Research On Concentration Distribution Characteristics And Influencing Factors Of DMSP In Surface Waters Of China's Offshore

Dimethylmercaptopropionic acid inner salt(DMSP)is an important osmotic regulator of marine algae,and its degradation product,dimethyl sulfide(DMS),has a significant impact on the regulation of global climate change.In this paper,the research objects are Emiliania huxleyi with high DMSP production and bloom prone to water,and Phaeodactylum tricornutum,which is a model algae of marine planktonic diatoms,and carried out indoor cultivation experiments to explore the main factors affecting the production of particle DMSP(DMSPp)by marine microalgae.,Below are key research findings:(1)In the culture experiments with different salinities,the optimal salinity for the growth and development of Emiliania huxleyi was 35‰,and that of Phaeodactylum tricornutum was30‰.In general,the increase in salinity in the culture environment has a promoting effect on the production of DMSPp in Coccolithophore and Phaeodactylum tricornutum.(2)In the culture experiment of different nitrogen nutrient concentration,it was found that the addition of nitrogen nutrient salt is beneficial to the growth of algae.However,when the added amount of nitrogen nutrient salt reaches a certain concentration,it has completely satisfied the growth of algae cells.The nutrient salt will not continue to be absorbed and utilized by the algae.The production of DMSPp in the two types of marine microalgae culture experiments showed the same trend,that is,with the increase of nitrogen nutrient concentration,the yield of single-cell DMSPp decreased.(3)In the cultivation experiment of different nitrogen sources,it was found that the growth of the two marine microalgae in the experimental group using soluble organic nitrogen(DON)as the nitrogen source was better than that in the experimental group using dissolved inorganic nitrogen(DIN)as the nitrogen source.(4)As a high-yielding species of DMSPp,Emiliania huxleyi has a DMSPp concentration much higher than that in Phaeodactylum tricornutum.The single-cell DMSPp concentration of the former is about 9-21 times of the latter's single-cell DMSPp concentration.In order to further clarify the potential impact of environmental factors on marine algae and DMSP in the seawater environment,and to enrich the research content of DMSP in my country's offshore waters,this paper carried out different seasons of total DMSP(DMSPt)in the Laizhou Bay in Bohai Sea,the Yellow Sea and Bohai Sea(the YS and BS)and Yellow Sea and East China Sea(the YS and ECS)in 2021.Field observation and analysis of its concentration variation characteristics and influencing factors provide a theoretical basis for further understanding of the formation mechanism of DMSPt in my country's offshore waters.The main findings are as follows:(1)The average concentration of DMSPt in the surface seawater of Laizhou Bay in May2021 is 68.86±43.07 nmol/L,which is more than twice that of August 2021.The high value area is located in the Laizhou Bay or at the mouth of the bay.Different from previous studies,the average concentration of DMSPt in the surface water of Laizhou Bay in January 2021 is69.18±41.48 nmol/L,which is consistent with the concentration in spring.The analysis found that there was no significant correlation between the DMSPt concentration in the surface seawater of Laizhou Bay in winter and Chl-a.We speculate that the high concentration of DMSPt in the surface seawater in winter may be caused by the high concentration of DMSPt in the sediments being agitated by high winds.(2)The average concentration of DMSPt in the surface waters of the YS and BS from May to June 2021 is 75.03±34.81 nmol/L,which is about twice that of August to September2021.The high-value area is located in the northern part of the BS.There is a significant positive correlation between DMSPt and Chl-a in seawater in summer.(3)In May 2021,the DMSPt concentration in the surface water of the YS and ECS was relatively high,with an average value of 111.42±128.00 nmol/L,which was 22 times and 4times the DMSPt concentration in the sea water in January and August 2021,respectively.On the whole,the high value areas in the spring and summer seasons are located in the Yangtze River estuary or its offshore areas.And their DMSPt concentration is significantly positively correlated with chlorophyll a(Chl-a).(4)Overall,in summer,the average concentration of DMSPt in the surface waters of the Laizhou Bay,the YS and BS and the YS and ECS is not much different(26.25-40.62 nmol/L).In the spring,the concentrations of the YS and BS and the Laizhou Bay are close,and the YS and ECS is 1.5 times that of the first two sea areas.However,the ratio of DMSPt/Chl-a in the YS and ECS in spring is only 1/6 of that in summer,and the DIN concentration is twice that in summer.It may be that high nitrogen inhibits the synthesis of DMSP by phytoplankton.This is confirmed by the negative correlation between the microalgae in indoor culture and the nitrogen nutrients in the environment.(5)In the overall investigation and research,it is found that the correlation between the concentration of DMSPt in the surface seawater and Chl-a ranges from large to small: the YS and ECS > the YS and BS > Laizhou Bay,that is,from the open sea to the area that is more affected by human activities.Within the bay,its relevance has gradually weakened.