Worldwide alterations to nutrient and carbon cycling by river damming

The damming of rivers represents one of the most far-reaching human modifications of the flows of water and associated materials from land to sea.  There is currently an ongoing boom in dam construction, particularly focused in emerging economies, which is expected to double the fragmentation of rivers on Earth.  This fragmentation will significantly modify global nutrient and carbon fluxes along the land-ocean aquatic continuum, through elimination of nutrients from the water column in reservoirs. The coastal zones into which river systems drain may suffer the brunt of this upstream change. Through the development of spatially explicit nutrient and carbon mechanistic models, we have quantified in-reservoir elimination and transformation fluxes for phosphorus (P), nitrogen (N), silicon (Si), and organic carbon (OC), including N₂O emissions fluxes. Results indicate a decoupling of these cycles in reservoirs, due to preferential retention of P, followed by Si, C, and N. This decoupling of nutrient cycles suggests that river damming could be changing the limiting nutrient in coastal zone worldwide. The consequence of these changes in dynamics could be a worldwide shift towards increased Si-limitation in coastal zones, increasing the potential for coastal eutrophication.