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案（公法111-5）资助的。在包括异质条件的大尺度上，生物地球化学机制的作用是实现氮和磷之间的化学计量平衡。然而，在局部地区，失衡可能会发展。劳伦森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。先前的研究表明，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生物地球化学过程，而不是由于硝酸盐作为一种保守物质的被动积累。硝酸盐/磷酸盐比率的极端化学计量不平衡（~ 10,000摩尔）是存在的，并且明显在增长。这组先前的发现揭示了两个主要问题。首先，使氮循环倾向于过量硝酸盐积累的主要生物地球化学控制点是什么？第二，极端的化学计量失衡是如何影响苏必利尔湖生物群的生态和进化的？在这个项目中，明尼苏达大学双城分校和州立鲍灵格林大学的研究人员将继续他们的研究项目，解决这两个问题，他们之前记录了苏必利尔湖的硝酸盐积累。该项目围绕着对苏必利尔湖和伊利湖中央盆地的N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生产速率。从氮平衡机制的角度来看，它们可以被认为是劳伦森大湖区的末端成员。苏必利尔湖包含了异养和自养微生物的地方性组合，而伊利湖和其他五大湖的可比生物则代表了世界性的进化枝。苏必利尔湖的极端化学计量失衡与独特的微生物组合之间的联系尚不清楚，但将在本研究中进行研究。更多的数据将在更大的上五大湖地区收集，包括休伦湖和密歇根湖北部。将构建大多数五大湖（苏必利尔湖已经完成）最新的氮质量平衡预算，并将其与水文通量联系起来，以深入了解整个劳伦森五大湖系统的氮动态。对水化学的观察将通过船上取样以及在浅水和深水中部署的硝酸盐传感器进行。过程研究将在水柱和沉积物-水界面进行，并将涉及敏感的稳定同位素技术。这些将包括测量NO3和NH4+被吸收成不同大小的馏分，水柱和沉积物之间不同形式的N和C的交换，硝化，反硝化和厌氧氨氧化。利用实时荧光定量PCR和DGGE技术研究氨氧化古菌（AOA）和细菌（AOB）的多样性和丰度。同样，反硝化菌和厌氧氨氧化菌的基因组成也将被研究，看看它们是否也以苏必利尔湖的新分支为代表。培养的硝化菌将在五大湖不同条件下的生长特征。该项目将为促进化学计量失衡的条件下氮循环的运作提供有价值的信息和见解。更广泛的影响：劳伦森五大湖是一个宝贵的区域资源和一个巨大的地球淡水水库。苏必利尔湖通常被认为是相对原始的，但湖中氮转化为硝酸盐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。该项目将支持在明尼苏达州和俄亥俄州培养一名博士后研究员和研究生。分配给BGSU的学生线路将保留给BGSU-Lorain县社区学院（LCCC）大学合作生物学学士学位课程的毕业生，这是一个创新的项目，旨在为Lorain及其周边县的居民提供一个在LCCC就读的同时参加学士课程的机会，这些县构成了俄亥俄州经济萧条的“铁锈地带”的一部分。参加大学合作伙伴关系的学生参加nsf资助的本科研究，该项目将为LCCC学生提供机会，其中许多人被认为是“非传统”的，他们将努力获得研究生学位。

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.