OCEAN PHOSPHORUS CYCLE AND THE ROLE OF MICROBES

FROM:  NATIONAL SCIENCE FOUNDATION
Revealing the ocean's hidden fertilizer
Tiny marine plants play major role in phosphorus cycle
Phosphorus is one of the most common substances on Earth.

An essential nutrient for every living organism--humans require approximately 700 milligrams per day--we're rarely concerned about consuming enough because it is in most of the foods we eat.

Despite its ubiquity and living organisms' dependence on it, we know surprisingly little about how it moves, or cycles, through the ocean environment.

Scientists studying the marine phosphorous cycle have known that phosphorus was absorbed by plants and animals and released back to seawater in the form of phosphate as these plants and animals decay and die.

But a growing body of research hints that microbes in the ocean transform phosphorus in ways that remain a mystery.

Hidden role of ocean's microbes

A new study by a research team from the Woods Hole Oceanographic Institution (WHOI) and Columbia University reveals for the first time a marine phosphorus cycle that is much more complex than previously thought.

The work also highlights the important but previously hidden role that some microbial communities play in using and breaking down forms of this essential element.

A paper reporting the findings is published this week in the journal Science.

"A reason to be excited about this elegant study is in the paper's last sentence: 'the environmental, ecological and evolutionary controls ...remain completely unknown,'" says Don Rice, program director in the National Science Foundation's (NSF) Division of Ocean Sciences, which funded the research through its Chemical Oceanography Program. "There's still a lot we don't know about the sea."

The work is also supported by an NSF Dimensions of Biodiversity grant.

"This is an exciting new discovery that closes a fundamental knowledge gap in our understanding of the marine phosphorus cycle," says the paper's lead author Ben Van Mooy, a biochemist at WHOI.

Much like phosphorus-based fertilizers boost the growth of plants on land, phosphorus in the ocean promotes the production of microbes and tiny marine plants called phytoplankton, which compose the base of the marine food chain.

Phosphonate mystery

It's been unclear exactly how phytoplankton are using the most abundant forms of phosphorus found in the ocean--phosphates and a strange form of phosphorus called phosphonates.

"Phosphonates have always been a huge mystery," Van Mooy says.

"No one's been able to figure out exactly what they are, and more importantly, if they're made and consumed quickly by microbes, or if they're just lying around in the ocean."

To find out more about phosphonates and how microbes metabolize them, the researchers took samples of seawater at a series of stations during a research cruise from Bermuda to Barbados.

They added phosphate to the samples so they could see the microbes in action.

The research team used ion chromatography onboard ship for water chemistry analyses, which allowed the scientists to observe how quickly microbes reacted to the added phosphate in the seawater.

"The ion chromatograph [IC] separates out the different families of molecules," explains Van Mooy.

"We added radioactive phosphate, then isolated the phosphonate to see if the samples became radioactive, too. It's the radioactive technique that let us see how fast phosphate was transformed to phosphonate."

Enter the microbes

The researchers found that about 5 percent of the phosphate in the shallow water samples was taken up by the microbes and changed to phosphonates.

In deeper water samples, which were taken at depths of 40 and 150 meters (131 feet and 492 feet), about 15 to 20 percent of the phosphates became phosphonates.

"Although evidence of the cycling of phosphonates has been mounting for nearly a decade, these results show for the first time that microbes are producing phosphonates in the ocean, and that it is happening very quickly," says paper co-author Sonya Dyhrman of Columbia University.

"An exciting aspect of this study was the application of the IC method at sea. In near-real-time, we could tell that the phosphate we added was being transformed to phosphonate."

Better understanding of phosphorus cycle

A better understanding of phosphorus cycling in the oceans is important, as it affects the marine food web and, therefore, the ability of the oceans to absorb atmospheric carbon dioxide.

The researchers say that solving the mystery of phosphonates also reinforces the need to identify the full suite of phosphorus biochemicals being produced and metabolized by marine microbes, and what physiological roles they serve for these cells.

"Such work will help us further resolve the complexities of how this critical element is cycled in the ocean," Dyhrman adds.

Grants from the Simons Foundation also supported the work.

-NSF-
Media Contacts
Cheryl Dybas, NSF

NUTRIENT POLLUTION AND HARMFUL ALGAL BLOOMS IN STREAMS

FROM:  NATIONAL SCIENCE FOUNDATION
Nutrient pollution from nitrogen and phosphorus reduces streams' ability to support aquatic life
Residence time of leaves and twigs, important to stream-dwelling species, can be halved

Nutrient pollution from nitrogen and phosphorus in streams has long been known to increase carbon production by algae, often causing nuisance and harmful algal blooms.

But according to results of a new study, nutrient pollution can also result in the loss of forest-derived carbon--leaves and twigs--from stream ecosystems, reducing the ability of streams to support aquatic life.

"Most people think of nitrogen and phosphorus pollution in streams as contributing to algae blooms," said Diane Pataki, program director in the National Science Foundation's (NSF) Division of Environmental Biology, which funded the research.

"But streams contain a lot of leaf litter, and this study shows that nutrient pollution can also stimulate carbon losses from streams by accelerating the breakdown of that litter. That helps us better understand how fertilizer runoff affects carbon transport and emissions from streams and rivers."

What matters: How long a leaf or twig floats in a stream

The findings, published today in the journal Science, demonstrate that the in-stream residence time of leaves and twigs, which provide energy to fuel stream food webs, may be cut in half when moderate amounts of nitrogen and phosphorus are added to a stream.

"This study shows that excess nutrients reduce stream health in a way that was previously unknown," said Amy Rosemond, an ecologist at the University of Georgia (UGA) and the paper's lead author.

"By increasing nutrients, we stimulate decomposition, and that can cause the loss of carbon that stream life depends on."

Stream food webs based on photosynthesis, leaves and wood

Stream food webs are based on carbon from two main sources.

One is algae, which uses photosynthesis to transform carbon dioxide in water into food.

The other is leaves and bits of wood from streamside forests. This forest-derived carbon usually persists year-round, making it a staple food resource for stream organisms.

Nitrogen and phosphorus play essential roles in decomposition of carbon by microbes and stream-dwelling insects and other invertebrates, but cause problems when they are present in excess amounts--as they increasingly are.

Widespread nutrient pollution

Nutrient pollution is widespread in the United States and worldwide, primarily due to land use changes such as deforestation, agriculture and urbanization.

Its effects on algae are well-known and very visible in the form of algal blooms.

Little was understood about how nutrient pollution affects forest-derived carbon in stream food webs, so Rosemond and her colleagues devised a set of experiments to find out.

Working at the Coweeta Hydrological Laboratory, an NSF Long-Term Ecological Research site in North Carolina, they set up a system to continuously add nutrients to several small headwater streams.

The first experiment ran for six years in two streams, and the second for three years in five streams, with different combinations of nitrogen and phosphorus to mimic the effects of different land uses.

The researchers found that the additional nutrients reduced forest-derived carbon in streams by half.

"We were frankly shocked at how quickly leaves disappeared when we added nutrients," said Rosemond. "By summer, the streams looked unnaturally bare.

"This is comparable to the doubling of carbon from algae that can occur with nutrient pollution, but it's not a zero-sum game.

"Increasing one form of carbon and decreasing another does not equate. These resources have unique roles in stream food webs, and nutrients are affecting their relative availability."

Many streams lack enough light for algae to grow, making forest-derived carbon their main source of energy. But forest-derived carbon is more than a source of food.

Leaves and twigs in streams take up pollutants

"Leaves and twigs, and the microbes that live on them, are also important in taking up pollutants like nitrogen and phosphorus," Rosemond said.

"Ironically, by stimulating the loss of these resources with nutrients, we lose a lot of their capacity to reduce the nutrients' effects. That means that more nutrients flow downstream where they can cause problems in lakes and estuaries."

Rosemond said she hopes the study's findings will be incorporated into policies aimed at reducing nutrient pollution.

"Our results provide a more complete picture of nutrient effects in streams."

Co-authors are Phillip Bumpers, David Manning and Bruce Wallace, all of UGA; Jonathan Benstead and Keller Suberkropp of the University of Alabama; Vladislav Gulis of Coastal Carolina University; and John Kominoski of Florida International University.

-NSF-
Media Contacts
Cheryl Dybas, NSF,

EPA SAYS OVER HALF OF U.S. RIVER AND STREAM MILES IN POOR CONDITION

FROM: U.S. ENVIRONMENTAL PROTECTION AGENCY
EPA Survey Finds More Than Half of the Nation’s River and Stream Miles in Poor Condition
WASHINGTON — Today, the U.S. Environmental Protection Agency released the results of the first comprehensive survey looking at the health of thousands of stream and river miles across the country, finding that more than half – 55 percent – are in poor condition for aquatic life.

"The health of our Nation’s rivers, lakes, bays and coastal waters depends on the vast network of streams where they begin, and this new science shows that America’s streams and rivers are under significant pressure," said Office of Water Acting Assistant Administrator Nancy Stoner. "We must continue to invest in protecting and restoring our nation’s streams and rivers as they are vital sources of our drinking water, provide many recreational opportunities, and play a critical role in the economy."

The 2008-2009 National Rivers and Stream Assessment reflects the most recent data available, and is part of EPA’s expanded effort to monitor waterways in the U.S. and gather scientific data on the condition of the Nation’s water resources.

EPA partners, including states and tribes, collected data from approximately 2,000 sites across the country. EPA, state and university scientists analyzed the data to determine the extent to which rivers and streams support aquatic life, how major stressors may be affecting them and how conditions are changing over time.

Findings of the assessment include:

- Nitrogen and phosphorus are at excessive levels. Twenty-seven percent of the nation’s rivers and streams have excessive levels of nitrogen, and 40 percent have high levels of phosphorus. Too much nitrogen and phosphorus in the water—known as nutrient pollution—causes significant increases in algae, which harms water quality, food resources and habitats, and decreases the oxygen that fish and other aquatic life need to survive. Nutrient pollution has impacted many streams, rivers, lakes, bays and coastal waters for the past several decades, resulting in serious environmental and human health issues, and impacting the economy.

- Streams and rivers are at an increased risk due to decreased vegetation cover and increased human disturbance. These conditions can cause streams and rivers to be more vulnerable to flooding, erosion, and pollution. Vegetation along rivers and streams slows the flow of rainwater so it does not erode stream banks, removes pollutants carried by rainwater and helps maintain water temperatures that support healthy streams for aquatic life. Approximately 24 percent of the rivers and streams monitored were rated poor due to the loss of healthy vegetative cover.

- Increased bacteria levels. High bacteria levels were found in nine percent of stream and river miles making those waters potentially unsafe for swimming and other recreation.

- Increased mercury levels. More than 13,000 miles of rivers have fish with mercury levels that may be unsafe for human consumption. For most people, the health risk from mercury by eating fish and shellfish is not a health concern, but some fish and shellfish contain higher levels of mercury that may harm an unborn baby or young child's developing nervous system.

EPA plans to use this new data to inform decision making about addressing critical needs around the country for rivers, streams, and other waterbodies. This comprehensive survey will also help develop improvements to monitoring these rivers and streams across jurisdictional boundaries and enhance the ability of states and tribes to assess and manage water quality to help protect our water, aquatic life, and human health. Results are available for a dozen geographic and ecological regions of the country.