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

位于墨西哥湾北部的路易斯安那州陆架系统由密西西比河及其许多支流提供，这些支流为该地区提供了大量的农业肥料养分。这些营养物质的输入，特别是氮素，导致了富营养化。富营养化是指像路易斯安那州陆架这样的水体富含溶解的营养物质，从而增加浮游植物的生长，最终导致底层水域氧气水平下降的过程。在这一地区确实观察到了这一点，硅藻--一种代表食物链基础的浮游植物--表现出不同的硅/氮(Si/N)比率。因为硅藻从硅中产生外壳，它们的生长不仅受到氮输入的控制，还受到硅的可用性的控制。较低的硅氮比表明，硅在调节系统中的硅藻生产方面可能发挥着越来越重要的作用。为此，南阿拉巴马大学的一位科学家将确定控制路易斯安那州陆架系统硅氮比变化的生物地球化学过程。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，为来自第一标题学校的低收入高中生提供的四个奖学金将有机会参加Dauphin Island海洋实验室为期一个月的夏季海洋科学课程，并被纳入研究项目。这项研究具有重大的社会效益，因为这是一个2.4万亿美元的国内生产总值收入与沿海资源捆绑在一起的领域。由于硅藻处于食物链的底部，而食物链是对沿海资源的生物控制，硅藻的生长对富营养化的响应是重要的研究。密西西比河及其支流的富营养化可能会影响硅藻生长的最佳硅氮比以下，从而改变墨西哥湾北部路易斯安那州陆架系统的生物景观。南阿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的硅藻生产方面发挥着重要作用。因此，了解控制硅循环的生物和非生物过程是至关重要的，因为硅藻在这个高产区域的食物链底部占据主导地位。这项研究将集中于以下问题：(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硅氮比的变化；(3)反向风化作用在隔离硅从而减少扩散孔隙水运输中的作用。为了实现这些目标，将使用一种新的分析方法，即PDMPO方法(化合物2-(4-pyridyl)-5-((4-(2-dimethylaminoethylamino-carbamoyl)methoxy)phenyl)oxazole)，定量测量特定分类群的二氧化硅产量)。

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.