The Influence of Bridge Shading on Submersed Aquatic Vegetation

To facilitate tourism, development, and growth in North Carolina's coastal plain, an abundant amount of bridges need to exist. An unavoidable consequence of bridge presence is shading, which can potentially affect submersed aquatic vegetation (SAV) growth. SAV is critically important to marine and freshwater ecosystems due to habitat and water quality benefits provided. Many species of SAV have the ability to morphologically adapt to changing environmental conditions. One example would be the growth of larger leaf surfaces when light is limiting in order to intercept more light for photosynthesis. Under current regulations, all area under a bridge in less than 2m of water must be mitigated to offset the possible loss of SAV due to shading. The cost of mitigation can be extremely expensive, on the order of $250,000 to $300,000 per acre. The quantification of the impact of bridge shading on SAV growth and presence is needed in order to determine the most appropriate mitigation level. This research will determine the effects of bridge shading by quantifying available light and conducting vegetation surveys in and around the bridge footprint. These studies will be performed on bridges varying in height and directional orientation to determine if these factors affect the amount and concentration of shading. SAV may be immediately affected during and just after bridge construction but this effect may be temporal and SAV could recolonize an area after a period of time. To determine the validity of this theory, bridges varying in construction dates will also be evaluated. The results of this research will allow North Carolina Department of Transportation (NCDOT) to create site specific mitigation assessments based on bridge height and orientation. This information would help to reduce mitigation costs and possibly alter bridge construction plans to reach a balance of cost and environmental impact.


  • English


  • Status: Completed
  • Funding: $109702.00
  • Contract Numbers:


  • Sponsor Organizations:

    North Carolina Department of Transportation

    Research and Development
    1549 Mail Service Center
    Raleigh, NC  United States  27699-1549
  • Project Managers:

    Kirby, John

  • Performing Organizations:

    North Carolina State University, Raleigh

    Department of Biological and Agricultural Engineering
    Box 7625
    Raleigh, NC  United States  27695
  • Principal Investigators:

    Richardson, Robert

  • Start Date: 20110816
  • Expected Completion Date: 0
  • Actual Completion Date: 20140815
  • Source Data: RiP Project 28804

Subject/Index Terms

Filing Info

  • Accession Number: 01489403
  • Record Type: Research project
  • Source Agency: North Carolina Department of Transportation
  • Contract Numbers: 2012-18
  • Files: RIP, STATEDOT
  • Created Date: Aug 8 2013 1:01AM