Long-term changes in nutrient regimes and their ecological effects in the Bohai Sea, China.

The nutrient regime has changed significantly in the Bohai Sea (BS) during the past six decades because of anthropogenic perturbations. Specifically, the concentration of DIN increased by about 7-fold from the end of the 1950s to the mid-2010s, while DIP and DSi concentrations decreased from the end of the 1950s to the beginning of the 1990s, and have since increased again. Unsynchronized changes in nutrient levels have led to changes in the nutrients structure, which has caused a series of ecological effects. Phytoplankton biomass increased by 6-fold from the 1960s to the mid-2010s. Additionally, phytoplankton composition shifted from a diatom-dominated to a dinoflagellate-dominated system, and the dominant species of macrozoobenthos changed. Red tides rarely occurred before the 1980s, but have occurred periodically and frequently since the 1990s. Finally, the BS ecosystem has shifted from an N-limited oligotrophic state before the 1990s to a potentially P-limited eutrophic state. • Dissolved inorganic nitrogen increased by 7-fold over the past 60 years in Bohai Sea • Dissolved inorganic phosphorus, dissolved silica decreased first and then increased • Phytoplankton biomass increased by 6-fold and the dominant species changed • Bohai Sea shifted from N-limited oligotrophic state to P-limited eutrophic state [ABSTRACT FROM AUTHOR]