The chapter discusses the significant role of rivers and inland waters in coupling biogeochemical cycles between land, oceans, and the atmosphere. It highlights that while carbon (C) discharged to the oceans is only a fraction of the C entering rivers from terrestrial ecosystems, most of this C is returned to the atmosphere as CO₂ or stored in sediments within wetlands and lakes. The text emphasizes the importance of understanding the interplay between reactivity, transport, and coupling among landscape components, such as uplands, riparian zones, streams, rivers, wetlands, and lakes. It also addresses how human activities significantly impact these processes, affecting carbon sequestration and coastal responses to ocean acidification. The chapter provides insights into the lateral export of C from terrestrial ecosystems, the erosion and burial of minerals and organic carbon (OC), and the influence of river exports of alkalinity and major ions on coastal systems. It concludes by suggesting that rivers receive, transport, and process the equivalent of terrestrial net ecosystem production (NEP) in their watersheds, challenging the traditional view of rivers as passive transporters.The chapter discusses the significant role of rivers and inland waters in coupling biogeochemical cycles between land, oceans, and the atmosphere. It highlights that while carbon (C) discharged to the oceans is only a fraction of the C entering rivers from terrestrial ecosystems, most of this C is returned to the atmosphere as CO₂ or stored in sediments within wetlands and lakes. The text emphasizes the importance of understanding the interplay between reactivity, transport, and coupling among landscape components, such as uplands, riparian zones, streams, rivers, wetlands, and lakes. It also addresses how human activities significantly impact these processes, affecting carbon sequestration and coastal responses to ocean acidification. The chapter provides insights into the lateral export of C from terrestrial ecosystems, the erosion and burial of minerals and organic carbon (OC), and the influence of river exports of alkalinity and major ions on coastal systems. It concludes by suggesting that rivers receive, transport, and process the equivalent of terrestrial net ecosystem production (NEP) in their watersheds, challenging the traditional view of rivers as passive transporters.