COLLABORATIVE RESEARCH: Anthropogenic Impacts on Carbon Cycling in the Sacramento-San Joaquin River Delta- Changes in Source, Nature and Age of Organic Carbon

有机碳是作为食物链基础的生物生产燃料的能源来源。在水生生态系统中，有机物来自水和土壤中分解的植物、藻类和浮游植物。一些有机物质来源是由河流从包括土壤和植物碎屑(陆源)在内的旱地来源输入的，这些来源往往质量较低，对水生生物作为食物来源的作用较小。其他来源的有机物质产生于沼泽、湖泊和其他水生系统中，往往具有更高的营养价值。近几十年来，人类活动改变了水生生态系统，改变了淡水流量，引入了外来或非本地物种，通过营养丰富和修建大坝导致水质下降。这些活动改变了提供给水生生态系统的碳的数量、来源和质量。该项目将使用加利福尼亚州萨克拉门托-圣华金河三角洲(下称“三角洲”)作为一个模型系统，以了解人类的变化如何影响代表过去100-200年的沉积物中碳的丰度、来源和年龄。该项目将使用“生物标志物”，即自然产生的化学示踪剂，研究从代表三角洲关键亚环境的地点收集的沉积物的有机碳组成，使我们能够确定有机碳的来源。这项研究的目标将是利用这些“生物标志物”来：(1)确定目前沉积在三角洲次生境中的沉积有机质(SOM)的水生和陆源成分的来源；(2)利用沉积物岩心中的生物标志物分布，确定人类活动如何改变输送到三角洲的有机质的组成；以及(3)利用放射性碳的自然丰度来确定有机碳(TOC)的平均年龄和特定来源的生物标志物，以分配有机质来源，并确定SOM的水生和陆源成分的放射性碳年龄。更广泛的影响这个项目将解决与人类对高度修改的生态系统--萨克拉门托-圣华金河三角洲中碳质量的影响有关的基本问题，并将测试关于群落结构和三角洲生境退化决定因素的基本假设。三角洲生境为养活世界大部分人口的鱼类和无脊椎动物提供了栖息地，维持这些动态生态系统具有明显的科学、社会和经济意义。据我们所知，我们的研究将是第一次将多生物标记物方法应用于三角洲环境中的环境变化问题，并在潜在恢复问题的背景下评估这些变化。拟议工作的更广泛影响还包括为学生提供独特的培训机会，以便在基础研究和应用研究之间进行跨学科研究，解决对生态系统科学至关重要的问题。该项目还将通过参与这项研究的三个机构的专门方案，在不同阶段(高中、本科生和研究生)开展代表不足的群体和学生的水产科学研究培训。

Intellectual Merit Organic carbon is the source of the energy that fuels biological production at the base of the foodweb. In aquatic ecosystems, organic matter derives from broken-up pieces of plants, algae and phytoplankton in the water and soil. Some sources of organic matter are imported by rivers from upland sources including soils and plant detritus (terrigenous sources), which tends to be lower in quality and less useful to aquatic organisms as a food source. Other sources of organic matter are produced within marshes, lakes and other aquatic systems and tend to be of higher nutritional value. In recent decades, human activities have altered aquatic ecosystems by changing freshwater flow, introducing exotic or non-native species, contributing to declining water quality through nutrient enrichment, and by the construction of dams. These activities have altered the amount, sources, and quality of carbon supplied to aquatic ecosystems. This project will use the Sacramento-San Joaquin River Delta, CA (referred to as the "Delta" hereafter) as a model system for understanding how human modifications influence the abundance, sources and age of carbon in sediments representing the past 100-200 years. The project will examine the organic carbon composition of sediments collected from sites representing key sub-environments of the Delta using "biomarkers", naturally-occurring chemical tracers that allow us to identify the sources of organic carbon. The objectives of this study will be to use these "biomarkers" to: (1) identify the sources of the aquatic and terrigenous components of sedimentary organic matter (SOM) currently being deposited within sub-habitats of the Delta; (2) determine how anthropogenic activities have altered the composition of organic matter delivered to the Delta using biomarker distributions in sediment cores, and (3) use the natural abundance of radiocarbon to determine the average age of organic carbon (TOC) and source-specific biomarkers to apportion organic matter sources and determine the radiocarbon ages of aquatic and terrigenous components of the SOM. Broader ImpactsThis project will address basic questions related to human impacts on carbon quality in a representative highly modified ecosystem-the Sacramento-San Joaquin River Delta and will test fundamental hypotheses about the determinants of community structure and degradation of deltaic habitats. Deltaic habitats provide habitat for fishes and invertebrates that feed a large proportion of the world's human population and sustaining these dynamic ecosystems is of clear scientific, social and economic significance. To the best of our knowledge, our study will be the first to apply a multi-biomarker approach to questions of environmental change in deltaic environments and assess these changes within the context of potential restoration issues. The broader impacts of the proposed work also include a unique training opportunities for students to conduct interdisciplinary research that addresses questions of fundamental importance to ecosystem science at the interface between basic and applied research. This project will also engage under-represented groups and students at various stages in their training (high school, undergraduate and graduate) in aquatic sciences research through specialized programs at the three institutions involved in this study.