What is the significance of Secchi disk readings?
Secchi disks are standard tools for inland lake monitoring along with measurements of chlorophyll a and phosphorus. Volunteer groups throughout the state and country take Secchi disk readings to indicate the current status of their lake and to compare with data from previous years. The Secchi disk provides a measure of the amount of suspended inorganic and organic matter in the water. Transparency readings in oligotrophic or low nutrient lakes are often greater than 15 feet (5 meters) whereas eutrophic or nutrient rich lakes have readings less than 7.5 feet (2.5 meters). Water clarity is related to amounts of suspended particles (turbidity) as well as amounts of phytoplankton and zooplankton. Instructions for use of a Secchi disk: • An aquatic science instructor will take selected members of the group to the shaded side of the vessel to perform the Secchi disk readings. If working from a dock, provide some kind of sunshade. • Make certain that the line on the Secchi Disk is free of tan
