Collaborative research: Non-Local Bacterial Transport of Nitrate within Sediments Underlying Oxygen Deficient Zones: A New Twist in the N Cycle

在这个项目中，南加州大学和普林斯顿大学的研究人员将在南加州海岸外的缺氧盆地和东亚热带北太平洋地区调查非本地细菌硝酸盐运输与区域性氮损失之间的联系。最近的研究表明，圣巴巴拉盆地底栖硝酸盐的消耗非常迅速(Sigman等人，2003年；Hammond等人，2006年)。然而，只有当SBB沉积物中的大部分硝酸盐吸收不涉及有机碳的呼吸，而是耦合到硫化物的氧化时，该流域的N、S和C通量的预算可能才能满足要求。在这一地区发现的细菌Thiopoca和Beggiatoa，已知在细胞内积累了多达500毫米的硝酸盐。它们将硝酸盐输送到沉积物中，深度可达数十厘米，在那里硝酸盐被用于硫化氢的氧化。这种非本地硝酸盐运移(在层状沉积物中)明显？中断？成岩序列的规律。在SBB、圣莫尼卡和圣佩德罗盆地的初步工作产生了地球化学和同位素证据，这与细菌在沉积物深处的运输以及随后硝酸盐向氮素(N_2)的转化一致。参与该项目的研究人员假设，硝酸盐的非局部细菌运输可能是缺氧地区区域和全球N收支中一个重要的、但以前被忽视的汇。他们将(1)检查有利于硝酸盐非本地细菌运输的地球化学框架；(2)确定这一过程对固定氮区域净损失的相对贡献；(3)确定和量化这一现象对上覆水柱中硝酸盐的ä15N的影响；以及(4)调查微生物硝酸盐运输与其他还原硝酸盐的反应(如Anammox)的可能耦合。该项目包括一次长途航行和四次短暂的圣佩德罗盆地航行，将为南加州大学和普林斯顿大学的本科生和研究生参与海洋学研究提供一个框架。携带硝酸盐的细菌的迹象一直是并将继续是在附近卡塔利纳岛举行的国际地质生物学夏季课程的一个感兴趣的话题。最后，这个项目将支持一位年轻的女研究人员的科学发展，她带头提出了这项建议。

In this project, researchers at the University of Southern California and Princeton University will investigate the link between non-local bacterial nitrate transport and regional nitrogen losses in oxygen deficient basins off the Southern California coast and regions of the Eastern Subtropical North Pacific. Recent studies suggest remarkably rapid benthic nitrate consumption in the Santa Barbara Basin (Sigman et al., 2003; Hammond et al., 2006). Yet, budgets for N, S and C fluxes in this basin may be only satisfied if a large fraction (up 100 % potentially) of nitrate uptake in SBB sediments does not involve the respiration of organic carbon, but instead is coupled to oxidation of sulfides. The bacteria Thioploca and Beggiatoa, found in this region, are known to accumulate up to 500 mM of nitrate intracellularly. They transport nitrate into the sediments, up to depths of tens of centimeters where nitrate is used for hydrogen sulfide oxidation. This non-local nitrate transport (within laminated sediments) clearly ?breaks? the rules of diagenetic sequence. Preliminary work in SBB and Santa Monica and San Pedro Basins produced geochemical and isotopic evidence which is consistent with bacterial transport and subsequent transformation of nitrate to dinitrogen (N2) at depth in the sediments.The researchers on this project hypothesize that non-local bacterial transport of nitrate may be a significant but previously overlooked sink in the regional and global N budgets of oxygen deficient zones. They will (1) examine the geochemical framework favorable for non-local bacterial transport of nitrate; (2) determine the relative contribution of this process to net regional losses of fixed N; (3) identify and quantify the effects of this phenomenon on the ä15N of nitrate in the overlying water column; and (4) investigate the possible coupling of microbial nitrate transport to other reactions that reduce nitrate, such as Anammox.This project, which includes one long cruise and four brief cruises to San Pedro Basin, will provide a framework for potential involvement of USC and Princeton undergraduate and graduate students in oceanographic research. The tell-tale signs of nitrate-transporting bacteria have been and will continue to be a topic of interest in the ongoing International Geobiology summer course on nearby Catalina Island. Finally, this project will support the scientific development of a young female researcher who spear-head this proposal.