珠江口夏季底层缺氧现象的数值模拟

Numerical Simulation on Hypoxia Phenomenon at the Bottom of Pearl River Estuary During Summertime

底层水体缺氧现象已经引起了人们的广泛关注.水体底层缺氧易造成水生生物的死亡,影响了水体的生态环境,造成水质严重下降,因此找出造成水体缺氧的原因有着非常重要的意义.通过一个三维的水动力生态模型模拟并研究了夏季珠江口底层的缺氧现象.分析结果表明,盐度锋面对珠江口水体表底层氧气交换的抑制作用及底层有机耗氧物质对溶解氧的大量消耗是造成底层缺氧现象的主要原因,但潮汐所导致的强混合可以破坏这种缺氧机制的形成;底层缺氧主要与河流输送的耗氧物质有关;作为主要营养盐参与生态系统循环的磷对底层溶解氧无明显影响.

Hypoxia phenomenon at the bottom of waters has aroused wide attention since early times.It can severely affect the ecosystem balance of the water,resulting in the declination of water quality by easily leading to the death of aquatic life.Therefore,finding out the reasons of water hypoxia has important significance.In this study,a three-dimensional ecological model was used to study the hypoxia phenomenon in the Pearl River Estuary during summer.Its hydrodynamic model was based on ROMS（regional ocean modeling system） and ecological model was based on the FENNEL ecological module.The results show that the dominating reasons leading to this phenomenon are the salt-front and the oxygen-consumption materials at the bottom of the water.The former restrains the exchange of oxygen that being rich in the surface water and poor in the bottom water in the Pearl River Estuary.However,strong tidal processes can weaken and ruin the hypoxia formation by enhancing the vertical mixing.Hypoxia has a close relationship with oxygen-consumption organic materials from the rivers.Being shown from the simulation result,as one of the main nutrients that engages in the circulation of the ecosystem,phosphate doesn＇t have obvious impact on bottom oxygen concentration.