The health of some of the largest rivers in the world and their ecosystems are deteriorating due to significant changes in their chemical composition caused by both human and natural activities.

New research analysed data from over 150 large rivers, including the Amazon in South America, the Colorado and Mississippi rivers in North America, the Yellow and Yangtze rivers from China, the Rhine from Europe, and the Ganges from India. The data which spans the last century has revealed that increasing concentrations of solutes such as potassium, chloride, calcium, and bicarbonates in the major river basins are causing cascading effects across the river ecosystems.

The analysis published in a new paper in the journal Nature Communications shows that there has been a significant increase in the amount of total dissolved solids by over 68 percent, while sulfate, sodium, and chloride levels increased by 142 percent, 86 percent, and 81 percent respectively, in the world’s rivers the last century alone.

The effects of which are being felt more acutely between the tropics and polar regions, where agriculture and urbanization are most intense. River acidification was also observed closer to the Equator, as the levels of bicarbonate, crucial for the health of rivers being present in rivers such as the Amazon in South America.

“Rivers are of immense importance to the sustainability of our planet. Large rivers are responsible for transporting huge quantities of different materials, ranging from sediment to fish,” said Alistair Borthwick, co-author of the paper, and a professor of Applied Hydrodynamics at the University of Plymouth.

Through the analysis, researchers sought to investigate how the increasing concentrations of solutes in major rivers, both due to human activities such as agriculture, mining, and dams, as well as naturally occurring processes, contribute to the seven river syndromes – acidification, alkalization, desalinization, hardening, mineralization, salinization and softening.

“We found solute-induced syndromes in major rivers that are having the greatest impact in the world’s temperate zone, owing to the weathering of rocks and human activities. Mitigation measures are urgently needed to defend rivers against large changes,” Borthwick added.

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