Dishwashers_ lawn mowers and cow manure

							Dishwashers, lawn mowers and cow manure

Dishwashers, lawn mowers and cow manure; what do these three things have in
common? They are all directly, or indirectly, sources of phosphorus. Why do I care, you
ask? What a good question! Allow me to elaborate.

We Minnesotans love our lakes. We have over 10,000 of them (not too many, not too
few) and we can lay claim to the largest freshwater lake by surface area – Lake Superior,
of course. (Lake Baikal in Siberia holds title to the largest freshwater lake by volume, but
who wants a summer cabin in Siberia anyway?) We love to swim in our lakes, we love to
fish in our lakes, and we love to visit cabins up north on our lakes. What we don’t love is
green, smelly lakes covered with a thick layer of oozing algae.

Guess what causes algae to grow? You guessed it – phosphorus! A certain amount of
algal growth is natural, as are a certain amount of lily pads, a certain amount of large
mouth bass, and a certain amount of aquatic invertebrates. When a lake becomes
eutrophic, however, things can get wacky. A eutrophic lake has an excess of nutrients,
often phosphorus, which enables some species of algae to grow out of control. The results
can be disastrous. No one likes to swim in algae, boat motors become mired in the goo,
and certain species of algae can even be harmful to people and animals.

One way we can prevent algal blooms on our local lakes is by limiting the amount of
phosphorus in the water. Since 2005, Minnesota State Law has banned the use of lawn
fertilizers with phosphorus, a big step toward reducing phosphorus over-load in our lakes.
The Minnesota Pollution Control Agency recently conducted a study to identify other
major sources of phosphorus, some of which include dishwasher detergent, grass
clippings and livestock manure. The combination of household and commercial
dishwasher detergent, for example, contribute about 3% of all the phosphorus pollution to
surface waters in Minnesota. This may not sound like much, but think how easy it would
be to eliminate 3% of our phosphorus problem simply by changing our dishwasher
detergents. A new law may be on its way, but in the meantime, you can look for
phosphorus-free detergent the next time you are shopping. Food soils and garbage
disposal waste combined contribute another 4% of the phosphorus loading. You can limit
your input by composting kitchen scraps rather then sending them down the garbage
disposal.

To find out more about phosphorus and its many sources you can visit the Minnesota
Pollution Control website at www.pca.state.mn.us/water/phosphorus.html.

Angie Hong is the Water Resource Educator for the East Metro Water Resource Education Program. She
can be reached at angie.hong@mnwcd.org or (651) 275-1136 ex. 35.