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Developing Sea Floor Disturbance Indices Based on Bottom Stress for Habitat Mapping and Marine Spatial Planning: P. Soupy Dalyander


Project Title: Developing Sea-Floor Disturbance Indices Based on Bottom Stress for Habitat Mapping and Marine Spatial Planning
Mendenhall Fellow: P. Soupy Dalyander, (508) 457-2290, sdalyander@usgs.gov
Duty Station: Woods Hole, MA
Start Date: October 1, 2010
Education: Ph.D. (Mechanical Engineering), University of Florida, 2008
Research Advisors: Brad Butman, (508) 457-2212, bbutman@usgs.gov; Rich Signell, (508) 457-2229, rsignell@usgs.gov; Chris Sherwood, (508) 457-2269, csherwood@usgs.gov; John Warner, (508) 457-2237; Page Valentine, (508) 457-2239, pvalentine@usgs.gov

Project Description: The continental margin of the United States hosts a variety of activities, including commercial fishing, shipping, waste disposal, and recreation, as well as production of energy from traditional and renewable sources. In addition, a wide range of organisms are unique to shelf habitats. In order to preserve the continental margin for these diverse and occasionally competing uses, a comprehensive and science-based approach to resource management is required (Roff and others, 2003). This need has been recognized at the highest levels of government, including in an Executive Order establishing a National Policy for the Stewardship of the Ocean, Coasts, and Great Lakes issued in July 2010 (Executive Order No. 13547, available online at http://www.whitehouse.gov/the-press-office/executive-order-stewardship-ocean-our-coasts-and-great-lakes/). One possible management strategy is marine spatial planning (MSP), a data-rich methodology in which existing ocean uses along with environmental characteristics are mapped and integrated to determine what oceanic regions are best reserved for what purposes.

The current study aims to increase understanding of the benthic environment for the purposes of MSP by exploring and characterizing sea-floor disturbance created by bottom shear stress. A variety of processes cause bottom stress, including persistent ocean or tidal currents and strong waves driven by storm events. Whereas one benthic environment may be tidally dominated and characterized by repetitive, low stress forcing, another environment will be shaped by infrequent high-stress events such as hurricanes or nor’easters (Hemer, 2006; Posey and others, 1996). Both the benthic habitat and the optimal anthropogenic uses for a region will be influenced by bottom stress; for example, stress events can resuspend sediment, dislodge benthic creatures including commercially valuable species such as clams and oysters, and scour around the foundation of industrial structures like oil platforms or wind turbines potentially leading to catastrophic failure (Hemer, 2006; Hernaández-Arana and others, 2003; Schapery and Dunlap, 1978).
 
In this study, the Coupled Ocean-Atmosphere-Wave-Sediment Transport (COAWST) modeling system will be used to simulate the hydrodynamics along the U.S. East Coast over extended periods (months to years), including simulation of wave- and current-induced bottom shear stress (Warner and others, 2008, 2010).  Model results will be validated against available empirical data on waves, tides, and circulation patterns.  The second component of the project will be developing robust ways of characterizing bottom stress, so that the wealth of model data generated can be distilled into useful spatially resolved parameterizations for the purpose of MSP.  For example, one possible characterization is the mean bottom shear stress; shown is a preliminary calculation using COAWST forecast data (see http://woodshole.er.usgs.gov/project-pages/cccp/public/COAWST.htm) for the period of January–October of 2010.  In this map, the effect of water depth on bottom shear stress is demonstrated, with shallower regions demonstrating relatively high bottom stress as a result of wave action.

Figure 1:  Mean bottom stress from COAWST forecast data for January-October, 2010.   Figure 1: Mean bottom stress from COAWST forecast data for January–October, 2010.

Additional characterizations (bulk and season statistics, spectral analysis, and so on) will be explored, and with input from potential users including marine spatial planners and other researchers the most robust characterizations of bottom stress will be identified.  These parameterizations will be calculated over the domain of the model to create spatially resolved maps of bottom stress characteristics that can be utilized by marine spatial planners and within other scientific, research, and policy communities with interest in the dynamics of the continental shelf.

References:
Hemer, M.A., 2006, The magnitude and frequency of combined flow bed shear stress as a measure of exposure on the Australian continental shelf:. Continental Shelf Research, v. 26, p.1258–1280.

Hernández-Arana, H.A., Rowden, A.A., Attrill, M.J., Warwick, R.M., and Gold-Bouchot, G., 2003, Large-scale environmental influences on the benthic macroinfauna of the southern Gulf of Mexico: Estuarine, Coastal and Shelf Science, v. 58, p. 825–841.

Posey, M., Lindberg, W., Alphin, T., and Vose, F., 1996, Influence of storm disturbance on an offshore benthic community: Bulletin of Marine Science, v. 59, p. 523–529.

Roff, J.C., Taylor, M.E., and Laughren, J., 2003, Geophysical approaches to the classification, delineation and monitoring of marine habitats and their communities: Aquatic conservation: Marine and Freshwater Ecosystems, v. 13, p. 77–90.

Schapery, R.A., and Dunlap, W.A., 1978, Prediction of storm-induced sea bottom movement and platform forces: Offshore Technology Conference Proceedings, Paper OTC 3259, p. 1789–1796.

Warner, J.C., Sherwood, C.R., Signell, R.P., Harris, C.K., and Arango, H.G., 2008, Development of a three-dimensional, regional, coupled wave, current, and sediment-transport model: Computers and Geosciences, v. 34, p. 1284–1306.

Warner, J.C., He, R., Zambon, J., and Armstrong, B., 2010, Development of a Coupled Ocean-Atmosphere-Wave-Sediment Transport (COAWST) Modeling System: Ocean Modeling, v. 35, p. 230–244.


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