Light and flow regimes regulate the metabolism of rivers

Mean annual temperature and mean annual precipitation drive much of the variation in productivity across Earth's terrestrial ecosystems but do not explain variation in gross primary productivity (GPP) or ecosystem respiration (ER) in flowing waters. We document substantial variation in the magnitude and seasonality of GPP and ER across 222 US rivers. In contrast to their terrestrial counterparts, most river ecosystems respire far more carbon than they fix and have less pronounced and consistent seasonality in their metabolic rates. We find that variation in annual solar energy inputs and stability of flows are the primary drivers of GPP and ER across rivers. A classification schema based on these drivers advances river science and informs management.

Automated summary

Mean annual temperature and precipitation do not explain variation in gross primary productivity (GPP) or ecosystem respiration (ER) in rivers. There is significant variation in the magnitude and seasonality of GPP and ER across US rivers. Rivers respire more carbon than they fix and have less consistent seasonality compared to terrestrial ecosystems. Variation in annual solar energy inputs and flow stability drive GPP and ER in rivers.