Seasonal and spatial variability of methane emissions from a subtropical reservoir in Eastern China

Abstract. Subtropical reservoirs are important source of atmospheric methane (CH₄). This study aims to investigate the spatiotemporal variability of CH₄ emission, using the methods of static floating chambers and bubble traps, from the water surfaces of Xin'anjiang Reservoir. Seasonal variability showed that CH₄ emission from the main reservoir body was high in autumn and low in spring, with medium values in summer and winter. The dynamics of CH₄ emission was flat from February to June, but fluctuated dramatically from July to January in the upstream river, which was interrupted by the bubbles in the second half year. However, CH₄ emission was largely influenced by the streamflow in the downstream river, with a minimum value in February due to an extreme low streamflow (275 m³ s⁻¹). Spatial variability showed the upstream river had the highest CH₄ flux (3.90 ± 7.80 mg CH₄ m⁻² h⁻¹), followed by the downstream river (0.50 ± 0.41 mg CH₄ m⁻² h⁻¹), and the main reservoir body stood the last place (0.01 ± 0.07 mg CH₄ m⁻² h⁻¹). Therefore, it was necessary to capture the variation of CH₄ emission from reservoirs in the space and time scales to avoid the error of estimating the CH₄ emission incorrectly.