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Freshwater ecosystems are at risk. Their future depends on how we manage them

LeRoy Poff stands in front of a river holding a small white tray with some samples on it.
LeRoy Poff
Stream ecologist LeRoy Poff conducts a stream survey in the mountains of Ecuador.

The planet’s average global temperature is on the rise, as are sea levels, and species extinctions. But, according to LeRoy Poff, professor of biology at Colorado State University, this biodiversity loss doesn’t impact all groups equally.

“On a global scale, freshwater species are being exterminated more rapidly than marine or terrestrial species, such that up to 40 to 50% of some major groups like amphibians or fishes are what we call imperiled, meaning that they are in threat of extinction,” Poff said.

Poff is one of the top-cited stream ecologists in the world, and he’s concerned about freshwater ecosystems.

“As the climate changes, and the atmosphere warms, this puts pressure on aquatic species and aquatic ecosystems. And these changing pressures cause species to shift their distributions and their community composition to change,” he said.

A diagram shows the threats freshwater ecosystems face: flow modification, species invasions, habitat degradation, water pollution and over-exploitation. Each threat has arrows pointing to all the other threats, indicating they are all connected.
LeRoy Poff
The many interconnected threats that freshwater ecosystems face.

Such a change could result in the loss of species, or the shifting of a system to an entirely new state. One example would be a forest suffering from so many repeated major disturbances, like wildfires, that local conditions no longer favor the growth of trees. Thus, a long-standing forests, and potential sources of timber, can become grasslands. But whether or not a system shifts depends on its resilience.

“Resilience is a widely used word. But in ecology, what it means more specifically, is the ability of a system like, say, a river ecosystem, to persist as a river ecosystem over time, even when it's disturbed,” Poff said.

A diagram shows that the adaptability and persistence of an ecological system can impact whether it transforms entirely.
Frederick Boltz and N. LeRoy Poff
Water Security
The three capabilities of a resilient system: Persistence (P), Adaptability (A), Transformability (P), where shapes represent system identity and colors represent function. Where highly resilient systems may persist in their current form, others may adapt to and still others may be transformed entirely. Figure adapted from F. Boltz & N. Poff et al, 2020

As a concept, the idea of resilience has been around since at least the 1970s. However, in the era of global warming, where ecological impacts are becoming increasingly obvious, resilience is often put to use as we deal with the mounting pressures on ecological systems and decide how to manage them now and into the future.

“If we want to maintain the current ecological state, then we can manage by trying to prevent it from changing, or we can accept that it is going to change and we can't really do much effectively about it and sort of manage the direction it goes to some extent," Poff said.

According to Poff, such an acceptance doesn’t mean simply allowing ecosystems to degrade or permitting widespread desertification. Rather, it is a proactive approach that requires careful implementation.

“As far as I'm concerned, restoring to some previous state or condition through management is really not necessarily viable, going into the future," Poff said. "Because the factors that shape ecosystems are changing, and the ecosystems themselves are prone to change.”

For more information, visit Poff's lab at Colorado State University.