Collaborative Research: Linking iron and nitrogen sources in an oligotrophic coastal margin: Nitrogen fixation and the role of boundary fluxes

合作研究：连接寡营养海岸边缘的铁和氮源：固氮和边界通量的作用

• 批准号: 2149091
• 负责人: Rene Boiteau
• 金额: $ 32.35万
• 依托单位: Oregon State University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2022
• 资助国家: 美国
• 起止时间: 2022-05-01 至 2024-03-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2149091&HistoricalAwards=false
• 关键词: Collaborative; Research; Linking; iron; nitrogen

This project will investigate how groundwater discharge delivers important nutrients to the coastal ecosystems of the West Florida Shelf. Preliminary studies indicate that groundwater may supply both dissolved organic nitrogen (DON) and iron in this region. In coastal ecosystems like the West Florida Shelf that have very low nitrate and ammonium concentrations, DON is the main form of nitrogen available to organisms. Nitrogen cycling is strongly affected by iron availability because iron is essential for both photosynthesis and for nitrogen fixation. This study will investigate the sources and composition of DON and iron, and their influence on the coastal ecosystem. The team will sample offshore groundwater wells, river and estuarine waters, and conduct two expeditions across the West Florida Shelf in winter and summer. Investigators will participate in K-12 and outreach activities to increase awareness of the project and related science. The project will fund the work of six graduate and eight undergraduate students across five institutions, furthering NSF’s goals of education and training. Motivated by preliminary observations of unexplained, tightly-correlated DON and dissolved iron concentrations across the West Florida Shelf (WFS), the proposed work will quantify the flux and isotopic signatures of submarine groundwater discharge (SGD)-derived DON and iron to the WFS, and evaluate the bioavailability of this temporally-variable source using four seasonal near-shore campaigns sampling offshore groundwater wells, estuarine, and riverine endmembers and two cross-shelf cruises. The work will evaluate whether SGD stimulates nitrogen fixation on the WFS, and the potential for the stimulated nitrogen fixation to further modify the chemistry of DON and dissolved iron in the region. The cross-shelf cruises will investigate hypothesized periods of maximum SGD and Trichodesmium abundance (June), and reduced river discharge and SGD (February), thus comparing two distinct biogeochemical regimes. The concentrations and isotopic compositions of DON and dissolved iron, molecular composition of DON, and the concentration and composition of iron-binding ligands will be characterized. Nitrogen fixation rates and Trichodesmium spp. abundance and expression of iron stress genes will be measured. Fluxes of DON and iron from SGD and rivers will be quantified with radium isotope mass balances. The impacts of SGD on nitrogen fixation and DON/ligand production will be constrained with incubations of natural phytoplankton communities with submarine groundwater amendments. Two hypotheses will be tested: 1) SGD is the dominant source of bioavailable DON and dissolved iron on the WFS, and 2) SGD-alleviation of iron stress changes the dominant Trichodesmium species on the WFS, increases nitrogen fixation rates and modifies DON and iron composition. Overall, the work will establish connections between marine nitrogen and iron cycling and evaluate the potential for coastal inputs to modify water along the WFS before export to the Atlantic Ocean. This study will thus provide a framework to consider these boundary fluxes in oligotrophic coastal systems and the relative importance of rivers and SGD as sources of nitrogen and iron in other analogous locations, such as coastal systems in Australia, India, and Africa, where nitrogen fixation and SGD have also been documented.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.

该项目将调查地下水排放方式如何为西佛罗里达州货架的沿海生态系统提供重要的营养。初步研究表明，地下水可以在该地区提供溶解的有机氮（DON）和铁。在诸如西佛罗里达州货架等硝酸盐和铵浓度非常低的沿海生态系统中，DON是生物体可用的氮的主要形式。氮循环受铁可用性的强烈影响，因为铁对于光合作用和氮固定都是必不可少的。这项研究将研究DON和铁的来源和组成，及其对沿海生态系统的影响。该团队将品尝离岸地下水井，河流和河口水域，并在冬季和夏季进行两次探险。调查人员将参加K-12和外展活动，以提高对项目和相关科学的认识。该项目将资助六个毕业生和八个基础学生的工作，从而进一步促进NSF的教育和培训目标。受到西佛罗里达州货架（WFS）的意外，紧密相关的DON和溶解的铁浓度的初步观察的动机，拟议的工作将量化潜艇地下水放电（SGD）don and Iron don and Iron don and Iron don and Iron to wfs的范围和临时临时序列的临时，并评估了临时的临时季节，并量化了临时的don and Iron。地下水井，河口和河流末端成员以及两次跨架巡游。这项工作将评估SGD是否刺激WFS上的氮固定，以及受刺激的氮固定的潜力，以进一步改变该地区DON和溶解铁的化学性质。跨货架巡航将调查最大SGD和TrichodeSmium丰度的假设时期（6月），以及减少的河流排放和SGD（2月），从而比较了两个不同的生物地球化学制度。将表征DON和溶解铁的浓度和同位素组成，DON的分子组成以及铁结合配体的浓度和组成。氮固定速率和毛状属属。将测量铁应激基因的丰度和表达。来自SGD和河流的DON和铁的通量将通过径向同位素质量平衡来定量。 SGD对氮固定和DON/配体产生的影响将受到与海底地下水修正案的天然浮游植物群落的孵育。将测试两个假设：1）SGD是WFS上可生物可利用的DON和溶解铁的主要来源，2）铁应力的SGD升级会改变WFS上的主要毛状毛虫物种，增加了氮固定速率，并提高了Don and Iron和铁的成分。总体而言，这项工作将建立海洋氮与铁循环之间的联系，并评估沿海投入的潜力，以在出口到大西洋之前修改沿WFS的水。因此，这项研究将提供一个框架，以考虑少亲子沿海系统中的这些边界通量，以及河流和SGD作为其他类似位置的氮和铁的相对重要性，例如澳大利亚，印度和非洲的沿海系统，例如氮气固定和SGD的诚实授予，并已通过nsf的授权进行了证明。优点和更广泛的影响审查标准。