Ohio Sea Grant Fact Sheets
Dr. Jeff Reutter’s Answers to Frequently Asked Questions
What is a harmful algal bloom?
A harmful algal bloom (HAB) is any large increased density of algae that are capable of producing toxins. In freshwater, such as Lake Erie, those algae tend to be cyanobacteria - more commonly known as blue-green algae - that are always present in the water to some extent, but which grow excessively under certain conditions. Many species of blue-green algae float so when the water is calm, they will form a scum at the surface. However, wind and waves mix them throughout the water column. The blooms that are most common in Sandusky Bay are composed of a species that does not float.
What makes cyanobacteria bloom?
Harmful algal blooms are caused by a combination of warm water temperatures (above 60 degrees Fahrenheit) and high concentrations of phosphorus in the water. Typically, a high concentration of phosphorus and nitrogen in cold weather will produce a bloom of diatoms, in cool weather we would expect a bloom of green algae, and in warm weather we often see blue-green algae.
Why do we focus so much on phosphorus?
Phosphorus is one of the three major components in most fertilizers, along with nitrogen and potassium. On a bag of fertilizer, the concentration of each is expressed as the N:P:K ratio, three numbers that show the relative amount of nitrogen to phosphorus to potassium in the bag (29-3-5 for example). If we put fertilizer on our lawns, our grass grows. If we put in on our crops, the crops grow. If we add it to water, algae grow. In freshwater, the single essential nutrient that is in the shortest supply is phosphorus (in saltwater, it is usually nitrogen). Therefore, if we reduce the supply of phosphorus, the bloom can’t grow.
How does phosphorus get into the water?
In Lake Erie, the majority of the phosphorus (approximately two-thirds) that causes HABs comes from agricultural fertilizer and manure runoff, when heavy rain washes soil and fertilizer into rivers and streams that eventually enter the lake. Some phosphorus also comes from sewage treatment plants, combined sewer overflows, cleaning products, faulty septic tanks, and residential lawn fertilizers.
However, lawn fertilizer was never a big problem, and in January 2013, the Scott's Miracle Grow Co. completely removed phosphorus from most of its lawn care products.
When does most phosphorus enter the lake?
The majority of phosphorus, or “load,” comes in during storms. We estimate that 80-90% enters the lake during heavy rain storms.
Is nitrogen important?
The simple answer is “yes.” Some species of blue-green algae require nitrogen to be in the water, which could come from agricultural runoff, sewage treatment plants, septic tanks, lawn fertilizer, etc. Other species can obtain nitrogen from the air and are referred to as "nitrogen fixers." It appears that nitrogen concentrations can determine the species of blue-green algae that blooms when phosphorus concentrations are high. They also seem to impact the ability of the algae to produce the toxin, so less nitrogen could make a bloom less toxic. This is likely due to the fact that the algal toxin is 14% nitrogen by weight, making nitrogen a major component of the toxin.
Where and when do HABs start in Lake Erie?
Because blue-green algae prefer warm water and high concentrations of phosphorus, they usually occur first in Maumee Bay at the mouth of the Maumee River and in Sandusky Bay at the mouth of the Sandusky River. Both bays are very warm and shallow, with very high percentages of agricultural land in their watersheds. The Maumee is the largest tributary to the Great Lakes and drains 4.2 million acres of agricultural land. As a result, both streams contain very high concentrations of phosphorus.
We divide Lake Erie into three basins. The Western Basin is west of Sandusky, the Eastern Basin is east of Erie, Pa., and the Central Basin lies between Sandusky and Erie. The Western Basin has an average depth of 24 ft., the Central Basin average depth is 60 ft., and the Eastern Basin has the deepest point—210 ft. HABs are most common in the Western Basin. Blooms in the Central Basin are very hard to predict, less severe, shorter lived, and cover less area than blooms in the Western Basin. The Eastern Basin does not get HABs, but it has unacceptably large densities of nuisance algae on the bottom.
Why do we have more HABs in Lake Erie than the other Great Lakes?
Lake Erie is the southernmost and shallowest of the Great Lakes. The other four Great Lakes are all over 750 ft. deep, but the deepest point in Lake Erie is 210 ft., and it is the smallest of the Great Lakes by volume. Therefore, Lake Erie is also the warmest of the Great Lakes. The watersheds around the other four Great Lakes are dominated by forest ecosystems, while the watershed around Lake Erie has the least forest land, the most agricultural land and the second most urban/suburban land. Therefore, Lake Erie gets more sediment and nutrients (fertilizer runoff, sewage, etc.) than the other lakes. Because it is the southernmost, shallowest, warmest, and gets the most nutrients, then biologically Lake Erie has to be the most productive of the Great Lakes. Indeed, Lake Erie has often produced more fish for human consumption annually than the other four Great Lakes, combined. However, it is possible to have too much of a good thing and a little bit of phosphorus helps to make Lake Erie the “Walleye Capital of the World,” but too much leads to too much algae and the wrong kinds of algae.
What happened in Toledo this weekend? (August 1-4, 2014)
Wind and water currents pushed the algal bloom that was present in the western basin of Lake Erie, near Toledo, into the area where the Toledo water plant takes in water from the lake. Wind also caused waves that mixed the cyanobacteria into the water column so they could be sucked into the water plant. Though not required by USEPA or OEPA, regular water testing is part of the plant's everyday routine. The plant was removing toxins from the raw lake water to produce the final drinking water, but on 2 August, the treated drinking water had a toxin concentration that was above the 1.0 ppb level recommended by the World Health Organization (WHO). When levels of algal toxin exceeded those recommended by the WHO, the city issued a drinking water ban.
NOAA’s Experimental Lake Erie Harmful Algal Bloom Bulletin is easily viewable on their website. The image from 1 August 2014 clearly shows that the bloom was limited to the extreme western end of the lake and covered the Toledo water intake. The image from 4 August shows how rapidly a bloom can grow and move in a short time. We recommend that all Lake Erie users monitor the location of blooms regularly. Fortunately blue-green algae contain a pigment that most other algae do not have, so the satellite can detect the light from this particular pigment and show us where the blooms are most severe (red color of the bulletin).
What toxin was found in the water? What does it do to people?
The toxin of greatest concern in Toledo was microcystin, which causes skin rashes, GI problems, and nervous system, liver and kidney damage. While most healthy adults recover from contact with the toxin, it can be more problematic to children, the elderly, and people with pre-existing conditions that weaken their systems. Exposure has also killed people in other parts of the world. The toxin can also be fatal to pets that drink or come in contact with contaminated water.
What do toxin levels mean?
The US does not currently have a national standard for safe microcystin levels, but the World Health Organization sets the maximum allowable amount of microcystin in drinking water at 1 part per billion (ppb) - about equivalent to 1 drop of toxin in an Olympic-sized swimming pool. While regulations vary across the Great Lakes region, Ohio follows that recommendation.
How big was the affected area? If the lake water is toxic, isn't it toxic everywhere?
All water plants routinely monitor the water they bring in for human use, so if the problem moves, affected areas will know about it quickly. The bloom that caused the Toledo incident was limited to Maumee Bay, but over the weekend, it expanded along the shoreline to near Port Clinton. The toxin can persist in the water for more than 30 days, but is rapidly diluted and quickly reaches safe levels when the bloom dissipates and as one moves away from the bloom.
How is toxin removed from the water?
Water treatment plants use activated charcoal (also called activated carbon) to remove toxic substances from the water. The toxins, such as microcystin, bind to the charcoal particles, which are then filtered out of the water again.
What about Lake Erie fish? Are they safe to eat?
What do I need to do now that the water ban is over?
If you were affected by the water ban, check with your local water utility on steps to take for cleaning/flushing your system with clean water. The Lucas County Health Department also offers guidance on their website
Do zebra and quagga mussels impact the HAB issue?
Yes. We found the first zebra mussel at Stone Lab on 15 October 1988 when a limnology class from Ohio State observed some on our docks as they were being removed. Recognizing the significance of this observation, we started a research project one month later on 15 November 1988 to document the spread. One year later, fall 1989, the density of zebra mussels in the Western Basin of Lake Erie reached 30,000/square meter. In the late 90’s the quagga mussel started to appear. It is a close relative and in the same genus as the zebra mussel, Dreissena. Over the years, the quagga has been replacing the zebra and most casual observers would have a difficult time telling them apart. They look like small clams, about as big as your thumbnail, do not have eyes, and are both filter feeders. They have a small tube or siphon that sticks out of the hinge of their shell through which they suck water out of the lake. They filter the small particles out of the water (algae and the microscopic bugs, or zooplankton, that eat the algae) as their food. They then excrete dissolved phosphorus—exactly the kind the algae need. Since they tend to live in greater concentrations in nearshore areas, they also then recycle the phosphorus and increase concentrations in these nearshore areas. While feeding, if they suck in a harmful form of algae, they stop filtering, spit it out, and then start filtering again. In the process, they remove the things that compete with zebra and quagga mussels.
Does climate change have an impact on Harmful Algal Blooms?
Yes. Blue-green algae or cyanobacteria prefer warm water, and temperatures over the last 50 years have been increasing, but a more important impact of climate change is an increased frequency of severe storms. In Ohio and the Midwest, severe storms that produce over 3 inches of rain in a 24-hour period have increased very significantly. Since 80-90% of the phosphorus entering the lake comes in during severe rain events, any significant impact in severe storms will add more phosphorus to the lake and make the HAB problem worse.
Could this happen again?
It is highly likely that conditions in the lake that led to this event will occur again this year and in future years until phosphorus loading is reduced by at least 40%. However, modification of operating procedures at water plants make it much less likely that a drinking water ban would be necessary.
How do we eliminate harmful algal blooms?
From the discussions above it should be obvious that we could make it colder, reduce the frequency of severe storms, eliminate zebra and quagga mussels, or reduce the amount of phosphorus going into the lake, and reducing nitrogen would also help. I don’t think anyone expects us to be quickly successful in reducing our contributions of green house gases to the atmosphere, so we can’t reduce the frequency of severe storms. With aquatic invasive species like zebra and quagga mussels we focus on preventing them from getting into the Great Lakes, because once they are in and established, there isn’t much we can do. Therefore, our only lever in eliminating HABs is to greatly reduce phosphorus loading, and the Ohio Phosphorus Task Force II report calls for a 40% reduction of phosphorus loading to eliminate or greatly reduce HABs in the Western Basin.