海口湾的台风及其对海水水质的影响机制分析

海口湾受台风影响全年以7～10月为盛行时期,尤以8～10月最盛.我们于1996年台风季节前、后在海口湾海域布设了10个监测站,进行了pH,DO,COD,PO₄-P,NO₂-N,NO₃-N和SiO₃-Si的监测,分析了它们在台风前后的变化,结合台风暴流的数值计算,初步探讨了因台风引起水质变化的机制,结果表明,台风、大浪和风暴流掀起海底沉降物或促使底层高营养盐的水体与表层强烈地混合,尤其是风暴流在湾顶辐聚,强烈的流速悬浮湾顶主要由生活污水排污口附近海域受污染的沉积物,一些污染物溶解于水体,伴随着台风而来的暴雨也将陆源污染物通过南渡江搬运到海口湾,使COD,PO₄-P,NO₂-N,NO₃-N和SiO₃-Si的含量台风后高于台风前.台风大浪和风暴流强烈的水交换作用使外海高DO的海水与湾内海水进行充分的交换,又使空气中的氧充分溶解于水体,使DO在该次台风后反而比台风前高,风暴流的水交换作用也使pH值在该次台风前后没有明显变化.

Discussion on typhoon occurred in the Haikou Bay and influencing mechanism on the sea water quality

The water quality parameters such as pH, DO, COD, PO4 - P, SiO3 - Si, NO2 - N, NO3 - N in the Haikou Bay were monitored respectively before and after No. 9618 typhoon occurring on September. 18, 1996. Based on the statistics of typhoon in the Haikou Bay and numerical calculation of stormy current, the mechanism of water quality variation caused by typhoon was discussed. The studies are as follows: The typhoons influenced on the Haikou Bay usually appear between July and November, most usually between August and October. The monitoring result before typhoon is different from that after typhoon. The stormy wave and windstorm current stir up the sediment in nearshore sea bottom and make bottom water mix with surface water strongly, specially windstorm current with strong velocity in the top bay stirs up higher pollutants sediment near sea area of discharge ditch, and strong rain with typhoon carries the pollutants from land through the Nandu River to enter into the Haikou Bay, so the contents of COD, PO4 - P, NO2 - N, NO3 - N, SiO3 - Si after typhoon are higher than those before typhoon. Windstorm current is violent, which made offshore high DO water exchange more frequently with inner bay water and oxygen in the air dissolve in sea water fast, so DO content after typhoon is higher than that before typhoon. This strong action of water exchange also causes pH change small before and after typhoon.