Unlocking the noble gas toolbox to quantify rates of denitrification and nitrogen fixation in marine systems

海洋生产力取决于氮的可用性。大气中78%是氮气，但这种形式的氮气对大多数生物来说是无用的。氮气溶解在海洋中，并通过固氮转化或固定为更活跃的形式。进入海洋的活性氮通过反硝化作用被逆转，反硝化作用将活性氮转化为氮气。测量固氮和反硝化之间的平衡是具有挑战性的，因为这些过程的速率相对于氮气的大量库存来说很小。此外，生物和物理过程都会影响氮气库存。研究人员将开发一种新方法来测量不受生物过程影响的三种稀有气体（氖气、氩气和氪气）以及氮气。他们将使用这种方法来量化固定氮平衡：固定氮产量减去固定氮损失率。这种方法有许多应用，包括确定营养管理策略以支持健康的沿海生态系统。这项工作将产生新的研究基础设施、教育材料和多样化的劳动力，从而造福社会。研究人员将开发测量固定氮平衡的技术。他们将准备一个关于康涅狄格州营养物污染的大学和高中课程模块。该模块将描述人类如何识别污染物的危害，并通过立法制定解决方案。这项工作将支持一名早期职业女性调查员、一名女性研究生和一名早期职业西班牙裔实验室经理。研究人员试图通过将多种惰性气体的测量纳入现有方案，提高广泛使用的测定底栖生物固定氮产生/去除的孵化技术（氮/氩技术和氮同位素配对技术）的可靠性。他们将确定在哪些条件下物理扰动会影响计算的氮通量，并制定定量方法来纠正这些影响。此外，研究人员将开发并演示一种通过原位测量在生态系统尺度上测量净生物氮通量的新方法，这将使监测动态海岸系统中固定氮的去除和产生成为可能。改进限制生物氮通量的工具将有助于解决最近关于海岸系统固定氮平衡的问题，并提高对海岸系统减弱富营养化能力的科学认识。研究人员将开发一种高精度、高通量的惰性气体分析方法，该方法改编自现有的商用仪器，并与科学界共享该方法。这项工作将使其他研究人员能够应用惰性气体测量来解决广泛的生物地球化学研究问题。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。

Ocean productivity depends on nitrogen availability. The atmosphere is 78% nitrogen gas, but this form of nitrogen is unusable to most organisms. Nitrogen gas dissolves in the ocean and is converted, or fixed, into more reactive forms through nitrogen fixation. Reactive nitrogen inputs to the oceans are reversed through denitrification, which converts reactive nitrogen to nitrogen gas. Measuring the balance between nitrogen fixation and denitrification is challenging because the rates of these processes are small relative to the large inventory of nitrogen gas. Also, biological and physical processes both impact the nitrogen gas inventory. The researchers will develop a new method to measure three noble gases (neon, argon, and krypton), which are not impacted by biological processes, as well as nitrogen gas. They will use this method to quantify the fixed nitrogen balance: the rate of fixed nitrogen production minus fixed nitrogen loss. This method has many applications, including identifying nutrient management strategies to support healthy coastal ecosystems. The work will benefit society by generating new research infrastructure, educational materials, and a diverse workforce. The researchers will develop technology to measure the fixed nitrogen balance. They will prepare a college and high school course module about nutrient pollution in Connecticut. The module will describe how humans have identified harms of pollutants and developed solutions through legislation. The work will support an early-career female investigator, a female graduate student, and an early-career Hispanic lab manager.The researchers seek to improve the reliability of widely used incubation techniques for determining benthic fixed nitrogen production/removal (the nitrogen/argon technique and nitrogen isotope pairing technique) by incorporating measurements of multiple noble gases into existing protocols. They will identify under which conditions physical perturbations can impact the calculated nitrogen fluxes and develop quantitative methods to correct for these effects. Additionally, the researchers will develop and demonstrate a new method for measuring net biological nitrogen fluxes at the ecosystem scale through in situ measurements, which will enable monitoring of fixed nitrogen removal and production in dynamic coastal systems. Improved tools for constraining biological nitrogen fluxes will help to resolve recent questions regarding the fixed nitrogen balance in coastal systems and improve scientific understanding of the capacity of coastal systems to attenuate eutrophication. The researchers will develop a high-precision, high-throughput method for noble gas analysis that is adapted from existing commercially available instrumentation and share the method with the scientific community. This work will enable other researchers to apply noble gas measurements to address a wide range of biogeochemical research questions.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.