Grantee Research Project Results
Final Report: Physical and Biological Processes Affecting the Distribution of Hypoxia on the Louisiana Continental Shelf
EPA Grant Number: R827785E02Title: Physical and Biological Processes Affecting the Distribution of Hypoxia on the Louisiana Continental Shelf
Investigators: Rabalais, Nancy N. , Turner, R. Eugene , Wiseman, William J. , Justic, Dubravko
Institution: Louisiana State University - Baton Rouge
EPA Project Officer: Chung, Serena
Project Period: March 17, 2002 through March 16, 2003
RFA: EPSCoR (Experimental Program to Stimulate Competitive Research) (1999) RFA Text | Recipients Lists
Research Category: EPSCoR (The Experimental Program to Stimulate Competitive Research)
Objective:
The objective of this research project was to better define the physical and biological processes affecting the distribution of low oxygen through experiments with instrumentation, empirical relationships, and modeling. Development of technological capabilities and expanded modeling efforts were to provide the necessary data sets to improve our research competitiveness, as well as support the development of human resources, particularly in public and graduate education. This research project focused on addressing research questions concerning vertical and horizontal transport of oxygen, timing, and duration of low oxygen, cross-shelf and alongshore dynamics, transformation of hypoxic water masses, and integration of the physics (winds, currents) with biological processes.
Summary/Accomplishments (Outputs/Outcomes):
As seen from the list of publications and presentations below, we were successful in integrating the physical data with the biological data for a better understanding of oxygen dynamics at the instrumented site. The existing model of Justic, et al. (1996, 1997) was used to develop hindcasting and forecasting capabilities. With our collaborators, we developed several models relating the flux of materials from the Mississippi River and relevant physical conditions on the continental shelf with the occurrence, historical trends, and size of the low oxygen area on the Louisiana shelf. These models will be used by the federal/state/tribal task force to gauge responses of the coastal ecosystem to mitigation measures for nutrient reduction within the Mississippi River watershed.
The significant departure of the size of the 2003 hypoxic area, compared to the predictions from the various models, indicated that the physical conditions of the coastal ecosystem prior to the survey are as important as the integrated flux of materials from the watershed. Comparisons of bottom oxygen data with wind and current data indicate considerable variability in the effect of tropical storms and hurricanes on the persistence of hypoxia. The variability is dependent on the size of the storm, its intensity, the speed of movement across the hypoxic area, and the strength of the stratification prior to impact from the higher winds and waves.
Technical Effectiveness of Methods
We conducted comparative analyses of four different oxygen meter technologies to reduce the maintenance required for this part of our research project. These data were shared with the private corporations loaning the instrumentation and presented at a scientific meeting. As a result of this work, Dr. Rabalais is involved in leading an oxygen probe technology meeting in January 2004, in conjunction with ACT. She also participated in the Ocean U.S. workshops and an Integrated Ocean Observing System Workshop in September 2003.
We compared the bottom-mounted acoustic Doppler current profiler (ADCP) data with a single point ADCP combined with the oxygen optode and found good correlation among the current speed and direction at the same water depth.
How Research Adds to Our Understanding of, or Solutions for, Environmental Problems or Is Otherwise of Benefit to the Environment and Human Health
The distribution and dynamics of hypoxia on the Louisiana continental shelf are intimately linked with the flux of fresh water and nutrients from the Mississippi River and the physical oceanography of the open Gulf of Mexico. Several models were developed that link the flux of materials and conditions on the continental shelf with the variability of hypoxia and the size of the hypoxic zone in mid-summer. The coupled physical/biological model closely approximated present conditions at a station in the core of the hypoxic zone. The same model was used to hindcast its occurrence historically, to forecast its severity under future scenarios of climate change, and to assess its response to nutrient management. These models will be used by the Hypoxia Task Force in its continuing assessment of the effectiveness of implemented nutrient management scenarios on the size of the hypoxic area. The goal for the Hypoxia Action Plan is a 5-year running average of less than 5,000 km2 for the hypoxic zone, dependent on a 30 percent total nitrogen reduction. Other models developed by us and our collaborators indicate that there will actually be a need for a 35-45 percent reduction in the total nitrogen load to achieve the hypoxia area size goal. The integrated current meter, wind, wave, and oxygen data provided the opportunity to define the conditions under which stratification and hypoxia were likely to develop. These physical data helped to better understand the influence of tropical storms and hurricanes on the distribution of hypoxia on the Louisiana shelf.
Modeling Component
The models employed were not developed specifically for this project but were used with the data that were generated from the instrumented mooring and other data collected under the National Oceanic and Atmospheric Administration Coastal Ocean Program Gulf of Mexico Ecosystem and Hypoxia Assessment Hypoxia Studies project and data provided by the U.S. Geological Survey. The models used are listed below:
Journal Articles on this Report : 13 Displayed | Download in RIS Format
Other project views: | All 44 publications | 18 publications in selected types | All 17 journal articles |
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Justic D, Rabalais NN, Turner RE. Modeling the impacts of decadal changes in riverine nutrient fluxes on coastal eutrophication near the Mississippi River Delta. Ecological Modeling 2002;152(1):33-46. |
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Justic D, Turner RE, Rabalais NN. Climatic influences on riverine nitrate flux: implications for coastal marine eutrophication and hypoxia. Estuaries 2003;26(1):1-11. |
R827785E02 (Final) R828009 (2001) R828009 (2002) R828009 (Final) |
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Justic D, Rabalais NN, Turner RE. Simulated responses of the Gulf of Mexico hypoxia to variations in climate and anthropogenic nutrient loading. Journal of Marine Systems 2003;42(3-4):115-126. |
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Justic,D, Rabalais NN, Turner RE. Coupling between climate variability and coastal eutrophication: evidence and outlook for the northern Gulf of Mexico. Journal of Sea Research 2005;54(1):25-35. |
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Rabalais NN, Turner RE, Scavia D. Beyond science into policy: Gulf of Mexico hypoxia and the Mississippi River. BioScience 2002;52(2):129-142. |
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Rabalais NN, Turner RE, Dortch Q, Justic D, Bierman Jr. VJ, Wiseman Jr. WJ. Nutrient-enhanced productivity in the northern Gulf of Mexico: past, present and future. Hydrobiologia 2002;475/476:39-63. |
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Rabalais N. We all live downstream (and upstream). Journal of Soil and Water Conservation 2003;58(3):52A-53A. |
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Rabalais NN, Turner RE, Wiseman Jr. WJ. Gulf of Mexico hypoxia, a.k.a. "The dead zone". Annual Review of Ecology and Systematics 2002;33:235-263. |
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Scavia D, Rabalais NN, Turner RE, Justic D, Wiseman WJ. Predicting the response of Gulf of Mexico hypoxia to variations in Mississippi River nitrogen load. Limnology and Oceanography 2003;48(3):951-956. |
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Turner RE, Rabalais NN, Justic D, Dortch Q. Future aquatic nutrient limitations. Marine Pollution Bulletin 2003;46(8):1032-1034. |
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Turner RE, Rabalais NN, Justic D, Dortch Q. Global patterns of dissolved N, P and Si in large rivers. Biogeochemistry 2003;64(3):297-317. |
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Turner RE, Rabalais NN. Linking landscape and water quality in the Mississippi River basin for 200 years. BioScience 2003;53(6):563-572. |
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Turner RE, Rabalais NN, Swenson EM, Kasprzak M, Romaire T. Summer hypoxia in the northern Gulf of Mexico and its prediction from 1978 to 1995. Marine Environmental Research 2005; 59(1):65-77. |
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Supplemental Keywords:
anoxia, Gulf of Mexico, Mississippi River, eutrophication, nonpoint source pollution, oxygen dynamics, climate variability., RFA, Scientific Discipline, INTERNATIONAL COOPERATION, Water, Waste, ECOSYSTEMS, Ecosystem Protection/Environmental Exposure & Risk, Aquatic Ecosystems & Estuarine Research, Water & Watershed, Restoration, climate change, Aquatic Ecosystem, Fate & Transport, Monitoring/Modeling, Terrestrial Ecosystems, Biochemistry, Ecology and Ecosystems, Aquatic Ecosystem Restoration, Watersheds, fate and transport, environmental monitoring, watershed management, environmental measurement, water circulation, sediment transport, coastal zone, continuous monitoring, particle reactive contaminants, restoration strategies, hypoxia, watershed influences, hydrology, integrated watershed model, aquatic ecosystems, environmental stress, source load modeling, watershed sustainablility, coastal ecosystems, water quality, ecosystem stress, ecology assessment models, ecological impact, ecological research, watershed restoration, heavy metals, MississippiRelevant Websites:
http://www.nos.noaa.gov/Products/pubs_hypox.html Exit
http://csc.noaa.gov/products/gulfmex/html/rabalais.htm Exit
http://water.epa.gov/type/watersheds/named/msbasin/index.cfm
http://www.riverwise.org/ Exit
The perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.