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

墨西哥湾北部的路易斯安那陆架系统由密西西比河及其许多支流提供养分，这些支流为该地区提供了大量的农业肥料营养。这些营养物质，特别是氮的输入导致了富营养化。富营养化是指像路易斯安那大陆架这样的水体在溶解营养物中变得丰富的过程，这些营养物增加了浮游植物的生长，最终导致海底氧气水平降低。这在这一地区已经被观察到，硅藻，一种代表食物链底部的浮游植物，显示出可变的硅/氮（Si/N）比率。因为硅藻的外壳是由硅形成的，所以它们的生长不仅受氮输入的控制，还受硅的可用性的控制。较低的Si/N比率表明，硅可能在调节系统中硅藻生产方面发挥越来越重要的作用。出于这个原因，南阿拉巴马大学的一位科学家将确定控制路易斯安那陆架系统中Si/N比率变化的生物地球化学过程。作为该项目的一部分，一名攻读博士学位的研究生和三名本科生将得到支持和培训。另外，4名低收入高中学生将获得奖学金，参加为期一个月的夏季海洋科学课程，并被纳入研究项目。鉴于该地区2.4万亿美元的国内生产总值收入与沿海资源息息相关，该研究具有重大的社会效益。由于硅藻是食物链的基础，是生物控制沿海资源，硅藻的生长对富营养化的反应是重要的研究。密西西比河及其支流的富营养化有可能改变墨西哥湾北部路易斯安那陆架系统的生物景观，影响矽氮比低于硅藻生长的最佳水平。南阿拉巴马大学的一位科学家认为，观察到的Si/N比的变化可能表明，硅现在在调节系统中硅藻的产生方面起着重要作用。因此，了解控制硅循环的生物和非生物过程是至关重要的，因为硅藻在这个高产地区的食物链中占据主导地位。重点研究以下问题：(1)再生硅源对硅藻生产的重要性；(2)重硅化硅藻比轻硅化硅藻更能适应硅氮比的变化；(3)逆风化作用在隔离硅从而减少扩散孔水输运中的作用。为了达到这些目标，一种新的分析方法，PDMPO方法（化合物2-（4-吡啶基）-5-（（4-（2-二甲氨基乙基氨基-氨基甲酰基）甲氧基）苯基）恶唑）将被用于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.