We analyzed the potential for eutrophication in major seas around China: the Bohai Gulf, Yellow Sea and
South China Sea. We model the riverine inputs of nitrogen (N), phosphorus (P) and silica (Si) to coastal
seas from 1970 to 2050. Between 1970 and 2000 dissolved N and P inputs to the three seas increased
by a factor of 2–5. In contrast, inputs of particulate N and P and dissolved Si, decreased due to damming
of rivers. Between 2000 and 2050, the total N and P inputs increase further by 30–200%. Sewage is the
dominant source of dissolved N and P in the Bohai Gulf, while agriculture is the primary source in the
other seas. In the future, the ratios of Si to N and P decrease, which increases the risk of harmful algal
blooms. Sewage treatment may reduce this risk in the Bohai Gulf, and agricultural management in the
other seas.