Managing nitrogen to restore water quality in China

In this article in Nature, Dag Hessen and colleagues combine a vast observational dataset on the concentrations of total nitrogen in water bodies and used nitrogen balance models to estimate local nitrogen discharge into the inland aquatic environment for the years 1955–2014. They then empirically identified the critical nitrogen-discharge threshold for each province as the total anthropogenic nitrogen discharge during the year in which pollution levels first breached the water-quality standard. Overall anthropogenic nitrogen is entering freshwaters in China at a rate nearly three times higher than the estimated ‘safe’ level. The article also discusses potential remedies and evaluates the costs of such strategies.