Collaborative Research: Sources and Sinks of Stoichiometrically Imbalanced Nitrate in the Laurentian Great Lakes

该奖项是根据2009年《美国复苏和再投资法》(公法111-5)资助的。在涵盖不同条件的大范围内，生物地球化学机制旨在实现氮和磷之间的化学计量平衡。然而，在当地，失衡可能会发展。劳伦斯五大湖是一个巨大的淡水系统，几十年来硝酸盐一直在稳步积累。以往的研究表明，在该系统的源头苏必利尔湖，硝酸盐进入湖水主要是由于湖内的生物地球化学过程，而不是像以前认为的那样，由于硝酸盐作为一种保守物质的被动积累。硝酸盐/磷酸盐的化学计量比存在极端的不平衡(约10,000摩尔)，而且还在明显增加。这组先前的发现揭示了两个主要问题。首先，哪些主要的生物地球化学控制点使N循环倾向于过量硝酸盐的积累？第二，极端的化学计量比失衡如何影响苏必利尔湖生物群的生态和进化？在这个项目中，明尼苏达双城大学和保龄格林州立大学的研究人员之前记录了苏必利尔湖中硝酸盐的积累，他们将继续他们的研究计划，并解决这两个问题。该项目围绕着对苏必利尔湖和伊利湖中央流域的氮同化、硝化、反硝化、厌氧氨氧化和微生物群落结构进行比较测量。这两种环境在许多方面都有很大的不同，包括氧化还原状态和有机碳的产生率。从氮平衡机制的角度来看，它们可以被视为劳伦斯五大湖的最终成员。苏必利尔湖包含异养和自养微生物的特有组合，而伊利湖和其他五大湖的可比生物代表着世界性的分支。苏必利尔湖极端的化学计量失衡和独特的微生物组合之间的联系尚不清楚，但将在这项研究中进行检验。将在包括休伦湖和密歇根湖北部在内的上五大湖更大的区域收集更多数据。将编制大多数五大湖(苏必利尔湖已经完成)的最新氮素质量平衡预算，并将其与水文通量联系起来，以深入了解整个劳伦斯五大湖系统的氮素动态。在浅水和深水水域，将通过船上采样和现场部署的硝酸盐传感器进行水化学观测。将在水柱和沉积物-水界面进行工艺研究，并将涉及敏感的稳定同位素技术。这些将包括测量不同粒级的NO3和NH4+的吸收，不同形式的N和C在水柱和沉积物之间的交换，硝化，反硝化和厌氧氨氧化。利用实时荧光定量聚合酶链式反应和凝胶电泳法对氨氧化古生菌和细菌的多样性和丰度进行了研究。同样，将研究反硝化细菌和厌氧氨氧化细菌的遗传组成，看看它们是否也被苏必利尔湖的新分支所代表。培养的硝化细菌的特征是在不同的条件下生长，通常是在五大湖上遇到的。该项目将提供有价值的信息和洞察氮循环在促进化学计量不平衡的条件下的运行情况。苏必利尔湖通常被认为是相对原始的，但湖中转化为硝酸盐的氮的最终来源尚不清楚，可能涉及过去分水岭的变化或其他人为因素。该项目将支持明尼苏达州和俄亥俄州的博士后研究员和研究生的培训。分配给北卡罗来纳州立大学的学生队伍将保留给北卡罗来纳州立大学-洛雷恩县社区学院(LCCC)大学合作生物学士项目的毕业生，该项目是一个创新项目，旨在为洛雷恩及周边县的居民提供在就读LCCC期间注册学士项目的机会。洛雷恩及周边县是俄亥俄州经济低迷的“锈带”的一部分。参加大学伙伴关系的学生参与NSF资助的本科生研究，这个项目将为LCCC的学生提供一个机会，他们中的许多人被认为是“非传统的”，为获得研究生学位而努力。

This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).Over large scales encompassing heterogeneous conditions, biogeochemical mechanisms act to achieve a stoichiometric balance between nitrogen and phosphorus. Locally, however, imbalances can develop. The Laurentian Great Lakes are a vast freshwater system where nitrate has been steadily accumulating for decades. Previous work has shown that in Lake Superior, the headwaters of the system, nitrate enters the lake water primarily due to in-lake biogeochemical processes, not due to passive accumulation of nitrate as a conservative substance as previously believed. An extreme stoichiometric imbalance of nitrate/phosphate ratios (~ 10,000 by moles) is present and is apparently growing. This set of prior findings opens up two major questions. First, what are the principal biogeochemical control points that tip the N cycle toward buildup of excess nitrate? And second, how does the extreme stoichiometric imbalance affect the ecology and evolution of Lake Superior's biota? In this project, researchers at the University of Minnesota - Twin Cities and the Bowling Green State University, who previously documented the nitrate buildup in Lake Superior, will continue their research program and address these two questions. The project is organized around making comparative measurements of N assimilation, nitrification, denitrification, anammox, and microbial community structure in Lake Superior and in the central basin of Lake Erie. These two environments differ greatly in many ways including redox state and organic carbon production rates. From the standpoint of N balancing mechanisms, they can be considered end members within the Laurentian Great Lakes. Lake Superior contains an endemic assemblage of heterotrophic and autotrophic microbes, whereas the comparable organisms in Lake Erie and other Great Lakes represent cosmopolitan clades. Connections between the extreme stoichiometric imbalance in Lake Superior and the unique microbial assemblage are unknown but will be examined in this study. Additional data will be collected across a larger region of the Upper Great Lakes including Lake Huron and northern Lake Michigan. Up-to-date mass balance budgets of nitrogen of the most of the Great Lakes (Lake Superior is already done) will be constructed and linked with hydrologic fluxes to gain insights into the dynamics of N across the entire Laurentian Great Lakes System. Observations of water chemistry will be made with ship-board sampling together with field-deployed nitrate sensors in shallow and deep waters. Process studies will be performed in the water column and at the sediment-water interface and will involve sensitive stable isotope techniques. These will include measurements of NO3 and NH4+ uptake into different size fractions, exchanges of different forms of N and C between the water column and sediments, nitrification, denitrification, and anammox. The diversity and abundance of ammonia oxidizing Archea (AOA) and bacteria (AOB) will be studied using quantitative real time PCR and DGGE. Similarly, the genetic composition of denitrifyers and anammox bacteria will be studied to see if they too are represented by novel clades in Lake Superior. Cultured nitrifyers will be characterized in terms of growth under different conditions typically encounterd across the Great Lakes. The project will yield valuable information and insight into the operation of the nitrogen cycle under conditions that promote stoichiometric imbalances.Broader Impacts: The Laurentian Great Lakes are a valuable regional resource and an immense reservoir of planetary fresh water. Lake Superior is often considered to be relatively pristine but the ultimate source of the N converted to nitrate in the lake is as yet unknown and may involve past changes to the watershed or other anthropogenic factors. This project will support the training of a Postdoctoral researcher and graduate students both in Minnesota and in Ohio. The student line allocated to BGSU will be reserved for a graduate of the BGSU-Lorain County Community College (LCCC) University Partnership B.S. in Biology program, an innovative program created to provide the residents of Lorain and surrounding counties, which form part of Ohio's economically-depressed "rust belt", a chance to enroll in bachelors programs while attending LCCC. Students enrolled in the University Partnership participate in NSF-funded undergraduate research and this project will afford an opportunity for a LCCC student, many of whom are considered "non-traditional", to work towards earning a graduate degree.