Study On Spatiotemporal Variation And Its Influence Mechanism Of Silicate In Typical Coastal Sea Areas Of Shandong Peninsula And Yellow Sea

The Yellow Sea is an important high-productivity shelf shallow sea in China.The coastal economy develops rapidly and is seriously affected by human activities.The study of nutrients in coastal waters is not only the basis for the healthy development of marine organisms,but also provides necessary information for alleviating the pressure of water environment and formulating ecological management and environmental protection strategies.Recent years,frequent human activities have led to the gradual prominence of marine environmental problems such as eutrophication.With the enrichment of artificially added N and P nutrients and the incremental construction of dams and other water conservancy facilities,Si in the marginal sea is gradually becoming a biological limiting nutrient substance.Phytoplankton such as diatoms,which use Si as essential nutrients,are gradually at a disadvantage in population competition.This study was carried out in the typical coastal waters of Shandong Peninsula and the Yellow Sea.By comparing the temporal and spatial changes of inorganic nutrients in the coastal waters of Yantai through six cruises from March to September 2017 and the similar months in the central North Yellow Sea,it was observed that there was an excess DSi addition in the Yantai coastal waters,however,no significant difference in DSi distribution between Aoshan Bay and the South Yellow Sea.The influence of various regulation mechanisms on different sea areas is discussed,and point out the additional DSi may come from the dissolution of permeable particles in the beach.Based on experimental data,model fitting and measured data,the output of dissolved beach permeable particles to DSi in Yantai Muping nearshore seawater is quantified.It shows that the contribution of dissolved beach permeable particles to Si cycle has important research significance under the background of global rivers' decreasing Si flux into the sea.A comparative analysis of the temporal and spatial changes of nutrients in the coastal waters of Muping,Yantai,and the central North Yellow Sea from March to September shows that the seasonal distribution characteristics of nutrients are obvious.There is no obvious vertical concentration gradient in spring,the nutrients concentration of each parameter is higher than that of the surface layer in summer.The vertical distribution of nutrients is significantly different under the influence of the thermocline and the central cold water mass.Influenced by the difference in water depth and the presence of cold water masses,the existence time of thermocline in the central sea area is significantly longer than that in the coastal sea area.Due to phytoplankton consumption in summer surface layer,the nutrients concentration of each parameter is maintained at a low concentration,while high value area exists in the bottom layer.Silicate regulation is mainly manifested in the surface photosynthetic utilization and respiration mineralization below the thermocline.While DSi distribution at the surface and bottom of the costal waters shows a gradual increase toward the sea.This indicates that in addition to photosynthetic consumption and respiration mineralization caused by biological effects,there are also additional silicate additions in the coastal waters.In summer,the hydrodynamic conditions of the coastal waters and the North Yellow Sea Cold Water Mass are poor,and the water body stays.Comparing and analyzing the distribution and variation law of DSi in the two sea areas,different from the North Yellow Sea,the addition of silicon(Si*)except for biological effects is basically constant.The Si*in the costal waters shows monthly increase,the relationship with salinity and Si*indicates that the controlling factors causing the monthly growth of Si*in the costal waters may come from the coast.Based on the analysis of various factors that may affect the changes of nutrients in coastal waters,such as rivers,atmospheric deposition and groundwater discharge,it is suggested that the dissolution of permeable sand particles is the possible cause of silicate accumulation in coastal waters.In summer,the nutrient concentration in the waters near the Subei Shoal and off the Yangtze River estuary in the is relatively high,which is influenced by nutrients transported to South Yellow Sea by the coastal currents in Subei and the Yangtze River Diluted Water.The concentration of nutrients in the surface layer of the central sea area maintain low,and the high value area of nutrients in the bottom layer is consistent with the range of Cold Water Mass,which is the result of organic matter remineralization and nutrients accumulation.In June,the stratification of Aoshan Bay was not obvious,and the concentrations of inorganic nutrients in various parameters were relatively low.Different from the coastal waters of Muping,Yantai,the silicate regulation of Aoshan Bay and the middle of the South Yellow Sea is mainly photosynthesis in surface and respiration mineralization below the thermocline,showing no obvious addition of silicate,which may be related to the short residence time of the water body.Based on experimental data and model calculation,the addition of DSi to the costal waters by tidal extraction and sand dissolution in mixed layer under surf zone wave is quantified.The net dissolved silicon flux of coastline calculated by the model is 1.69×103?4.91×103 mol yr-1 m-1,which is basically consistent with the field investigation result of 3.57×103 mol yr-1 m-1 in Yantai Muping coastal waters,indicating that there are sand-beach permeable particulates dissolved and exported DSi to Yantai Muping coastal waters to increase its monthly concentration.At the same time,the flux of dissolved silica in the Yellow Sea was quantitatively estimated,and an attempt was made to construct the budget of silica in the Yellow Sea.Compared with the flux of source and sink of silica,the research significance of dissolved silica in the sand was pointed out.