[Carbon dioxide fluxes at the water-air interface and the main influencing factors from diffe-rent aquaculture systems of Sebastes schlegelii and Chlamys farreri]

Abstract

The static chamber-gas chromatography method was applied to observe CO₂ fluxes across the water-air interface from different aquaculture systems, including four groups of mesocosms, i.e., blank control system (CK), monoculture system of Sebastes schlegelii (F), monoculture system of Chlamys farreri (B) and polyculture system of S. schlegelii and C. farreri (FB). Meanwhile, the physical, chemical and biological indices of the water were measured. The results showed that the group CK was a stable CO₂ source, with the mean flux of 12.42 mg·m^-2·h^-1. The group B was a CO₂ source during the early and middle periods of the experiment and a CO₂ sink at the end of the experiment, with the mean flux during the experiment being 10.95 mg·m^-2·h^-1. The change trends of CO₂ flux in the group F and FB were generally consistent, acting as CO₂ sources in the early period and as CO₂ sinks subsequently. The mean fluxes of those two groups during the expe-riment were -3.53 and -10.49 mg·m^-2·h^-1, respectively. Water pH was a good predictor for CO₂ flux across the water-air interface according to the result of regression analysis, with pH value of 8.25 as the critical threshold between efflux and influx. The net primary production of water column was the main factor influencing the CO₂ flux, indicating that phytoplankton might be the main internal force regulating the CO₂ flux across the water-air interface. Our results indicated that C. farreri at present stocking density in the polyculture system could promote phytoplankton biomass as well as primary production and therefore enhance the CO₂ sink function.

Keywords: CO 2 flux; Chlamys farreri; Sebastes schlegelii; aquaculture system; water-air interface.