NSF ARTICLE ON PROBLEMS WITH SOME GREEN LAKES AND RIVERS

FROM:  NATIONAL SCIENCE FOUNDATION
Earth Day is on the horizon. But is 'greener' always better?

Not when it's the bright green waters of algae-fouled lakes and rivers
Going green. On Earth Day and every day, being "greener" is linked with good things like lowering your carbon footprint and eating locally-grown foods.

But not when it comes to drinking or swimming in the bright green waters of lakes fouled by algae, says Hans Paerl, an environmental scientist at the University of North Carolina at Chapel Hill.

In freshwater lakes around the world, such algae blooms often result from an overabundance of what's known as cyanobacteria, or blue-green algae.

Cyanobacteria form widespread, very visible blooms that look like blue-green paint or scum floating on the water. They may be toxic to humans and other animals.

These filamentous bacteria clump into mats that cover a lake's surface from one shore to the other, using up oxygen in the water and eventually turning the lake's depths into a dead zone.

From Lake Taihu, China, to Lake Erie in the U.S.

It was June 2007, and water spouting from kitchen faucets in Wuxi, China, was pea-soup green. The water came from Taihu, China's third largest lake.

Cyanobacteria obscured the surface of the 900-square-mile lake and quickly overwhelmed the intake plant for the city of Wuxi's drinking water.

Chinese officials scooped 6,000 tons of algae from Taihu and diverted water from the Yangtze River to flush the lake. However, says Paerl, the bloom persisted. "It was fall when it finally abated."

Two weeks into the bloom, Paerl was in China, leaning over the side of a small boat to take samples of Taihu's scum.

He discovered that the algae is similar to that found in blooms in North Carolina's ponds, rivers and estuaries, and in many larger bodies of water such as Lake Erie, Lake Victoria and the Baltic Sea.

"Nowhere are the blooms worse than on Taihu, however," says Paerl, whose work is funded by an NSF Dimensions of Biodiversity grant. "Habitat for fish, crabs and other aquatic species is becoming endangered."

Ten million people also depend on Taihu for drinking water, fisheries and tourism.

Lake Erie on the border of the United States and Canada faces the same challenges.

In 2011, a record-breaking bloom of similar cyanobacteria to the species that plagued Taihu smothered Lake Erie, turning it a bright-green that showed up on satellite images.

At the bloom's peak in October, it expanded to more than 1,930 square miles, three times larger than any Lake Erie bloom on record.

New "recipe" for controlling algae blooms

The "recipe" for controlling the problem, says Paerl, "has been to reduce phosphorus finding its way into lakes from sources on land like fertilizers. That's based on the long-standing paradigm that phosphorus is the key nutrient limiting freshwater algae blooms."

But another element, nitrogen, flowing into lakes and rivers is increasing more rapidly than phosphorus. "It's led researchers to question whether both nitrogen and phosphorus should be controlled to stem the tide of proliferating algae blooms," says Paerl.

Lake Taihu, he says, is a "looking glass" for addressing such nutrient overenrichment and toxic algae blooms.

"Our NSF Dimensions of Biodiversity project is determining what roles specific nutrients like nitrogen and phosphorus play in the frequency and extent of algae blooms in lakes, and how they affect these ecosystems."

Data from experiments on the relationship between nutrients and algae blooms are being used to formulate a nutrient reduction management strategy. Scientists hope it will lead to the control of blooms in Taihu and other lakes.

The goal, Paerl says, is to find new ways of ensuring sustainable uses of lakes prone to blooms.

Other scientists involved in the research are Wayne Gardner of the University of Texas, Ferdi Hellweger of Northeastern University and Steven Wilhelm of the University of Tennessee.

"Harmful cyanobacteria blooms caused by excessive phosphorus and nitrogen are threatening freshwater lakes worldwide," says Simon Malcomber, lead NSF program director for Dimensions of Biodiversity, which is supported by NSF's Directorates for Biological Sciences and Geosciences.

"This research shows the importance of taking a holistic approach to understanding harmful cyanobacteria blooms," says Malcomber. "Only with an ecosystems approach can long-term successful sustainability strategies be formulated."

Chain of events links land and lake

The complex chain that leads to algae blooms in freshwater begins not in lakes but on land.

Farmers often overfertilize their fields. The excess fertilizer, laden with nutrients like phosphorus and nitrogen, washes into creeks and rivers, where it's eventually carried to lakes.

"Nitrogen is necessary for increasing crop yields," says Paerl, "but plants are inefficient at taking it up. More fertilizer is often added than plants need."

Only a fraction of the nitrogen applied to soils ends up in crops; in some regions, it's less than 20 percent. The rest is on the loose.

When the excess eventually reaches freshwater, it fertilizes aquatic algae such as cyanobacteria--just as it encourages plants on land to grow. The algae proliferate, becoming massive blooms.

As the algae die, they fall to the lake's bottom and are digested by microorganisms. The process removes oxygen from the water, creating low-oxygen "dead zones," fish kills and tainted waters.

Extreme algae blooms: The new normal?

Are algae blooms in lakes around the world a new normal?

Scientists are working to find answers.

"This important work is linking the diversity and identity of algae with nitrogen cycling and harmful algal blooms in heavily affected freshwater lakes," says Mike Sieracki, Dimensions of Biodiversity program director in NSF's Division of Ocean Sciences.

This week at an NSF-funded workshop--Global Solutions to Regional Problems: Collecting Global Expertise to Address the Problem of Harmful Algal Blooms--researchers discussed the current science on algae blooms, and identified knowledge gaps in bloom prevention and mitigation.

"We hope that this workshop will lead to strategies to mitigate future blooms in waterbodies in the U.S. and around the world," says Bill Cooper, program director in NSF's Division of Chemical, Bioengineering, Environmental and Transport Systems.

Meeting topics included the biology of bloom-forming species, environmental factors underlying bloom formation, sensor development in bloom detection, prediction of blooms, and best practices for control.

"New nutrient reduction strategies," wrote Paerl and colleagues in the journal Science in October 2014, "should incorporate point and non-point sources, including nitrogen removal in wastewaters, optimization of fertilizer application, and erosion controls.

"An investment in joint phosphorus and nitrogen controls will counter the very high costs of harmful algal bloom events and the losses of freshwater resources worldwide."

It's the only way, Paerl says, to keep blooms of cyanobacteria and other algae in check. When it comes to lakes and rivers, streams and ponds, "going green" means anything but.

-- Cheryl Dybas, NSF

THE ALGAE BLOOM OF DOOM

Lake Erie , Photo by Lynn Betts, USDA/Wikipedia Commons

FROM: NATIONAL SCIENCE FOUNDATION
Exxtreme Algae Blooms: The New Normal?
A 2011 record-breaking algae bloom in Lake Erie was triggered by long-term agricultural practices coupled with extreme precipitation, followed by weak lake circulation and warm temperatures, scientists have discovered.

The researchers also predict that, unless agricultural policies change, the lake will continue to experience extreme blooms.

"The factors that led to this explosion of algal blooms are all related to humans and our interaction with the environment," says Bruce Hamilton, program director at the National Science Foundation (NSF), which funded the research through its Water, Sustainability and Climate (WSC) Program.

WSC is part of NSF's Science, Engineering and Education for Sustainability (SEES) initiative.

"Population growth, changes in agricultural practices and climate change are all part of the equation," says Hamilton. "These findings show us where we need to focus our attention in the future."

Results of the research are published in this week's online early edition of the journal Proceedings of the National Academy of Sciences (PNAS).

Algae overtakes a lake in Iowa.  Credit:  Wikimedia Commons.

"The 'perfect storm' of weather events and agricultural practices that occurred in 2011 is unfortunately consistent with ongoing trends," says Anna Michalak, the paper's lead author and a scientist at the Carnegie Institution for Science's Department of Global Ecology, located at Stanford University.

"That means that more huge algal blooms can be expected in the future, unless a scientifically-guided management plan is implemented for the region."

Freshwater algal blooms may result when high amounts of phosphorus and nitrogen are added to the water, usually as runoff from fertilizer.

These excess nutrients encourage unusual growth of algae and aquatic plants.

When the plants and algae die, decomposers in the water that feed on them use up oxygen, which can drop to levels too low for aquatic life to thrive.

At first the Lake Erie algae were almost entirely Microcystis, an organism that produces a liver toxin and can cause skin irritation.

The scientists combined sampling and satellite-based observations of the lake with computer simulations to track the bloom.

It began in the lake's Western region in mid-July and covered an area of 230 square miles.

At its peak in October, the bloom had expanded to more than 1,930 square miles. Its peak intensity was more than three times greater than any other bloom on record.

The researchers looked at numerous factors that could have contributed to the bloom, including land-use, agricultural practices, runoff, wind, temperature, precipitation and circulation.

They found that three agriculture management practices in the area can lead to increased nutrient runoff: autumn fertilization, broadcast fertilization (uniform distribution of fertilizer over the whole cropped field), and reduced tillage.

These practices have increased in the region over the last decade.

Conditions in the fall of 2010 were ideal for harvesting and preparing fields and increasing fertilizer application for spring planting.

A series of strong storms the following spring caused large amounts of phosphorus to flow into the lake.

In May alone rainfall was more than 6.5 inches, a level more than 75 percent above the prior 20-year average for the month.

This onslaught resulted in one of the largest spring phosphorus loads since 1975, when intensive monitoring began.

Lake Erie was not unusually calm and warm before the bloom. But after the bloom began, warmer water and weaker currents encouraged a more productive bloom than in prior years.

The longer period of weak circulation and warmer temperatures helped incubate the bloom and allowed the Microcystis to remain near the top of the water column. That had the added effect of preventing the nutrients from being flushed out of the system.

The researchers' data did not support the idea that land-use and crop choices contributed to the increase in nutrient run-off that fueled the bloom.

To determine the likelihood of future mega-blooms, the scientists analyzed climate model simulations under both past and future climate conditions.

They found that severe storms become more likely in the future, with a 50 percent increase in the frequency of precipitation events of .80 inch or more of rain.

Stronger storms, with greater than 1.2 inch of rain, could be twice as frequent.

The researchers believe that future calm conditions with weak lake circulation after a bloom's onset are also likely to continue, since current trends show decreasing wind speeds across the United States.

That would result in longer-lasting blooms and decreased mixing in the water column.

"Although future strong storms may be part of the new normal," says Michalak, "better management practices could be implemented to provide some relief to the problem."

The research was also supported by the NOAA Center for Sponsored Coastal Ocean Research and the Lake Erie Protection Fund.

-NSF-