Impact of Seabed Resuspension on Oxygen and Nitrogen Dynamics in the Northern Gulf of Mexico: A Numerical Modeling Study
Impact of Seabed Resuspension on Oxygen and Nitrogen Dynamics in the Northern Gulf of Mexico: A Numerical Modeling Study
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海底再悬浮对墨西哥湾北部氧气和氮气动态的影响：数值模拟研究
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发表时间：
2018
期刊：
影响因子：
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通讯作者：
Kehui Xu
中科院分区：
文献类型：
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作者：
J. Moriarty;C. Harris;M. Friedrichs;K. Fennel;Kehui Xu
再悬浮通过将海底有机物带入水柱而影响沿海环境的水质，这会增加再矿化，改变海底通量，降低水的透明度，并影响氧气和营养物质的动态。然而，几乎所有的水柱生物地球化学数值模型都简化了海底和底边界层过程，而忽略了再悬浮。在这里，我们实施了一个水动力-沉积物运输-生物地球化学耦合模型该模型是在墨西哥湾北部实施的，那里的夏季缺氧程度对海床和底层边界层过程很敏感。结果表明，在再悬浮过程中，底水中颗粒有机物的再矿化作用增加了一个数量级。这增加了沉积物的氧气消耗和氨生产，其定义是海底氧气和氨的通量之和，加上由于再悬浮的有机物在水柱中的氧气消耗和氨生产。与再悬浮引起的海底通量和还原化学物种的氧化相比，再矿化作用的增加对生物地球化学动力学的影响更大。再悬浮对底水生物地球化学的影响随着颗粒有机质有效性的增加而增加，这受泥沙运移模式的影响。总体而言，当在数值模型中按一个月的时间尺度对大陆架进行平均时，侵蚀和沉积循环约占沉积物耗氧量的三分之二，几乎占所有沉积物氨生产的比例。通俗易懂的语言摘要在沿海水域，氧气和氮的水平会影响鱼类和其他生物的健康。例如，在墨西哥湾，夏季在“底层水”的海床附近形成了称为“缺氧区”或“死亡区”的低氧区域。然而，可能很难理解和量化底层水中氧和氮水平的变化，因为：(1)那里的水质受到许多不同的物理和生物过程的影响；(2)观测研究受到成本、安全和技术进步的限制。为了补充以前的观测研究，本文使用了一种新的数值模拟方法，该方法考虑了海床和水中的许多物理和生物过程。具体地说，我们使用该模型来评估再悬浮，特别是从海床向水中的有机物夹带如何影响墨西哥湾北部的氧气和氮水平。模型结果表明，再悬浮增加了底水中有机物的分解，降低了底水中的氧水平，增加了底水中的铵(一种氮)水平。这种影响在海底有机质丰富和再悬浮频繁的地区最大。这些模拟结果可以帮助科学家和环境管理人员了解再悬浮如何影响底层水中的氧气和氮水平。
Resuspension affects water quality in coastal environments by entraining seabed organic matter into the water column, which can increase remineralization, alter seabed fluxes, decrease water clarity, and affect oxygen and nutrient dynamics. Nearly all numerical models of water column biogeochemistry, however, simplify seabed and bottom boundary layer processes and neglect resuspension. Here we implemented HydroBioSed, a coupled hydrodynamic-sediment transport-biogeochemical model to examine the role of resuspension in regulating oxygen and nitrogen dynamics on timescales of a day to a month. The model was implemented for the northern Gulf of Mexico, where the extent of summertime hypoxia is sensitive to seabed and bottom boundary layer processes. Results indicated that particulate organic matter remineralization in the bottom water column increased by an order of magnitude during resuspension events. This increased sediment oxygen consumption and ammonium production, which were defined as the sum of seabed fluxes of oxygen and ammonium, plus oxygen consumption and ammonium production in the water column due to resuspended organic matter. The increases in remineralization impacted biogeochemical dynamics to a greater extent than resuspension-induced seabed fluxes and oxidation of reduced chemical species. The effect of resuspension on bottom water biogeochemistry increased with particulate organic matter availability, which was modulated by sediment transport patterns. Overall, when averaged over the shelf and on timescales of a month in the numerical model, cycles of erosion and deposition accounted for about two thirds of sediment oxygen consumption and almost all of the sediment ammonium production. Plain Language Summary In coastal waters, oxygen and nitrogen levels affect the health of fish and other organisms. In the Gulf of Mexico, for example, low-oxygen regions called hypoxic areas or "dead zones" form in the summertime near the seabed in "bottom water". It can be difficult to understand and quantify variations in bottomwater oxygen and nitrogen levels, however, because: (1) water quality there is affected by many different physical and biological processes; and (2) observational studies are limited by cost, safety and technological advances. To complement previous observational studies, this paper used a new numerical modeling approach that accounts for many physical and biological processes in the seabed and water. Specifically, we used the model to evaluate how resuspension, especially the entrainment of organic matter from the seabed into the water, affected oxygen and nitrogen levels in the Northern Gulf of Mexico. Model results indicated that resuspension increased the decomposition of organic matter, decreasing oxygen levels and increasing ammonium (a form of nitrogen) levels in bottom water. This effect was largest in regions with abundant seabed organic matter and frequent resuspension. These modeling results can help scientists and environmental managers understand how resuspension affects oxygen and nitrogen levels in bottom waters.