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，生物地球化学机制发挥作用，以实现氮和磷之间的化学计量平衡。然而，在地方上，可能会出现不平衡。劳伦特五大湖是一个巨大的淡水系统，数十年来硝酸盐一直在稳步积累。以前的工作表明，在上级湖，该系统的源头，硝酸盐进入湖水主要是由于在湖泊生态地球化学过程，而不是由于被动积累的硝酸盐作为一个保守的物质，如以前所认为的。硝酸盐/磷酸盐比例的极端化学计量不平衡（约10，000摩尔）是存在的，并且显然正在增长。这组先前的发现提出了两个主要问题。 首先，使氮循环倾向于过量硝酸盐积累的主要地球化学控制点是什么？第二，极端的化学计量不平衡是如何影响苏必利尔湖上级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鲍林绿色州立大学的研究人员，他们以前记录了苏必利尔湖上级中硝酸盐的积累，将继续他们的研究计划，并解决这两个问题。 该项目的组织围绕氮同化，硝化，反硝化，厌氧氨氧化和微生物群落结构在上级湖和伊利湖中央盆地的比较测量。这两种环境在许多方面有很大的不同，包括氧化还原状态和有机碳的产生速率。从N平衡机制的角度来看，它们可以被认为是劳伦特五大湖内的终端成员。上级湖包含一个特有的异养和自养微生物的组合，而在伊利和其他五大湖的可比生物代表世界性的分支。超级上级湖的极端化学计量不平衡和独特的微生物组合之间的联系是未知的，但将在这项研究中进行检查。更多的数据将在五大湖上游的更大区域收集，包括休伦湖和密歇根湖北方。最新的质量平衡预算的氮的大部分五大湖（上级湖已经完成）将被构建和连接水文通量，以深入了解整个劳伦特五大湖系统的动态N。水化学观测将采用船上取样以及在浅水和深水沃茨实地部署的硝酸盐传感器。工艺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NH 4+吸收到不同的尺寸级分，交换不同形式的N和C之间的水柱和沉积物，硝化，反硝化和厌氧氨氧化。采用真实的实时定量PCR和DGGE技术研究了氨氧化古菌（AOA）和细菌（AOB）的多样性和丰度。同样，将研究浮游生物和厌氧氨氧化细菌的遗传组成，以确定它们是否也由苏必利尔湖上级的新分支代表。培养的硝化细菌将在不同条件下的生长方面的特点，通常横跨五大湖。该项目将产生有价值的信息，并深入了解氮循环的运作条件下，促进化学计量不平衡。更广泛的影响：劳伦特五大湖是一个宝贵的区域资源和一个巨大的水库行星淡水。苏必利尔湖上级通常被认为是相对原始的，但最终来源的氮转化为硝酸盐的湖泊是未知的，可能涉及过去的变化的分水岭或其他人为因素。该项目将支持在明尼苏达州和俄亥俄州培养博士后研究员和研究生。分配给BGSU的学生线将保留给BGSU-Lorain County Community College（LCCC）University Partnership BS的毕业生。生物学计划，一个创新的计划，旨在为洛兰和周边县的居民提供一个机会，在参加LCCC的同时，参加学士课程，这些县是俄亥俄州经济萧条的“锈带”的一部分。参加大学伙伴关系的学生参加NSF资助的本科生研究，这个项目将为LCCC学生提供一个机会，其中许多人被认为是“非传统”，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.