Responses of chlorophyll a to added nutrients, Asian dust, and rainwater in an oligotrophic zone of the Yellow Sea: Implications for promotion and inhibition effects in an incubation experiment

Abstract

[1] Increasing anthropogenic atmospheric deposition of nutrients, trace metals, and toxic substances to oceans may synergistically enhance or inhibit some specific phytoplankton growth, subsequently modulating primary productivity. In this study, onboard incubation experiments were performed in the southern Yellow Sea in the spring of 2011 to explore the responses of microphytoplankton, nanophytoplankton, and picophytoplankton to various combinations of added substances. The water samples used were collected at a lower nutrient concentration zone with an N/P ratio of 10, where satellite data showed a bloom on the eleventh day after collection. The bloom also occurred in the control experiment on the ninth to eleventh days. We simulated atmospheric input by artificially adding Asian dust, rainwater, nitrogen (dissolved inorganic N), phosphorus (P), and iron (Fe). The addition of a large amount of Asian dust increased both the maximum concentration of chlorophyll a (Chl a) and the conversion efficiency index of N into Chl a (CEI) by~40% and~30%, respectively, compared to the control, indicative of promoting growth of the phytoplankton. However, no promotion effect on phytoplankton growth was observed when the addition of Asian dust was reduced to10% of the original amount. The addition of rainwater increased the maximum concentration of Chl a bỹ 40% but decreased the CEI by~40%, indicating inhibition coexisting with promotion of some phytoplankton species. Moreover, the size-fractioned Chl a data showed that the inhibition effect pertained to nanophytoplankton and occurred following the bloom (after the eighth day).Citation: Liu, Y., T. R. Zhang, J. H. Shi, H. W. Gao, and X. H. Yao (2013), Responses of chlorophyll a to added nutrients, Asian dust, and rainwater in an oligotrophic zone of the Yellow Sea: Implications for promotion and inhibition effects in an incubation experiment,

Phytoplankton growth response to Asian dust addition in the northwest Pacific Ocean versus the Yellow Sea

“…Unlike in HNLC and LNLC regions of the oceans, the response of phytoplankton to dust deposition in coastal seas that receive a relatively large quantity of nutrients from rivers is poorly understood. A few studies showed that dissolved N from the added dust likely stimulated phytoplankton growth in the Yellow Sea (YS; Liu et al, 2013). Added Fe instead of other dissolved nutrients from atmospheric deposition played an important role in stimulating phytoplankton growth in the East China Sea (Meng et al, 2016).…”

“…Water samples in the incubated bottles were collected before the additions to characterize the baseline seawater samples and immediately after the additions to characterize the amended seawater (day 0). Surface seawater was pumped into the microcosm equipment, i.e., three large plastic vessels, to stabilize the temperature of the incubation systems (Liu et al, 2013). The incubation experiments were processed over 9-10 days under natural light.…”

“…Observational and modelling studies have demonstrated that external nutrient input can stimulate primary productivity, strengthen nitrogen fixation, alter phytoplankton size, and potentially enhance carbon sequestration by the biological pump in the ocean (Mills et al, 2004;Maranon et al, 2010;Liu et al, 2013). A wellrecognized aspect of dust deposition is the iron fertilization effect in high-nutrient low-chlorophyll (HNLC) regions (Martin, 1991;Boyd et al, 2007).…”

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

“…Trace metals were found to have a toxic effect on marine phytoplankton and inhibit their growth (Bielmyer et al, 2006;Echeveste et al, 2012). Liu et al (2013) found that inhibition coexisted with the promotion of phytoplankton species in incubation experiments in the southern Yellow Sea in the spring of 2011 by adding Asian dust samples to collected seawater. However, the calculated dry atmospheric deposition fluxes of Fe increased by a factor of 124-2370 % in dust day samples.…”

“…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.…”