Shields Lake is 30-acre lake in the City of Forest Lake, MN. The lake eventually flows to Forest Lake and it has a watershed that is 538-ac in size. The lake is eutrophic, experiences excessive summer algae blooms, and has poor water quality (high phosphorus concentrations, large amounts of algae, low water clarity), and has…
The key to a successful alum application is the formation of the floc and the precise placement of the floc on the lakebed. The floc is formed when the liquid alum mixes with lake water immediately after application. It is a whitish-green precipitant, is more dense than water and sinks through the water column at…
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.
The nutrient of concern in lakes is phosphorus. Algae, like terrestrial plants, require phosphorus to grow.
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.
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.
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.
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.
Alum has been repeatedly shown to be safe for humans. Alum is a common
food additive and has also been used for decades to clean our drinking
water before consumption. HAB uses the exact same drinking water certified
alum when preforming a lake improvement application.
Aluminum is considered a non-essential metal because fish and other aquatic life do not need it to function. There is a large body of scientific literature documenting the safe use of alum in lake environment conditions, which has allowed the North American
Lake Management Society to fully endorse its use (NALMS, 2017).