Influence Of Nutrients Input On Mirco-phytoplankton In Eutrophied Estuary And Bay

Harmful algae blooms(HABs) occur in sea areas all over the world. Posing increasing impacts on marine ecosystem and human health. As a result, the research on prevention and cure of HABs has become the most important ecological and environmental issue which should be resolved urgently. Eutrophication, the manifestation of nutrients enhancing aquatic primary productivity, is often indicated by the presence of HAB in river-dominated coastal ecosystems, rivers are playing main roles in transporting nutrients from the land to the sea. Nutrients input via river is the most important reason for eutrofication and HABs occurrence.In this thesis, the relation between nutrients input and phytoplankton community structure in eutriphied estuary and bay is studied. Base on the data obtained during field observarions in the Changjiang estuary in spring of 1986 and 2002, the historical and present states of eutrophication are evaluated by eutrophication index (E value). The influence of nutrients input via river on the growth of Skeletonema costatum and Procentrum donghaisense is studied. The results show that: the sea of the Changjiang estuary is polluted more seriously in 2002 than that in 1986.The average of eutrophication index (E value) in the Changjiang estuary in 2002 is 9.31, and the E value in 1986 is 1.51. The average density of P.donghaisense in 2002 is 34.5 times more than that in 1986. During this period(1986-2002), the proportion of Skeletonema costatum in that phytoplankton decreased from 21.7% to 2.8%.The impact of nutrients input on the structure of HAB phytoplankton is studied by mesocosm experiment in September 2005 in Jiaozhou bay,Qingdao. The result show that the dominant species of phytoplankton are Eucampia zoodiacus,Skeletonema costatum,Chaetoceros curvisetus. Silicate is the main limiting nutrient factor of phytoplankton growth here. The diatom will bloom firstly, and dinoflagellate maybe bloom later after diatom. The scale of bloom caused by pulsed nutrients supply is smaller than one-off nutrient supply, and further more, the time of HAB bloom caused by pulsed nutrients supply is 1 day later than that caused by one-off nutrient supply.A HAB diatom Skeletonema costatum was introduced into the model that is to elucidate whether phytoplankton growth could be influenced by an environmental fluctuation such as a pulsed nutrient supply. It showed characteristic responses to different intervals of nutrient supply. S. costatum showed large fluctuations in cell density in response to pulses of nutrients,and the frequency of fluctuation in cell density equal to the frequency of nutrients pulsed supply. The maximum of cell density of S. costatum under 1 day nutrients pulsed is lower than cell density under 5 days nutrients pulsed or 10 days nutrients pulsed. And the time that get to the max cell density under 1 day nutrients pulse is later than the time under 5 days nutrients pulsed or 10 days nutrients pulsed. Furthermore, the average uptake rate on nutrients under 10 days nutrients pulsed is the largest among 3 different nutrient pulsed supply modes, and the average uptake rate on nutrients under 5 days nutrients pulsed is the least among these, especially on the nitrate and silicate.