River ecosystem metabolism and carbon biogeochemistry in a changing world

River networks represent the largest biogeochemical nexus between the continents, ocean and atmosphere. Our current understanding of the role of rivers in the global carbon cycle remains limited, which makes it difficult to predict how global change may alter the timing and spatial distribution of riverine carbon sequestration and greenhouse gas emissions. Here we review the state of river ecosystem metabolism research and synthesize the current best available estimates of river ecosystem metabolism. We quantify the organic and inorganic carbon flux from land to global rivers and show that their net ecosystem production and carbon dioxide emissions shift the organic to inorganic carbon balance en route from land to the coastal ocean. Furthermore, we discuss how global change may affect river ecosystem metabolism and related carbon fluxes and identify research directions that can help to develop better predictions of the effects of global change on riverine ecosystem processes. We argue that a global river observing system will play a key role in understanding river networks and their future evolution in the context of the global carbon budget.

Automated summary

River networks are the largest biogeochemical connection between land, ocean and atmosphere. Our understanding of the role of rivers in the global carbon cycle is limited, making it difficult to predict how global change will affect riverine carbon sequestration and greenhouse gas emissions. This review summarizes the current state of river ecosystem metabolism research and provides estimates of carbon flux from land to rivers. The study highlights the importance of a global river observing system in understanding river networks and their future evolution in the context of the global carbon budget.