Secchi Transparency Slide Show - Eutrophic Lake
Secchi transparency (clarity) is a quick and easy measurement of lake's water quality. Secchi transparency provides an indirect measure of the amount of suspended material in the water; which in many Minnesota lakes - is the amount of algae in the water. Secchi transparency (clarity) can vary greatly among Minnesota’s lakes and tends to decrease as algal concentrations increase over the summer.
Watch the water clarity of each of the Eutrophic lake as it changes over the summer, including some "underwater" shots as well.
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Eutrophic lakes tend to have decreased transparency, macrophyte problems and an elevated level of nutrients. Secchi images from this eutrophic lake were taken in May, June, July, August, September and October, 2006. Images include a view from above and below the water’s surface. Watch the slide show to see how the water clarity changes over time in response to increases or decreases in algae (chlorophyll-a) concentrations in this eutrophic lake.
Chlorophyll-a samples were collected at the same time the photos were taken. These chlorophyll values provide a measure of the amount of algae in the water. They also allow us to estimate an in-lake Secchi and total phosphorus (TP) concentration based on the interrelationship correlation established by Carlson’s Trophic State Index. Chlorophyll-a data from our eutrophic lake yielded concentrations ranging from 20 to nearly 300 g/L (micrograms per liter or ppb-parts per billion). Based on these chlorophyll values, we would estimate that mid-lake Secchi transparency ranged from about 0.5 – 3.0 feet over the course of the summer. Subsequently, mid-lake TP concentrations would be estimated to range from about 50 – 300 g/L.