Streams Clean Up Our Act
When Sherri Johnson and a team of stream ecologists from Oregon State University started their 24-hour marathon stream survey on a warm July day in 2004 in downtown Eugene, they got some funny looks at first. They were first spotted wading around in the middle of Amazon Creek, a concrete-bottomed canal that runs through town below street level.
Passersby called down, "Are you trapped? Do you need help out?”
"Oh no, we're supposed to be down here!” Johnson responded heartily.
Processing their samples at the nearby fairgrounds didn't make it look any better. "Here we are walking around with plastic syringes in downtown Eugene,” Johnson, a research ecologist with the U.S. Forest Service, laughs as she recalls it.
But unbeknownst to these Eugenians, one of the largest coordinated stream studies in the United States was unfolding below them. And these syringe-toting ne'er-do-wells were investigating how streams keep our environment clean from nitrogen-based pollutants like fertilizers and fallout from power plants.
In the largest U.S. study of its kind, Johnson and 30 fellow researchers joined forces to tromp through and sample 72 streams in 8 regions across the country and Puerto Rico. They found that streams filter out about half of the nitrate pollution they receive before it reaches places where it can do real damage--coastal areas like Puget Sound.
Tiny river dwellers like algae, fungi and bacteria clean up nitrate by taking it up as a nutrient or transforming it into harmless nitrogen gas. Healthy streams with vibrant ecological communities and natural, meandering channels are best at slowing down and absorbing the nitrogen before it reaches the coast.
Johnson and Oregon State researchers Linda Ashkenas, Stanley Gregory, and Daniel Sobota were co-authors on a recent publication of the results of the 72 stream study in Nature as part of the ongoing Lotic Intersite Nitrogen eXperiment, or LINX.
"It's extremely valuable,” says Robert Naiman, a stream ecologist at the University of Washington, about the LINX study. "It shows us how to ward off these big problems by looking at some of the smallest organisms on earth.”
This is great news, but it comes with a caveat. The researchers found that streams with more nitrate, mostly from human sources like fertilizer, fallout from fossil fuel burning, and sewage, were less efficient at filtering it. This pattern held up regardless of whether the stream was forested, agricultural, or urban.
"Streams can't process everything we give to them. They aren't sewers,” Johnson says. And the disturbing reality is that we're moving in the direction of putting more nitrate into our local streams, not less. Globally, we've more than doubled the nitrogen that was in play in natural systems before industrialization.
"We have so upset the nitrogen balance that it's pretty scary,” says Peter Kiffney, a research ecologist at the National Marine Fisheries Service in Mukilteo, Wash.
As this nitrogen makes its way through our streams and rivers, the magic dust that made our food grow faster spins off into monstrous growth we can't control when it hits the coasts. There the buildup feeds massive algae blooms, often of harmful or toxic species that outcompete the more benign members of the food chain.
When these blooms die, they decay and deplete oxygen in the water, leading to the famous dead zones of the Gulf of Mexico and Chesapeake Bay, and smaller ones that have emerged in Puget Sound.
What's unique about our area, Kiffney says, is how serious the consequences are once this nitrate enters the Puget Sound. Species nearly or already endangered, like the salmon and herring who call the Sound home, are even more threatened by low-oxygen conditions. The whole ecology of the Sound can be affected by these overloads of nitrogen, he says. Even shorebird populations have changed.
The recent LINX study points a way out. It highlights the importance of protecting stream communities so they can keep doing what they do best: slowing down the discharge of nitrate through natural channels that allow contact with creatures that can filter nitrogen.
The ecological term for this sounds like a crazy new dance: nutrient spiraling. It's a measure of long a nutrient like nitrate stays in the water before it gets a new dance partner, like a floating plant or diatom that uses it as a nutrient. The shorter the spiral, the better it is for coastal communities.
To trace these micro dance steps, the research teams set up a pump with a steady drip of nitrate labeled with a naturally occurring but rare isotope that they could follow down these "wadeable” local streams. Then they set out on a 24-hour stream scavenger hunt, sampling in the middle of the night with headlamps, to see where the labeled nitrate ended up half a mile down the river.
In most studies, about half of it showed up downstream, but the other half was absorbed by the tiny denizens of the river. Floating plants, algae, and fungi took it up as a nutrient. A smaller amount was cranked into nitrogen gas by bacteria that form filmy coatings on stream beds and rocks.
In this process, called denitrification, bacteria use nitrate the way we use oxygen--to break down their food. Then they exhale nitrogen gas the way we puff out carbon dioxide, taking that nitrogen out of circulation in the watershed and putting it back in the air, where it's hardly noticed among the nearly 80% nitrogen gas that makes up our atmosphere. It's the last dance partner that nitrate will have for a long time, and for humans, that's a good thing.
But denitrification occurs mostly in the nooks and crannies of stream beds and sediments, where pockets of low-oxygen environments occur. Headwater streams and wetlands are especially important environments for denitrification, according to Naiman, and need more protection in our region. "They've largely been ignored in regulatory actions,” he says. "These small streams get the brunt of everything.”
The group of 31 scientists that form the LINX study have been working together since 1995, in a collaboration that covers watersheds in Oregon, Massachusetts, North Carolina, Michigan, Wyoming, Arizona, New Mexico and Puerto Rico. The study was led by Patrick Mulholland, an aquatic ecologist at Oak Ridge National Laboratory in Tennessee.
Having this enormous coverage allowed the researchers to say something big about streams in the United States. Using the data, they built a watershed model showing that if nitrogen isn't absorbed in small headwater streams, it can accumulate to dangerous levels as it flows through into larger rivers. Naiman was alarmed by this "creeping breakdown of the system” caused by nutrient overload.
"If you don't have too much [nitrate], the little streams take care of it all and you don't notice it much,” he says. "But as things become progressively worse, it actually begins to permeate the whole drainage network, until finally, as more and more sites are overloaded, it just transfers the problem downstream.”
In addition to the nitrate already in play, the use of artificial fertilizers will most likely ramp up with increased cultivation of biofuel crops. The growth of coal-fired power plants also creates a quiet, invisible rain of nitrate.
But studies on this scale can encourage people to work out these problems, says Kiffney. "In some places it might give them more urgency to clean up their act.”
Getting people to see their streams as living, flourishing environments might be the first step. Johnson waxes poetic when she talks about the plants, insects, and tadpoles who make up stream communities. Even concrete-bottomed channels can have algae as important contributors. She finds a lot of people don't know what's in their local streams.
Naiman recalls setting up traps in small streams that ran through people's backyards on the way to bigger rivers like the Stillaguamish and Snoqualmie.
"We were getting all sorts of Coho and Chinook, dace and lamprey,” he says. "These were running right through people's yards where they were mowing the grass right up to the stream. They'd come up and say, ‘Gosh, we never knew there were fish in this stream--I use this stream to dump all my grass clippings in.'”
Naiman points out that Europe is even farther along than we are with nitrogen woes. "If we don't want to go down that road, and we want to retain our quality of life, we need to protect stream areas and wetlands, no matter how small.”
Deirdre Lockwood is a graduate student in oceanography at the University of Washington.
Top: Oregon State researchers sampled Mack Creek, a forested stream in the Blue River basin of the McKenzie River. The stream runs through the Andrews Experimental Forest in Oregon's Central Cascade region. Photo: Sherri Johnson/US Forest Service
Bottom: On the urban end of the spectrum, the researchers sampled Amazon Creek, a concrete-bottomed channel in Eugene, Ore., part of the Long Tom drainage basin. Photo: Sherri Johnson/US Forest Service