Du Yunfei, Han Xiangju, Wang Ya Ping, Fan Daidu, Zhang Jicai
State Key Laboratory of Marine Geology, Tongji University, Shanghai 200092, China.
State Key Laboratory of Estuarine and Coastal Research, East China Normal University, Shanghai 200241, China.
Water Res. 2025 Jul 1;279:123349. doi: 10.1016/j.watres.2025.123349. Epub 2025 Feb 21.
The suspended sediment front (SSF) in the Yangtze River Estuary significantly affects regional circulation, water quality, and productivity. However, the quantitative understanding of its multiscale spatio-temporal variations and associated ecological effects remains largely limited. Utilizing suspended sediment concentration remote sensing data from 2012 to 2018, we applied an improved gradient-based front detection algorithm to identify SSFs. Our analysis highlighted significant variability in the SSF and established its oscillating boundaries. The mean longitude location of the front is approximately 122.2°E, extending up to 122.8°E, with its occurrence frequency negatively correlated with water depth. The control effect of estuarine engineering projects on lateral sediment exchange results in the more frequent occurrence of stable banded fronts in these areas. The SSF exhibits notable spatial pattern variability and fluctuations on tidal to interannual scales. Compared to other tidal types, the front extends furthest offshore during spring tides due to enhanced tidal mixing and seaward residual flow. The seasonal variations in the frontal location are closely related to ocean dynamic processes, jointly controlled by the mixed layer depth, wind speed, wind direction, wave intensity, and sea surface temperature. The direct influence of sediment load from the Yangtze River is most pronounced in July, coinciding with peak sediment load. The interannual variations indicate a strong correlation between frontal migration and sediment load. Meanwhile, extreme storm events cause significant resuspension of bed sediments, resulting in substantial offshore movement of the SSF (>14 km), with effects persisting for at least 2 days. Major floods modulate the short-term fluctuation range of the front by significantly increasing the sediment transport flux. Further investigation into the ecological effects of the SSF reveals that in summer, the dual front system comprising the SSF and plume front strongly controls estuarine primary productivity, with regions of high chlorophyll-a concentration aligning well with the seaward oscillation boundary of the SSF. Temperature, salinity, and nutrient concentration near the SSF also exhibit drastic changes. Conversely, in winter, insufficient runoff results in a single SSF system, leading to suboptimal nutrient, temperature, and light conditions, and consequently, very low primary productivity.
长江河口的悬沙锋（SSF）对区域环流、水质和生产力有显著影响。然而，对其多尺度时空变化及相关生态效应的定量认识仍极为有限。利用2012年至2018年的悬沙浓度遥感数据，我们应用一种改进的基于梯度的锋面检测算法来识别悬沙锋。我们的分析突出了悬沙锋的显著变异性，并确定了其摆动边界。锋面的平均经度位置约为东经122.2°，延伸至东经122.8°，其出现频率与水深呈负相关。河口工程项目对横向泥沙交换的控制作用导致这些区域更频繁地出现稳定的带状锋面。悬沙锋在潮汐到年际尺度上表现出显著的空间格局变异性和波动。与其他潮汐类型相比，由于潮汐混合增强和向海余流，锋面在大潮期间向海延伸最远。锋面位置的季节变化与海洋动力过程密切相关，受混合层深度、风速、风向、波浪强度和海表面温度共同控制。长江泥沙负荷的直接影响在7月最为明显，与泥沙负荷峰值一致。年际变化表明锋面迁移与泥沙负荷之间存在很强的相关性。同时，极端风暴事件导致床底泥沙大量再悬浮，致使悬沙锋向海大幅移动（>14公里），影响持续至少2天。大洪水通过显著增加输沙通量来调节锋面的短期波动范围。对悬沙锋生态效应的进一步研究表明，在夏季，由悬沙锋和羽状锋组成的双锋系统强烈控制河口初级生产力，叶绿素a高浓度区域与悬沙锋的向海摆动边界吻合良好。悬沙锋附近的温度、盐度和营养盐浓度也呈现剧烈变化。相反，在冬季，径流不足导致单一的悬沙锋系统，导致营养盐、温度和光照条件欠佳，进而初级生产力极低。
