The past few decades have seen a massive increase in global coastal eutrophication, for which nitrogen enrichment is usually the primary causative agent. Based on field monitoring data from coastal waters during dry, wet, and normal flow seasons in 2016, the distribution characteristics of dissolved inorganic nitrogen (DIN) and its influencing factors were studied. The level of DIN pollution was evaluated, and its contribution to the eutrophication in the coastal waters was analyzed. Furthermore, the main source and relationships of DIN were also discussed. The results showed that the concentration of DIN ranged from 0.008 mg/L to 0.384 mg/L, with an average of 0.114 ± 0.087 mg/L. Areas of high DIN concentration (>0.2mg/L) were located in coastal waters adjacent to Haikou City and Qiongzhou Strait in all seasons. The species and composition of DIN in the coastal waters showed seasonal variation. N-NO${}_3^{-}$ and N-NH${}_4^{+}$ were the main species of DIN. The contribution of DIN to eutrophication ranged from 21.2% to 47.8%, with a mean value of 34.6% $\pm$ 4.2%. Under poor nutrient condition (EI<1), the contribution of DIN fluctuated with increasing of eutrophication index (EI). When EI was greater than 1, the contribution of DIN to the eutrophication remained stable. During the investigation period, the concentration of DIN showed a significantly negative correlation with dissolved oxygen. DIN was an important factor contributing to eutrophication, but it was not the decisive factor. With increasing EI, the contribution of chemical oxygen demand and dissolved inorganic phosphorus may become more important. The results provided a scientific basis for effectively solving the DIN pollution problem in the coastal waters of Hainan Island.

在过去的几十年中，全球沿海富营养化现象大量增加，为此，氮的富集通常是主要的诱因。基于2016年干，湿，正常汛期沿海水域的现场监测数据，研究了溶解性无机氮（DIN）的分布特征及其影响因素。评价了DIN污染水平，并分析了其对沿海水域富营养化的影响。此外，还讨论了DIN的主要来源和关系。结果表明，DIN的浓度范围为0.008 mg / L至0.384 mg / L，平均为0.114±0.087 mg / L。在所有季节中，高DIN浓度（> 0.2mg / L）的区域都位于海口市和琼州海峡附近的沿海水域。沿海水域中DIN的种类和组成呈现季节性变化。否${}_3^{-}$ 和N-NH${}_4^{+}$是DIN的主要种类。DIN对富营养化的贡献范围从21.2％到47.8％，平均值为34.6％$\pm$4.2％。在营养条件差（EI <1）下，DIN的含量随富营养化指数（EI）的增加而波动。当EI大于1时，DIN对富营养化的贡献保持稳定。在研究期间，DIN的浓度与溶解氧呈显着负相关。DIN是导致富营养化的重要因素，但不是决定性因素。随着EI的增加，化学需氧量和溶解的无机磷的贡献可能变得更加重要。研究结果为有效解决海南岛沿海水域DIN污染问题提供了科学依据。