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和东亚热带北太平洋地区的缺氧盆地调查非本地细菌硝酸盐运输和区域氮损失之间的联系。最近的研究表明，圣巴巴拉盆地的底栖生物硝酸盐消耗非常迅速（Sigman et al., 2003; Hammond et al., 2006）。然而，只有当SBB沉积物中硝酸盐吸收的很大一部分（可能高达100%）不涉及有机碳的呼吸作用，而是与硫化物的氧化作用相结合时，该盆地的N、S和C通量预算才可能得到满足。已知在该地区发现的细菌硫斑菌和Beggiatoa可在细胞内积聚高达500毫米的硝酸盐。它们将硝酸盐输送到沉积物中，深达数十厘米，在那里硝酸盐被用于硫化氢氧化。这种非局部硝酸盐运输（在层状沉积物中）显然中断了。成岩序的规律。SBB盆地、圣莫尼卡盆地和圣佩德罗盆地的初步工作提供了地球化学和同位素证据，这些证据与沉积物深处的细菌运输和随后的硝酸盐转化为二氮（N2）一致。该项目的研究人员假设，硝酸盐的非本地细菌运输可能是缺氧区区域和全球氮收支中一个重要但以前被忽视的汇。他们将(1)研究有利于硝酸盐非本地细菌运输的地球化学框架；(2)确定该过程对固定N区域净损失的相对贡献；(3)确定并量化该现象对上覆水柱中硝酸盐ä15N的影响；(4)研究微生物硝酸盐转运与其他还原硝酸盐反应（如厌氧氨氧化）的可能耦合。该项目包括一次前往圣佩德罗盆地的长途巡航和四次短途巡航，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。在附近的卡塔利娜岛正在进行的国际地球生物学夏季课程中，硝酸盐运输细菌的迹象已经并将继续成为一个感兴趣的话题。最后，该项目将支持一名年轻女性研究人员的科学发展。

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.