Case Study: Reducing Phosphorus Levels with Alum

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Restoring A 50-Acre Lake with High Toxic Algae Concentrations

Fremont State Lake is a 50-acre sand pit lake located near Fremont, NE. This lake is a popular destinated for swimming, fishing, kayaking, and boating. However, this recreational lake had a long history of poor water quality with frequent swimming beach closures due to high algal toxic concentrations.

The Problem: High Levels of Phosphorus

In suitable quantities, nutrients like phosphorus are beneficial to aquatic environments. However, water quality issues can arise when nutrient levels become extreme.

Excessive phosphorus levels were the main cause of the toxic algal blooms in Fremont Lake. Internal phosphorus loading (leaching from the lakebed sediments) was the primary nutrient source.

Implementing the Solution: Alum

Before the alum application, average summer total phosphorus was 139 μg/L, chlorophyll a was 100 μg/L and water clarity was only 14 inches. Our experts took this historical data and developed a plan of action to restore water quality and clarity.

In May of 2007, over five days, a buffered alum application (28,442 gallons of alum and 13,234 gallons of sodium aluminate) was performed.

Dramatic Water Quality Improvements

The application resulted in dramatic water quality improvements. State of Nebraska agencies reported the following data during the first three summers after the alum application:

  • Total phosphorus was reduced by 85% to 21 µg/L
  • Chlorophyll a was reduced by 92% to 8 µg/L
  • Water clarity increased over 8 feet
  • Algal toxins were eliminated & the lake was re-opened for recreation

Want to know more about this project?

Click here for a detailed report of our restoration of Fremont Lake.

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