Lake Erie algae bloom grew so large, it broke the scale

Monday, November 23, 2015, 5:25 PM - This summer, experts warned of a near-record algal bloom in Lake Erie. Even that extreme prediction fell short, though, as this year's toxic algae became so severe, it broke the scale.

Lake Erie has a recurring problem. Each year, during the summer months, a combination of warm waters in the shallow lake's west end, along with sunny weather and phosphorus from sources such as commercial agricultural runoff, sewage and industry, results in a population explosion of cyanobacteria - producing what's known as a harmful algal bloom (HAB).

For over a decade, the US National Oceanic and Atmospheric Administration (NOAA) has been monitoring the extent of these algal blooms in the lake. In recent years, scientists have been plotting these blooms on the Lake Erie Severity Index. Ranked on a scale of zero to 10, the upper limit of the index corresponds to the bloom observed in 2011 - then the most severe bloom ever recorded.

In their forecast for the 2015 bloom, NOAA set an expected severity of 8.7 on the Index, with a potential to go up to 9.5. This was based on conditions through June, especially the nutrient "load" - the amount of phosphorous nutrients that were expected to discharge into the lake prior to reaching the peak of the season.

According to NOAA's Experimental Lake Erie Harmful Algal Bloom Bulletin, dated November 10, 2015, this year's algal bloom went off the top of that scale - with a Lake Erie Severity Index rating of 10.5.

and reaches its maximum extent on September 6, 2015. Images courtesy NASA's MODIS Terra and Aqua instruments.

According to NOAA:

This bloom was unusual in that it started early, in mid-July, achieving maximum biomass in mid-August. Over a 40-day period from late July to the end of August, the biomass detected from satellite exceeded that of any other time period we have monitored, except for the first week of October, 2011. On August 5th, dense scum covered up to 300 square miles of the western basin; this occurred again on August 15th. The 2015 bloom did expand to cover a large area of the central basin. In September, two major cold fronts brought strong winds that disrupted bloom growth and weaken the bloom, causing it to decline much faster than previous major blooms.

Even though this bloom developed into the most severe on record so far, it had less of an impact than previous extreme blooms - the one in 2011, and the 2014 bloom which forced residents of Toledo to turn off their taps for a day in August. In those previous years, the blooms developed closer to shorelines, having a more direct impact on water supplies and on beaches. This year, the bloom was much more spread out, through the central portion of the lake.

One important thing to note regarding this record-setting bloom - it could have been far worse.

Even breaking through the top of the Lake Erie Severity Index scale as it did, the only reason this bloom did not become even more severe was due to the weather. According to the NOAA forecasters, it was two major cold fronts passing through the area that disrupted its growth, as the strong winds over the lake mixed the algae deeper down into the water. This robbed the bloom of its energy source - sunlight - weakening it and preventing it from growing even worse.

RELATED: Toxic algae blooms could boost your cellphone battery

Why are these blooms harmful?

As a bloom spreads throughout the surface layer of lake water, the cyanobacteria release toxins known as microcystins into the environment. Simply swimming in water with high concentrations of microcystins can cause symptoms such as stomach cramps, vomiting, diarrhea, fever, headache, muscle and joint pain, and weakness, as well as skin and eye irritation, sore throat and allergic reactions. If these toxins enter the drinking water supply in sufficient amounts, such as during extreme outbreaks, symptoms can develop that cause liver and kidney damage, or life-threatening bouts of gastroenteritis, aka "stomach flu" (especially for children and the elderly).

Coupled with these toxins, further problems occur due to the life cycle of the cyanobacteria. Since individual bacteria only live for a very short time, even as the bloom spreads, millions of them die in the process. The death and decay of the bacteria strips oxygen from the water (hypoxia), and the dead organisms form a layer of scum on the surface. Thus, the living bacteria in the top layer of the water absorbs sunlight for photosynthesis while at the same time more sunlight is blocked from reaching deeper waters by this scum on the surface. This combination kills off important plant and microorganism species that live deeper down, and as well as any organisms that depend upon them, worsening the hypoxia in the lake water. Some regions of the lake can become "dead zones," with massive fish die-offs ("fish kills") that can make the situation worse.

Sources: NOAA (pdf) | The Weather Network

Watch below: Science@NASA presents The Good, The Bad and the Algae