Simulated Global Coastal Ecosystem Responses to a Half-Century Increase in River Nitrogen Loads Geophysical Research Letters

Coastal ecosystems are increasingly threatened by anthropogenic stressors such as harmful algal blooms and hypoxia through the combined effects of eutrophication and warming. As a major terrestrial nitrogen source to the ocean, rivers play a key role in shaping coastal nitrogen budgets and biogeochemical cycling. Combining an enhanced-resolution, global ocean biogeochemical model with temporally changing river inputs, we estimate that elevated river nitrogen loads alone resulted in a 5.8% increase (16.6 Tg) in the global coastal nitrogen inventory from 1961 to 2010, accompanied by increases in coastal net primary productivity (+4.6%) and benthic detrital flux (+7.3%). The ecosystems most sensitive to added nitrogen were those with long residence times and strong nitrogen limitation. While even enhanced-resolution global models remain limited in their capacity to resolve shelf-scale responses, these basic factors provide two relevant axes for frameworks assessing the comparative coastal ecosystem susceptibility to enhanced nitrogen loads, and the effectiveness of mitigation strategies Grant no. NA18OAR4320123