Properties of Light in Water Refraction Attenuation with depth Light and Trophic Status Secchi Disk Application

Note refraction Light Penetration & Attenuation Amount reflected depends on wave conditions and ice cover. Light that penetrates the surface may then be absorbed, reflected or transmitted. Light intensity decreases logarithmically with depth; a process called attenuation 1% I o (I o ) Euphotic zone

Different wavelengths of light absorb differently in pure water. Blues and greens penetrate deepest and reds the least. Why the “deep blue sea”? Particles and colored dissolved organic matter will further influence how quickly different colors of light are absorbed in natural waters. Attenuation (or extinction) coefficient (k is defined as: k = (ln I o – lnI z ) / z Light intensity at a given depth can be calculated as: I z = I o e -kz

Secchi Depth and Trophic Status (k) Secchi depth (Z SD ) can be used to estimate the attenuation coefficient (k). k = 1.7 / Z SD ; This translates into the 1% light level being 2.7 times Z SD, or that 16% of surface irradiance remains at the Z SD.