Effects of stocking density and water quality on greenhouse gas (CO2, CH4, N2O) fluxes from inland saline whiteleg shrimp Penaeus vannamei culture ponds

Objective This purpose of study was to evaluate the influence of different stocking densities on greenhouse gas emissions in inland saline whiteleg shrimp Penaeus vannamei aquaculture systems, with a focus on CO2, CH4, and N₂O fluxes. Methods A 105-d culture trial of whiteleg shrimp was conducted in earthen ponds under three stocking densities: 30, 45, and 60 individuals per 1,000, m2, each in triplicate. Gas samples were collected using an acrylic chamber that was fitted with a suction pump and analyzed using gas chromatography–mass spectrometry. Fluxes of CO2, CH4, and N2O were monitored periodically throughout the culture period. Results The average CO2 fluxes in stocking densities 30, 40, and 60 were −9.1 ± 8, −23 ± 10, and −11 ± 5.7 mg/m2 daily, respectively, indicating net CO2 uptake. Mean CH4 fluxes were 933.1 ± 51, 463 ± 42, and 234 ± 22 parts per billion/m2 daily, while N2O fluxes were 122 ± 38, 425 ± 85, and 440 ± 84 m2/d, respectively. All gases showed distinct temporal variations. Negative CO2 fluxes were attributed to higher phytoplankton assimilation relative to respiratory release during warmer periods. Methane emissions were influenced by dissolved oxygen, water depth, and trophic status, whereas N2O fluxes were mainly regulated by pH and nitrogen availability. Stocking density significantly affected N2O emissions, while CO2 and CH4 fluxes were not directly influenced. Conclusions The study demonstrates that shrimp stocking density plays a significant role in regulating N2O emissions in inland saline aquaculture systems, but its effect on CO2 and CH4 fluxes is limited. Optimizing stocking density and appropriate pond management are therefore essential to minimize greenhouse gas emissions and enhance the environmental sustainability of intensive inland saline shrimp farming.