The Influence Of Typhoon-induced Precipitation On The Supplementary Of Biogenic Elements, The Abundance And Structure Of Phytoplankton In Jiaozhou Bay

Typhoon-induced precipitation events occur frequently, they have animmeasurable impact on coastal ecosystem, and have brought adverse factor ofcoastal economic society and economic development. Therefore it has importantsignificance that understanding and grasping the changes of hydrological, chemicaland biological factors about offshore environment after the rain, discussing theinfluence of heavy rainfall process on the supplements of the nutrient and the growthof phytoplankton on the offshore ecosystem.Based on the torrential rain in Qingdao by the influence of typhoon "davey" asthe research background, Jiaozhou Bay as the research object, and through a numberof sampling trips in Jiaozhou Bay and major rivers emptied into the bay, mesocosmexperiment and other means to realize the research that a series of changes about thesupplementary of the biogenic elements and the growth condition of phytoplanktonafter the rain. The main results are as follows:1、According to a number of sampling trips in major rivers emptied into theJiaozhou Bay and the rainfall data collected in the process of rain, the results showthat the content changes of SS and PO₄-P is shorter duration and faster response thanDIN and SiO₃-Si in the process influenced by the rainfall. While the composition ofDIN is changing around the rainfall （before the rainfall, NO₃-N/DIN up to75%, withthe occurrence of rainfall, NO₃-N/DIN decreased, NH₃-N/DIN increased gradually,and finally a combination of both became the main component of the DIN）. The inputof PO₄-P and SiO₃-Si caused by land source rainwater was significant, the fluxes ofPO₄-P、 SiO₃-Si caused by land source rainwater to the Jiaozhou Bay were91.07×10³mol/d and1002.03×10³mol/d which were respectively24times and18times over the same period without rainfall. The atmosphere wet deposition fluxes of DIN, PO₄-P and SiO₃-Si were81.29×10⁴mol/d,60.22×10³mol/d,67.27×10³mol/dduring the rainfall.2、Based on the data in July, August of2012, the supplement and distribution ofthe biogenic elements influenced by the rainfall was analysed.（1） Compared with those before the rainfall, biogenic elements were significantlyhigher after the rainfall in the Jiaozhou Bay.18days after the rainfall, the high valuearea of the five nutrients was in the northeastern part of the gulf, other regionsrecovered to the level before the rainfall.（2） Before the rainfall, there were potential limitation of PO₄-P in Dagu RiverEstuary and Licun River Estuary, SiO₃-Si may be limited or potentially limited in thecenter of the bay. One day after the rainfall, the nutrients throughout the bay were notlimited except the bay estuary.18days after the rainfall, PO₄-P was a potentiallimiting factor in the middle of the bay, the proportion of SiO₃-Si/PO₄-P andSiO₃-Si/DIN were conducive to the growth of diatoms throughout the bay.（3） Before the rainfall, the lower degree of eutrophication occurred mainly in thenorth of the Tuandao and Dagu River Estuary connection, and increasing gradually tothe northeast. One day after the rainfall, the eutrophication area was further increased,only the estuary of the bay did not reach eutrophication level.18days after the rainfall,eutrophication was slightly higher than the level before the rainfall, most areas wereclose to1that means it is in a eutrophication critical state.3、Through the ecological mesocosm experiment, it achieves a live simulation ofthe changes of the hydrological, biological and chemical factors after the rainfall inJiaozhou Bay. Chl a showed the variation of increasing at first, then decreasing in thefour bags which have different salinity gradient. The Chl a of M3appeared to rapidgrowth after reduced, this salinity may be more favorable to the growth andreproduction of phytoplankton. But overall there are some differences between thephenomena of the mesocosm experiments and the results of field survey, mesocosmexperiments can not simulate live marine conditions completely.4、The results of principal component analysis about the main environmentalfactors affecting the growth of phytoplankton can be seen before and after the rainfall, rainfall was the main reason for changes in the structure of the principal componentabout environmental factors. And18days after the rainfall, the principal componentof the main environmental factors was back to the state before the rainfall, nutrientsand salinity had always been the main environmental factors affecting the growth ofphytoplankton. The total species and total abundance of phytoplankton had decreasedsignificantly, also changed in the number and structure of the dominant species（inshore species increase, oceanic species decrease）.