Use of biochar derived from Spartina alterniflora to reduce sediment methane (CH4) production potential during non-farming period in earthen aquaculture ponds

Biochar has been proposed as an effective material for mitigating greenhouse gas emissions from farmlands, but comparable information for earthen aquaculture ponds is limited. A field study was conducted to investigate the effects of adding biochar (200–1600 kg ha⁻¹) derived from the invasive plant Spartina alterniflora on sediment physico-chemical properties, CH₄ production potential (P_CH4), and the relevant functional gene abundances in earthen aquaculture ponds during the non-farming period. The results indicated that biochar treatments increased sediment porosity and salinity, while decreasing dissolved organic carbon and microbial biomass carbon. Biochar-treated sediments also exhibited a significantly lower abundance of mcrA gene especially in the early drainage stage, and a higher abundance of pmoA gene especially in the intermediate and final drainage stages. Consequently, the mean P_CH4 in biochar-treated sediments (1.28–21.12 ng g⁻¹ d⁻¹) was 57–73% lower than in the control group (5.41–39.45 ng g⁻¹ d⁻¹). The reduction in P_CH4 did not differ between biochar produced at 300 °C vs. 500 °C and was not dependent on the amount of biochar added. The findings suggest that using biochar derived from S. alterniflora can be a cost-effective method to control the spread of this invasive plant and reduce CH₄ production in aquaculture pond sediment during the non-farming period.