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Sources of Atmospheric
Deposition: Scott Ensign

Project Title: Sediment and Nutrient Trapping in Tidal Freshwater Rivers: Implications of Sea-Level Rise on Coastal Morphology and Biogeochemistry
Mendenhall Fellow: Scott Ensign
Duty Station: Reston , VA
Start Date: February 2, 2011
Education: Ph.D. (Ecology), University of North Carolina Chapel Hill
Research Advisors: Greg Noe, (703) 648-5826,; Cliff Hupp, (703) 648-5207,
  Scott Ensign

Project Description: The tidal freshwater zone between rivers and estuaries is a dynamic region of sediment transport from continents to the oceans. The riparian floodplain of coastal rivers stores a considerable portion of the sediment and biogeochemically important nutrients (carbon, nitrogen and phosphorus) (Noe and Hupp, 2009), but these processes are poorly understood within the tidal zone of rivers. Tides affect both the longitudinal direction of sediment transport (marine versus terrestrial material) and the lateral distribution of suspended sediment across the floodplain where material is ultimately stored. Adding to the complexity is that tidal influence is advancing inland as sea level rises, so understanding contemporary processes and patterns of sediment and nutrient storage requires knowledge of the geomorphic evolution of tidal rivers.

To address this issue, we are studying sediment deposition rates along rivers of the mid Atlantic and southeastern U.S. coast, and relating these deposition rates to patterns in tidal river flow. Our goal is to determine how different tidal regimes affect sediment deposition and storage and ultimately how these processes contribute to geomorphic evolution of coastal rivers as sea level rises.  We are using a variety of techniques to link tidal dynamics with sediment deposition in river floodplains:

    1. Annual measurement of sediment, carbon, nitrogen, and phosphorus deposition along the tidal gradient using marker horizons and sedimentation tiles
    2. Measurement of long-term sediment deposition rates using 210Pb and 137Cs in sediment cores
    3. Measurement of tidal flow regime using acoustic Doppler current profiles
Location of the Choptank, Pocomoke, and Newport Rivers   Location of the Choptank, Pocomoke, and Newport Rivers. 

Top inset photo shows the tidal freshwater riparian forest bordering the Choptank River channel at the inland extent of tidal influence. 

Middle inset shows installment of feldspar clay marker pad in the riparian floodplain of the lower Pocomoke River. 

Lower inset shows a digital elevation model of the Newport River with the tidally-influenced portion of the stream network in blue.


Anticipated Results: Measurement of sediment, carbon, nitrogen and phosphorus deposition along tidal rivers will help us understand the delivery of these important elements to estuaries where water quality impacts occur, such as the Chesapeake Bay and Pamlico Sound. Quantifying how tidal regime affects sediment deposition will help explain how river geomorphology changes due to tides, and will contribute towards prediction of how sea level rise  will influence coastal ecosystems. 

Noe, G.B., and Hupp, C.R., 2009, Retention of riverine sediment and nutrient loads by coastal plain floodplains: Ecosystems, v. 12, p. 728–746.

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Last modified: 16:08:27 Thu 13 Dec 2012