CH4 and CO2 emissions in water networks of rice cultivation regions

Abstract

Rice cultivation regions have a high density of open water networks to meet the requirements of rice growth and production. These open water networks have a significant risk of carbon (C) emissions due to agricultural production, but the C emissions from these waters are not clearly recorded in previous studies. Therefore, this study aimed to explore the pattern and internal mechanism of methane (CH₄) and carbon dioxide (CO₂) emissions from multiple types of waters (i.e., river, fish pond, reservoir, and ditch) in a typical rice cultivation region in southwestern China. The annual CH₄ and CO₂ fluxes were higher in the downstream river (2.79-94.89 and 39.39-1699.98 mg m^-2 h^-1) and ditch (8.80-74.99 and 123.43-542.65 mg m^-2 h^-1, respectively) and lower in the reservoir (-0.67 to 3.45 and -239.15 to 141.50 mg m^-2 h^-1) (P < 0.05). The monthly trends of CH₄ and CO₂ fluxes from the middle river and ditch were driven by interactive reactions of rice cultivation practices and precipitation. In contrast, the emission patterns of CH₄ and CO₂ from the lower river, upper river, and fish pond were mainly driven by domestic sewage discharge, precipitation, and aquaculture practices, respectively. This study suggested that river and ditch were more sensitive to C emissions than other waters, and the rice production period was the critical period for controlling C emission. Although rice paddy soils yield more cumulative emissions of CH₄, water networks in rice cultivation regions were possible hotspots for C emissions due to the higher emission intensities, which were largely overlooked before. Thus, it is necessary to refine and promote practices to better mitigate C emissions from waters in rice cultivation regions in the future.

Keywords: Ditch; Fish pond; Global warming potential; Rice cultivation regions; River.