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: 2148989
• 负责人: Angela Knapp
• 金额: $ 55.92万
• 依托单位: Florida 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 2025-04-30
• 项目状态: 未结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2148989&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如何向西佛罗里达大陆架的沿海生态系统输送重要的营养物质。初步研究表明，地下水可能同时供应该地区的溶解有机氮和铁。在像西佛罗里达大陆架这样的沿海生态系统中，硝酸盐和铵的浓度非常低，DON是生物可利用的氮的主要形式。氮循环受到铁有效性的强烈影响，因为铁对光合作用和固氮都是必不可少的。本研究将探讨DON和铁的来源、组成及其对沿海生态系统的影响。科考队将对近海地下水井、河流和河口水域进行取样，并在冬季和夏季对西佛罗里达大陆架进行两次考察。研究人员将参加K-12和外展活动，以提高对该项目和相关科学的认识。该项目将资助5个机构的6名研究生和8名本科生的工作，进一步推进NSF的教育和培训目标。在对西佛罗里达大陆架（WFS）不明原因的、紧密相关的DON和溶解铁浓度的初步观察的推动下，本研究将量化海底地下水排放（SGD）产生的DON和铁到WFS的通量和同位素特征，并通过四个季节性近岸运动，采样海上地下水井、河口和河流末端成员，以及两次跨大陆架巡航，评估这种临时变化源的生物利用度。这项工作将评估SGD是否会刺激WFS上的固氮，以及受刺激的固氮是否会进一步改变该地区DON和溶解铁的化学性质。跨大陆架巡航将调查假设的SGD和Trichodesmium丰度最大的时期（6月），以及河流流量和SGD减少的时期（2月），从而比较两种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。测定固氮率、铁胁迫基因丰度和表达量。用镭同位素质量平衡定量分析SGD和河流中DON和铁的通量。SGD对固氮和DON/配体产生的影响将受到天然浮游植物群落与海底地下水修正的孵育的限制。本文将验证两种假设：1)SGD是WFS上生物可利用DON和溶解铁的主要来源；2)SGD对铁胁迫的缓解改变了WFS上的优势Trichodesmium物种，增加了固氮速率，改变了DON和铁的组成。总的来说，这项工作将建立海洋氮和铁循环之间的联系，并评估沿海输入在出口到大西洋之前改变WFS沿岸水的潜力。因此，本研究将提供一个框架来考虑这些贫营养海岸系统中的边界通量，以及河流和SGD作为其他类似地点氮和铁来源的相对重要性，如澳大利亚、印度和非洲的海岸系统，在这些地方，固氮和SGD也有记录。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

项目成果

Defining the Realized Niche of the Two Major Clades of Trichodesmium: A Study on the West Florida Shelf

• DOI: 10.3389/fmars.2022.821655
• 发表时间: 2022-06
• 作者: Kristina A. Confesor;C. Selden;K. E. Powell;Laura A. Donahue;T. Mellett;S. Caprara;A. Knapp;K. Buck;P. Chappell

Quantitative and qualitative comparison of marine dissolved organic nitrogen recovery using solid phase extraction

固相萃取回收海洋溶解有机氮的定量和定性比较

• DOI: 10.1002/lom3.10558
• 发表时间: 2023
• 期刊: Limnology and Oceanography: Methods
• 作者: Miranda, Carlos;Boiteau, Rene M.;McKenna, Amy M.;Knapp, Angela N.
• 通讯作者: Knapp, Angela N.