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

有机碳是在食物网的基础上为生物生产提供燃料的能源。在水生生态系统中，有机物来源于水和土壤中的植物、藻类和浮游植物的破碎碎片。一些有机物来源是由河流从高地来源输入的，包括土壤和植物碎屑（陆源来源），这些来源往往质量较低，对水生生物作为食物来源的用处较小。其他有机物来源是在沼泽、湖泊和其他水生系统中产生的，往往具有较高的营养价值。近几十年来，人类活动通过改变淡水流量、引入外来或非本地物种、通过营养物质的富集和水坝的建设导致水质下降，改变了水生生态系统。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（以下简称“三角洲”）作为模型系统，以了解人类活动如何影响过去100-200年沉积物中碳的丰度、来源和年龄。该项目将使用“生物标记物”（一种自然产生的化学示踪剂）检查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。本研究的目的是利用这些“生物标志物”：(1)确定目前沉积在三角洲亚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记物分布确定人类活动如何改变输送到三角洲的有机质组成；(3)利用放射性碳的自然丰度确定有机碳（TOC）的平均年龄；利用特定来源的生物标记物确定有机质来源，并确定SOM中水生和陆源组分的放射性碳年龄。更广泛的影响本项目将在一个具有代表性的高度改变的生态系统——萨克拉门托-圣华金河三角洲——中解决与人类对碳质量的影响有关的基本问题，并将测试有关群落结构决定因素和三角洲栖息地退化的基本假设。三角洲栖息地为鱼类和无脊椎动物提供栖息地，为世界上很大一部分人口提供食物，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个将多生物标志物方法应用于三角洲环境变化问题的研究，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，使他们能够在基础研究和应用研究之间的界面上进行跨学科研究，解决对生态系统科学至关重要的问题。本项目还将通过参与本研究的三个机构的专门项目，让代表性不足的群体和学生（高中、本科和研究生）参与水产科学研究的不同阶段的培训。

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.