Fish Lake in Maple Grove

Phosphorus in Lakes (P in H2O)

Did you know that roughly 40% of Minnesota’s rivers, lakes and streams are impaired? Environmental specialists around the state are striving to clean things up and get the P out of our H2O.

Every two years, the Minnesota Pollution Control Agency (MPCA) creates a list of impaired waters that do not meet water quality standards. According to MPCA monitoring, about 40% of Minnesota’s lakes and streams are impaired for conventional pollutants. You can see if your favorite lakes are on the list here:

Environmental specialists around the state are striving to clean up Minnesota’s impaired waters by reducing nutrients and sediment reaching them, and also by neutralizing pollutants trapped in lakebeds.

Reducing the quantity of and improving the quality of stormwater runoff is a key action they focus on. Low Impact Development (LID) standards are promoting the installation of many successful best management practices (BMPs), such as filtration basins, permeable pavements, tree trenches, raingardens, and stormwater capture and reuse systems in new developments to reduce runoff and mimic natural pre-development hydrology. Many of these practices can be installed on developed properties.

One of the key pollutants managed by these practices is phosphorus (P), which is a component of organic materials such as leaves and grass clippings, pet waste, fertilizers and eroded soil. All water bodies receive phosphorus from the atmosphere and natural decomposition of aquatic plants, but problems “bloom” when  they receive excessive deposits of nutrients from other sources. Leaves, pet waste and fertilizer reach our surface waters when they are carried into storm drains by rain running off of lawns, parking lots and other hard surfaces. This is called external loading.

algae in Fish Lake

Algae and aquatic plants in Fish Lake

Phosphorus damages lakes by feeding the growth of excessive algae. One pound of phosphorus can create 500 pounds of algae. Large algae blooms reduce lake clarity and impede the growth of other aquatic plants, and can deplete oxygen levels and harm fish. This process is called eutrophication. Algae blooms are also just plain unpleasant for swimming and boating, activities many Minnesotans hold dear.

A certain amount of phosphorus in suspended solid form can be removed from stormwater before it reaches our lakes and streams. Phosphorus in dissolved form requires special treatment. Adding iron filings to filtration basins is proving to be a successful BMP for removing phosphorus before it reaches surface waters. Studies on Iron Enhanced Sand Filters (IESF) conducted by the University of Minnesota St. Anthony Falls Laboratory (SAFL) have proven the science and tests on real world installations are supporting the findings. Water in Motion is working with developers to create operations, maintenance and inspection documentation for filtration basins containing IESF.

Once phosphorus settles in a lake, it’s more troublesome. It leads to a lake becoming eutrophic,  a process in which rich amounts of nutrients and minerals create excessive growth of algae, which leads to diminished oxygen content, which harms fish and other aquatic organisms.

Fish Lake, listed as an impaired lake in Maple Grove, Minnesota, is eutrophic. Three Rivers Park, the Elm Creek Watershed Management Commission and the MPCA  conducted water quality studies  and found that most of the phosphorus affecting the lake’s water was being released by enriched sediment at the bottom of the lake. This leaching of phosphorus from the lakebed is called internal loading. It ultimately increases the amount of phosphorus available for algal uptake and growth. Three Rivers Park District worked with the City of Maple Grove, the Fish Lake Area Residents Association, and the Elm Creek Watershed Management Commission to pursue a strategy to correct the problem and bring the lake into compliance with state water quality standards.

boat treating Fish Lake with alum for phosphorus

Alum barge treating Fish Lake in 2017 to reduce phosphorus.

As a result of successful treatments in other Minnesota lakes, Fish Lake is being treated with a chemical compound called alum. Alum is commonly used in the kitchen for pickling and by water treatment facilities for treating drinking water. When applied properly, it is safe to use in a lake to control phosphorus released by lake bottom sediment. A specially designed watercraft applies alum at the surface of the lake. As the alum falls through the water column it binds with the phosphorus, creating a floc that settles on the lakebed and traps it at the bottom of the lake, making it unavailable for algae to feed on. Initial applications were applied in 2017 and subsequent application is planned for 2019. Fish Lake will continue to be monitored for water quality improvement.

The goal of this and many other water quality initiatives is to rehabilitate the lake so it can be removed from the impaired waters list. What are things you can do to improve water quality in your community?

  • Keep leaves and grass clippings out of the street.
  • Keep fertilizer off paved surfaces and sweep up excess.
  • Pick up pet waste.

For more information about stormwater best management practices, please contact us.