渤海氮磷营养盐和叶绿素浓度时空分布数值模拟与富营养化评估

当前渤海富营养化风险仍居高不下,严重制约了环渤海社会经济可持续发展。开展近海富营养化评估与趋势分析是国家生态安全保障的需求, 其难点在于富营养化评价要素长期演变进程高质量数据的获取。基于HAMSOM海洋生态模型, 通过修正溶解有机氮(dissolved organic nitrogen, DON)的难/易降解组分降解动力学形式, 构建了适用于富营养化评估与趋势分析的渤海三维水动力/生物地球化学耦合模型。利用2019年渤海春、夏、秋、冬四个季节DON、溶解无机氮(dissolved inorganic nitrogen, DIN)、溶解无机磷(dissolved inorganicphosphorus, DIP)和叶绿素a(chlorophyll a, chl a)调查结果, 对模型进行了校正, 并利用1980年至2020年的长期调查结果进行了验证, 模拟结果与调查结果相比较, 在数值大小和变化趋势上均吻合较好, 相对标准偏差、相似性系数和Kappa系数分别为24%、0.77和0.60。利用模型模拟计算的DIN、DIP、DON和chl a长期演变进程数据, 计算了营养状态质量指数(nutritional quality index, NQI)。结果表明, 当前渤海富营养化状态整体上处于贫营养状态, 但在渤海湾、辽东湾和莱州湾湾底近岸海域处于富营养状态, 季节上5~10月份处于中等富营养化状态, 从长期变化趋势看, 渤海整体上富营养化状态趋于改善。与复合富营养化指数(compound eutrophication index, CEI)对比表明, 渤海富营养化评估按NQI计算结果与按CEI计算结果相当吻合, 相似性系数为0.83。文章建立的渤海富营养化评估方法具有较高可靠性, 可用于渤海富营养化评估。

NUMERICAL SIMULATION AND EUTROPHICATION ASSESSMENT OF SPATIOTEMPORAL DISTRIBUTION OF NITROGEN, PHOSPHORUS, AND CHLOROPHYLL CONCENTRATIONS IN THE BOHAI SEA

At present, the risk of eutrophication in the Bohai Sea remains high, seriously constraining the sustainable development of the social and economic environment around the Bohai Sea. Conducting assessment and trend analysis of nearshore eutrophication is required for national ecological security. However, the difficulty lies in obtaining high-quality data on the long-term evolution process of eutrophication assessment elements. Based on the HAMSOM marine ecological model, we constructed a three-dimensional hydrodynamic/biogeochemical coupling model suitable for eutrophication assessment and conducted trend analysis for the Bohai Sea by modifying the degradation kinetics of dissolved organic nitrogen (DON) as a difficultly/easily degradable component. The model was calibrated using the survey results of DON, dissolved inorganic nitrogen (DIN), dissolved inorganic phosphorus (DIP), and chlorophyll a (chl a) in four seasons of 2019 in the Bohai Sea. The model was validated using long-term survey results from 1980 to 2020. Results show that the simulation results agree well with the survey results in terms of numerical magnitude and trend. The relative standard deviation, similarity coefficient, and Kappa coefficient are 24%, 0.77, and 0.60, respectively. The nutritional quality index (NQI) was calculated using long-term evolution process data of DIN, DIP, DON, and chl a simulated by the model. The results indicate that the current eutrophication status of the Bohai Sea is generally in oligotrophic state, while in eutrophic state in the coastal waters of the Bohai Bay, Liaodong Bay, and Laizhou Bay but in mesotrophic state from May to October. In long-term view, the overall eutrophication status of the Bohai Sea tended to improve. The compound eutrophication index (CEI) shows that the eutrophication assessment results calculated by CEI are quite consistent with those calculated by NQI, with a similarity coefficient of 0.83. The eutrophication assessment method established in this study has high reliability and can be used for eutrophication assessment in the Bohai Sea.