The Bohai Sea is a shallow-water, semi-enclosed marginal sea of the Northwest Pacific. Since the late 1990s, it has suffered from nutrient over-enrichment. To better understand the eutrophication characteristics of this important coastal sea, we examined four survey datasets from summer (June 2011), late autumn (November 2011), winter (January 2016), and early spring (April 2018). Nutrient conditions in the Bohai Sea were subject to seasonal and regional variations. Survey-averaged N/P ratios in estuarine and nearshore areas were 20−133. In contrast, the central Bohai Sea had mean N/P ratios of 16.9 ± 3.4 in late autumn, 16.1 ± 3.0 in winter and 13.5 ± 5.8 in early spring, which are close to the traditional N:P Redfield ratio of 16. In summer, both dissolved inorganic nitrogen (DIN) and dissolved inorganic phosphate (DIP) were used up in the surface waters of the central Bohai Sea, suggesting that the biological consumption of DIN and DIP may also follow the Redfield ratio. Wintertime nutrient budgets of the central Bohai Sea water were then established based on a mass balance study. Our results suggest that the adjacent North Yellow Sea supplied additional DIP to the central Bohai Sea via wintertime water intrusion, balancing terrigenous excess DIN that was introduced in summer. A water-mixing simulation combining these two nutrient sources with atmospheric nitrogen deposition suggests that eutrophication in the central Bohai Sea will likely be enhanced by the large-scale accumulation of anthropogenic nitrogen in adjacent open oceans. Such changes in nutrients may have fundamentally contributed to the recent development of algal blooms and seasonal hypoxia in the central Bohai Sea.

渤海是西北太平洋的浅水半封闭边缘海。自1990年代后期以来，它一直遭受营养过高的困扰。为了更好地了解这一重要沿海海域的富营养化特征，我们检查了夏季（2011年6月），秋季（2011年11月），冬季（2016年1月）和初春（2018年4月）的四个调查数据集。渤海的营养状况根据季节和区域变化而变化。河口和近岸地区的调查平均N / P比为20-133。相比之下，渤海中部的平均N / P比在深秋为16.9±3.4，在冬季为16.1±3.0，在初春为13.5±5.8，与传统的N：P Redfield比值接近。夏季，渤海中部的表层水都用尽了溶解性无机氮（DIN）和溶解性无机磷酸盐（DIP），这表明DIN和DIP的生物消耗也可能遵循Redfield比率。然后根据质量平衡研究确定了渤海中部海水的冬季养分预算。我们的结果表明，邻近的北黄海通过冬季水浸向渤海中部提供了额外的DIP，从而平衡了夏季引入的陆源过量DIN。将这两种营养物源与大气氮沉积结合的水混合模拟表明，渤海中部的富营养化可能会因邻近公海中人为氮的大规模积累而得到增强。