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 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.
