The biogeochemistry and ecology of tidal freshwater rivers Public Deposited

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  • March 21, 2019
  • Ensign, Scott Howard
    • Affiliation: College of Arts and Sciences, Curriculum in Environment and Ecology
  • Tides propagate up coastal rivers far upstream from the saline estuary, changing the direction and strength of river flow and the extent of riparian inundation over short time scales. This dissertation explores the effect of tides on river morphology and evolution, nitrogen cycling, and primary production. I examined river hydraulics and channel morphology in the Newport River, N.C. to evaluate how tides change stream power and sediment transport. Tides suppressed stream power in the upper tidal river but enhanced stream power in the lower tidal river. Sediment transport increased from upstream to downstream along the tidal continuum. These patterns suggested the mechanisms by which rivers evolve from non-tidal to tidal during sea level rise. Nitrogen removal in tidal rivers via denitrification is potentially affected by these spatial patterns. Denitrification rates and the lag period prior to the onset of denitrification were measured in riparian habitats of the Newport River. Temporal variation in denitrification over an 11 month period was greater than spatial variation within or between habitat types. A 4.6 hr lag time between floodplain inundation and the onset of denitrification was measured in the field and laboratory experiments. Landscape-scale modeling of these processes indicated that tidal inundation dynamics exerted as strong an influence on nitrogen attenuation as did rates of denitrification. Tidal hydrology also had a profound influence on primary production. Monitoring and mesocosm experiments showed that phytoplankton growth was enhanced by both the geomorphic influence of tides and the increased residence time in the channel. During spring and summer, nitrogen and phosphorus limit phytoplankton growth in the non-tidal river, and zooplankton grazing may limit phytoplankton growth in the tidal river. Understanding the mechanisms by which tides affect hydrogeomorphology in rivers, and the subsequent impacts on biogeochemical and biological processes is a fundamental step towards conceptual integration of the tidal zone with river networks. Fluvial form and function are essential to applied sciences, such as river restoration and biogeochemical modeling, but are also fundamental for anticipating the future impacts of sea level rise on coastal rivers.
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  • In Copyright
  • "... in partial fulfillment of the requirements for the degree of Doctor of Philosophy in the Curriculum for the Environment and Ecology."
  • Piehler, Michael
Degree granting institution
  • University of North Carolina at Chapel Hill
Place of publication
  • Chapel Hill, NC
  • Open access

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