Studies On Nutrients In The Sea-surface Microlayer And Subsurface Water In The Southern Yellow Sea And Jiaozhou Bay

Nutrients provide necessary for phytoplankton growth and they are the majorbiogenic material of phytoplankton, meanwhile, they are the important foundation ofthe marine food chain and marine primary productivity. nutrients could be enriched toa great degree in the microlayer, implying that the surface microlayer might play aspecial role in oceanic environmental system, Nutrients in the microlayer might bedifferent even if the quality of water body is similar,. Therefore, it is great significanceof studiying the content of nutrients in the sea surface microlayer, enrichmentmechanism and eutrophication for understanding the biogeochemical cycle ofnutrients. In addition, it is the basis for the study in the sea micro-surfacecontamination of nutrients.In the present dissertation, the concentration distributional characteristics andspatio-temporal variations of nutrients and the enrichment extents of nutrients in thesea-surface microlayer were studied systematically in the southern Yellow Sea andJiaozhou Bay and the water quality status in Jiaozhou Bay was assessed by using theassessment model of potential eutrophication. The main research results are asfollows:1. Based on observed nutrient data collected in the sea-surface microlayer （SML）and subsurface water of the southern Yellow Sea during Sep2010and Jun2011,the results showed that the proportion of NO₃^--N and NH₄⁺-N was similar insummer, while NH₄⁺-N was the main existing form of the inorganic nitrogen （DIN）in spring. It indicated that the composition of DIN had an obvious seasonalvariation. The distribution of DIN, PO₄^3--P and SiO₃^2--Si was consistent, the highvalue of nutrients were found in the south of southern Yellow Sea where wasmainly influenced by diluted water of Yangtze River and the concentrations ofnutrients decreased gradually from northeast to southwest of southern Yellow Seaand decreased from inshore to offshore sites.The concentrations of nutrients in the microlayer were closely correlated withthose in the corresponding subsurface water, implying that there was a strongexchange effect between the microlayer and subsurface water. The sea-surfacemicrolayer displayed enrichment for nutrients in different degrees and the mean enrichment factors was more than one. Non-parametric analysis of Wilcoxin testof the dissolved inorganic nutrients concentration results showed that the NO₂--Nand PO₄^3--P in autumn and NO₂--N in summer appeared a significant enrichmentin the sea-surface microlayer.No strong correlations were observed between dissolved inorganic nutrientsand environmental factors, suggesting that single environmental was not the solefactors controlling the concentration of nutrients. Because of the southern YellowSea is inshore, which was influenced by temperature, salinity, phytoplankton,terrestrial input and the diluted water of Yangtze River together. These were strongcorrelations among dissolved inorganic nutrients, implying that the nutrients hadsimilar sources.2. Based on observed nutrient data collected in the sea-surface microlayer （SML）and subsurface water of the Jiaozhou Bay during Jun-Dec2010and Jan-Feb,Mar-May2011, the results showed that the distribution of nutrients in thesea-surface microlayer was the same as in subsurface water and the concentrationsof nutrients decreased gradually from the northeast to the southwest and baymouth in Jiaozhou Bay in different seasons. In the seasonal variations, the highaverage concentration of nutrients in autumn and summer and low value in winterand spring, this was related to terrigenous input. In the monthly variations, thechange of the nutrient concentration in each month was clearly. No strongcorrelations were observed between nutrients and Chl-a, but the month had a lowconcentration of nutrients, in the while, there was a high concentration of Chl-a,suggesting that Chl-a could control nutrients in Jiaozhou Bay to a certain extent.The nutrients concentrations in the microlayer were closely correlated withthose in the corresponding subsurface water in each season in Jiaozhou Bay,implying that an important source of the nutrient in the sea-surface microlayermight be the bottom water. The correlations were positive among the nutrientsindicated that their sources are similar. Nutrients had strong negative correlationwith salinity in spring, summer and autumn, in contrast, the correlation becameweak in winter. It might be less terrigenous input in winter and the effect ofphytoplankton activity was increased.Phosphorus was the limiting factor of phytoplankton in the sea-surfacemicrolayer and subsurface water in the Jiaozhou Bay in each season.Phosphorus-limitied potential eutrophication was more serious in the spring and winter and value of N/P ratio is larger. The potential eutrophication level in thesea-surface microlayer was higher than that in the subsurface water in somestations due to enrichment for nutrients in the sea-surface microlayer. Thesea-surface microlayer displayed an obvious enrichment for nutrients, in particular,for nitrogenous inorganic substances which were significant enrichment.