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

陆地表面有机物的侵蚀及其通过河流的运输反映了地球生物系统和地质系统之间的中心联系。准确确定大型河流系统中有机物质的来源一直是困难的，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确定特定有机分子的同位素组成，即植物叶片中的蜡质分子，并通过向下游输送这些分子来追踪这些分子，从而提供关于河流中有机物质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，这项工作将收集关于它们的来源、整合和保存的信息，这对理解气候信号将是重要的。这项研究将在秘鲁亚马逊河安第斯源头的Kosñipata-Madre de Dios河系进行。亚马逊是地球上最大的河流之一，也是最重要的生物地球化学系统，但从安第斯山脉侵蚀的有机物质的来源和命运仍不清楚。河流输送颗粒有机物(POM)中碳的同位素分析已经得到了广泛的应用，并有助于我们理解碳循环。以前的工作特别侧重于散装碳的分析(例如，散装聚甲醛的稳定碳同位素和放射性碳组成)，代表复杂混合物的平均组成。这一新项目将研究河流POM中特定有机分子的同位素组成，特别是植物叶蜡，以及它们的来源植物和储存它们的土壤。叶蜡化合物是有用的，因为它们只来自陆地生物量，没有来自水生生物的复杂输入。主要焦点将放在叶蜡的稳定氢同位素组成(增量D)上，它反映了植物所用源水的同位素组成。这将得到与伍兹霍尔海洋研究所合作进行的放射性碳分析的补充。采样将在Kosñipata-Madre de Dios内的海拔梯度上进行。由于科斯尼帕塔-马德雷-迪奥斯地区降水的D增量存在海拔梯度，就像在许多其他山区环境中一样，研究人员假设，叶蜡成分可以作为来源指纹，以确定POM的来源，并评估这种变化在空间上是如何变化的，从高海拔到低海拔，跨越前陆漫滩，以及在风暴事件期间在时间上。这些信息对于限制使用生物标志物同位素组成重建古气候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外勤站和大学的同事的合作的支持，反过来，私人情报员将与秘鲁的同事合作，在外勤站为一系列本科生和公众访问者提供基于研究的教育材料，以及为美国和秘鲁的本科生和研究生学位课程提供讲座材料。学生的教学和学习将是该项目的重要组成部分，南加州大学的1名博士和4名本科生将有机会参与关于碳循环和气候系统的重要问题的实地和实验室研究。

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.