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 firstname.lastname@example.org or (651) 275-1136 ex. 35.
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