Impacts of large-scale aquaculture activities on the seawater carbonate system and air-sea CO2 flux in a subtropical mariculture bay, southern China

Tingting Han; Rongjun Shi; Zhanhui Qi; Honghui Huang; Xiuyu Gong

doi:10.3354/aei00400

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Aquaculture Environment Interactions

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AEI 13:199-210 (2021) - DOI: https://doi.org/10.3354/aei00400

Impacts of large-scale aquaculture activities on the seawater carbonate system and air-sea CO₂ flux in a subtropical mariculture bay, southern China

Tingting Han¹, Rongjun Shi¹, Zhanhui Qi^1,2,*, Honghui Huang^1,2, Xiuyu Gong¹

¹Guangdong Provincial Key Laboratory of Fishery Ecology Environment, Key Laboratory of South China Sea Fishery Resources Exploitation and Utilization, Ministry of Agriculture, South China Sea Fisheries Research Institute, Chinese Academy of Fishery Sciences, Guangzhou 510300, PR China
²Southern Marine Science and Engineering Guangdong Laboratory (Guangzhou), Guangzhou 511485, PR China

*Corresponding author: qizhanhui@scsfri.ac.cn

ABSTRACT: In this study, the variations of the seawater carbonate system parameters and air-sea CO₂ flux (F_CO₂) of Shen’ao Bay, a typical subtropical aquaculture bay located in China, were investigated in spring 2016 (March to May). Parameters related to the seawater carbonate system and F_CO₂ were measured monthly in 3 different aquaculture areas (fish, oyster and seaweed) and in a non-culture area near the bay mouth. The results showed that the seawater carbonate system was markedly influenced by the biological processes of the culture species. Total alkalinity was significantly lower in the oyster area compared with the fish and seaweed areas, mainly because of the calcification process of oysters. Dissolved inorganic carbon (DIC) and CO₂ partial pressure ( pCO₂) were highest in the fish area, followed by the oyster and non-culture areas, and lowest in the seaweed area. Oysters and fish can have indirect influences on DIC and pCO₂by releasing nutrients, which facilitate the growth of seaweed and phytoplankton and therefore promote photosynthetic CO₂ fixation. For these reasons, Shen’ao Bay acts as a potential CO₂ sink in spring, with an average F_CO₂ ranging from -1.2 to -4.8 mmol m^-2 d^-1. CO₂ fixation in the seaweed area was the largest contributor to CO₂ flux, accounting for ca. 58% of the total CO₂ sink capacity of the entire bay. These results suggest that the carbonate system and F_CO₂ of Shen’ao Bay were significantly affected by large-scale mariculture activities. A higher CO₂ sink capacity could be acquired by extending the culture area of seaweed.

KEY WORDS: Carbonate chemistry · Air-sea CO₂ flux · F_CO2 · Seaweed culture · Oyster culture · Shen’ao Bay

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Cite this article as: Han T, Shi R, Qi Z, Huang H, Gong X (2021) Impacts of large-scale aquaculture activities on the seawater carbonate system and air-sea CO₂ flux in a subtropical mariculture bay, southern China. Aquacult Environ Interact 13:199-210. https://doi.org/10.3354/aei00400

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AEI 13:199-210 (2021) - DOI: https://doi.org/10.3354/aei00400