Based on laboratory culture of harmful alga on iron and phosphorus uptake, and the study of accu-mulation of iron-phosphorus in cores and release of iron and phosphorus from surficial sediments collected in the Pearl River Estuary, the reasons of the high frequency of phytoplankton bloom therein are discussed. The results show that Fe starvation can make algal growth rate slow down and the peak of cell number decrease. Fe and P contents in algal cell bear a significant correlation and the molar ratio of P:Fe is ~356:1, suggesting that algal uptake of Fe and P is synergistic. Total Fe and total P in sediments are positively correlated and Fe-P is the main species of inorganic sedimentary P. Through continuous leaching with agitation, 34.26%―80.21% of exchangeable P and 4.04%―22.52% of ex-changeable Fe are released from surficial sediments, implying that the accumulation of Fe-P in sedi-ments is available for providing nutrients (P and essential Fe) for the demand of phytoplankton bloom. These factors might be responsible for a higher frequency of red tides than other marine regions.
Combining numerical diagnosis from atmospheric science with biogeochemical methods,a model of the potential correlation of monsoons with red tide emergence in the East China Sea is constructed.The model is designed based on an in-depth investigation of the time-space relationship of aerosol and red tide events in the East China Sea from 2005 to 2006,and a continuous monitoring of atmospheric particulates at two stations.The study shows that every red tide event investigated has a close relationship with aerosols coming from the northwest (wind direction in winter) along with subsidence flow.The elemental abundance of total suspended particulate in Hangzhou and Tiantai is different from that of soil background levels,indicating atmospheric particulates there are brought in by winter winds.There is a significant correlation between the content of iron and phosphorous in atmospheric particulates,which mainly exist in binding materials between particulates.In addition,the confined absorption of iron and phosphorous by red tides is related to the intensity of sunlight.These results provide new information regarding the mechanism for the high frequency of red tides in the East China Sea.The results also provide a scientific basis for establishing new pathways for pre-warning and forecasting of red tide disasters.
WENG HuanXin TIAN RongXiang JI ZhongQiang YU XinAn
