In Praise of Messy Rivers
Who has a beaver as a lab mascot? A river scientist who links nature’s toothy engineer to healthy ecosystems, clean water, and climate benefits
By Rob Novak
THWAP! The North American beaver sounds an alarm by slapping its rudder-like tail on the surface of freshwater wetlands – akin to the alarm Ellen Wohl sounds with scientific findings that reveal the importance of river systems to people, ecosystems, and the world’s changing climate.
Yes, one alarm comes from the continent’s largest rodent, an environmental engineer that for millennia has busily built dams and remastered river tributaries into broad, silty ponds and wetlands. The other comes from one of Colorado State’s most eminent scientists, a University Distinguished Professor and leader in the field of fluvial geomorphology, the study of environmental health through the lens of river systems.
But there’s a direct connection: Wohl and her laboratory colleagues are demonstrating through mounting research that complex river networks support diverse natural ecosystems, provide clean water for an array of users, help control devastating floods, and function as critical sinks that keep carbon out of the atmosphere and, thus, help slow the pace of climate change. In poetic terms, Wohl compares river networks to the circulatory system of the human body, in which even the tiniest vessels and points of nutrient exchange are vital to the health of the whole. Dry streams that carry water only during downpours. Small tributaries. Underground connections. And shallow ponds and wetlands – the kinds built by beaver. These and other components of a river system, or watershed, have life-sustaining roles, Wohl has found.
“A river network is not simply a gutter. It is an ecosystem, and all the parts, unseen or seen, matter,” she wrote in a treatise published in January. It urged policymakers to maintain key provisions of the federal Clean Water Act that protect small streams and wetlands.
Indeed, Wohl’s work demonstrates the value of physically complex rivers. She touts the “messy river,” with undercut banks, bars in the channel, secondary channels, boulders, debris, and logjams. Messy rivers, she notes, provide abundant habitat and encourage species diversity. Their physical complexity resists the damaging ecological impacts of floods, drought, and wildfire. Connectivity among the parts leads to broad ecosystem health and clean water, Wohl wrote in an analysis for the Global Water Forum in Fall 2016. Increasingly, she is working to discover how much carbon is stored in rivers, streams, and flood plains, which is essential to understanding how river systems help protect the planet – and people – from climate change.
As Wohl and other scientists affirm such benefits, their findings are propelling a global trend in river restoration. It seeks to balance negative impacts of dams, levees, channel modification, flow regulation, and removal of wood and beaver dams from river systems – steps that have improved efficiency of water flow to agriculture, cities, and industry, but have diminished some lesser-known benefits of river systems. The trend, which has gained steam over two decades, has resulted in U.S. restoration projects that collectively cost more than $1 billion annually. “Among the greatest challenges to river restoration, however, is encouraging people to not only accept, but to embrace, the perceived messiness that accompanies physical complexity,” Wohl noted in the Global Water Forum analysis. “Let us learn to sustain this messiness, for it supports the river ecosystems on which we all depend.”
In Spring 2017, Wohl was named a University Distinguished Professor, CSU’s highest academic honor, awarded to a small group of professors who are international leaders in their fields. Her research findings are influencing the scientific understanding of rivers, their forms, functions, and benefits – revelations that shape river management and restoration. How influential is Wohl? A single paper she authored, titled “River restoration,” has been cited an astonishing 535 times by other researchers since its publication in 2005 in Water Resources Research. For her contributions to science-based knowledge, she has earned prestigious awards from the American Geophysical Union and the European Geosciences Union.
Wohl’s scientific findings are helping to propel a global trend in river restoration. It seeks to balance negative impacts of dams, levees, channel modification, flow regulation, and removal of wood and beaver dams from river systems – steps that have improved efficiency of water flow to agriculture, cities, and industry, but have diminished some lesser-known benefits of river systems.
An avid kayaker in her leisure time, Wohl has conducted river research around the world, with a recent focus on the role of instream wood in carbon cycling, stream metabolism, and river ecosystem productivity. Many of her field studies center on streams in Rocky Mountain National Park and elsewhere in Colorado. That brought her to beaver dams – the quintessential way to examine downed wood in rivers and large-scale environmental effects.
It’s no coincidence that Wohl and graduate students in her Fluvial Geomorphology Lab claim the beaver as their mascot. They have a plush beaver toy named Chewy. They delight in beaver puns. They share beaver memes picked up through social media. Beaver tchotchkes adorn Wohl’s office. And her forthcoming book – about beaver, their natural history, and ecological benefits – is titled Saving the Dammed.
By cutting and manipulating wood into waterways, beaver create Wohl’s favorite kind of river: the messy kind. The kind whose multiple channels flood mountain meadows, creating boggy wetlands. In enviro-speak, these wetlands are carbon sinks – holding carbon dioxide, the No. 1 greenhouse gas, out of the atmosphere by trapping it in rich muck. Wetlands accumulate soil and organic matter so well, and slow down gas-releasing activity so effectively, that they are thought to hold up to 30 percent of the estimated global soil carbon while occupying as little as 5 percent of its land surface, studies have shown.
For this and other reasons, some North American river restoration efforts include reintroduction of beaver to historic ranges, where populations were decimated by the fur trade. In other places, river managers use manmade dams, called “beaver dam analogs,” to accomplish the work of beaver.
“Some of the dating we have from beaver-occupied sites in Rocky Mountain National Park show a carbon sink on the order of thousands of years,” said Wohl, noting trees and exposed soils hold carbon for a fraction of that time. “Storing organic carbon in flood plains is something we can have an effect on and see measurable change in a short time period. Beaver are pretty good at that.”
Yet changes in water tables and vegetation, among many other factors, make beaver reintroduction a complex proposition. “You can’t just expect to bring beaver in, and they’ll fix everything to store carbon like we want them to,” Juli Scamardo, a graduate student in Wohl’s lab, explained.
So the fluvial geomorphology team continues its work tracking carbon through watersheds and seeking to understand the benefits of beaver in those systems. During these studies, student researchers are inspired by the professor who is bringing new attention to rivers.
“Ellen is a phenomenal mentor,” said DeAnna Laurel, who recently earned a doctorate in geosciences with Wohl as her adviser. “It’s the perfect combination of guidance, but also allowing room to explore and find things out on your own. She’s totally my role model – I’d love to be like her someday.”
Michael Smith Natural Resources Building
Students studying geosciences – and pursuing degrees in eight other disciplines in the Warner College of Natural Resources – are learning in a soaring new wing of the Michael Smith Natural Resources Building. The wing opened in Fall 2018 and encompasses 50,000 square feet of classrooms, teaching laboratories, and meeting and office space. The $20 million project was made possible with generous donations from, among others, college namesake Ed Warner and building namesake Michael Smith.
Read more in SOURCE.