Emission of CO and CH 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 CO and CH emission has rarely been assessed. To understand the emission pattern of CO and CH from ditches, this study investigated the emission fluxes of CO and CH in a three-level ditches system in Chengdu Plain, China. The results showed that the emission of CO and CH ranged from 70.38 to 950.40 mg C m h and 6.51-74.99 mg C m h, respectively, and was higher in spring and summer than other seasons in all ditches (P < 0.05). On the other hand, the emission of CO and CH 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 CO, while CH 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 CH 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.