A lake covered in green slime is a sure sign of high levels of nitrogen and phosphorous.
Most South Dakota lakes are phosphorus-rich, according to Paul Lorenzen, an environmental scientist at South Dakota Department of Environment and Natural Resources. “When we’re looking at lake data, nitrogen limitation is generally what we see.”
Efforts to use aluminum sulfate, a coagulant which binds phosphorus forming flocs that settles to the bottom of the lake, have produced only short-term results.
“Turbulence can cause the floc to come up, releasing the phosphorus,” explained Kyungnan “Karen” Min, an instructor in the Department of Civil and Environmental Engineering. In addition, low oxygen levels in the lake can trigger phosphorus release
She and assistant professor Guanghui Hua are investigating whether sediment capping will increase the effectiveness of a chemical treatment that uses a layer of phosphorus-binding particles on top of sediment to minimize re-suspension and reduce phosphorus release.
Through laboratory experiments, Min and Hua are testing three inexpensive, readily available natural minerals as capping materials. The two-year project is supported by the U.S. Geological Survey 104b program administered through the South Dakota Water Resources Institute with matching funds from the East Dakota Water Development District and South Dakota State University.
The researchers tested alum coagulation followed by adding sand, limestone or zeolite as a capping material and compared their performances to a commercial product designed to prevent phosphorus release.
After determining the correct alum dosage for coagulation, doctoral student Sepideh Sadeghi performed column testing using sediment and overlaying the Lake Kampeska water samples. During the 80-day experiment, Sadeghi used a mixer to agitate the water every 10 days for five minutes at a speed of 500 rpm to simulate the passage of a motor boat.
All alum-capping material combinations helped the floc settle to the bottom, resist turbulence and prevent re-suspension better than alum alone, according to Min. However, limestone and zeolite produced results similar to those from the more-expensive commercial product.
“The results are promising,” said Hua. However, Min cautioned, “This is not a permanent solution, but can extend the time required before reapplication is needed.”
The next step will be to perform a cost evaluation and test the most promising combination in a South Dakota lake.