ECO RESTORATION: Can rivers and lakes recover from drought?

CHENNAI: Europe’s intense summer heat waves have brought rivers across the continent to their lowest levels in years. Major waterways like the Rhine, Danube and Po are warming and at critically low levels, threatening agriculture, commerce, drinking water and natural ecosystems. The European Drought Observatory has reported that nearly 50% of the continent is under a drought warning, with some analysts calling it in the worst in 500 years.

As we continue to burn fossil fuels that make the planet hotter, heat waves and drought are expected to become more frequent and intense. Countries will have to adapt and deal with the consequences. What do lower water levels and higher temperatures mean for rivers and lakes?

Lower levels aren’t just bad news for our well-being — they’re also detrimental to the health of rivers and lakes themselves, as well as the wildlife dependent on them. When water levels fall, living space is restricted and plant and animal populations struggle to coexist, Jose Pablo Murillo, program officer at the Stockholm International Water Institute, told DW. Water quality declines, and ecosystems are disrupted.

And variations in both temperature and levels that are outside normal limits can “quickly increase the risk of drastic changes in the conditions of river and lake ecosystems,” he said. “This damage is not only limited to the rivers, but can extend to adjacent ecosystems upstream and downstream that depend on the services that rivers provide such as drinking water, food supply, irrigation and nutrients,” Murillo added.

Because warmer waters are hospitable environments for bacteria and other pollutants, drinking water risks contamination. Lower water levels, mean it’s less likely those pollutants will be diluted and washed away. “When an ecosystem is under high stress for a long period of time it becomes increasingly difficult for it to recover,” added Murillo.

Warmer waters also disrupt the delicate balance in aquatic ecosystems.

“Temperature is crucial for aquatic ecosystems as it influences the chemistry of water,” said Murillo. “As the water temperature rises, water holds less dissolved oxygen.” Without that oxygen, it becomes more challenging for the local biota — aquatic plants and animals — to survive. Some researchers have pointed to low oxygen levels as an aggravating factor in the recent mass fish die-off in the Oder River between Germany and Poland. Historically low water levels since 2018, along with high water temperatures of around 25 degrees Celsius (77 Fahrenheit), mean fish in the river are stressed.

Murillo said lower oxygen levels and increased nutrient pollution can end up stimulating the growth of freshwater algae, a process called eutrophication. “These issues can reinforce each other,” he said. “For example, higher concentrations of nutrients can result in algal blooms that decrease oxygen levels. This can lead to the death of biota, which increases the nutrient load, and so on.”

That’s the case in Lake Erie, on the border between Canada and the United States, where agricultural nutrient runoff has seen the return of toxic algal blooms in the western basin. Both countries managed to cut algal blooms in the latter half of the 20th century by reducing runoff. But warmer lake waters have seen a recurrence of the algae over the last 20 years, especially in 2011, 2014 and 2015. This has created “dead zones” of depleted oxygen, causing many fish deaths.

This article was provided by Deutsche Welle