There's a climate threat lurking in rivers around the world. New research shows where

Rivers and streams offer far more than pretty scenery or an opportunity for a summertime cool-off. They make up an important component of a global system that determines how much carbon is stored in soil or sent into the atmosphere.

New research shows that human activities are directly disrupting this system and increasing the amount of carbon sent into the atmosphere.

When tree litter falls into a waterway, it becomes fuel for an entire ecosystem. Microorganisms feast on the detritus, fish consume it or it falls into the river bed where the carbon becomes trapped.

But human activity can speed up the decomposition of leaves and other litter, sending more carbon dioxide up into the atmosphere. One key element is a warmer climate, which makes microbes more active. Chemicals from fertilizer, like phosphorus and nitrogen, also nourish microbes and lead to faster litter decomposition.