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

合作研究：劳伦斯五大湖的蓝藻、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。伊利湖在夏季遭受每年反复出现的大规模有毒蓝藻水华，而苏必利尔湖在风暴事件后经历较小的局部蓝藻水华。蓝藻水华具有有害的生态、人类健康和经济影响。这些水华是一种全球现象，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，这两者都可能对生态系统有害。了解不同类型的蓝藻如何影响营养循环仍然是一个主要的知识空白。该项目旨在更深入地了解五大湖生态系统的长期状况。研究方法结合了新的和已有的方法。将与匹兹堡水研究、教育和推广合作实验室、五大湖委员会有害藻华合作和伊利湖地区研究网络合作，与当地和区域水资源利益方分享项目成果和影响。教育是该项目的核心部分，培训机会面向下一代科学家，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质微生物学领域接受最先进的培训，并与跨学科的科学家团队合作。这项研究将研究氮循环、浮游植物群落组成和氯化色素的氮同位素组成，以评估现代劳伦斯五大湖的蓝藻生产力以及过去数百年来蓝藻水华的历史记录。氯化色素的氮同位素组成有望为了解初级生产力和蓝藻对出口生产和氮循环的相对重要性提供一个强有力的新指标。这一代理不仅对现代系统的管理有价值，而且对增进我们对蓝藻在整个地球历史上的作用的理解也有重要的意义。该项目将在现代水生生态系统中测试这一分子同位素替代物，以评估其有效性：(1)确定蓝藻与真核藻类(例如硅藻)对初级生产力的相对贡献；(2)评估蓝藻生产力(包括水华)的出口产量；以及(3)在沉积记录中限制蓝藻的历史生产力。将以富营养化和季节性蓝藻水华为特征的系统(伊利湖)与以微微蓝藻生产力为特征但几乎没有大规模蓝藻水华的系统(苏必利湖)进行比较，将提供有关蓝藻可能对碳和氮循环产生影响的范围的信息。有关氮循环的更多信息将来自对整个年度循环的固体和溶解氮物种的分析，以及对沉积物过程的季节性研究，以通过不同的过程测量相关的沉积物氮去除速率。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势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.