Dynamics of phytoplankton community structure in the South China Sea in response to the East Asian aerosol input

Abstract

<jats:p>Abstract. Recent studies have demonstrated atmospheric deposition as an important source of bioreactive compounds to the ocean. The South China Sea (SCS), where aerosol loading is among the highest in the world, however, is poorly studied, particularly on the in situ response of phytoplankton community structures to atmospheric deposition. By conducting a series of microcosm bioassays at different hydrographical locations and simulating different aerosol event scales, we observed both positive and negative responses to the input of East Asian (EA) aerosol with high nitrogen (N) and trace metal contents, in terms of biomass, composition and physiological characteristics of phytoplankton communities. High levels of aerosol loading relieved phytoplankton nitrogen and trace metal limitations in SCS, and thus increased total phytoplankton biomass, enhanced their physiological indicators (e.g. photosynthetic efficiency) and shifted phytoplankton assemblages from being dominated by picoplankton to microphytoplanton, especially diatoms. However, under low levels of aerosol loading, the composition shift and biomass accumulation were not apparent, suggesting that the stimulation effects might be counterbalanced by enhanced grazing mortality indicated by increased abundance of protist grazers. Trace metal toxicity of the aerosols might also be the reason for the reduction of picocyanobacteria when amended with high EA aerosols. The magnitude and duration of the deposition event, as well as the hydrographical and trophic conditions of receiving waters are also important factors when predicting the influence of an aerosol deposition event. Our results demonstrated different responses of phytoplankton and microbial food web dynamics to different scales of atmospheric input events in SCS and highlighted the need for achieving an accurate comprehension of atmospheric nutrient on the biogeochemical cycles of the oceans.</jats:p>

Phytoplankton Response to Saharan Dust Depositions in the Eastern Mediterranean Sea: A Mesocosm Study

“…An increase of the overall phytoplankton carbon biomass was also observed, but this effect was less pronounced (1.5-fold). The positive response of phytoplankton to dust addition is largely in accordance with many previous microcosm and mesocosm experiments performed in oligotrophic low nutrients low chlorophyll (LNLC) sites, such as in the east ( ; Tsagaraki et al, in review) and west Mediterranean basins (Bonnet et al, 2005;Lekunberri et al, 2010;Romero et al, 2011;Ridame et al, 2014), in the Atlantic Ocean (Marañón et al, 2010) and in South China Sea (Guo et al, 2012). Besides the single-addition experiment, additional mesocosm containers were subjected to three consecutive inoculations with smaller amounts of Saharan dust (RA treatment) in order to better simulate the recurrent pattern of Saharan dust events in the eastern Mediterranean, where continuing dust deposition events may occur over a period of several days (Meloni et al, 2008;Gaetani and Pasqui, 2014;Vincent et al, 2016).…”

“…Microcosm and mesocosm experimental studies performed mostly in NW Mediterranean and the Atlantic Ocean demonstrated that inputs of dust and aerosols enhanced primary production (Ridame and Guieu, 2002;Bonnet et al, 2005;Marañón et al, 2010) and phytoplankton biomass (Guo et al, 2012;Giovagnetti et al, 2013), as well as bacterial abundance Marañón et al, 2010) and/or bacterial respiration (Pulido-Villena et al, 2014). However, phytoplankton and heterotrophic prokaryotes did not show a consistently positive response, in terms of biomass and production, to dust additions nor presented similar patterns among all experiments.…”

“…The biological responses mediated through the release of nutrients from dust particles depended on the environmental conditions (e.g., nutrient regime), the quantity/quality of the dust added and the initial composition and physiological state of the various osmotroph groups present in the sampled seawater. For example, concerning phytoplankton, input of small amounts of dust particles in oligotrophic seawaters of South China Sea did not result in biomass accumulation or community structure changes, while large amounts of dust resulted in the increase of both biomass and photosynthetic efficiency (Guo et al, 2012). During a bioassays experiment performed in the Atlantic Ocean, where a certain amount of dust was added to microcosms representing different degrees of oligotrophy, it was found that primary production was stimulated only in the least oligotrophic waters (Marañón et al, 2010).…”

Atmospheric and Fluvial Nutrients Fuel Algal Blooms in the East China Sea

“…Synechococcus abundance was lowest in the "high" aerosol treatment ( Figure 1J). These negative responses could be due to competition (i.e., if picoplankton were outcompeted due to aerosol fertilization of other species in the community), or toxicity from trace metals Guo et al, 2012). The PCA suggests that the responses are likely a combination of these factors.…”

The concentration, source and deposition flux of ammonium and nitrate in atmospheric particles during dust events at a coastal site in northern China

“…This hypothesis has been evaluated through incubation experiments, in situ experiments and the use of satellite observational data (Banerjee and Kumar, 2015;Guo et al, 2012;Liu et al, 2013;Shi et al, 2012;Tan and Wang, 2014). However, the process is dynamic due to the worldwide changing emissions of NO x and NH 3 in the last few decades.…”