US Army Corps of Engineers
Portland District

Overview of controlling factor: Light

Shoot density versus depth graphicLight refers to the solar energy utilized by plants in photosynthesis, termed "photosynthetically active radiation" (PAR).

The figure at right shows eelgrass density at various elevations PAR levels in Willapa Bay, Washington, and Coos Bay, Oregon (Thom et al. 2003).

Stressors that affect light:

  • Extreme climatic events
  • Logging
  • Marinas and overwater structures
  • Volcanic activity
  • Wastewater discharges

Ecosystem structures that are affected by light:

  • Plankton
  • Scrub-shrub forest emergent marsh
  • Mud / sand flats
  • Submerged aquatic vegetation

 Interactions and equations:

  • Turbidity vs. sub-aquatic vegetation density
  • Light attenuation vs. Secchi depth

Contact information

Ronald Thom, Ph.D
360-681-3657

Marine Research Operations, PNNL
1529 W. Sequim Bay Rd.
Sequim, WA 98382