Light Penetration refers to the amount of sunlight that penetrates the water column and reaches various depths. In the water column, sunlight is absorbed and scattered by suspended particles, dissolved substances, and the water itself. We monitor light penetration to determine if it is sufficient to support phytoplankton photosynthesis. The attenuation coefficient describes the rate at which light penetration decreases with depth. For example, a high attenuation coefficient represents a rapid decrease in the light over depth, such as when there is a high concentration of suspended particles.The plot contains two depth profiles of light penetration that were obtained using a a quantum sensor. Light penetration is presented as light intensity, i.e. the percentage of the light measured at 1m depth. Light data can also be used to analyze long term light penetration temporal variability. Note: No light data from 2002-2006.

Plot Description:
1. This light profile was measured in San Pablo Bay on February 6, 1996. The attenuation coefficient was 3.6, so the sunlight was being absorbed rapidly by suspended particles. Light was completely absent at about 2.5 meters. This condition is typical of northern San Francisco Bay, which sustains high concentrations of suspended solids. Only the shallow upper layers of the water column have sufficient sunlight for photosynthesis.

2. This light profile was measured in Central Bay on February 6, 1996. In this case sunlight was present down to 5 meters (the attenuation coefficient was 1.2). Usually the Central Bay has relatively clear water, with maximum light penetration reaching 8 meters.