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(N2O)是一种强有力的温室气体。它在破坏臭氧方面也起着重要作用。一氧化二氮是由低氧海洋环境中的微生物产生的，是大气中N2O的重要来源。非洲西海岸的北部本格拉上升流系统是主要的海洋缺氧区之一。尽管人们认识到本格拉北部上升流系统是N2O的重要来源，但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，一组地球化学家和微生物生态学家将研究本格拉北部上升流系统沉积物中的N2O循环。这项工作的目标是描述沉积物在这一特定系统中以及更广泛的范围内所起的作用，以提高科学家在不断变化的环境条件下预测这种重要温室气体未来排放的能力。该项目将支持南卡罗来纳大学(USC)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，南卡罗来纳大学将接待这些国家的学生进行为期六周的实习。该小组正计划在美国和南部非洲开展大规模的外展和教育活动。本格拉北部上升流系统中不同的N2O产生和消费过程的贡献将通过在两次机会巡航中收集的样本来确定。将生成和合成稳定的同位素和同位素数据、15N标记的速率测量以及分子生态学数据，以确定1)N2O的沉积物-水柱净通量，2)不同过程的N2O产生和消耗速率，3)环境条件(例如氧气(O2)、硫化氢(H2S)、营养物质浓度、O2渗透深度以及有机质元素组成)的控制，以及4)测量的速率与导致细菌、古生物和微生物产生N2O的活跃过程以及细菌和古生物N2O消耗的活跃过程之间的联系。该项目将结合多同位素质量平衡和总基因组/转录组数据，理清这些不同过程的相对贡献。这项研究将生成一个全面的数据集，其中包含有关古生菌、细菌(包括大型化学自养硫化细菌)、真菌和其他微生物真核生物在环境条件下对N2O产生的贡献的新信息。沉积物数据将补充作为另外两个NSF的一部分同时收集的水柱N2O浓度、稳定同位素、同位素、速率测量和微生物生态数据)。沉积物和水柱N2O数据将被合并到基于氮的三维物理/生物地球化学模型中。这些数据将引起环境科学家的兴趣，包括化学和生物海洋学家和地球化学模型师，以帮助改进对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智力优势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.