The biotic and abiotic controls on the Silicon cycle in the northern Gulf of Mexico

位于墨西哥湾北方的路易斯安那大陆架系统由密西西比河及其许多支流提供水源，这些支流从农业肥料中为该地区提供了大量营养物质。 这些营养物质的输入，特别是氮，导致了富营养化。 富营养化是一个过程，其中水体如路易斯安那大陆架变得富含溶解的营养物，增加浮游植物的生长，最终导致底部沃茨的氧气水平降低。 这一点在这一地区确实观察到了，硅藻是一种代表食物链基础的浮游植物，其硅/氮（Si/N）比率存在变化。 由于硅藻的外壳是由硅形成的，它们的生长不仅受氮的输入控制，还受硅的可用性控制。 较低的Si/N比表明，硅可能在调节系统中的硅藻生产中发挥越来越重要的作用。 因此，南亚拉巴马大学的一位科学家将确定控制路易斯安那大陆架系统硅/氮比变化的地球化学过程。 作为该项目的一部分，一名正在攻读博士学位的研究生和三名本科生将得到支持和培训。 此外，四个奖学金的低收入，高中学生从标题1学校将获得参加为期一个月的夏季海洋科学课程在多芬岛海洋实验室，并被列入研究项目。 这项研究具有重大的社会效益，因为这是一个2.4万亿美元国内生产总值收入与沿海资源挂钩的领域。 由于硅藻是在食物链的基础上，是生物控制说，沿海资源，硅藻的生长响应于富营养化是很重要的研究。富营养化的密西西比河及其支流有可能改变生物景观的路易斯安那州陆架系统在墨西哥湾北方的影响硅/氮比低于那些是最佳的硅藻生长。 南亚拉巴马大学的一位科学家认为，观察到的硅/氮比的变化可能表明硅现在在调节系统中硅藻的生产方面起着重要作用。 因此，了解控制硅循环的生物和非生物过程至关重要，因为硅藻在这个高产地区的食物链基础上占主导地位。 该研究将重点关注以下问题：（1）回收硅源对硅藻生产的重要性;（2）重硅化硅藻能否比轻硅化硅藻更有效地适应Si/N比的变化;和（3）反向风化在封存硅中的作用，从而减少扩散孔隙水运输。 为了实现这些目标，将使用一种新的分析方法，定量测量分类群特异性二氧化硅产生的PDMPO方法（化合物2-（4-吡啶基）-5-（（4-（2-二甲基氨基乙基氨基-氨基甲酰基）甲氧基）苯基）恶唑）。

The Louisiana Shelf system in the northern Gulf of Mexico is fed by the Mississippi River and its many tributaries which contribute large quantities of nutrients from agricultural fertilizer to the region. Input of these nutrients, especially nitrogen, has led to eutrophication. Eutrophication is the process wherein a body of water such as the Louisiana Shelf becomes enriched in dissolved nutrients that increase phytoplankton growth which eventually leads to decreased oxygen levels in bottom waters. This has certainly been observed in this area, and diatoms, a phytoplankton which represents the base of the food chain, have shown variable silicon/nitrogen (Si/N) ratios. Because diatoms create their shells from silicon, their growth is controlled not only by nitrogen inputs but the availability of silicon. Lower Si/N ratios are showing that silicon may be playing an increasingly important role in regulating diatom production in the system. For this reason, a scientist from the University of South Alabama will determine the biogeochemical processes controlling changes in Si/N ratios in the Louisiana Shelf system. One graduate student on their way to a doctorate degree and three undergraduate students will be supported and trained as part of this project. Also, four scholarships for low-income, high school students from Title 1 schools will get to participate in a month-long summer Marine Science course at the Dauphin Island Sea Laboratory and be included in the research project. The study has significant societal benefits given this is an area where $2.4 trillion gross domestic product revenue is tied up in coastal resources. Since diatoms are at the base of the food chain that is the biotic control on said coastal resources, the growth of diatoms in response to eutrophication is important to study.Eutrophication of the Mississippi River and its tributaries has the potential to alter the biological landscape of the Louisiana Shelf system in the northern Gulf of Mexico by influencing the Si/N ratios below those that are optimal for diatom growth. A scientist from the University of South Alabama believes the observed changes in the Si/N ratio may indicate silicon now plays an important role in regulating diatom production in the system. As such, understanding the biotic and abiotic processes controlling the silicon cycle is crucial because diatoms dominate at the base of the food chain in this highly productive region. The study will focus on following issues: (1) the importance of recycled silicon sources on diatom production; (2) can heavily-silicified diatoms adapt to changing Si/N ratios more effectively than lightly-silicified diatoms; and (3) the role of reverse weathering in sequestering silicon thereby reducing diffusive pore-water transport. To attain these goals, a new analytical approach, the PDMPO method (compound 2-(4-pyridyl)-5-((4-(2-dimethylaminoethylamino-carbamoyl)methoxy)phenyl)oxazole) that quantitatively measures taxa-specific silica production would be used.