Biotic and Abiotic Controls on Nitrous Oxide Dynamics in Denitrifying Bioreactors

肥料用于各种农业实践，以提高作物产量，养活不断增长的美国和全球人口。然而，这种肥料的使用导致环境中活性氮（N）过量，影响水质并降低水体的商业和娱乐价值。 进入水体的大部分氮来自农业和雨水径流等来源。 木屑生物反应器（WBR）是一种低成本的方法来减少这些来源的氮污染，但它们也会产生一氧化二氮（N2 O），一种主要的温室气体和臭氧消耗物质。 本项目将探讨如何设计和操作WBR以减少N污染，同时最大限度地减少N2 O作为废物的释放。 该项目将为环境工程博士提供培训。学生，并将在干领域的本科研究助理提供研究经验。 社区外联将通过卡尤加湖浮动教室进行，这是一个基于船只的平台，供K-12学生和社区成员参与有关纽约手指湖水资源和质量的问题。如果成功，该项目将提供并完善一种保护国家水安全的低成本方法。工程和自然生态系统在陆地-水边界的非点源氮污染的缓解是至关重要的，但可以有反应性N和N2 O排放的生物去除之间的权衡。本项目的目标是推进机械理解的耦合之间的水-空气的质量传递和微生物转化的控制N2 O命运的环境中的陆地-水生界面，WBR选择作为一个代表性的系统进行调查。 这项研究的工作假设是，在多孔介质中的地下水位波动导致截留的空气相的孔隙结构中，和交换的氧气（O2）和N2 O之间的移动的水和非移动的气相是一个关键的影响N2 O积累内和出口WBR由于O2抑制微生物N2 O还原动力学和N2 O分配到气相。 该项目采用了补充技术，包括溶解气体和稳定同位素示踪测量和建模，定量成像和下一代测序，以解开微生物消耗气体转移对水性N2 O平衡的影响，并解释两相（空气-水）系统中的N2 O行为。 具体任务包括：1）用非平衡对流-弥散-传质模型解释溶解气体示踪实验数据，以量化水文状况对多孔介质中N2 O和O2两相传输的影响; 2）通过溶解O2和15 N同位素测量成像，评估水文驱动的O2交换对抑制微生物N2 O还原的作用;和3）通过宏基因组和基因表达分析评估最近鉴定的“进化枝II”N2 O还原微生物在调节WBR中N2 O命运中的作用。 这项研究的结果将推进一个统一的机制框架，整合生物和非生物过程控制的N2 O排放的水-陆界面，该奖项反映了NSF的法定使命，并被认为值得通过使用基金会的智力价值和更广泛的评估来支持。影响审查标准。

Fertilizer is used in various agricultural practices in order to increase the yield of crops to feed the growing US and global population. However, this fertilizer use has led to an excess of reactive nitrogen (N) in the environment that impacts water quality and reduces the commercial and recreational value of water bodies. A majority of the N entering water bodies is from sources such as agriculture and stormwater runoff. Woodchip bioreactors (WBRs) are a low-cost method to reduce N pollution from these sources, but they can also produce nitrous oxide (N2O), a major greenhouse gas and ozone-depleting substance. This project will explore how to design and operate WBRs to reduce N pollution while minimizing the release of N2O as a waste product. This project will provide training for an environmental engineering Ph.D. student and will provide research experiences for undergraduate research assistants in a STEM field. Community outreach will be conducted through the Cayuga Lake Floating Classroom, a boat-based platform for engagement of K-12 students and community members on issues relating to New York Finger Lakes water resources and quality. If successful, this project will provide and refine a low-cost method for protecting the Nation's water security. Engineered and natural ecosystems at land-water boundaries are critical for the mitigation of nonpoint source N pollution, but there can be tradeoffs between biological removal of reactive N and N2O emissions. The goal of this project is to advance mechanistic understanding of couplings between water-air mass transfer and microbial transformation as controls of N2O fate in environments at terrestrial-aquatic interfaces, with WBRs chosen as a representative system for investigation. The working hypothesis for this study is that water table fluctuations in porous media lead to entrapment of air phases in the pore structure, and that exchange of oxygen (O2) and N2O between the mobile water and immobile gas phase is a key influence on N2O accumulation inside and export from WBRs due to O2 inhibition of microbial N2O reduction kinetics and N2O partitioning into gas phases. This project employs complementary techniques including dissolved gas and stable isotope tracer measurements and modeling, quantitative imaging, and next-generation sequencing to disentangle the effects of microbial consumption from gas transfer on aqueous N2O balances and to account for N2O behavior in two-phase (air-water) systems. Specific tasks include: 1) Interpretation of dissolved gas tracer experimental data with nonequilibrium advection-dispersion-mass transfer models to quantify the impact of hydrologic regime on two-phase transport of N2O and O2 within porous media; 2) Evaluating the role of hydrologically-driven O2 exchange on inhibiting microbial N2O reduction via imaging of dissolved O2 and 15N isotope measurements; and 3) Evaluating the role of recently-identified "clade II" N2O-reducing microbes in regulating N2O fate in WBRs via metagenomic and gene expression analysis. Results of this research will advance a unified mechanistic framework to integrate biotic and abiotic process controls on N2O emissions from aquatic-terrestrial interfaces, and will inform the design and hydrologic management of WBRs and other engineered systems for the interception of nonpoint source nitrogen.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.