A discussion on typhoon occurred in the Haikou Bay and impact mechanism on seawater quality

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 Typhoon 9618 occurring on Sep.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 is discussed.The typhoon impact on the Haikou Bay usually appears between July and November,most usually between August and October.The monitoring results before a typhoon were different from that.The stormy wave and windstorm cur rent stir up the sediment in near-shore bottom and make the bottom water mix with the surface water strongly,specially windstorm current with strong velocity at the head of the bay stirs up higher pollu tants sediment near sea area of sewage outfall,and heavy rain with typhoon carries the pollutants from land through the Nandu River to the Haikou Bay,so the contents of COD,PO₄-P,NO₂-N,NO₃-N,SiO₃ after a typhoon are higher than those before.Windstorm current is violent,which makes offshore high DO water exchange more frequently with inner bay water and oxygen in the air dissolves in sea water faster,so DO content after typhoon is higher than that before typhoon.This strong action of water exchange also causes lower pH change before and after the typhoon.