Temporal variability of greenhouse gas fluxes in monoculture of tilapia in ponds

Abstract

Aquaculture is a vital industry that provides high-quality nutrition for humans. In 2022, global aquaculture production surpassed that of capture fisheries for the first time, ensuring stable food supplies and promoting sustainable ecological development. However, intensive aquaculture is a notable source of greenhouse gas (GHG) emissions, with many of its emission mechanisms still not fully understood. Tilapia is a key aquaculture species known for its rapid growth, environmental adaptability, high reproductive rate, and tolerance to salinity. This study monitored three brackish water tilapia farming ponds in Xuejia District, Tainan, Taiwan, throughout 2023, measuring the fluxes of carbon dioxide (CO₂), methane (CH₄), nitrous oxide (N₂O), and related environmental parameters monthly during both the non-culture and culture periods. The ponds functioned as minor carbon sinks during the early and late culture periods but became net carbon sources during the main culture period. The average fluxes measured were 1555.59 ± 2349.40 mg m⁻² day⁻¹ for CO₂, 3.38 ± 3.36 mg m⁻² day⁻¹ for CH₄, and 0.68 ± 0.39 mg m⁻² day⁻¹ for N₂O, all calculated based on GWP₁₀₀, all acting as sources to the atmosphere. When transfer to CO₂ equivalent, CO₂ was the dominant emission gas, contributing approximately 78% of total emissions, followed by CH₄ (13%) and N₂O (9%). The greenhouse gas fluxes showed significant temporal variation, likely driven by microbial and phytoplankton activity influenced by environmental factors such as water temperature, alkalinity, nitrite, and ammonia nitrogen concentrations. This study highlights that tilapia culture can elevate GHG emissions, underscoring the need for improved management strategies to mitigate environmental impacts.