Emission of CO2 and CH4 from a multi-ditches system in rice cultivation region: Flux, temporal-spatial variation and effect factors

Man-made multi-level ditches system is designed to irrigate, drain and collect runoff from surrounding fields. It is not only the conduit of water and field carbon, but also the linear-like wetland with complex carbon cycling. However, the contribution of ditches system to CO₂ and CH₄ emission has rarely been assessed. To understand the emission pattern of CO₂ and CH₄ from ditches, this study investigated the emission fluxes of CO₂ and CH₄ in a three-level ditches system in Chengdu Plain, China. The results showed that the emission of CO₂ and CH₄ ranged from 70.38 to 950.40 mg C m^‑2 h^‑1 and 6.51–74.99 mg C m^‑2 h^‑1, respectively, and was higher in spring and summer than other seasons in all ditches (P < 0.05). On the other hand, the emission of CO₂ and CH₄ increased along with the decreasing ditches size. Besides, it is found that the precipitation, water table depth and water DO concentration might contribute to the emission of CO₂, while CH₄ was possibly influenced by precipitation, water table depth, temperature, water DO and DOC concentration. Moreover, it is suggested that terrestrial external input and in-situ metabolism might be the main sources of C emission, and in-situ source might largely contribute to CH₄ emission. To reduce the C emission, it is necessary to improve fertilization and irrigation methods, limit soil pollutants transferring into ditches, and frequently dredge sediments in future.