Scientists sample the world's rivers to assess the planet's health
Max Holmes and Bernhard Peucker-Ehrenbrink spend a lot of time upriver—one day bundled in a parka on the icy banks of the Fraser River in Canada, another day paddling in small dugout canoes called pirogues through jungles along the steamy Congo River.
"Usually I think I have the most incredible job on Earth," said Holmes, "and other times I think it's the most miserable. In the Arctic, the thickness of the bugs around you is unbelievable. We've got clothing covering everything we can cover, even our heads, so we're hot, and we're sweaty. We spray all our clothes with DEET. It holds 'em back a little. If we weren't here, I guess they'd have to go look for a moose."
The two have teamed up to lead the Global Rivers Observatory project—fanning out with students, collaborators, and citizens to sample the world's major rivers and analyze their chemical makeup.
"We're interested in how disturbances influence the chemistry of the rivers," said Holmes, an Earth systems scientist at the Woods Hole Research Center (WHRC). "And what the chemistry of the rivers can tell us about what's happening in the watershed areas through which they flow."
A lot has been happening along rivers in recent decades, and at a rapid pace. Human activities—deforestation, dams, mining, manufacturing, sewage, livestock wastes and fertilizers from farming—disturb river flows and add chemicals to rivers and the coastal oceans they flow into. Meanwhile, climate change and rising temperatures are melting back glaciers, altering the planetary water cycle that delivers rainfall, thawing frozen permafrost, raising water temperatures, and threatening other significant impacts on the rivers and the ecosystems around them.
"We need to do this research now," said Peucker-Ehrenbrink, a geochemist at Woods Hole Oceanographic Institution (WHOI). "Now is the period of change. We are conducting an experiment on our planet: Population growth, erosion, pollution, temperature, have all been going up and will continue to go up for a couple of decades. It's a unique opportunity to understand how the surface of our planet responds to those changes"—and to find ways to mitigate the threats or adapt to the changes.
Incised across continents, river systems are a key component of the planet's circulatory system, acting much like veins in our bodies. Like the blood in veins, river water also transports a variety of chemical compounds from nutrients to waste products. As veins deliver blood back to the heart, rivers carry water through watershed lands back to the sea. Through various seasons—winter and summer, rainy and dry—river flows rise and fall, like a planetary pulse.
"Just like when a person goes to a doctor to get a physical, and the doctor takes a blood sample and analyzes the blood to learn something about the health of the person, we do a really similar thing on rivers," said Holmes. "We collect water and measure the chemical composition of that water, and that can tell us something about the health of the river and its tributaries."
“Hydrologists find out how river flow changes with the seasons, which is equivalent to doctors taking your pulse to find out the blood pressure,” said Peucker-Ehrenbrink. “Then we follow up with the equivalent of doing internal medicine and blood work. Both are necessary to know the health of the patients.”
In this case, the patients are the watersheds through which the rivers flow, and their conditions are changing rapidly. Armed with plastic jugs, bottles, beakers, tubes, poles, filters (and a bicycle pump to pump water through them), the researchers with their students and colleagues fly across the globe, and then pile into buses, vans, canoes, or boats, sometimes with armed guides, to help them reach the rivers they want to sample.
The seeds of the project germinated when Holmes worked with Marine Biological Laboratory scientist Bruce Peterson studying the changing ecology and biogeochemistry of several Arctic rivers. The project expanded when Holmes and Peucker-Ehrenbrink combined their approaches into “a happy marriage,” they said—with Holmes sampling a few rivers repeatedly and Peucker-Ehrenbrink taking single samples from as many rivers as possible.
So far, Global Rivers Observatory researchers have worked on rivers that span a range of climate, soil, and population conditions: the Kolyma, Lena, Yenisey, and Ob Rivers in Russia; the Fraser and Mackenzie Rivers in Canada, and the Yukon River in Canada and Alaska—all ice-covered in winter; the Ganges, Brahmaputra, and Yangtze Rivers in Asia, whose flows are influenced by monsoonal rains; the Amazon in a tropical rainforest; the largely pristine tropical Congo River, and most recently the heavily populated and developed Mississippi. These are eight of the ten largest rivers on Earth.
All river systems start in high country, where rain or snow falls on mountain rock. That's where the similarity ends.
Different elements dissolve into river water from the different rock types each river flows over. Different climates produce different vegetation, whose decomposition introduces different chemical compounds. Agriculture, industry, and sewage treatment add to the chemical soup.
Rivers carry a signal of all these inputs from the land to the coastal ocean, said Peucker-Ehrenbrink, and each compound, element, or ion has a story to tell about the rivers.
Major ions such as calcium, sodium, and silicon reveal the rock types in the rivers' watersheds. Carbon, nitrogen, and phosphorus compounds, from decomposed plants or from fertilizers or wastes, disclose the vegetation and land use along the rivers.
Trace elements such as mercury, arsenic, and chromium provide information about natural soil types or industrial contamination.
Water samples collected in the field are distributed to collaborators at WHOI, WHRC, and other institutions, where scientists specialize in analyzing different chemical compounds. At WHOI, Britta Voss and Jerzy Blusztain analyze strontium isotopes, and Alec Wang measures inorganic carbon, for example. At WHRC, scientists Rob Spencer, Paul Mann, and Kate Bulygina investigate dissolved organic matter. Tim Eglinton and colleagues at the Federal Institute of Technology (ETH) in Zürich, Switzerland, examine radiocarbon ages of organic carbon compounds. WHOI chemist Marco Coolen has begun analyzing DNA on particles filtered from river water to identify microbes living in rivers and changes in microbe populations. WHOI engineer Chip Breier is building automated sampling instruments for the project. The plan is to measure even more elements—"the whole periodic table," said Peucker-Ehrenbrink.
Carbon is a primary target of the Global Rivers Observatory project. It is a fundamental component in rocks, living things, fossil fuels, and the greenhouse gas carbon dioxide. Tracking how carbon compounds cycle between air, rock, water, and organisms reveals the interdependent workings of the planet's land, ocean, atmosphere, and life.
"You can imagine a tree high up in the Himalaya losing a leaf," said Peucker-Ehrenbrink. "That leaf extracted carbon from carbon dioxide in the air via photosynthesis. The leaf decomposes, becomes part of the soil, and some of its carbon gets flushed into the river and is dissolved in compounds in the water. Or the carbon attaches itself to a grain of sand, and the carbon is transported downriver. Other parts may not decompose entirely, and turn into what we call particulate organic carbon." These particles sink, flow downstream, or are eaten by animals and microbes, respired, and converted back to inorganic carbon dioxide that may end up in shells, sediments, or the atmosphere.
Different waters, different concerns
The diverse rivers are also windows into ongoing environmental processes that the scientists seek to understand.
Around Arctic rivers, for instance, carbon-rich decomposing vegetation is locked in permafrost. But rapid Arctic warming may thaw the permafrost, hasten decomposition, and release large amounts of methane, a potent greenhouse gas that could trigger further and even greater warming. That, in turn, could cause more thawing that releases more carbon compounds into the rivers and into the Arctic Ocean, spurring even further changes to the ecosystem.
In the Ganges-Brahmaputra river system, sediments contain toxic arsenic. Will climate changes release more arsenic into river waters and ground waters? How will suspected changes in the monsoons affect the rivers? Farther east, how will the mammoth Three Gorges Dam affect the Yangtze River and coastal ecosystems?
The Mississippi brings an excess offertilizers from agricultural runoff to the Gulf of Mexico; every spring, this causes blooms of marine plants that deplete oxygen and create “dead zones” where no fish can live. Dams on the Mississippi have also reduced the flow of sediment previously carried to now-eroding coastlines.
Along the Amazon and Congo River basins, unregulated mining and farming, and deforestation from logging, are increasing and will cause changes.
A tale of one river
The Fraser River in British Columbia illustrates the interconnected complexities of climate effects.
"The Fraser is one of the biggest salmon habitats and salmon runs in the world," said Peucker-Ehrenbrink. "Salmon are kind of picky fish. They don't like water warmer than about 20°C [68°F]."
But tributaries to the Fraser are warming, and some already reach nearly 20°C in summers. Worse, mountain pine beetles are killing trees around the Fraser basin. Warming is to blame: Winters are less harsh now, and beetles survive to eat through the forest unchecked.
"It's likely that British Columbia is losing probably 80 percent of its pine trees," said Peucker-Ehrenbrink. "When the trees aren't there anymore, the sun hits the ground, and the ground heats up. If the rain falls on that warmer ground, the water that runs into the tributaries and eventually into the Fraser will be warmer than before. Any further increase in temperatures could fundamentally change this basin and may threaten it as a salmon habitat. How will this place look 20, 30, maybe 40 years from now?"
Partners for the job
To accumulate this big picture of the planet's circulation system requires many partners.
"The partnerships vary," said Peucker-Ehrenbrink, "from large science institutions like East China Normal University to smaller institutions like the University of the Fraser Valley, where undergraduates sample the Fraser every other week. On the Congo, where they have little equipment and no reliable power, we pay people to sample for us. And on the Lena River, we work with schools. School kids drill holes in the ice to sample once a month in winter. We wouldn't be able to do that."
Students also contribute paintings and drawings illustrating the influence of rivers on their lives. Artwork from students near the Lena River has become an exhibition that has traveled to the United Nations, Washington D.C., Russia, Poland, and Alaska.
The scientists are also enlisting "citizen scientists." Holmes and Peucker-Ehrenbrink created single-use sampling packs that they will send to people living near or visiting rivers, with containers, bags, bottles, and directions for how and where to collect water.
"They go do it once and send the sample," said Peucker-Ehrenbrink. "If they want to do more, they can get more involved. We train them to do more sampling. We entice them to become local partners."
Another goal of the project is to create a repository to preserve samples of water and particles from all the tributaries of all the rivers collected over all seasons and years—an archive of how the rivers were at times before they changed.
"Water flows past and is gone," said Peucker-Ehrenbrink. "Maybe ten years from now you want a sample of 2010 Fraser River water, where do you go? How do you get it? We're archiving it as well as we can, as things are changing, to analyze in the future with methods we don't have or know about today. I would give a lot for a 1930 or 1960 water sample from the Mississippi! But it's gone."
"In 2100, we'll see that there was an urgent need to look at the transition time," he said. "If we miss that, if we miss doing the measurements and gaining understanding, we've done ourselves and following generations a real disservice—because that opportunity will not come back."