Blue-green algae (cyanobacteria) have been around for billions of years. Typically blooming during the summer months, they tend to prevail in nutrient rich standing waters. When nutrient concentrations throughout the watershed (and associated runoff) increase, blooms become more frequent and longer sustained as blue-green algae have a tendency to outcompete other phytoplankton groups.
These microscopic organisms are naturally present in Minnesota waterbodies at low levels. When conditions are favorable the number of algae can increase dramatically forming “pea-soup” blooms and scums on the water surface.
Some cyanobacterial species produce toxins that when ingested or inhaled, can cause short- and long-term health effects. Effects range from tingling, burning, numbness, drowsiness, and dermatitis to liver or respiratory failure possibly leading to death. Not all cyanobacteria produce toxins, but the presence of blue green algae is a marker for a potential hazard. The Minnesota Pollution Control Agency advises that for human and pet safety it is best to stay out during these conditions.
The health of our water resources depends largely on the decisions that landowners make on their properties. When waterfront lots are developed, a shift from native plants and trees to impervious surfaces and lawn often occurs.
Impervious surfaces are defined as hard, man-made surfaces that make it impossible for rain to infiltrate into the ground. Examples of impervious surfaces include rooftops, paved driveways, and concrete patios. By making it impossible for rainwater to infiltrate into the soil, impervious surfaces increase the amount of rainwater that washes over the soil surface and feeds directly into lakes and streams. This rainwater runoff can carry pollutants such as sediment, lawn fertilizers, which directly contribute to proliferation of blue-green algae blooms.
Lawns in and of themselves are not particularly harmful and can provide an area for families to recreate. However, problems arise when lawns are not property maintained, over-fertilized, located in areas important to wildlife habitat, or located on steep slopes.
Common lawn species, such as Kentucky bluegrass, are often dependent on chemical fertilizers and require mowing. Excess chemical fertilizers are washed directly into the adjacent water during precipitation events. The phosphorus and other nutrients in fertilizers, which produce lush vegetative growth on land, are the same nutrients which fuel algae blooms and decrease water clarity in a lake. Additionally, since common lawn species have very shallow root systems, when lawns are located on steep slopes, the impacts of erosion can be intensified. Avoiding establishing lawns on steep slopes and at the water-land interface can provide direct positive impacts on lake water quality.
One of the best practices for a lake property is to allow for a buffer along your lakeshore. The wider the strip, the better, but even a strip just a few feet wide can make a big impact in reducing nutrients running off your lawn and directly into the lake. The taller, grassy and perennial vegetation can slow the water running off your lawn, and give it an opportunity to infiltrate into the soil. If you decide to plant native species, the larger and deeper root systems further increase soil infiltration. Plus, they may be able to utilize and store any excess nutrients from fertilizer. These buffer strips can be comprised of just turf grass you are not mowing, to a mixture of native grasses, sedges, flowering perennials, and shrubs. The more native species and diversity that you include in your buffer, the more effective it will be in stopping runoff from entering the lake. Flowering plants can help increase the aesthetics of the buffer, as well as create critical pollinator habitat. The deep root systems of the native perennials and shrubs also can help stabilize your shoreline which will reduce erosion and mitigate flooding issues.
Property owners farther from the lakeshore also play a role in slowing the flow of water across the landscape towards lakes and rivers. Installation of rain gardens or rain barrels to collect roof or runoff as well as the planting of trees all have a cumulative effect on our waterways.
For more information contact the Pine Soil and Water Conservation District at 320-216-4240 or the Pine County Planning & Zoning office at 320-216-4220.
The Authors: Jeremy Williamson is with the Pine County Planning and Zoning Department, while Paul Swanson is with the Pine Soil and Water Conservation District.