Flowing water picks up carbon from the places it passes. The carbon may come from the bedrock, soil, plants or animal remains.
Some carbon is carried dissolved in the water, while some is solid - like soils and sediments, and organic matter that's fallen in. The river flows on, linking the land, fresh water, and coastal systems of the world.
When a river slows down, it drops some of its solid load. Much of the sediment is deposited where the river meets the sea, while the dissolved carbon disperses into the sea.
This page forms part of the hints for Element On The Move.