Carbon dioxide as the primary greenhouse gas emission in hard clam (Meretrix taiwanica) aquaculture

Abstract

Hard clam (Meretrix taiwanica) aquaculture is one of the most important shellfish farming sectors in Taiwan, covering approximately 16,000 hectares and accounting for 40% of the nation's aquaculture area. Pond management practices, including the use of animal manure and sediment tilling, strongly influence nutrient cycling and microbial processes during cultivation. Although clam shell formation involves calcium carbonate precipitation that releases CO2, the net greenhouse gas balance of clam ponds remains poorly understood. This study monitored three brackish-water clam ponds in Taizi Village, Yunlin County, Taiwan, throughout 2024, measuring monthly fluxes of carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O) and related environmental parameters during both non-culture and culture periods. The ponds functioned as CO2 sinks before stocking and after harvesting but became CO2 sources during the culture stage. The ponds consistently acted as a CH4 sink, but an N2O source. The average fluxes were 1,126.88 +/- 5,735.56 mg m-2 day-1 for CO2, - 0.52 +/- 1.06 mg m-2 day-1 for CH4, and 0.88 +/- 0.90 mg m-2 day-1 for N2O. When expressed as CO2-equivalents (GWP100), CO2 contributed 90% of total emissions, followed by N2O (10%). These patterns likely reflect complex interactions among biological activity, microbial processes, alkalinity, and oxygen levels within the pond ecosystem. Overall, this study demonstrates that clam aquaculture can contribute to greenhouse gas emissions, underscoring the need for improved management strategies to mitigate environmental impacts.