DIRECT GREENHOUSE GAS EMISSIONS FROM A PILOT-SCALE AQUAPONICS SYSTEM

Agricultural production systems are known to be large contributors to global greenhouse gas (GHG) emissions and many studies have focused on the mitigation of GHG emissions from open-field and other traditional crop production practices. Little attention has been given to direct emissions from non-traditional production systems such as aquaponics. Here we determine direct GHG emissions (CO2, CH4, N2O) from a pilot-scale biofloc, decoupled aquaponics facility. We also determine how emissions from unit operations differ based on a set of environmental and operational parameters e.g. temperature, feeding rate, suspended solids, plant height, water flow rate, and nitrate levels. Major unit operations included a biofloc fish tank stocked with tilapia, a solids settling clarification system, and a climate-controlled greenhouse in which cucumber plants were grown in substrate culture. The study was separated into three seasons. In the summer of 2019, different pH treatments for cucumber irrigation water were tested. In the fall of 2019 and winter of 2020, emissions from perlite versus pine bark substrates were tested during cucumber production. Measurements indicated that aerial GHG emissions in intensively aerated areas of the fish tank were 4.7 to 46.8 times higher than those in areas with low-intensity aeration. High methane emissions (up to 44.8 g m(-2) d(-1)) from the clarification system indicated anaerobic activity. Results from plant production showed a negative relationship between pH and N2O efflux (p=0.0001) while the choice of plant growth substrate had no significant effect on direct GHG emissions. Overall, carbon sequestration in plants could offset 40% to 62% of direct GHG emissions from the aquaponics system. This study provides insight into operational parameters that affect direct GHG emissions from aquaponics systems and provides data to support life cycle assessments.

Automated summary

This study investigates the direct greenhouse gas (GHG) emissions from a biofloc, decoupled aquaponics facility. The results showed that the intensively aerated areas of the fish tank had significantly higher GHG emissions compared to low-intensity aeration areas. The clarification system was found to have high methane emissions, indicating anaerobic activity. The choice of plant growth substrate did not have a significant effect on GHG emissions. Overall, carbon sequestration in plants could offset a significant proportion of direct GHG emissions from the aquaponics system.