[Temporal and Spatial Variation Characteristics of Methane, Carbon Dioxide, and Nitrous Oxide Concentrations and the Influencing Factors in Small Aquaculture Pond]

Abstract

As an important source of greenhouse gases, the changes in greenhouse gas concentrations of aquaculture ponds are not only the basis for accurate quantification of greenhouse gases emissions but are also important for identifying their influencing factors. The spatial and temporal variation characteristics of CH₄, CO₂, and N₂O concentrations and the influencing factors in a typical small aquaculture pond in the Yangtze River Delta were analyzed based on the headspace equilibrium-gas chromatograph method. Except in spring, the concentrations of CH₄, and N₂O appeared high at noon or afternoon and were influenced by water temperature. Impacted by water temperature and aquatic plant photosynthesis, the concentrations of CO₂ were high in the morning when photosynthesis was weak. The concentrations of CH₄ and CO₂ were the highest in autumn and the lowest in winter. The mean concentrations of CH₄ in autumn and winter were 176.34 nmol·L^-1 and 32.75 nmol·L^-1, respectively, which were mainly affected by air temperature, water temperature, and dissolved oxygen. The average CO₂ concentrations in autumn and winter were 134.37 μmol·L^-1 and 23.10 μmol·L^-1, respectively, and were mainly affected by aquatic vegetation photosynthesis and pH. N₂O concentration was the highest in summer and the lowest in winter, with mean values of 97.05 nmol·L^-1 and 19.41 nmol·L^-1, respectively, which were mainly affected by air temperature and water temperature. In terms of the vertical spatial variations of the three greenhouse gases, the concentration of CH₄decreased with water depth in summer, and the concentration differences between the surface layer and the bottom and middle layers were 71.28 nmol·L^-1 and 42.80 nmol·L^-1, respectively. The concentration of CH₄ increased with water depth in autumn, and the concentration difference between the bottom layer and surface layer was 163.94 nmol·L^-1. The CO₂ concentration increased with water depth in summer and autumn. The concentration differences between the bottom and surface concentrations were 18.69 μmol·L^-1 and 29.90 μmol·L^-1, respectively. N₂O concentration showed no obvious change in the vertical direction. For the horizontal variations, the concentrations of CH₄, CO₂, and N₂O in the feeding area in summer and in chicken manure in spring were approximately 1.34-1.98 times and 1.95-2.42 times those in other areas, respectively, and the concentrations of N₂O and CO₂ in spring and summer were approximately 1.13-1.26 times and 1.39-1.74 times those in other areas.

Keywords: CH4, CO2, and N2O concentration; aquaculture pond; influencing factors; temporal spatial variation characteristics.