Published today in Global Change Biology, this paper demonstrates the surge in barrier removals in freshwater systems and the various concerns that have consequently arisen.

Although freshwater systems only cover 2.5% of the Earth’s surface, they provide a wide range of ecosystem services, including vital water supplies, flood control, and biodiversity conservation.

Years of disturbance and overexploitation, compounded by climate change and invasive species, have led to the decline in freshwater species populations by over 85%.

Barriers in rivers are a major problem for many native species, especially those that migrate between rivers and seas to reproduce, such as European eels and Atlantic salmon.

Ellen Dolan from the School of Biological Sciences at Queen’s led the research, she said:

“For such species, barriers are an immediate threat to the long-term health of their populations. Removing longstanding barriers seems like an obvious management solution, however, doing so risks worsening other overlooked ecosystem threats.”

One of these is the spread of invasive species following barrier removal, with invaders often thriving in recently disturbed and well-connected freshwater habitats. Invasive species have often accumulated below barriers, which prevent their further spread.

Removing barriers could increase biological invasions, leading to ecological damage, economic losses in fisheries, damage to infrastructure, and the rise of waterborne diseases that could impact water quality and human health.

Ellen added: “We warn that river restoration programmes which focus solely on the benefits of barrier removals for native species movements—without careful management of invasive species—may undermine conservations efforts.”

Dr Ross Cuthbert from Queen’s was also involved in this research, he commented:

“As global barrier removals gain momentum, thousands of water impoundments have been dismantled over the last few decades. While the benefits of restoring natural flow are well-documented, the spread of invasive species following these removals has been largely overlooked.”

This study calls for a more integrated approach in restoration planning, where invasive species management is a fundamental part of barrier removal frameworks.

Ellen states:

“Through this article, we challenge the assumption that barrier removals are universally beneficial. We call for long-term monitoring with more nuanced, data-driven approaches to river restoration.”

This project was funded by the Department of Agriculture, Environment and Rural Affairs, Northern Ireland.

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