Monitoring Algal Blooms in the Great Lakes Basin
Scientists apply cutting-edge technologies to monitor algal blooms in Lake Erie and the upper Great Lakes.
In the summer of 2014 the city of Toledo instituted a days long water consumption ban for the approximately 500,000 customers they serve in northwest Ohio. A bloom of Microcystis algae in Lake Erie’s western basin, in the vicinity of the city’s water intake station, led to the water consumption ban.
Microcystis, sometimes referred to as a blue-green algae, is one of a number of cyanobacteria genera capable of producing microcystin, a class of toxins that are potentially harmful to humans and other animals following consumption of toxin-containing water.
Such cyanobacteria blooms, different from from non-toxic nuisance algal blooms, are often referred to as harmful algal blooms (HAB).
The 2014 algal bloom event in Lake Erie is part of a larger problem affecting bodies of water across the globe that may be driven in part by changes brought about by climate change.
Predicting Algal Blooms
The preconditions necessary for algal blooms, whether harmful or nuisance species of algae, are complex and multifactorial, and include increasing water temperatures and the introduction of invasive species such as zebra and quagga mussels.
The most important driver for HABs in lakes is the introduction of excess nutrients essential for algal growth, especially nitrogen and phosphorus. Climate change models predict increased runoff into rivers as a result of changes in precipitation — more intense rain storms — in the Great Lakes basin.
Most of these nutrients arrive in Lake Erie through runoff from agricultural land in the Maumee River watershed, according to Dr. Steven Ruberg, group leader in marine instrumentation at the National Oceanic and Atmospheric Administration’s (NOAA) Great Lakes Environmental Research Laboratory (GLERL) in Ann Arbor, Michigan.
“When we do a bloom forecast, the strongest correlation on the yearly basis on bloom aerial extent is with the Maumee river,” he said.
Dr. Ruberg and his GLERL colleagues research techniques to monitor phosphorous levels in the lakes in an effort to predict cyanobacterial blooms and associated toxin levels.
The team utilize a number of systems to monitor nutrient loading in the lake, as well as lake’s phosphorus and nitrogen levels.
Not unlike recognizing the early symptoms of a disease in a patient, the solutions these scientists pursue using Lake Erie as the patient, allow them to alert lake communities when their water systems may be threatened.
The GLERL group methods currently in use and under development include:
- Aerial and satellite monitoring of the western basin of Lake Erie to assess the extent of algal blooms over time for the lake.
- Buoys deployed in the lake to provide real time changes in the populations of cyanobacteria by assessing changes in the abundance of two pigments in the algae — chlorophyll and phycocyanin — utilized by the algae for photosynthesis. Phycocyanin is unique to cyanobacteria and finding increased phycocyanin alerts officials of potential HABs.
- Environmental sample processors (ESP) detect daily microcystin toxin levels as well as organism samples for later genetic analysis. Microcystin is usually kept inside the cyanobacteria and a toxin is released when the organism dies. Not all cyanobacteria are capable of producing toxin; the rapid genetic analysis identifies whether the blooms are harmful.
- There is a lot of information gathered from these various technologies; it’s important that the scientists and coastal community leaders can trust the information being provided. To this end, the daily data collected from the buoys and ESP are compared to measurements of the same information collected in weekly water samples from a ship sent out to sample Lake Erie directly.
These data collection efforts have confirmed the Maumee River as the primary source of nutrient loading into Lake Erie.
The Wind
The monitors placed around the western basin of Lake Erie allowed the scientists to identify a second important indirect source of nutrients contributing to algae blooms: the wind.
Winds blowing across the lake from the right direction with enough speed can churn up water and sediments in the lake’s shallows leading to suspension (lifting) of sediments from the lake’s bottom.
Algae can not access nutrients being held in the sediments unless these sediments move up in the water.
“We don’t see strong correlation with wind events (and algal blooms) except in the nearshore areas where satellites can’t pick it up as readily. The stronger the wind event, the further out it impacts the lake. A large area of the western basin can be re-suspended because it’s so shallow,” Ruberg said.
The differences in response to nutrients and increases in algae between nearshore and the central deeper basin provide an added layer of complexity to the algal bloom problem.
Dr. Mark Rowe, a scientist at the University of Michigan’s Cooperative Institute for Great Lakes Research, is interested in understanding how the hydrodynamics (how water moves) within the lakes affect the Great Lakes biology and ecology.
“One of the topics of current interest in Great Lakes management is in nearshore water quality,” he said. “Early models of the Great Lakes were of a well-mixed box to determine nutrient management. Now with more detailed hydrodynamic models, we’re able to model movement of nutrients from the nearshore to offshore regions,” Dr. Rowe said.
If you’ve ever been swimming in the Great Lakes and noticed a sudden change from tolerable water temperatures to much colder temperatures as swam deeper to the the bottom, that border between the warm surface and the cold bottom is referred to as the thermocline.
The thermocline does more than take your breath away as you swim to the bottom of a lake, it demarcates the border between two distinct ecosystems.
The warmer, less dense (lighter) water at the surface that is warmed by the sun’s energy is separated from the deeper, colder more dense (heavier) water nearer the bottom of the lake.
The thermocline acts as a barrier to the movement of oxygen into these deeper regions, preventing mixing of the surface and deep waters. The thermocline keeps oxygen lower in the deepest regions of the lakes while the surface waters are well oxygenated.
Waves caused by the wind can lower oxygen causing a problem for living creatures in the lakes.
Dead Zones Discovered in the Lake
Dr. Rowe’s team of scientists placed sensors in Lake Erie to monitor oxygen levels in deep offshore waters. They were trying to relate oxygen level changes to nutrients coming into the lake and cyanobacteria blooms.
They discovered that hypoxic (very low oxygen) zones develop in the deep waters following algal bloom events.
Hypoxic zones, some times called dead zones by the news media, develop in water in response to nutrients and algae(see figure below for pictorial summary):
- Nutrient (nitrogen and phosphorous) run off into waters.
- Algae feed on the nutrients and increase in numbers.
- As the algae die, they sink to the bottom deep waters in large numbers.
- Decomposition of the dead algae requires oxygen, pulling oxygen from the water, lowering the dissolved oxygen levels even lower, with regions of hypoxia developing.
Hypoxia can negatively affect water quality for human consumption. Low dissolved oxygen itself wouldn’t affect taste or appearance of water, but Dr. Rowe said that hypoxia alters the chemistry within these lake zones.
“The same process that depletes the water of oxygen at the bottom produces carbon dioxide, and this decreases the pH of the water making it more more acid and corrosive to water systems at treatment plants,” he said.
As we know from the situation in Flint, Michigan, corrosion over time can expose people to lead and copper present in the pipes that deliver water to people’s homes.
In addition to the potential for corrosive conditions from hypoxic water, there can be issues with discolored water drawn from hypoxic zones.
Algal Blooms in the Upper Great Lakes
There is interest and concern as to whether the algae bloom problem documented to be present seasonally in Lake Erie may develop in the upper Great Lakes.
Lake Erie is the smallest, shallowest, and warmest of the lakes, providing an environment conducive to algal blooms.
“It (algal blooms) already is a problem in Green Bay; it’s a problem in the Bay of Quinte in Ontario and Lake St. Clair in Canadian waters through the Thames river, which is a heavily sedimented river through agriculture. We already have seen Microcystis in the Saginaw Bay, and already have a program there,” said Dr. Ruberg.
The next step to address this issue is to develop a seasonal program based on what they’ve learned by studying Lake Erie.
Much has been learned about how and why algal blooms have reemerged as a problem in Lake Erie so many decades after the lake was pronounced dead from similar blooms in the 1960s and 1970s.
There’s a been a pledge to cut phosphorous influx into Lake Erie by 40 percent by both the U.S. and Canada, but nobody really knows what impact this would have on the health of Lake Erie or the rest of the Great Lakes.
Dr. Henry Vanderploeg, a senior ecologist at the GLERL, warned we shouldn’t be too quick to draw conclusions from how Lake Erie responds to these proposed cuts in phosphorous to the upper Great Lakes. “We’re running an experiment without really knowing what might happen in Lake Erie, let alone much larger lakes such as Lake Michigan,” he said.
There is no single solution to the problem of algal blooms in Lake Erie and the upper Great Lakes, particularly going forward with the challenges presented by climate change in the Great Lakes basin.
A continued pursuit of knowledge about the problems provide hope that we’ll have the understanding necessary to identify the solutions to the next problems that will surely arise.
