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Marine Ecology Progress Series

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MEPS 609:87-99 (2019)  -  DOI:

Biological regulation of pH during intensive growth of phytoplankton in two eutrophic estuarine waters

Yafeng Zhang1,2, Yonghui Gao2, David L. Kirchman3, Matthew T. Cottrell3, Rong Chen1, Kuo Wang1, Zhangxian Ouyang2, Yuan-Yuan Xu2, Baoshan Chen2, Kedong Yin1,*, Wei-Jun Cai2,*

1School of Marine Sciences, Sun Yat-Sen University, Guangzhou 510006, PR China
2School of Marine Science and Policy, University of Delaware, Newark, Delaware 19716, USA
3School of Marine Science and Policy, University of Delaware, Lewes, Delaware 19958, USA
*Corresponding authors: ,

ABSTRACT: Estuarine inorganic eutrophication results in high biomass of phytoplankton and elevates pH in the surface layer. However, its effects on the carbonate system are not well understood. We conducted incubation experiments using low-, moderate- and high-salinity waters enriched with nutrients in Delaware Bay and the Pearl River Estuary to examine effects on the carbonate system. The results showed that as phytoplankton grew, pH increased and dissolved inorganic carbon (DIC) decreased. However, the decrease in DIC was not fully accounted for by the production of organic carbon. This indicates that some C was missing during high phytoplankton growth. The missing C appeared to depend on the water buffering capacity, as it was largest when pH was highest in the low-salinity estuarine water. Total alkalinity (TA) decreased more in the low-salinity water with nutrient additions in both estuaries. We proposed that carbonate precipitation was formed at high pH driven by high phytoplankton growth, which is confirmed by a model simulation of TA. The model simulation based on the stoichiometric ratio of -Δ106DIC:Δ17TA demonstrated the difference between simulated and observed TA. The difference disappeared when carbonate precipitation formation was considered in the model, indicating carbonate precipitation formation could account for the missing C, the decrease in TA and the increase in pH. We concluded that the mechanism of CO2 being released from carbonate precipitation due to bloom-induced high pH benefits further photosynthesis, thus enhancing the biological pump efficiency in estuarine and coastal ecosystems.

KEY WORDS: Phytoplankton blooms · pH · Dissolved inorganic carbon · Total alkalinity · Estuary

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Cite this article as: Zhang Y, Gao Y, Kirchman DL, Cottrell MT and others (2019) Biological regulation of pH during intensive growth of phytoplankton in two eutrophic estuarine waters. Mar Ecol Prog Ser 609:87-99.

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