Collaborative research: The Nitrifying of Lake Superior and Its Intersections with the P and Fe Cycles

摘要：在过去的世纪，苏必利尔湖上级沃茨中硝酸盐的浓度从大约2000年的2000年增加了6倍。五是以。30 μ mol L ~（-1）。 今天，硝酸盐在生长季节结束时仍然超过生物需求。虽然氮浓度的增加并不令人惊讶，但考虑到苏必利尔湖长达50年的氮周转率，以及主要森林流域缺乏重要的当地氮源，苏必利尔湖的增加幅度和速度是令人惊讶的。为了阐明这种令人印象深刻的硝酸盐积累的原因，来自明尼苏达大学、鲍林绿色州立大学和罗格斯大学的研究人员将对苏必利尔湖的上级氮循环进行研究，并结合限制营养物质和浮游生物群落对不同营养物质供应制度的反应的研究。硝化和反硝化速率，以前假定为零，将测量稳定同位素示踪剂和其他方法。 硝酸盐湖的来源和转化将使用氮和氧的稳定同位素在湖泊，溪流和河流，以及在大气中的天然丰度进行跟踪。 除了测试硝酸盐吸收的限制外，科学家团队还将探索这个大湖中的N循环及其与P和Fe循环的交叉点。 磷的缺乏，沿着寒冷和黑暗的物理条件，可能是理解缺乏生态系统同化添加的硝酸盐的重要因素。铁也可能发挥重要作用，因为它在浮游生物利用硝酸盐中起着关键作用。事实上，可能是铁的缺乏限制了浮游生物利用硝酸盐的能力，使得浮游生物即使在硝酸盐过剩的情况下也是氮缺乏的。 除了开发一个新的水柱氮模型和数据集的几个地球化学不同池溶解的磷和铁（与空间和时间覆盖大部分的湖泊），这项研究也将产生一个显着改善知识的氮循环在世界上最大的湖泊。

ABSTRACTOCE- 0352291 / OCE- 0352274 / OCE 0352208The concentration of nitrate in Lake Superior waters has increased steadily during the past century by six-fold from ca. 5 to ca. 30 umol L-1. Today, nitrate remains in excess of biotic demand at the end of the growing season. Though the increase in nitrogen concentration is not surprising, the magnitude and rate of increase in Lake Superior are, considering the long, fifty-year N turnover rate of the lake, and the absence of significant local sources of N to the mainly forested watershed. To elucidate the causes of this impressive nitrate build up, researchers from the University of Minnesota, Bowling Green State University, and Rutgers University will undertake studies of the Lake Superior nitrogen cycle, combined with studies of limiting nutrients and the responses of plankton communities to differing nutrient supply regimes. Nitrification and denitrification rates, previously assumed to be zero, will be measured with stable isotope tracers and with other methods. Sources and transformations of the lakes nitrate will be traced using natural abundances of stable isotopes of nitrogen and oxygen in the lake, in streams and rivers, and in atmospheric sources. In addition to testing the limitation on nitrate uptake, the team of scientists will also explore the N cycle and its intersection with the P and Fe cycles in this large lake. Shortages of P, along with cold and dark physical conditions, are likely important factors in understanding lack of ecosystem assimilation of added nitrate. Iron too may play an important role because of its critical role in nitrate utilization by plankton. Indeed, it may be that absence of iron limits the ability of the plankton to utilize nitrate such that the plankton are N deficient even in the presence of nitrate surplus. In addition to developing a new water column nitrogen model and data sets for several geochemically distinct pools of dissolved P and Fe (with both spatial and temporal coverage of large portions of the lake) this research will also yield a dramatically improved knowledge of the nitrogen cycle in the worlds' largest lake.