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Nutrients in atmospheric wet deposition and their ecological effects on Jiaozhou Bay in summer and autumn 2015

XING Jianwei;SONG Jinming;YUAN Huamao;LI Xuegang;LI Ning;DUAN Liqin;WANG Qidong;ZUO Jiulong;Key Laboratory of Marine Ecology and Environmental Sciences,Institute of Oceanology,Chinese Academy of Sciences;University of Chinese Academy of Sciences;Function Laboratory of Marine Ecology and Environmental Sciences, Qingdao National Laboratory for Marine Science and Technology;  
Recently,owing to anthropogenic activities such as fossil fuel combustion and agricultural fertilization,the amounts of nutrients and other pollutants entering the marine environment via atmospheric wet deposition have been increasing. Large amounts of nutrients input resulting from short-term heavy rainfall may result in the temporary eutrophication of surface waters,and could even lead to red tides. Therefore,research has presently been focused onatmospheric wet deposition. Jiaozhou Bay,North China,is a typical semi-closed bay negatively affected by natural changes and anthropogenic activities. With the rapid development of the economy,society,and the population growth of Qingdao City,anthropogenic activities have resulted in ecological environmental deterioration,such as frequent occurrence of smog and sandstorms. This has resulted in a considerable increase in the transfer rate of terrigenous pollutants into the sea via atmospheric wet deposition. Thus,research on the nutrients of atmospheric wet deposition in Jiaozhou Bay has received considerable attention from governments,society,and scientists. To evaluate the nutrients influxes by atmospheric wet deposition and their ecological effects on Jiaozhou Bay,33 wet deposition samples were collected in Jiaozhou Bay from June to November 2015. The concentrations of nutrients( NH_4-N,NO_3-N,NO_2-N,PO_4-P,and SiO_3-Si),dissolved total nitrogen( DTN),and dissolved organic nitrogen( DON) were determined using a continuous flow analyzer. Results showed significant differences among the monthly average concentrations for nutrients,and negative relationships between several nutrients and the amount of precipitation. The concentrations of NH_4-N and NO_3PO_4-P-N in the rainwater were high,whereas the concentrations of NO2-N,PO_4-P and SiO_3-Si were low. Dissolved inorganic nitrogen( DIN) was the dominant species,accounting for 74.1% of DTN with DON accounting for 25.9% of DTN. The wet deposition fluxes of DIN,DON,PO_4-P and SiO_3-Si were estimated as 141. 7 mmol m~(-2)a~(-1),61. 87 mmol m~(-2)a~(-1),0. 35 mmol m~(-2)a~(-1),and 0. 12 mmol m~(-2)a~(-1),respectively. Temporal variations of the wet deposition fluxes of nutrients were evident,since they were affected by the amount of precipitation and the origin of nutrients. Significantly positive correlations were observed among different nitrogen forms( except for DON),suggesting that they had the same origin. The emission of inorganic nitrogen from agricultural activities was the main source of the DIN wet deposition in Jiaozhou Bay. The fluxes of DIN,DON,PO_4-P and SiO_3-Si by atmospheric wet deposition accounted for 9. 04%,10. 24%,0. 57%,and 0. 17% of the total external influxes of Jiaozhou Bay,respectively. The total influxes of PO_4-P via atmospheric wet deposition in summer and autumn could support new productivities of 0.575 mg C m~(-2)d~(-1)and 1.42 mgCm~(-2)d~(-1),respectively. The average molar ratio of DIN/P in the rainwater was 1,617,which was well above that in the seawater of Jiaozhou Bay,indicating that large amounts of nutrients inputs from sudden heavy rainfall could aggravate the P and Si limitation and further affect the nutrient structures of surface waters,as well as phytoplankton community structures and size-fractioned structures in Jiaozhou Bay. As one of the essential branches of the biogeochemical cycle of biogenic elements,the contribution of atmospheric wet deposition to the nutrient budgets and possible potential ecological effects on Jiaozhou Bay ecosystem cannot be neglected
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