Collaborative Research: Multi-isotope and microbial ecology approaches to investigate sedimentary nitrous oxide production and consumption in the northern Benguela upwelling system

一氧化二氮（N2 O）是一种强有力的温室气体。它在破坏臭氧层方面也起着重要作用。海洋低氧环境中的微生物产生一氧化二氮，是大气中N2 O的重要来源。非洲西海岸外的北方本格拉上升流系统是主要的海洋缺氧区之一。尽管认识到北方本格拉上升流系统是一个重要的N2 O来源，它仍然是一个研究不足的生态系统，特别是沉积环境。在这项研究中，一个地球化学家和微生物生态学家小组将调查北方本格拉上升流系统沉积物中的N2 O循环。这项工作的目标是描述沉积物在这一特定系统中的作用，以及更广泛的作用，以提高科学家在不断变化的环境条件下预测这一重要温室气体未来排放的能力。该项目将资助南卡罗来纳州和佛罗里达州立大学的三名本科生和三名研究生。该项目包括与南非和纳米比亚的科学家合作。作为该项目的一部分，南卡罗来纳州大学将接待来自这些国家的学生进行为期六周的实习。该小组正在计划在美国和南部非洲开展大量的推广和教育活动。将利用两次机会巡航期间收集的样本来确定北方本格拉上升流系统中不同N2 O产生和消耗过程的贡献。将生成和合成浓度、稳定同位素和同位素异构体数据、15 N标记速率测量以及分子生态学数据，以确定1）N2 O的净沉积物-水柱通量，2）不同过程的N2 O产生和消耗速率，3）环境条件的控制（例如，氧（O2）、硫化氢（H2S）和营养物浓度、O2渗透深度以及有机物元素组成），以及4）测量速率与导致细菌、古生菌和微生物真核生物产生N2 O以及细菌和古生菌消耗N2 O的活性过程之间的联系。该项目将通过结合多同位素质量平衡和元基因组/转录组数据来解开这些不同过程的相对贡献。该研究将生成一个全面的数据集，其中包含有关古细菌，细菌（包括大型化学自养硫化物氧化细菌），真菌和其他微生物真核生物对环境条件下N2 O生产的贡献的新信息。沉积物数据将补充水柱N2 O浓度、稳定同位素、同位素异构体、速率测量和微生物生态学数据，这些数据是作为另外两个NSF的一部分同时收集的。沉积物和水柱N2 O数据将纳入三维氮基物理/地球化学模型。这些数据将有利于环境科学家，包括化学和生物海洋学家和地球化学建模者，以帮助改善海洋环境中温室气体排放的预测。该奖项反映了NSF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。

Nitrous oxide (N2O) is a potent greenhouse gas. It also plays an important role in the destruction of ozone. Nitrous oxide is produced by microorganisms in low-oxygen marine environments, which are important sources of N2O to the atmosphere. The northern Benguela Upwelling System off the west coast of Africa is one of the major oceanic Oxygen Deficient Zones (ODZs). Despite the recognition that the northern Benguela Upwelling System is a significant source of N2O, it remains an understudied ecosystem, particularly the sedimentary environment. In this study, a team of geochemists and microbial ecologists will investigate N2O cycling in northern Benguela Upwelling System sediments. The goal of the work is to describe the role of sediments both in this particular system and more broadly, in order to improve scientists’ ability to predict future emissions of this important greenhouse gas under changing environmental conditions. The project will support three undergraduates and three graduate students at the University of South Carolina (USC) and Florida State University. The project includes collaboration with scientists in South Africa and Namibia. The University of South Carolina will host students from each of these countries for six week internships as part of the project. The team is planning substantial outreach and educational activities in the U.S. and southern Africa.The contribution of different N2O producing and consuming processes in the northern Benguela Upwelling System will be determined with samples collected during two cruises of opportunity. Concentration, stable isotopic and isotopomer data, 15N-labeled rate measurements as well as molecular ecology data will be generated and synthesized to determine 1) the net sediment-water column flux of N2O, 2) N2O production and consumption rates for different processes, 3) controls by environmental conditions (e.g., oxygen (O2), hydrogen sulfide (H2S), and nutrient concentrations, O2 penetration depth, as well as organic matter elemental composition), and 4) the link between measured rates and the active processes that lead to N2O production by bacteria, archaea, and microbial eukaryotes, as well as bacterial and archaeal N2O consumption. This project will disentangle the relative contribution of these different processes by combining multi-isotope mass balance and meta-genomic/transcriptomic data. The study will generate a comprehensive dataset with new information on the contribution of archaea, bacteria (including large chemoautotrophic sulfide-oxidizing bacteria), fungi and other microbial eukaryotes for N2O production in relation to environmental conditions. The sediment data will complement water-column N2O concentration, stable isotope, isotopomer, rate measurement, and microbial ecology data collected concurrently as part of two other NSF). Sediment and water-column N2O data will be incorporated in a 3-dimensional nitrogen based physical/biogeochemical model. This data will be of interest to environmental scientists, including chemical and biological oceanographers and geochemical modelers, to help improve predictions of greenhouse gas emissions in marine environments.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.