Relations Between Prorocentrum Donghaiense Bloom And Environmental Factors And Nitrogen Cycle Processes In The Water Column In The Spring East China Sea Coastal Area

In recent years,the East China Sea coastal has become a region where the harmful algal bloom frequently occurred,the research of algal bloom in this area is more and more.Algal blooms can deplete an amount of dissolved oxygen and release toxin,that affect the nature of the sea-water and threaten the survival of marine life and have an impact on human health.we surveyed 2016 algal blooms along the East China Sea in spring,and main environmental factors,and determinate the rates of nitrogen cycling processes in the main water bodies,According to the specific situation and related parameters of Prorocentrum donghaiense algal blooms,we discussed the interaction of algal blooms with environmental factors,and discussed the main nitrogen cycle processes in water body of algal bloom area.In this paper,Prorocentrum donghaiense algal blooms is divided into two parts(southern region and northern region)and four stages according to historical research and algal bloom,biomass,algae density,algal culture experiment of this cruise,we can discussed more detailed.Prorocentrum donghaiense algal bloom are regulated by a variety of factors.In spring,the Yangtze River diluted water and minjiang diluted water bring the surface water of low salnity,high nitrogen,high nitrogen and phosphorus ratio to the East China Sea,providing a material basis for Prorocentrum donghaiense algal blooms in East China Sea;within a certain range(16-19 ?),when the temperature was higher,the Prorocentrum donghaiense algal blooms was stronger in the East China Sea.In the surface and subsurface low salt water affected by diluted water,Prorocentrum donghaiense algal blooms are more likely to erupt;In addition,the turbidity can indirectly affect phytoplankton growth by altering the light transmittance of the water body;Under the condition of low sunlight,the surface water body tends to obtain higher biomass,Prorocentrum donghaiense may be adapted to the low light environment more.In addition,the ingestion of zooplankton,the secretion of toxins and the change of wind field,flow field may also affect the processes of Prorocentrum donghaiense algal blooms in the East China Sea.In this study,we discussed in detail the physical parameters,the concentration range of different inorganic and organic nutrients,particles and chlorophyll-a,and their profile,distribution regular,afterward,,we discussed the relationships between these parameters,distributions and the algal bloom area,algal bloom stages,and discussed the special phenomenon according to the specific situation of each station.The algal blooms in the East China Sea were more favorable in the southern zone of ECS than the northern part of ESC because of superior environmental conditions,the Prorocentrum donghaiense algal blooms were more stronger in the northern region,the consumption of nitrate,SRP and dissolved organic phosphorus was more significant than the north region.According to correlations between the concentration of nitrite,nitrate,silicon and the concentration of chlorophyll-a in shallow water(<13 m)of the South China Sea,the eruption of Prorocentrum donghaiense algal blooms in the southern region consumed nitrite and nitrate,and release net silicate,while the correlations is weaker in northern region.The profile ranges of SI/DIN in all stations is 0.8-8.5,DIN was consumed strongly following Prorocentrum donghaiense algal blooms in the East China Sea,which significantly increases the level of SI/DIN in the upper water;the range of DIN/DIP was 16-580,High DIN/DIP is conducive to the eruption of Prorocentrum donghaiense algal blooms in the East China Sea,the eruption of algal blooms makes the DIN/DIP continues to rise;when the biomass is low(Chl-a<4?mol/L),the phytoplankton of the northern region priority use DIP of TDP,when DIP concentration above 0.3 ?mol/L,DIP tends to be exploited,DOP tends to be released,when DIP concentration below 0.2 ?mol/L,DIP and DOP are in a state of consumption,compared to the northern region,algal blooms of the southern region is more stronger,the consumption of DOP is also stronger;the Prorocentrum donghaiense algal blooms in the East China Sea is accompanied by the DIN significant consumption and the consumption of DIN is stronger than DON,contrast to southern region,in the northern region,DON may be more likely to be exploited;urea concentration and its proportion in dissolved organic nitrogen(-4%)are low,along with DON net consumption,Urea also tends to be net consumed;In the eruption stage of Prorocentrum donghaiense algal blooms in the East China Sea,the consumption of Urea is the most strongest,while algal blooms dissipated,urea/DON show increasing;The eruption of Prorocentrum donghaiense algal blooms in the East China Sea was associated with the net utilization of nitrite,while the southern region was more significant than that in north region;The over-saturation of dissolved oxygen in 3-10 m water body in research area is caused by the high intensity oxygen production at the eruption stage of Prorocentrum donghaiense algal bloom,The uptake rates ranges of NH4+?NO3-?urea is 6.83-804.90 nmol N·L-·h-1,1.67-227.18 nmol N·L-1·h-1 and 0.32-33.86 nmol N·L-1·h-1 in the surface water and fluorescence maximum water.When NH4+ concentration above 4 ?mol/L,the uptake of NO3-is significantly inhibited,But the uptake rates of urea is not inhibited by NH4+.The RPI(Relative preference index)of Phytoplankton uptake NH4+ and urea above 1,indicating strong preference for both ammonia and urea;The absorption of NH4+?NO3-?urea is obviously inhibited under dark environment,The dark uptake rates ranges of NO3-is 0.24-7.41 nmol N·L-1·h-1,it is the most inhibited,The uptake rates of NH4+ and urea decrease 25%to 80%and 28%-90%in dark environment,respectively;The inhibitory effect of light on NH4+ and urea uptake was relatively small in the eruption stage of Prorocentrum donghaiense algal blooms in the East China Sea;in eruption stage of algal bloom,The total light uptake rates of NH4+,NO3-and urea is the most strongest and the ratio of NH4+ uptake rates and the total light uptake rates is more high than initial stage;Compared with light,substrate concentration is another important factor affecting the light absorption rate,especially urea,when the urea is low(<0.3?mol/L),the urea concentration is the controlling factor of urea uptake rates.Distribution of the nitrification rates is low in surface layer,in 5-20 m depth,the rates has a maximum value and in the bottom the rates increases,the overall range of nitrification rates is 4.09-4746.32 nmol N·L-1·d-1;Urea oxidation rates increases following the increasing of depth,the range of Urea oxidation rates is 0.03-35.65 nmol N·L-1·d-1;the low nitrification rates of surface water may be due to light inhibiting nitrification microbial activity;the existence of a maximum nitrification rate may be due to the degradation of organic matter,which provides a richer substrate and decreasing of the inhibition of illumination;the high nitrification rate of the bottom water may be due to more available substrate for the nitrification process,because of NH4+ release by the sediment suspension or the NH4+ carried by settling particles;The nitrification rates in southern stations is generally low than northern region,under the strongest algal blooms in the southern region,the competition of phytoplankton to the NH4+ substrate limit nitrification rates and urea oxidation rates.The dispersal stage of algal bloom in the East China Sea,The average of the water column integral of nitrification and urea oxidation rates is higher,which may be due to the weakening of the substrate competition by phytoplankton and the degradation of organic matter,which provides more substrates for ammonia-oxidizing microorganisms and urea-oxidizing microorganisms.In addition,the nitrification rates and the urea oxidation rates are significantly related(R2=0.3244,P<0.0001),the RPI values of phytoplankton uptake of NH4+ and urea also have a good relationship(k=0.8,R2=0.9305).These phenomena indicate that there may be an intrinsic connection between NH4+ and the urea substrate or the nitrogen cycle processes associated with both NH4+ and urea.