The recent floods in France, Belgium, the UK and Germany remind us again of the danger of the climate crisis. Europe’s rivers however can be key components of both climate mitigation and adaptation. Cleaning them up and restoring them is an expensive undertaking – but it’s worth the price. Paul Hockenos reports.

Europe’s rivers have been grossly mistreated: turned into concrete-lined canals for the purposes of commerce, farmland irrigation, drainage, and hydroelectric power. One study shows that they’re obstructed by more than one million man-made barriers, such as dams, weirs, and ramps. Pollution, urban development, and engineering maul the ecosystems that could be critical to helping mitigate climate breakdown.

Rethinking rivers

As we live in an age of pronounced climate crisis, it is high time that the very concept of rivers be rethought. Of course, they’ll continue to transport goods and generate electricity, but this can happen in less intrusive ways, for example, with state-of-the-art hydro power plants, and the elimination of old, obsolete dams. Rethinking rivers means broadening our horizons and seeing them as sources of recreation and cooling, as reservoirs of biodiversity, as managers of floodwaters, and sinks for organic carbon – thus playing an important role in emissions reduction.

A fact overlooked in most considerations of emissions reduction: like oceans, healthy riverine ecosystems can hold massive amounts of carbon. “Freshwater wetlands can be significant carbon sinks,” found a 2020 Australian study. But, the study noted, when a wetlands hydrology was altered, its ability to sequester carbon was reduced and even led to the release of previously stored soil carbon. “Rehabilitating a wetland’s water table,” the authors found, “has the potential to restore the natural process of wetland soil carbon sequestration and storage.” A corroborating study in Nature magazine found “strong evidence that restoration of floodplains can increase carbon sequestration.”

“Floodplains are widespread along streams and rivers and could potentially intercept carbon eroded from watersheds,“ a US government study argued. “Prior studies suggested that floodplain soils in the U.S. could have very large rates of carbon sequestration through sedimentation inputs, but great uncertainty exists on the magnitude, sources, and fate of that carbon,” the 2015 study admits. “Greater inputs of carbon from sedimentation could be offset by increased rates of greenhouse gas release from floodplain soils.”

Moreover, the restored rivers themselves, with more natural continuum, can also carry organic carbon into oceans, where it is trapped. “Carbon is transported by rivers to the oceans and once that carbon reaches the ocean it is stored naturally in deep sea sediments for millions of years,” according to a BBC Earth report. A 2015 US study found that freshwater rivers and streams transport or store more than 110 million tonnes of carbon each year, some – but not all – of which is stored in its own ecosystem or that of the oceans they flow into.

And, at Woods Hole Oceanographic Institution, researchers found that river transport of carbon to the ocean is “an important piece of the global carbon cycle.” “The world’s rivers act as Earth’s circulatory system, flushing carbon from land to the ocean and helping reduce the amount that returns to the atmosphere in the form of heat-trapping carbon dioxide,” argued the study’s lead author. “Some of that carbon – ‘new’ carbon – is from decomposed plant and soil material that is washed into the river and then out to sea. But some of it comes from carbon that has long been stored in the environment in the form of rocks – ‘old’ carbon – that have been eroded by weather and the force of the river.”

An international 2022 study showed that rivers and lakes in tropical regions with preserved forests sequester a tenth of the carbon in these locations. Amazonian lakes trap carbon dioxide at a rate nearly 40 percent higher than the rainforest itself.

Hydroelectric plants are a tough call because they mar rivers egregiously but generate zero-carbon electricity. According to a Belgian researcher, dam reservoirs trap nearly 20 percent of the organic carbon moving from land to ocean via the world’s rivers.

First steps

The EU’s Biodiversity Strategy 2030 has set the goal of removing the barriers to 25,000 km of European rivers by 2030, making them “free flowing” and thus capable of sustaining ecosystems that store carbon.

Switzerland is way out in front, having spent € 56 billion to clean up and restore its rivers with sewer systems, wastewater treatment plants and other wastewater disposal facilities by now. Today, even those that stream through the urban centers of Geneva, Bern, Zurich, and Basel are so clean that fish species such as perch, pike and grayling fish are abundant again – and the rivers’ cool current a means for city dwellers to bear the ever higher temperatures. Munich’s Isar River is another win-win-win success story: the new floodplains trap carbon, eliminate flooding, and serve as beaches for citizens. Biodiversity too has thrived since its completion ten years ago.

The views and opinions in this article do not necessarily reflect those of the Heinrich-Böll-Stiftung European Union.