OCE-PRF Effects of below-ground complexity on seagrass sediment structure and function

该奖项全部或部分由2021年美国救援计划法案（公法117-2）资助。海洋沉积物通过代谢（“分解”）有机物质或将其掩埋，控制海洋中碳的命运。然而，沉积物在某种程度上是一个“黑匣子”。沉积物中的化学和生态学密切相关，因此很难确定哪些过程控制新陈代谢。这一问题在海草床中更为突出，因为海草床是重要的沿海生态系统和碳埋藏量非常高的地点。海草的根创造了复杂的结构，与周围的沉积物交换营养物质和氧气，穴居动物可以通过混合和冲洗沉积物来增加沉积物的新陈代谢。这导致海草沉积物代谢的变化，目前还没有得到很好的解释。拟议的研究将把海草根结构和动物群落的差异与沉积物代谢率的变化联系起来。这项研究的结果将为管理和保护海草床的战略提供信息，并预测其宝贵的生态系统服务的变化。来自代表性不足群体的本科生将参与研究，并指导他们自己的研究项目。该项目的研究结果将被改编成关于“隐藏的复杂性”的初中/高中课程计划，向学生讲授自然界的物理结构、化学和生态之间的关系。拟议研究的总体目标是将海草根和根茎的复杂物理结构和地球化学活动纳入海草地下环境模型，以评估该环境的哪些特征影响沉积物代谢。密集、复杂的根垫可能会使沉积物更加密集，并驱动更高的沉积物代谢率，根的三维结构可能会控制哪些动物可以生活在那里，并通过扩展来控制动物的代谢增强活动。该项目的具体目标是：（1）确定海草根和根茎形成的物理化学环境如何影响大型底栖动物功能多样性，（2）评估在扩展的海草床中不同地点沉积物物理化学环境的变化如何对应于沉积物代谢的变化，和（3）评估海草类群之间沉积物物理化学环境的差异如何对应于沉积物代谢的变化。物理结构将使用CT成像来表征，地球化学模式将使用平面光电二极管成像和有针对性的微剖面来测量。将使用多物理场建模技术将结构和地球化学数据整合在一起，以模拟海草根部周围沉积物的地球化学渗透。然后将这些模型结果与原位底栖室的沉积物代谢测量结果进行比较，以得出关于根系对沉积物总氧合和动物群行为的影响的结论。将非破坏性CT和平面光电管成像结合到一个统一的模型中，将为以前仅在有限程度上描述的海草沉积物的3D结构提供有价值的信息。开发的方法也将用于其他研究人员研究复杂的“不透明”系统，如沼泽，红树林和土壤。通过描述地下结构的变化，这项工作将提供对其过程的机械理解，然后可以将其与海草生态系统中的大规模模式联系起来，为海草的保护，恢复和管理提供宝贵的知识，该奖项反映了NSF的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准。

This award is funded in whole or in part under the American Rescue Plan Act of 2021 (Public Law 117-2).Marine sediments control the fate of carbon in the ocean by either metabolizing (“breaking down”) organic matter or burying it away. However, sediments are somewhat of a “black box”. Chemistry and ecology are closely connected in sediments, making it difficult to identify which processes control metabolism. This problem is even more pronounced in seagrass beds which are important coastal ecosystems and sites of very high carbon burial. Seagrass roots create complex structures that exchange nutrients and oxygen with the surrounding sediment, and burrowing animals can increase sediment metabolism by mixing and flushing water through sediments. This results in variability in seagrass sediment metabolism that is currently not well explained. The proposed research will link differences in seagrass root structure and animal communities to variation in sediment metabolism rates. The results of this research will inform strategies to manage and protect seagrass beds and anticipate changes in their valuable ecosystem services. Undergraduates from underrepresented groups will be involved in the research and mentored in their own research projects. The findings of the project will be adapted into a middle/high school level lesson plan on “Hidden Complexity” to teach students about the relationships between physical structure, chemistry and ecology in nature. The overarching goal of the proposed research is to integrate the complex physical structure and geochemical activity of seagrass roots and rhizomes into a model of the seagrass below-ground environment to assess which features of that environment affect sediment metabolism. Dense, complex root mats may oxygenate sediments more and drive higher sediment metabolism rates, and the 3D structure of the roots may control what fauna can live there and by extension the metabolism-enhancing activities the fauna perform. Specific goals of the project are to; (1) determine how the physical-chemical environment created by seagrass roots and rhizomes influences macrofaunal functional diversity, (2) assess how variation in the sediment physical-chemical environment at different locations in an expanding seagrass bed corresponds to variation in sediment metabolism, and (3) assess how differences in the sediment physical-chemical environment between seagrass taxa corresponds to variation in sediment metabolism. Physical structure will be characterized using CT imaging and geochemical patterns will be measured using planar optode imaging and targeted microprofiling. The structural and geochemical data will be integrated together using multiphysics modeling techniques to simulate geochemical permeance into the sediment around seagrass roots. These model results will then be compared to measurements of sediment metabolism from in situ benthic chambers to draw conclusions about the influence of roots on total sediment oxygenation and faunal behavior. The combination of non-destructive CT and planar optode imaging into a unified model will provide valuable information on the 3D structuring of seagrass sediments previously only described to a limited extent. The developed methodologies will also be of use to other researchers studying complexity in “opaque” systems, such as marshes, mangroves, and soils. By describing variation in below-ground structure, this work will provide a mechanistic understanding of its processes that can then be connected to larger-scale patterns in seagrass ecosystems, generating valuable knowledge for seagrass conservation, restoration, and management, and informing on seagrass susceptibility to climate change.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.