Effects Of Sand Dust Addition And Nutrient Input On Phytoplankton In The Offshore Waters

The eastern marginal seas of China are important economic sea area in China.The development and research in the Yellow Sea and the East China Sea are related to the sustainable use of national strategic resources and the sustainable development of the sea environment This paper is based on the national key R&D project "the biogeochemical processes and climatic effects of the active gas of the source in the continental shelf in Eastern China Sea".The effects of dust and nutrient input on the growth of marine phytoplankton were studied in three mesocosm experiments(D7 in the spring of 2017,A4 and P6 in the summer of 2018)and a laboratory incubation.The results are showed as follows:1.Station D7 is located between the Yellow Sea and East China Sea.The N:P ratio in seawater is 16.The nitrogen and phosphorus nutrients are relatively abundant A total of 26 species in 17 genera in diatom and 3 species in 3 genus dinoflagellates were identified in this culture.The dominant spec ies in the early stage of cultivation were mainly diatoms,such as Thalassionsira sp.,Chaetoceros sp.and Nitzschia closterium.Diatoms also dominant in the later stages,but the cell density of Alexandrium minutum and Peridinium conicum increased.The chlorophyll a content varies from 0.12-4.20?g/L.The input of nitrogen and phosphorus nutrition promoted the growth of phytoplankton.The addition of sand dust had no obvious effect on the growth of phytoplankton.Acidification had little effect on the structure of phytoplankton community.2.Station A4 is located in the Yellow Sea,and the N:P ratio is 3.33.The growth of phytoplankton is mainly restricted by nitrogen.In this culture,a total of 39 spelcies in3 phylums 32 genus were identified,including diatom,dinoflagellate and cyanobacteria,.The addition of inorganic nitrogen can promote the growth of phytoplankton.The main dominant species are Thalassionsira sp.,Nitzschia closterium and Skeletonema costatum.The addition of inorganic phosphorus culture and sand dust can not effectively promote the growth of phytoplankton.Acidification has little effect on the growth and community structure of phytoplankton.The addition of copepod has promoted the growth of phytoplankton,especially Prorocentrum donghaiense.3.Station P6 is located in the East China Sea,with ain N:P ratio of 0.5,showing a severe nitrogen limit in seawater.In this culture,a total of 44 species in 3 phylums 25 genus were identified,including diatoms,dinoflagellates and cyanobacteria.The addition of inorganic nitrogen promoted the growth of phytoplankton.The main dominant species were diatom Nitzschia closteerium.The addition of inorganic phosphorus culture and sand dust could not promote the growth of phytoplankton.4.The input of inorganic nitrogen and phosphorus nutrients can effectively promote the growth of Skeletonema dohrnii.The growth of Skeletonema dohrnii is obviously inhibited under low silicon concentration.The growth of Skeletonema dohrnii were promoted by the addition of iron.DMS content in Skeletonema dohrnii was low under low nutrient concentration.Although a small amount of sand dust can not effectively improve the growth state of Skeletonema dohrnii,but it can increase the nutrient salt of the blank seawater and properly alleviate the deficiency of nutrients..