Characteristics of CO₂ and CH₄ Concentrations and Fluxes of the Inlet and Outlet Waters of Jurong Reservoir in an Agricultural Small Watershed

This study investigated the dynamics of CO₂ and CH₄ emission fluxes in Jurong Reservoir based on field measurements for two years. Results show that the concentrations and fluxes of CO₂ and CH₄ showed obvious spatial variations in this reservoir. The annual average CO₂ concentration and emission flux at the inlet point A was (108.57±14.27) μmol·L^-1 and (210.55±36.58) mmol·m^-2·d^-1, respectively, and at the inlet point B was (162.74±17.86) μmol·L^-1 and (338.74±47.25) mmol·m^-2·d^-1, respectively, which were significantly higher than those at the outlet point (28.04±3.53) μmol·L^-1 and (10.05±4.04) mmol·m^-2·d^-1, respectively. The annual average CH₄ concentration and emission flux at the inlet point B (747.05±190.63) nmol·L^-1 and (1.84±0.46) mmol·m^-2·d^-1, respectively, were significantly higher than those at the outlet point (115.75±15.75) nmol·L^-1 and (0.11±0.02) mmol·m^-2·d^-1, respectively. Similarly, there were obvious seasonal variations in CO₂ and CH₄ concentrations and fluxes in the Jurong Reservoir. The concentrations and emission fluxes of both CO₂ and CH₄ showed a pattern of high in warm season and low in cold season, which were influenced by water temperature, dissolved oxygen concentration and precipitation. The input of exogenous nitrogen also participated in affecting the spatial variations of CO₂ and CH₄ concentrations and fluxes. Overall, the agricultural small watershed Jurong Reservoir is an emission source of atmospheric CO₂ and CH₄, and the carbon emission flux of this reservoir is higher than the average values of domestic reservoirs.