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Fluxes to estuarine and coastal environments

 

Suspended-sediment dynamics at Blackwater National Wildlife Refuge

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Overview

The USGS Patuxent Wildlife Research Center conducts extensive research on the evolution of tidal wetlands, considering biological productivity and physical forcings including sea-level rise and subsidence. An important component of tidal marsh evolution is sediment supply. At Blackwater National Wildlife Refuge, in Maryland, one marsh complex (BW) has undergone massive subsidence in the last century, while a nearby complex (FB) appears to be stable.Two field campaigns, in the spring and fall of 2011, aimed to quantify the sediment availability to these two distinctly different areas of Blackwater National Wildlife Refuge.  The rates of sediment flux to and from these complexes were previously unknown.

Historic marsh loss at Blackwater National Wildlife Refuge

Marsh loss at Blackwater National Wildlife Refuge (U.S. Fish & Wildlife Service)

Measuring flows in the Blackwater River

Measuring flows in the Blackwater River, the main conduit for sediment transport

Results

High-temporal resolution data indicated that the Blackwater River wetland complex, with a vast open-water area, is susceptible to wind-wave resuspension and ultimately sediment export due to dominant NW winds. A nearby complex on the Transquaking River, on the other hand, is near a large sediment source that may contain an estuarine turbidity maximum. This estuarine feature may be partially responsible for maintaining adjacent tidal marsh. The results demonstrate the temporal and spatial complexity of estuarine sediment transport and its potential effect on marsh sustainability. The data can be accessed here.

The conceptual model below, developed from this work, suggests that wetlands with a reliable sediment transport portfolio may be more resilient to sea-level rise and other destructive forces.

Conceptual model of sediment transport

Conceptual model of sediment portfolio for four wetlands (top row from Chesapeake Bay; bottom row from San Francisco Bay)

References

Ganju, N.K., Dickhudt, P.J., Montgomery, E.T., Brennard, Patrick, Derby, R.K, Brooks, T.W., Guntenspergen, G.R., Martini, M.A., Borden, Jonathan, and Baldwin, S.M., 2012, Summary of oceanographic and water-quality measurements near the Blackwater National Wildlife Refuge, Maryland, 2011: U.S. Geological Survey Open-File Report 20121099, available only at http://pubs.usgs.gov/of/2012/1099/.

Ganju, N. K., Nidzieko, N. J., and Kirwan, M. L., 2013, Inferring tidal wetland stability from channel sediment fluxes: Observations and a conceptual model. Journal of Geophysical Research: Earth Surface, 118(4), 2045-2058. PDF File 

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Page last modified: 12/28/2011