Type
Text
Type
Dissertation
Advisor
Lwiza, Kamazima M.M. | Zhang, Minghua Zhang | Wang, Dong-Ping | Wilson, Robert | Oey, Lie-Yauw | Lermusiaux, Pierre.
Date
2015-12-01
Keywords
Physical oceanography | Bacteria, GOTM, Hypoxia, Long Island Sound, Microbial loop, ROMS
Department
Department of Marine and Atmospheric Science.
Language
en_US
Source
This work is sponsored by the Stony Brook University Graduate School in compliance with the requirements for completion of degree.
Identifier
http://hdl.handle.net/11401/76193
Publisher
The Graduate School, Stony Brook University: Stony Brook, NY.
Format
application/pdf
Abstract
The occurrence and spread of hypoxia in coastal waters is known to depend strongly on nutrients, primary production, water column structure, wind and tidal mixing. Accurate prediction of the onset, intensity and areal extent of hypoxia remains a challenge. Previous modeling efforts have needed to ‘tune’ vertical mixing or phytoplankton respiration in order to obtain results that agree with field observations of dissolved oxygen (DO). We use a one-dimensional physical model coupled with a biogeochemical model to establish mechanistic links between factors involved in the evolution of seasonal hypoxia in western Long Island Sound. The coupled model includes bacterial dynamics, which allows accurate prediction of the onset of late summer hypoxia and subsequent recovery. The cost of not including the bacterial dynamics in the model is an overestimation of bottom DO by as much as 700% in summer. By including bacterial dynamics, we eliminate the need to distort vertical mixing or phytoplankton respiration rate to simulate observed seasonal variability in DO. Along with the importance of the bacterial dynamics, it is instructive to conduct a thorough examination of other mechanisms influencing hypoxia. These mechanisms may include DO production by plankton growth and surface oxygen supply, DO consumption by organic matter remineralization both in the water column and the sediment, DO transport by vertical mixing and horizontal advection. In order to explore these mechanisms and quantify their individual impacts on seasonal hypoxia, we analyze the rates of DO consumption/production, which include the surface flux of DO, detritus remineralization or bacterial consumption, sedimentary DO consumption, as well as horizontal advection of DO. By quantifying these dynamic terms in DO control equation, we are able to demonstrate that DO consumption rate associated with bacterial activities has significantly the largest influence. We also find that perturbing wind mixing contributes at most 30% to the late summer DO variability. Advection plays a non-trivial role in hypoxia development. Ignoring horizontal advection leads to up to 40% of under-estimation of DO during low DO season. DO variability is sensitive to horizontal advection during low DO season. An examination of DO consumption/ventilation rates indicates that horizontal advection has same order of impact as planktonic photosynthesis in terms of oxygen generation, but it is on three orders less than bacterial DO consumption. | The occurrence and spread of hypoxia in coastal waters is known to depend strongly on nutrients, primary production, water column structure, wind and tidal mixing. Accurate prediction of the onset, intensity and areal extent of hypoxia remains a challenge. Previous modeling efforts have needed to ‘tune’ vertical mixing or phytoplankton respiration in order to obtain results that agree with field observations of dissolved oxygen (DO). We use a one-dimensional physical model coupled with a biogeochemical model to establish mechanistic links between factors involved in the evolution of seasonal hypoxia in western Long Island Sound. The coupled model includes bacterial dynamics, which allows accurate prediction of the onset of late summer hypoxia and subsequent recovery. The cost of not including the bacterial dynamics in the model is an overestimation of bottom DO by as much as 700% in summer. By including bacterial dynamics, we eliminate the need to distort vertical mixing or phytoplankton respiration rate to simulate observed seasonal variability in DO. Along with the importance of the bacterial dynamics, it is instructive to conduct a thorough examination of other mechanisms influencing hypoxia. These mechanisms may include DO production by plankton growth and surface oxygen supply, DO consumption by organic matter remineralization both in the water column and the sediment, DO transport by vertical mixing and horizontal advection. In order to explore these mechanisms and quantify their individual impacts on seasonal hypoxia, we analyze the rates of DO consumption/production, which include the surface flux of DO, detritus remineralization or bacterial consumption, sedimentary DO consumption, as well as horizontal advection of DO. By quantifying these dynamic terms in DO control equation, we are able to demonstrate that DO consumption rate associated with bacterial activities has significantly the largest influence. We also find that perturbing wind mixing contributes at most 30% to the late summer DO variability. Advection plays a non-trivial role in hypoxia development. Ignoring horizontal advection leads to up to 40% of under-estimation of DO during low DO season. DO variability is sensitive to horizontal advection during low DO season. An examination of DO consumption/ventilation rates indicates that horizontal advection has same order of impact as planktonic photosynthesis in terms of oxygen generation, but it is on three orders less than bacterial DO consumption. | 215 pages
Recommended Citation
Liu, Ling, "Advancing numerical prediction of physical and biological processes in Long Island Sound" (2015). Stony Brook Theses and Dissertations Collection, 2006-2020 (closed to submissions). 2130.
https://commons.library.stonybrook.edu/stony-brook-theses-and-dissertations-collection/2130