No abstract

No abstract

As China's only continental sea, the Bohai Sea is a relatively closed environment and is vulnerable to natural changes and human activities. In this paper, the long-term variations in nutrients in the Bohai Sea and the potential influencing factors were analyzed based on historical summer and winter data from 1978 to 2016. The results showed that the concentrations of dissolved inorganic nitrogen (DIN) in the Bohai Sea continuously increased from 1990 and rapidly increased after 2002, the phosphate (PO 4 -P) concentration exhibited a decreasing trend, and the silicate (SiO 3 -Si) concentration decreased from 1978 to 1987 and increased from 1987 to 2008. The nutrient concentrations were lower in summer than in winter, and the bottom concentrations were higher than the surface concentrations in summer, whereas the vertical differences were insignificant in winter. The dominant factor determining the long-term variations in DIN were atmospheric deposition and nonpoint sources due to various human activities; the primary factors affecting PO 4 -P were riverine inputs and nonpoint sources related to natural changes and human activities; the primary factors afftecting SiO 3 -Si were riverine inputs. The N/P ratio followed the DIN variation, the Si/P ratio followed the SiO 3 -Si variation, and the Si/N ratio decreased. The nutrient ratios were lower at the bottom than at the surface and were lower in winter than in summer. The nutrient limitation changed from nitrogen limitation to phosphorus and silicon limitations. The long-term nutrient variations in the Bohai Sea have potential ecological impacts on the local red tide features.Plain Language Summary Nutrients are important to primary productivity and thus important to marine ecosystems. Nutrient variations in coastal oceans may potentially impact the occurrence of ecological disasters. As the only continental sea in China, the Bohai Sea is a relatively closed environment and is vulnerable to natural and anthropogenic impacts. We found that the concentration of dissolved inorganic nitrogen in the Bohai Sea increased from 1990 to 2006; the phosphate concentration decreased from 1978 to 2016, and the silicate concentration decreased before 1987 and increased after 1987. We also found that N/P increased and Si/N decreased. The nutrient concentrations were higher, whereas the nutrient ratios were lower in winter than in summer. In summer, the bottom nutrient concentrations were higher than the surface concentrations, whereas the bottom ratios were lower than the surface ratios; in winter, the vertical differences were insignificant. The primary factors driving the silicate variations were riverine inputs related to natural changes and human activities; the primary factors in the phosphate variations could be riverine inputs and nonpoint sources related to natural changes and human activities; the dominant factor in the dissolved inorganic nitrogen variations could be atmospheric deposition and nonpoint sources due to various human activities. The red tide features in the...

No abstract