In Lakes, Cat Tails and Algal Blooms could be a Toxic Methane Feedback

We know that creating new lakes with dams is not a good idea climate wise, as emissions of methane are thought to be significant.

Turns out that under current conditions, existing lakes can become significant sources as well – another example of not-so-positive positive feedback in the climate system.

Inside Climate News:

Blooms of harmful algae in the nation’s waters appear to be occurring much more frequently than in the past, increasing suspicions that the warming climate may be exacerbating the problem.

The Environmental Working Group (EWG) published newly collected data on Tuesday reporting nearly 300 large blooms since 2010. Last year alone, 169 were reported. While NOAA issues forecasts for harmful algal blooms in certain areas, the advocacy group called its report the first attempt to track the blooms on a nationwide scale.

The study comes as scientists have predicted proliferation of these blooms as the climate changes, and amid increasing attention by the news media and local politicians to the worst cases.

Just as troubling, these blooms could not only worsen with climate change, but also contribute significantly to greenhouse gas emissions.

EWG based its study on news reports and before-and-after satellite images that show the expansion of the blooms. Though the rapid increase in the annual numbers might reflect more thorough observations and reporting in recent years, Craig Cox, who focuses on agriculture for EWG, said the numbers may still be on the low side.

In 2014, the news was especially urgent in Toledo, where a toxic algal bloom in Lake Erie forced health officials to declare the water unsafe for drinking and bathing. Harmful algae blooms had been common in the western part of Lake Erie from the 1960s through the 1980s, but they had diminished with better pollution controls—until about a decade ago, according to NOAA.

Now the blooms—thick undulating mats of green—have become an annual occurrence there.

The root cause of the problem lies mainly in agricultural runoff that contains phosphorus, which encourages algal growth.

At a recent conference, the mayor of Toledo pointed the blame for the continuing problem squarely at the Ohio Farm Bureau Federation, saying that lawmakers in the state were too intimidated by the group to support legislation to deal with the problem. “It’s probably the most powerful interest group in Ohio,” Mayor Wade Kapszukiewicz said in an interview.

Kapszukiewicz noted that the city spent billions of dollars upgrading its water treatment facility more than a decade ago and that there have been no sewage overflows into the lake since then, and yet the blooms are getting worse. “Toledoans are paying for a problem we didn’t create,” he said.

“Nutrient runoff” comes from sewage and other sources, but mostly from fertilizer and manure, which are especially high in phosphorus.

Meanwhile, researchers have found evidence that algal blooms are not just consequences of climate change, but are also sources of climate-warming emissions.

In a study released in March, researchers affiliated with the University of Minnesota, Minnesota Sea Grant and the U.S. Environmental Protection Agency found that, globally, lakes and manmade “impoundments” like reservoirs emit about one-fifth the amount of greenhouse gases emitted by the burning of fossil fuels. The majority of that atmospheric effect comes from methane, an especially potent short-lived climate pollutant.

“We found that, as the lakes go greener, more eutrophic, the atmospheric effect of the lakes skyrockets,” said John Downing, the paper’s lead researcher and director of the Minnesota Sea Grant. “That’s because plants are decomposing and shooting methane and CO2 into the atmosphere.”

Downing and his colleagues also found that even small increases in harmful algal blooms could impact the atmosphere. “Basically a little increase [in algal blooms] could cause the greenhouse effect of lakes to increase 5 to 40 percent,” Downing said.

Since the study was published, Downing and his colleagues have continued looking into changes in Lake Erie, which Downing called “one of the poster children for algal blooms.”

“The atmospheric impact of those gases coming out of Lake Erie right now is probably 18 times the atmospheric effects of all the cars in the city of Detroit,” Downing said.

“If we take Lake Erie and change it, and make it as green as the part around Toledo, then the carbon emissions from the lake increases two-and-a-half more times and the atmospheric impact is equivalent to adding another seven million cars on the road,” he said.

“People are concerned that [algal blooms] stink and they hurt their pets,” Downing said. “But there’s another reason to not have your lakes ruined: They can change the climate in a significant way.”

And in a separate study:

Yale Environment 360:

Warming global temperatures have helped boost the growth of freshwater plants like cattails in the world’s lakes in recent decades. Now, scientists have found that this surge in aquatic plant growth could double the methane being emitted from lakes — already significant sources of methane — over the next 50 years.

The research, published in the journal Nature Communications, reveals a previously unknown climate feedback loop, where warming triggers the release of greenhouse gases, which in turn triggers more warming — similar to what is happening with Arctic’s melting permafrost. Freshwater lakes currently contribute as much as 16 percent of the world’s methane emissions, compared with just 1 percent from oceans.

Lakes produce methane when plant debris is buried in sediment and consumed by microbes. The scientists studied differences in methane production from biomass that originated in lakeside forests and from dead aquatic plants growing in the water. They found that forest-derived biomass helped to actually trap carbon in the lake sediment, reducing methane emissions. But aquatic plant biomass actually fueled methane production. Lake sediment full of decaying cattails produced over 400 times the amount of methane as sediment with plant debris from coniferous trees, and almost 2,800 times the methane from deciduous tree-filled sediment.

“The organic matter that runs into lakes from the forest trees acts as a latch that suppresses the production of methane within lake sediment,” Erik Emilson, an ecologist at Natural Resources Canada and lead author of the study, said in a statement. “Forests have long surrounded the millions of lakes in the northern hemisphere, but [they] are now under threat. At the same time, changing climates are providing favorable conditions for the growth and spread of aquatic plants such as cattails, and the organic matter from these plants promotes the release of even more methane from the freshwater ecosystems of the global north.”

Using models of the Boreal Shield, a lake-filled ecosystem that stretches across central and eastern Canada, Emilson and his colleagues calculated that the number of lakes colonized by just the common cattail (Typha latifolia) could double in the next 50 years — resulting in a 73 percent increase in lake-produced methane in that part of the world alone.