Recent reports of dogs dying from blue-green algae in Minnesota lakes are drawing attention to the causes of algae blooms – the stuff that turns the water in many lakes various shades of green in the summer. Most of the 7,000 or so types of algae are not toxic, but in large amounts some forms can pollute lakes, rivers and streams. Algae vary in size from small, single-cell forms to giant sea kelp. Without algae on earth for the past three billion years, life would not exist as we know it today. Algae comprise much of the food source for aquatic organisms and produce oxygen that enriches both the water and air. Excessive algae, however, is usually the most visible result of water pollution, floating on lakes like a smelly green blanket. One of the forms, blue-green algae, produces toxins that can affect humans and animals. It can be fatal to animals and birds that ingest large amounts. In contact with humans, it can cause skin and eye irritations, or stomach ailments, if swallowed. More information about toxic algae is available on the Minnesota Pollution Control Agency (MPCA) Web site www.pca.state.mn.us/water/clmp-toxicalgae. “We’re taking a lot of calls about blue-green algae, and in some areas it’s pretty severe,” says Steve Heiskary, MPCA lake scientist. “The heat is allowing blue-green to really flourish by providing prime conditions to use the available nutrients. While more severe in high-nutrient shallow lakes, it’s even affecting some of the better quality lakes.” Just like flowers in a garden or crops in farm fields, water, warmth and food nourish the growth of algae. In lakes there’s plenty of water, and in summer, we all enjoy the sun’s warmth. The deciding factor in the amount of algae in lakes lies in the amount of “food” they get – primarily nitrogen and phosphorus. These nutrients come from many sources, which exceed natural conditions due to human activitiy. As in leaves or gas, chlorophyll gives algae its green color. Algae use chlorophyll to capture energy from sunlight to feed on surrounding nutrients. How we fertilize lawns, maintains septic systems, treat waste water, develop our lakeshores and run our farms and businesses can make the difference between a green lake and a clear lake. In the late 1960s, researchers discovered phosphorus to be a major cause of algae growth and degrading lake water quality. It arrives lakeside via point sources such as wastewater treatment plants, and nonpoint sources, including runoff from farm fields, lawns and streets. And it stays around for longer than anyone understood in those days. “While we have long recognized the impact of excess phosphorus and nitrogen on lake water quality, we did not have enforceable water quality criteria (standards) for the protection of lakes,” says Heiskary. “The MPCA is in the process of developing nutrient criteria, in conjunction with a nationwide federal effort, to protect lake and stream water quality.” Public hearings on proposed updates to water quality standards rules, including excess nutrients in lakes are scheduled to begin Aug. 29. Additional details about meeting start times and directions to all offices listed are available on the MPCA Web site www.pca.state.mn.us/water/standards/rulechange:
Nutrients in runoff feed algae in lakes, streams
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