Temporal variability of air-water gas exchange of carbon dioxide in clam and fish aquaculture ponds

Abstract

The growing trend of land-based aquaculture has heightened the significance of comprehensively assessing air-water carbon dioxide (CO₂) gas exchange in these inland waters, given their potential impact on carbon neutral strategies. However, temporal variations of partial pressure of CO₂ (pCO₂) and CO₂ flux in clam and fish aquaculture ponds were barely investigated. We assessed the water surface pCO₂ in one to five months intervals by deploying a lab-made buoy in three clam ponds and three fishponds located in tropical and subtropical climates. Measurements were conducted over a 24 h period each time, spanning from April 2021 to June 2022, covering the stocking, middle, and harvesting stages of the culture cycle. Diurnal pCO₂ variations were dominantly controlled by biologically driven changes in dissolved inorganic carbon and total alkalinity (~97 %), while temperature and salinity effects were minor (~3 %). Clam ponds acted as a sink of atmospheric CO₂ during stocking stages and transitioned to a source during middle to harvesting stages. In contrast, fishponds acted as a source of atmospheric CO₂ throughout culture cycles and CO₂ flux strengthened when reaching harvesting stages. Overall, clam ponds acted as a weak sink for atmospheric CO₂ (-2.8 ± 17.3 mmol m^-2 d^-1), whereas fishponds acted as a source (16.8 ± 21.7 mmol m^-2 d^-1). CO₂ emission was stronger during daytime coinciding with higher windspeeds compared to nighttime in fishponds. We suggest incorporating high temporal resolution measurements to account for diurnal and culture-stage variations, enabling more accurate estimates of air-water CO₂ flux in aquaculture ponds. Moreover, the findings of this study highlight the importance of feeding, aeration, and biological activities (photosynthesis, remineralization, and calcification) in controlling the air-water CO₂ flux in aquaculture ponds and such information can be used in implementing better strategies to achieve carbon neutral goals.

Keywords: CO(2) flux; Carbon neutral; Controlling factor; Culture stage; Feeding; pCO(2).