Collaborative Research: Cyanobacteria, Nitrogen Cycling, and Export Production in the Laurentian Great Lakes

合作研究：劳伦森五大湖的蓝藻、氮循环和出口生产五大湖拥有地球上约20%的淡水，近几十年来受到人类活动的影响越来越大。伊利湖在夏季遭受大规模的，每年重复的，有毒的蓝藻繁殖，而苏必利尔湖在风暴事件后经历较小的，局部的蓝藻繁殖。蓝藻大量繁殖对生态、人类健康和经济都有危害。这些水华是一种全球现象，可以在湖泊和海洋中观察到，并可能导致低氧条件和毒素的产生，这两种情况都可能对生态系统有害。了解不同类型的蓝藻如何影响养分循环仍然是一个主要的知识差距。该项目旨在对五大湖生态系统的长期状态提供更深入的了解。研究方法结合了新的和已有的方法。项目结果和影响将与匹兹堡水研究、教育和推广合作实验室、大湖委员会有害藻华合作组织和伊利湖地区研究网络合作，与当地和区域水利益相关者分享。教育是该项目的核心部分，培训机会针对下一代科学家，包括博士后、研究生和本科生。学生和博士后将在快速发展的生物地球化学和地球微生物学领域接受最先进的培训，同时与跨学科的科学家团队合作。本研究将研究氮循环、浮游植物群落组成和叶绿素的氮同位素组成，以评估现代劳伦森五大湖的蓝藻生产力，以及过去几百年来蓝藻大量繁殖的历史记录。叶绿素的氮同位素组成有望为了解蓝藻的初级生产力和对出口生产和氮循环的相对重要性提供强有力的新代理。这种代理不仅对现代系统的管理有价值，而且对增加我们对蓝藻在整个地球历史中的作用的理解具有重要意义。该项目将在当代水生生态系统中测试这种分子同位素代用物，以评估其功效：(1)确定蓝藻与真核藻类（如硅藻）对初级生产的相对贡献；(2)评估蓝藻产量的出口产量（包括繁殖）；(3)限制沉积记录中蓝藻的历史生产力。以富营养化和季节性蓝藻华（伊利湖）为特征的系统与以piccyanobacteria productivity为特征，但几乎没有大规模蓝藻华（苏必略湖）为特征的系统进行比较，将提供有关蓝藻对碳和氮循环影响范围的信息。关于氮循环的进一步信息将来自对整个年循环的固体和溶解氮种类的分析，以及沉积物过程的季节性研究，以测量通过不同过程相关的沉积物氮去除率。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Collaborative Research: Cyanobacteria, Nitrogen Cycling, and Export Production in the Laurentian Great LakesThe Great Lakes hold about 20% of the freshwater on Earth and have been increasingly impacted by human activities in recent decades. Lake Erie suffers from large, annually recurring, toxic cyanobacterial blooms in summer, whereas Lake Superior experiences smaller, localized cyanobacterial blooms after storm events. Cyanobacterial blooms have harmful ecological, human health, and economic implications. These blooms are a global phenomenon, observed in lakes and oceans, and can lead to low oxygen conditions and the production of toxins, both of which can be harmful for ecosystems. Understanding how different types of cyanobacteria influence nutrient cycling remains a major knowledge gap. This project aims to provide a deeper understanding of the long-term state of the Great Lakes ecosystem. The research approach combines new and established methods. Project results and implications will be shared with local and regional water interests in partnership with the Pittsburgh Collaboratory for Water Research, Education, and Outreach, the Great Lakes Commission Harmful Algal Blooms Collaborative, and the Lake Erie Area Research Network. Education is a central part of this project and training opportunities target next generation of scientists, including postdoctoral, graduate, and undergraduate students. The students and postdoc will receive state-of-the-art training in the rapidly developing fields of biogeochemistry and geomicrobiology, while working with an interdisciplinary team of scientists.This study will examine nitrogen cycling, phytoplankton community composition, and the nitrogen isotopic composition of chloropigments in order to evaluate cyanobacterial productivity in the modern Laurentian Great Lakes as well as the historical record of cyanobacterial blooms over the past several hundred years. The nitrogen isotope composition of chloropigments is expected to provide a powerful new proxy for understanding primary productivity and the relative importance of cyanobacteria to export production and nitrogen cycling. This proxy would be valuable not only for management of modern systems but has important implications for increasing our understanding of the role of cyanobacteria throughout Earth history. This project would test this molecular isotopic proxy in contemporary aquatic ecosystems to assess its efficacy for: (1) determining the relative contributions of cyanobacteria vs eukaryotic algae (e.g., diatoms) to primary production; (2) evaluating export production of cyanobacterial productivity (including blooms); and (3) constraining historical cyanobacteria productivity in the sedimentary record. Comparison of a system characterized by eutrophication and seasonal cyanobacterial blooms (Lake Erie) with one characterized by picocyanobacteria productivity, but the near-absence of large-scale cyanobacterial blooms (Lake Superior), will provide information about the range of impacts that cyanobacteria can have on carbon and nitrogen cycling. Further information regarding nitrogen cycling will be derived from analysis of solid and dissolved nitrogen species throughout the annual cycle, as well as seasonal studies of sediment processes to measure associated sediment nitrogen removal rates through different processes.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.