Background - Phosphorus
People need a balanced diet with certain nutrients to remain healthy. Part of that balance diet might include nice chocolate bar every now and again, which is fine if it isn't all the time. When a person does eat too much of something, like the chocolate bar, it can lead to health problems such as diabetes or weight gain.
Lakes, like people, also need a balanced diet. With the right balance of nutrients, a lake will support a healthy population of plants and animals. A lake will also become sick if it receives too much of a good thing. The "chocolate bar" to the lake is a nutrient called phosphorus.
Phosphorus is a naturally occurring element found in rocks, soil, and organic material. You may ask, "how can something that occurs naturally be considered pollution?" The amount of phosphorus that exists naturally in Maine's lakes has been increased by human activities within a lake's watershed. Sources of nutrient pollution include fertilizers, livestock and pet waste, septic systems, and soil erosion. If there are more nutrients than trees, shrubs, and grasses can use or that can be bound in the soil or duff layer, the excess will runoff during a storm.
Phosphorus is called the limiting nutrient when it comes to lakes, controlling the amount of aquatic plants that can grow. This means that phosphorus is normally found in very small amounts, but it is something that plants need to grow. When there is too much phosphorus, tiny plants, called algae, grow very rapidly in an event known as an algal bloom.
When an algal bloom occurs, the water appears green, slimy and cloudy, and it can give off an awful odor. This is not the kind of water where you want to go swimming, boating, or fishing, and it can hurt property values.
When the large quantities of algae die, they fall to the lake bottom where they decompose and deplete oxygen levels. In clear, cold lakes, decreasing the oxygen supply in deep water puts stress on coldwater fish like trout and salmon.
When there is little or no oxygen contained in the bottom water, phosphorus already trapped in the bottom sediment is released, thus increasing the amount of available phosphorus. This results in phosphorus recycling: a vicious cycle of algal blooms, oxygen depletion, phosphorus release and more algal blooms.
For more information about phosphorus and nutrients:
See "In Our Back Yard" articles such as:
- "Lawns green, Lakes Clean"
- "Growing grass the green way"
The Economics of Lakes - Dollars and Cents
Go to: Bacteria, Soil, Thermal, Toxics
