A GIS-based method for modeling methane emissions from paddy fields by fusing multiple sources of data.

Quantification of regional methane (CH4) gas emission in the paddy fields is critical under climate warming. Mechanism models generally require numerous parameters while empirical models are too coarse. Based on the mechanism and structure of the widely used model CH4MOD, a GIS-based Regional CH4 Emission Calculation (GRMC) method was put forward by introducing multiple sources of remote sensing images, including MOD09A1, MOD11A2, MOD15A2H as well as local water management standards. The stress of soil moisture condition (f(water)) on CH4 emissions was quantified by calculating the redox potential (Eh) from days after flooding or falling dry. The f(water)-t curve was calculated under different exogenous organic matter addition. Combining the f(water)-t curve with local water management standards, the seasonal variation of f(water) was obtained. It was proven that f(water) was effective in reflecting the regulation role of soil moisture condition. The GRMC was tested at four Eddy Covariance (EC) sites: Nanchang (NC) in China, Twitchell (TWT) in the USA, Castellaro (CAS) in Italy and Cheorwon (CRK) in Korea and has been proven to well track the seasonal dynamics of CH4 emissions with R2 ranges of 0.738-0.848, RMSE ranges of 31.94-149.22 mg C/m2d and MBE ranges of -66.42- -14.79 mg C/m2d. The parameters obtained in Nanchang (NC) site in China were then applied to the Ganfu Plain Irrigation System (GFPIS), a typical rice planting area of China, to analyse the spatial-temporal variations of CH4 emissions. The total CH4 emissions of late rice in the GFPIS from 2001 to 2013 was in the range of 14.47-20.48 (103 t CH4-C). Ts caused spatial variation of CH4 production capacity, resulting in the spatial variability of CH4 emissions. Overall, the GRMC is effective in obtaining CH4 emissions from rice fields on a regional scale.

Study on nitrogen removal from rice paddy field drainage by interaction of plant species and hydraulic conditions in eco-ditches.

Eco-ditches (ecological ditches) not only drain water from rice paddies, but also facilitate the removal of nitrogen (N). We established an experiment with both static and flowing water in 2017 to observe N removal from rice paddy drainage by eco-ditches containing three different types of monoculture vegetation: Zizania aquatica, Canna indica L., and Pontederia cordata. Results showed that ammonia volatilization and plant uptake contributed little to N removal. Harvest of Z. aquatica from the eco-ditch during the late growing season had an appreciable effect on N removal. However, harvest of C. indica L. and P. cordata had negligible effects. During static test, the concentration of total N (TN) and ammonium N (NH4+-N) and the pH all decreased from the surface to the bottom of water. The concentration of nitrate N (NO3--N) did not exhibit stratification. In a flowing water experiment, ditches with Z. aquatica, C. indica L., and P. cordata had the following average removal rates: TN 15.8%, 11.6%, and 27.9%; NO3--N 4.2%, 8.4%, and 17.8%; NH4+-N 22.8%, 16.4%, and 37.5%, respectively. The removal rates of TN and NH4+-N decreased with the increase of water level, while that of NO3--N increased significantly. Nitrogen removal rates decreased with the increase of influent TN concentration or flow rate. Nitrogen removal rate of P. cordata ditch was highly dependent on the influent TN concentration, but the flow rate was not as important due to the great drag caused by its large density. While the contrary was observed in the C. indica L. ditch. For Z. aquatica ditch, both the flow rate and the TN concentration had a strong negative correlation with the N removal rate.