will gather information about their sourcing, integration and preservation that will be important for understanding climate signals. The research will be based in the Kosñipata-Madre de Dios river system, in the Andean headwaters of the Amazon River in Peru. The Amazon is one of the planet's largest rivers and most important biogeochemical systems, and yet the source and fate of organic material eroded from the Andes remains unclear. Isotopic analysis of carbon in particulate organic matter (POM) transported by rivers has already found wide application and contributed to our understanding of the carbon cycle. Previous efforts have particularly focused on analyses of bulk carbon (e.g., stable carbon isotopic and radiocarbon composition of bulk POM), representing the average composition of a complex mixture. This new project will look at the isotopic composition of specific organic molecules within river POM, particularly the plant leaf waxes, as well as the plants from which they are derived, and soils in which they are stored. Leaf wax compounds are useful as they are derived only from terrestrial biomass, with no complicating input from aquatic organisms. The main focus will be on the stable hydrogen isotope composition (delta D) of leaf wax, which reflects the isotopic composition of the source water used by plants. This will be complemented by radiocarbon analyses through collaboration with Woods Hole Oceanographic Institution. Sampling will occur across a gradient in elevations within the Kosñipata-Madre de Dios. Because there is an elevation gradient in the delta D of precipitation in the Kosnipata-Madre de Dios, as in many other mountainous environments, investigators hypothesize that the leaf wax composition can act as a source fingerprint, to identify where POM is derived, and to assess how this varies spatially, from high to low elevation, and across the foreland floodplain, as well as temporally, during storm events. This information will be vital to constraining the use of biomarker isotopic composition for paleo-climate reconstruction, and for quantifying and tracing Andean organic carbon in the Amazon system. The research program will facilitate a wide-ranging international and inter-disciplinary collaboration, with research and education activities in three countries (US, Peru, and UK). The Peruvian fieldwork is supported by collaborations with colleagues at the field stations and university in Peru, and in turn the PIs will work with colleagues in Peru to provide research-based educational materials at the field stations for a range of undergraduate and public visitors as well as lecture material for undergraduate and graduate degree courses in the US and in Peru. Student teaching and learning will be a vital component of the project, with research opportunities for 1 PhD and 4 undergraduate students at the University of Southern California to be involved in field and laboratory research on important questions about the carbon cycle and the climate system.

陆地表面有机物的侵蚀及其通过河流的输送反映了地球生物系统和地质系统之间的中心联系。查明大型河流系统内有机物质的来源一直很困难，但对于理解和量化碳循环至关重要，碳循环是气候系统的一个重要方面。该项目的目标是通过识别特定有机分子（即植物叶子中的蜡质分子）的同位素组成，并通过追踪这些分子向下游的运输，提供有关河流中有机物来源的有价值的新信息。这些相同的分子也用于过去的气候重建，这项工作将收集有关它们的来源、整合和保存的信息，这对于理解气候信号非常重要。该研究将在秘鲁亚马逊河安第斯源头的科斯尼帕塔-马德雷德迪奥斯河系进行。亚马逊河是地球上最大的河流和最重要的生物地球化学系统之一，但安第斯山脉侵蚀的有机物质的来源和命运仍不清楚。对河流输送的颗粒有机物 (POM) 中的碳进行同位素分析已得到广泛应用，并有助于我们了解碳循环。以前的工作特别集中于散装碳的分析（例如散装 POM 的稳定碳同位素和放射性碳成分），代表复杂混合物的平均成分。这个新项目将研究河流 POM 中特定有机分子的同位素组成，特别是植物叶蜡，以及它们来源的植物和储存它们的土壤。叶蜡化合物非常有用，因为它们仅源自陆地生物质，没有来自水生生物的复杂输入。主要重点是叶蜡的稳定氢同位素组成（δ D），它反映了植物使用的水源水的同位素组成。与伍兹霍尔海洋研究所合作，放射性碳分析将对此进行补充。采样将在科斯尼帕塔-马德雷德迪奥斯境内的海拔梯度上进行。由于科斯尼帕塔-马德雷德迪奥斯地区的降水三角洲 D 存在海拔梯度，与许多其他山区环境一样，研究人员推测，叶蜡成分可以作为来源指纹，以确定 POM 的来源，并评估风暴事件期间这种变化在空间上、从高海拔到低海拔、整个前陆洪泛区以及时间上的变化。这些信息对于限制使用生物标记同位素组成进行古气候重建以及量化和追踪亚马逊系统中的安第斯有机碳至关重要。该研究计划将促进广泛的国际和跨学科合作，在三个国家（美国、秘鲁和英国）开展研究和教育活动。秘鲁的实地工作得到了与秘鲁实地考察站和大学同事的合作支持，反过来，PI 将与秘鲁的同事合作，在实地考察站为一系列本科生和公众参观者提供基于研究的教育材料，以及美国和秘鲁的本科生和研究生学位课程的讲座材料。学生教学将是该项目的重要组成部分，南加州大学的 1 名博士生和 4 名本科生将有机会参与有关碳循环和气候系统重要问题的现场和实验室研究。

项目成果

Dual isotope evidence for sedimentary integration of plant wax biomarkers across an Andes-Amazon elevation transect

• DOI: 10.1016/j.gca.2018.09.007
• 发表时间: 2018-12
• 期刊: Geochimica et Cosmochimica Acta
• 影响因子: 5
• 作者: S. Feakins;Mong Sin Wu;C. Ponton;V. Galy;A. West

Mixing as a driver of temporal variations in river hydrochemistry: 1. Insights from conservative tracers in the Andes-Amazon transition: ANDES-AMAZON TRIBUTARY MIXING

混合作为河流水化学时间变化的驱动因素：1.安第斯山脉-亚马逊过渡期保守示踪剂的见解：安第斯山脉-亚马逊支流混合

• DOI: 10.1002/2016wr019733
• 发表时间: 2017
• 期刊: Water Resources Research
• 影响因子: 5.4
• 作者: Torres, Mark A.;Baronas, J. Jotautas;Clark, Kathryn E.;Feakins, Sarah J.;West, A. Joshua
• 通讯作者: West, A. Joshua

Altitude effect on leaf wax carbon isotopic composition in humid tropical forests

• DOI: 10.1016/j.gca.2017.02.022
• 发表时间: 2017-06
• 期刊: Geochimica et Cosmochimica Acta
• 影响因子: 5
• 作者: Mong Sin Wu;S. Feakins;R. Martin;A. Shenkin;L. Bentley;B. Blonder;N. Salinas;G. Asner;Y. Malhi