Algal Blooms: A Potential Threat for the Great Lakes
Climate change and agricultural practices create fertile environments for algal blooms in the Great Lakes.
In early August 2014, Toledo, Ohio citizens lost access to drinking water. Lake Erie hadn’t dried up overnight. The loss of water to their homes was attributed to an explosive growth of a Microcystis — a ubiquitous microorganism that lives throughout the world’s waterways. It had made Toledo’s water harmful to the 500,000 people who rely on it. After three days, the bloom dissipated but left the city shaken and scrambling to ensure the crisis would not be repeated. Toledo’s mayor compared it to 9/11.
So far, a similar algae crisis hasn’t resurfaced in Toledo, but the chaos prompted investigations into how algae could have such a paralyzing impact on a community’s access to water.
Algal Blooms Defined
Algae are a diverse group of organisms defined by their ability to produce oxygen through photosynthesis, but are unlike plants familiar to most people.
Algae are found in the scuzz blanketing the bottom of a birdbath, the green slime on the sidewalk beneath a leaky pipe, and even the nori wrapped around a sushi roll.
Despite the imagery associated with them as being pond scum, algae can be incredibly useful. For example, their photosynthetic activity was the source of Earth’s first oxygen and today’s land plants can be traced back to freshwater green algae.
An algal bloom is a marked by an increase in algal growth. Algal blooms are part of that eons-old natural seasonal cycle, but they become problematic when certain human actions push algae abundance to extreme concentrations. When a concentrated bloom happens, algae visibly color lake waters, threaten water supplies, and harm marine organisms such as fish, sea turtles, dolphins, or manatees.
Algae are diverse. Several species of one genus of potentially harmful algae, Microcystis, can produce and release microcystin, a toxin that can harm humans and other animals if ingested. Microcystis is what shut down Toledo’s water in 2014.
Not only have algal blooms appeared in Lake Erie, but increasing blooms are a global problem. Blooms have been found in China and Australia lakes and Florida waters.
Causes of Algal Blooms
The prevention of algal blooms in Lake Erie has proven to be a challenge. Fertilizer from farms in the Maumee River watershed washes off the fields into the river with heavy rains, eventually draining into the lake.
Climate change could be making this problem worse.
In Michigan, predicted heavy sporadic rains are expected to increase thanks to climate change resulting in the movement of more phosphorus-bearing soil into rivers, which then can feed into the Great Lakes. Nitrogen and phosphorus, but especially phosphorus, encourages the growth of Microcystis.
Changing agricultural practices can avoid some of this risk. However, climate change compounds the risks to Michigan’s waterways. A 2009 National Climate Assessment report created by a team of more than 300 experts has shown a rapid increase in temperature especially between 1950 and 2010. And the United States Geological Survey predicts that average high temperatures in Michigan could rise by seven degrees Fahrenheit by 2100.
Toxins in the water supply and Great Lakes
Expanding agriculture and increasing human populations (whose laundry detergents and sewage might bear phosphorus) along with changing precipitation patterns and warmer weather all contribute to the spread of blooms.
These complex and emerging patterns foreshadow possible threats to the upper Great Lakes.
Invasive filter feeders like quagga and zebra mussels strain beneficial phytoplankton and zooplankton and other materials out of the water. These feeders allow more sunlight to reach deeper in to the lakes. Although a clear lake is ideal for swimming, clear lakes provide perfect conditions for algal blooms.
The warming of the Great Lakes can be detrimental. When surface water cools, it sinks, mixing with the water at the bottom. The warming of lakes can prevent this beneficial mixing process. Algal blooms can grow longer in warm lake waters creating a dead zone where low-oxygen water collects at the bottom.
As seen in the figure above, higher water temperature changes provide favorable conditions for cyanobacteria blooms. Under warmer climate conditions, a thick layer of warm surface water (pale blue) develops, driving the thermocline (the horizontal line separating the less dense warm surface waters from the colder deeper water) further down into the water depths.
This partitioning prevents mixing of the two waters, making the surface favorable for cyanobacteria growth. Microcystis containing microcystin toxin are buoyant because they float to the surface to capture the sun’s energy.
Excess nutrients in the water from increased runoff, especially phosphorus and nitrogen, feed increased numbers of Microcystis into the water. When the Microcystis die, the toxin is released in the water and can reach municipal water treatment plants.
While algal blooms may threaten parts of the Great Lakes in a warming climate, a host of researchers, volunteers, and careful farmers are actively addressing these problems. We investigated some of those solutions to problems endangering the Great Lakes in this in-depth project.
