Phosphorus: Threat to our Lakes

The word "phosphorus" has a negative connotation when talking about lakes.  So what is so bad about phosphorus and where does it come from?  Today I will answer these questions and offer some simple tips to practice to prevent phosphorus from entering our lakes.  This information applies to those who do not live on lakes as well, because all water is connected and those that live in the city of Detroit Lakes have an impact on Detroit Lake.

So first of all, what is so bad about phosphorus?  Phosphorus is a nutrient that "feeds" lakes.  In fact, it is the limiting nutrient in most Minnesota lakes.  This means that the plants and algae in the lake have everything available they need for growth (sunlight, warmth) except for phosphorus.  In extremely clear lakes, the lack of plants and algae is due to the sufficiently low availability of phosphorus.  So any phosphorus that is added to the lake is taken up by plants and algae and causes them to multiply.  Over time, the lake becomes "greener".  One pound of phosphorus added to a lake can yield 500 lbs of aquatic plants and algae.

Phosphorus is a natural element.  It is an essential element to all life on earth because it is in DNA.  Phosphorus exists in soils, minerals and living organisms.  Phosphate is taken up by plants from soils, utilized by animals that consume plants, and returned to soils as animal waste.

Phosphorus can enter rivers and lakes in many different ways.  First, phosphorus in soils is almost entirely associated with soil particles.  When soil particles are carried to a river or lake in runoff, this phosphorus enters the lake.  Second, when lawns or fields are over fertilized, the excess fertilizer can be carried by runoff into streams and lakes.  Thirdly, phosphorus is in human and animal waste and can enter lakes through poorly managed septic systems and runoff from animal feedlots. 

It is true that erosion and runoff have been occurring since the glaciers receded and naturally add phosphorus to streams and lakes. However, this process is extremely slow.  Humans have sped up this process by altering the landscape, building cities and lawns, practicing agriculture and industry.  We add phosphorus to our lakes much faster than it would naturally.

So what can you do to reduce your contribution of phosphorus to our lakes and streams?  Minnesota legislature passed a statewide law that restricts the application of phosphorus fertilizer to established turf.  Make sure if you buy fertilizer for your lawn it is phosphorus-free.  In addition, before fertilizing your lawn do a soil test to see if you actually need it. 

To minimize runoff, consider planting a buffer strip of native grasses, wildflowers and shrubs along your shoreline and limit the amount of impervious surface on your lot.  Impervious surface is an area where water cannot sink into the ground, but flows over it such as roofs, driveways and patios.

Have your septic tank or holding tank inspected to make sure it is treating waste properly.  Keeping your septic system working properly will not only protect the lake, but extend the life of your system and avoid costly repairs and replacements.

This fall, make sure you take your leaves to the Becker compost site and don't deposit them in lakes, streams or wetlands.  Leaves contain phosphorus and as they breakdown the phosphorus is released. 

If we are all aware of our phosphorus contributions to lakes and streams, we can work together to keep our lakes clean.

Enjoy the lakes!

Moriya Rufer is the Lakes Monitoring Program Coordinator for RMB Environmental Laboratories in Detroit Lakes, 218-846-1465, lakes.rmbel@eot.com.