Light at sediment
The amount of light under water is an important ecological factor for the establishment and growth of macrophyte's. For the establishment by sprouting light at the sediment is an important stimulating factor. When 4% of the surface light reaches the sediment, this is considered sufficient for the germination of aquatic plants.
The percentage of light at the sediment is Iz / I0 * 100%
- Iz = light at depth z (W/m2)
- I0 = light below the water surface (W/m2)
- K = attenuation coefficient (m-1)
- d = water depth (m)
Measured attenuation is tuned to the phytoplankton and aquatic plants sensitive spectrum (PAR: Photosynthetic Active Radiation 400-700 nm). Therefore measured attenuation delivers a more reliable measure of the potential primary production than Secchi depth (visibility). Empirical relationships on primary production and germination of seeds, therefore, can better be based an attenuation coefficient.