The Bloom is Off the Lake…But Only for Now
-By Patricia Nease, Watershed Manager
This summer’s cyanobacteria outbreak in Damariscotta Lake may have you wondering: what is cyanobacteria, what do we need to do to prevent future outbreaks, and are harmful/nuisance algae blooms likely in other waters that Midcoast Conservancy cares for?
Cyanobacteria are photosynthesizing bacteria, often called blue-green algae, and are a natural part of our aquatic ecosystems and have been for billions of years. There are many different species of cyanobacteria, and they can live in freshwater, estuarine and saltwater environments. Lakes, ponds and rivers all have communities of phytoplankton that cycle throughout the growing season as seen in the figure. In warmer waters, with high levels of nutrients, cyanobacteria populations are released from competition with algae and dominate the phytoplankton community. If it’s a particularly warm summer, like we saw this year, a lake can experience a ‘bloom’. Blooms of cyanobacteria can be concerning because in addition to decreasing water clarity, cyanobacteria can also create toxins. With cooler temperatures, and more windy lake conditions, cyanobacteria shift from being the dominant phytoplankton and the ‘bloom’ breaks up. However, the cyanobacteria are never removed from the system. Some cyanobacteria will overwinter in the sediments at the bottom of lakes and take up nutrients, only to recirculate into higher parts of the lake with ice out.
What can we do about active cyanobacteria blooms? Unfortunately there’s no “quick-fix” for cyanobacteria blooms; we can’t clean up a bloom that’s already happening so we have to wait for cooler night-time temperatures and increasing winds in the Fall to break up blooms. Climate change is likely to increase the frequency and duration of cyanobacteria blooms in Maine, and potentially in Damariscotta Lake if we aren’t careful. With climate change comes warmer summer temperatures, increased intensity of rain events, and reduced ice coverage. Warmer summer temperatures that extend further into the Fall can delay the break-up of cyanobacteria, and ice coverage of the lake. Intense and sustained rain events are more likely to exceed the infiltration capacity of soil leading to “overland flow” and increasing erosion. Sediment particles carry phosphorus, so any sediment entering the lake also brings nutrients too. Reducing erosion by maintaining at least a 10 foot vegetated buffer between houses and roads, paired with routine septic maintenance and reducing or eliminating fertilizer use, can dramatically reduce the amount of nutrients that enter the lake and decrease the likelihood of future cyanobacteria outbreaks or blooms.
To dive deeper into cyanobacteria, visit our Damariscotta Lake page. For current lake information, follow the Damariscotta Lake Watch Facebook page or Instagram account.
Graphic courtesy of aterontheweb.org
