| Harmful algal bloom (HAB) is a common marine disaster along the coastal areas in the world, especially in recent years. It is considered that marine eutrophication is the basic condition for HAB although there are many factors which can influence its blooming. HAB cannot be forecasted since its outbreak mechanism has not been clear up to now. Therefore, it is very important of how to control or mitigate HAB. In this dissertation, we studied the effects of nutrient concentrition, composition and structure on HAB in typical areas in China (including Jiaozhou Bay, Hong Kong coastal area and its adjacent waters to Pearl River Estuary) by the means of the field investigations and indoor incubation experiment. Nutrients characterics and its influence on the occurance of HAB were compared and discussed. On the basis of the previous studies, the kinetics of clay/MMH coagulating red tide organisms was conducted. A new clay-complex system was selected for removal of different species of red tide organisms and a primary study of mortality rate on Penaeus japonicus and Lateobax japanicus was finished with the system. The main results are as follows:Mariculture area in Jiaozhou Bay: Firstly, nutrients concentrations in the investigated area were higher than the average of overall Jiaozhou Bay in the surface water in summer partially due to the mariculture along coast. Secondly, ammonium was the major composition of DIN (dissolved inorganic nitrogen), both silicate and phosphate concentrations may be the limitation factors for the growth of phytoplankton in this area. N/P ratio was increased significantly, Si/N and Si/P ratios were decreased during a period of HAB. The exhaustion of silicate and phosohate led to the death of red tide organisms. On the other hand, a new form of phosphous, matrix-bound phosphine (PH3), was found in the sediment in this area* in December of 2001. The results showed that PH3 concentrations were various with different layers and with different stations. The highest PH3 concentration in our investigation reached 685ng/kg (dry), which was much higher than those in terrestrial paddy soil, marsh and landfill that had been reported up to now. The correlation analysis indicated that there was apparently correlation between the concentrations of PH3 and the organic phosphorus in the bottom layer of sediment (R2=0.83). The discovery of PH3 in sediment will give us some new ideas on the mechanisms of phosphorus supplement and biogeochemical cycle in Jiaozhou Bay.* Coastal waters of Hong Kong (HK): Generally, nutrient concentrations in Hong Kong coastal waters (Porter Shelter) were higher during winter and lower in autumn. Chl.a concentration was higher in summer and lower in winter. According to the analysis of nutrient concentrations, the relative frequencies of nitrogen limitation both in spring and summer were above 30% and reached 87.5%in autumn especially. Relative frequency of phosphat limitation was 45.8% in winter. Because silicate concentration was higher, relative frequency of silicate limitation in this ares was lower in the whole year. * Adjacent waters to Pearl River Estuary in HK: Influenced by the fresh water from Pearl River Estuary, nutrient concentratons were abundant in this area comparing to HK coastal waters. There were remarkable negative correlations between silicate/nitrate and salinity in the surface waters. Comparing to the HK coastal waters, nitrate was the main form in the consisting of DIN in this area. The highest value of Chl.a was in summer. Chl.a concentration in this area was higher than that in HK coastal waters and similar to that in the mariculture area in Jiaozhou Bay. Relative frequency of phosphate limitation was higher than that of silicate. Since the concentraton of DIN was so much abundant, the frequency of DIN limitation was nearly zero.Nutrients addition experiment: A red tide of symbiotic algae-ciliate Merionecta rubra (previously Mesodinium rubrum) occurred on December 1, 2000 in Porter* Shelter of Hong Kong. Nutrient addition...
|
PDF Full Text Request