What is Alum and How Does it Work?

Alum (aluminum sulfate) is a nontoxic liquid that
is commonly used in water treatment plants to
clarify drinking water. It’s use in lakes began in
the early 1970’s and is used to reduce the amount
of phosphorus in the water. Lower amounts of phosphorus lead to lower amounts of algae and the symptoms associated with poor water quality. Alum is most often used to control phosphorus release from the lake bottom sediments (internal loading). Research has shown that even when external sources of phosphorus from the surrounding watershed are lowered, the internal cycling can continue to support signi cant nuisance algal blooms.

Where Does All of This Phosphorus Come From?

Phosphorus enters lakes from two sources. Phosphorus entering the lake from outside sources are called external sources. These sources originate in the watershed and are either directly rinsed into the lake or flow to a stream that enters the lake. Common external sources include lawn fertilizers, septic systems, agricultural practices, stormwater, soil erosion and geese: anything that causes phosphorus to enter the lake from the watershed.
Once the external source of phosphorus enters the lake, it is deposited in the lakebed and is recycled back into the water column. This is the second source of phosphorus and it originates from within the lake itself. This is called an internal source and these inputs are most common during the summer
and winter when water oxygen concentrations are low or zero near the bottom. This condition causes changes in the chemistry of the lakebed that lead to the phosphorus leaching out of the sediment and into the water.

Property Values and Water Quality

Lake property is aesthetically and economically desirable throughout the world and it is well-established that property values are tightly linked to the quality of the lake.

The Hazards of Toxic Algae

Cyanobacteria (a.k.a. blue-green algae) are a type
of algae which can produce toxins and are often found in lakes with high phosphorus concentrations. Human exposure to cyanobacteria can lead to skin irritation, allergic reactions, gastrointestinal symptoms and respiratory problems. Pets and livestock are more likely to drink large quantities of lake water, potentially resulting in illness and/or death.

What are algae?

Algae are microscopic, free- floating organisms that are commonly found in lakes. They are similar to terrestrial plants in that they also require sunlight and nutrients to grow. Algae are the important base of the aquatic food web that ultimately supports juvenile
and adult fish. However, the excessive growth of
undesirable types of algae (Cyanobacteria) causes severe water quality problems. Cyanobacteria (a.k.a. blue-green algae) thrive when nutrients are high and are capable of producing toxins. They grow rapidly to cause blooms and scums and are usually associated with nearly all lake water quality problems.

Lotus Lake Project Description

Lotus Lake is a 248-acre lake in the city of Eden Prairie, MN with an average depth of 16 feet and a maximum depth of 31 feet.  The lake is eutrophic, experiences excessive summer algae blooms, and has poor water quality (high phosphorus concentrations, large amounts of algae, low water clarity).  Lotus is listed as…