Date Awarded


Document Type


Degree Name

Doctor of Philosophy (Ph.D.)


Virginia Institute of Marine Science


The temporal spectral light environment of shallow areas of the lower Chesapeake Bay was characterized by cosine collection of downwelling diffuse irradiance at 12 wavelengths between 400 and 700 nm. An extensive monthly and site comparison of spectral attenuation coefficients is presented and compared with previous measurements of the light quality environment of the Chesapeake Bay and other estuaries and marine waters. Spectral irradiance and attenuation of light in a mangrove creek and Thalassia testudinum bed of Laguna de Terminos, Campeche, Mexico and their relationships to wind-driven suspension of particulate matter, and dissolved substances from the mangrove swamp is also discussed. A review of the physics of spectral attenuation in estuaries is included. Particular attention was given to the relationship between the occurrence of seagrasses (Zostera marina mainly) in the Chesapeake Bay and spectral attenuation. Potential losses of photosynthetically storable radiation (PSR) due to reduced light quality in non-vegetated areas is calculated. A theoretical homeostatic relationship between seagrass leaf baffling of the water column, light quality and critical bed size is presented. The logic and output of a digital ecosystem simulation model of theoretical estuarine photosystem responses to simulated varying underwater light quality is presented. The model assumes that photosystems adapt to maximize power. Conclusions include: a dramatic pattern of seasonal spectral attenuation in the lower Chesapeake Bay; seasonal differences in spectral attenuation between vegetated and unvegetated sites; 63% less violet light was able to pass through a meter of water at unvegetated sites in May than vegetated sites.



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