珠江口水动力特征与缺氧现象的研究进展

Progress on the hydrodynamic characteristics and the hypoxia phenomenon in the Pearl River Estuary

珠江口受径流、潮流和南海近岸环流等综合影响,水动力条件复杂。潮汐性质为不规则半日潮,潮振幅由南向北逐渐增加,潮流以往复流为主,流向与岸线走向基本一致。锋面与潮动力和径流量有关。珠江口表层和底层的盐度锋呈与岸线平行的方向。冬季,锋区明显紧靠珠江口西侧的海岸线;而夏季表层受径流影响,使得锋区向外海迁移,而底层锋的位置则相对变化不大;且无论冬季还是夏季,底层锋都比表层更加显著。潮汐动力对咸潮入侵具有一定的影响。当径流动力不足时,潮汐动力占主导,因而咸潮强度会明显增强,咸潮上溯也可以影响河口锋面的强度与位置。此外,由于潮汐、风及上升流间歇性破坏层化,令溶解氧垂向对流及扩散的方向和强度随潮汐发生周期性变化,因此,珠江口的水动力特征显著地影响到珠江口底层缺氧现象。文章总结了前人对珠江口的水动力环境和缺氧现象的研究结果,并讨论了未来研究中值得关注的一些问题。

The Pearl River Estuary is affected by river discharge, tidal currents and the near-shore circulation in the South China Sea. Thus, its hydrodynamic condition is very complicated. The tide at the Pearl River Estuary is mainly irregular semidiurnal type, its tidal amplitude increases from south to north, and its tidal flow reciprocates obviously along the coastline. The tidal front is related to the tidal dynamics and river discharge. The surface and bottom salinity fronts are mainly parallel to the shoreline. In winter, the surface front is apparently near the west coastline of the estuary, whilst in summer, the front spreads away from the estuary because of river discharge. The bottom front is not affected obviously by the season, and in both summer and winter seasons, the bottom front is stronger than the surface front. The tidal dynamics could affect the saline water intrusion. When the river discharge is weak, the tidal dynamics become predominant;therefore, the strength of the saline water intrusion becomes stronger, and the saline water intrusion could influence the strength and position of the front. Furthermore, because the tide and upwelling could destroy the water stratification occasionally, the direction and the strength of vertical convection of dissolved oxygen could change periodically with tides. The hydrodynamics of the Pearl River Estuary obviously influence the bottom hypoxia of the estuary. This paper summarizes the progress on the hydrodynamic characteristics and the hypoxia, and discusses some issues that are worth studying in the future.