Influence Of Asian Dust Deposition On The Growth Of Phytoplankton In China Marginal Seas

Atmospheric deposition has been considered an important source of bio-availablenutrients such as N, P, Si and trace metals like Fe and Cu to phytoplankton living inshelf seas and open oceans. It has been proposed that this external nutrient/trace metalinput enhances primary production (PP) and changes the structure and metabolism ofmicrobial planktonic communities, and may even trigger biogenic blooms in oceans.So could regulate atmospheric CO2through their mediation in the sea-air CO2exchange process, and influence the marine production and chimate. As an importantaspect of atmospheric deposition, the character of dust deposition were the largerinfluence area and the higher deposition amounts in short time, so has received morespecial attention in recent years. Asian dust is one of the four major dust emissionzones in the world, and can impact the China marginal seas, even North Pacific Oceanthrouth long-distance transport. On-board incubation experiments were performed inMarch and May of2011, March and June of2013to explore the responses ofchlorophyll a concentration to Asian dust and various combinations of addedsubstances in China marginal seas, including Southern Yellow sea (SYS), East ChinaSea (ECS) and Southern China Sea (SCS), to explort the influence of Asian dustdeposition on the ecosystem of China marginal seas.The incubation experiments conducted in March of2011suggested:1) Thesurface seawater temperature (SST) maybe the most important physical factor forbiogenic bloom at our study ocean area, and photosynthetically available radiation(PAR) had little change;2) The relatively large amount of Asian dust (Dust-b) addedcould promote a greater increase in phytoplankton biomass, in contrast to the control,and the promotion effect was partially associated with the added N and also partiallyrelated to the increase of the CEI and the synergistic effect of macronutrients and tracemetals leached from the Asian dust. However, treatment with a lower amount of Asiandust (Dust-a) had no significant influence on either concentrations of Chl a or the CEI in contrast to the control;3) The addition of N exhibited a promotion effect on Chl aconcentration indicated the N limitation in the SYS;4) The addition of rainwater hada promotion effect on the growth of phytoplankton, however, calculated CEI waslower than that in the control, suggesting that the inhibition effect coexisted with thepromotion effect;5) The size structure of phytoplankton had shifted to some extent,while nano-phytoplankton was always the predominant species.Incubation experiments conducted in June of2013in SYS suggested:1) FromMarch to June, P has become the first limiting factor at the same region, but theaddition of N could’t promote the growth of phytoplankton;2) For the lower Chl aand nutrients concentration in central of SYS, there was no obvios response to theaddition of Asian dust aerosol and rainwater, maybe for the most of nutrients suppliedthrough dust was DIN, and the amount of P was lower;3) At G6station,picophytoplankton was always the predominant throuthout the experiment, but at H7,the size structure of phytoplankton shifted, nanophytoplankton became predominantspecies at the end of experiment;4) Prorocentrum dentatum and Dinoflagellate werethe dominant species in summer of SYS. At station of G6, for the addition of dustpromote the growth of Nitzschia.sp. In the N+P, N+P+Fe groups, Dinoflagellate andProrocentrum were the dominant species. For station of H7, the dominant specieswere Prorocentrum minimum and Nitzschia.sp in P treatmens, addition of N and Ppromote the growth of Diatom, but the dominant species were different.Experiments conducted in May of2011in ECS suggested:1) The higherconcentration of dust had promotion effect, but the lower amount had no effect on thephytoplankton biomass;2) Additon of N had the obvious promotion effect, however, P,Fe and P+Fe had no obvious fertilization effect, so they were not the limiting factorsin May;3) Microphytoplankton was the predominant in the original seawater (38.5%),but nanophytoplankton became predominant species from9thday to the end, andespecially in the P+Fe and N treatmens.Experiments conducted in SCS at spring of2013suggested:1) At station of A3and A6, the addition of Asian dust aerosol and N, N+P, N+P+Fe could increase thebiomass obviously. At WG2station, maybe for the oligotrophic nutrients condition, all treatments including P and rainwater had positive effect;2) At station of A3,Chaetoceros spp and Leptocylindrus danicus were the predominant species in all thetreatmens. But Dinoflagellate was the predominant at station of WG2, and thenbecame Nitzschia.sp for the addition of Asian dust aerosol and nutrients, andChaetoceros spp in the N-added group.From the four mesocosm experiments conducted in China marginal seas showedthat in marine environment with different nutrients conditions, the response ofphytoplankton to the addition of Asiand dust were various.1) In central of SYS, thefertilization effect of atmospheric deposition was obvios in spring, and the limitingfactor was N in March, changed to P in June, and the ddition of nutrients mainlypromoted the gowth of Diatom;2) For the eastern of ECS, N was the first limitingfactor in sping, and for the lower amount of DIN released from the Asin dust, so theinput had little impact on the algae growth;3) Atmospheric deposition had obviouspromotion effect in the northeast of SCS, and mainly promoted the growth of Diatom.