In a rhythm that’s pulsed through epochs, a river’s plume carries sediment and nutrients from the continental interior into the ocean, a major exchange of resources from land to sea. More than 6,000 rivers worldwide surge freshwater into oceans, delivering nutrients, including nitrogen and phosphorus, that feed phytoplankton, generating a bloom of life that in turn feeds progressively larger creatures. They may even influence ocean currents in ways researchers are just starting to understand. But today, in rivers around the world, humans are altering this critical phenomenon. In many places, the culprit is a dam. Researchers led by Annalisa Bracco, professor in the School of Earth and Atmospheric Sciences, investigated these dynamics in a study of the plume created by the Mekong River, the 12th-longest river in the world. The study found that current and proposed Mekong River dams will dramatically reduce its annual mean flow, its seasonal cycle, and sediment loading. The scientists argue that a reduced productivity of the offshore water of the South China Sea along the pathway of the summer jet may be an undesirable outcome as well. Other EAS researchers in the study are Xiyuan Zeng, graduate student, and Filippos Tagklis, postdoctoral scholar. 

The Oceans Are Missing Their Rivers
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