Study highlights how humans and nature are causing significant changes to health of global rivers

Many of the world's largest rivers are experiencing significant changes in their chemical composition as a result of natural and human activity, according to new research.

This is resulting in increased levels of solutes such as calcium, potassium, chloride and bicarbonates flowing through our major river basins and estuaries and ending up in the ocean, scientists say.

Over the space of almost a decade, an international team established a global database of runoff and solute concentration data (some of it spanning more than a century) for almost 150 large rivers.

They included the Colorado and Mississippi (USA), the Amazon (South America), the Congo (Africa), the Rhine (Europe), the Yellow and Yangtse rivers (China), and the Murray (Australia).

Writing in Nature Communications, researchers say a detailed analysis of this data shows there have been significant increases in total dissolved solids (68%), chloride (81%), sodium (86%) and sulfate (142%) fluxes from rivers to oceans worldwide.

These effects are particularly being felt between the polar regions and the tropics, where urbanization and agriculture are at their most intense. However, acidification was also observed close to the equator as a result of bicarbonate levels vital for river health being present in the rivers of South America.

With about 6,400 million tons of solutes reaching the sea from rivers each year, such changes can lead to damaging consequences for humans and ecosystems - termed river syndromes - once certain critical levels of solutes are exceeded.