基于DNDC模型模拟江汉平原稻田不同种植模式条件下温室气体排放

稻田被认为是温室气体CH_4和N_2O的主要排放源之一。湖北省江汉平原地区水稻常年种植面积约8×105 hm2,占湖北省水稻种植面积的40%左右。研究江汉平原地区稻田温室气体排放特征,对于评估区域稻田温室气体排放以及稻田温室气体减排具有重要意义。目前,DNDC模型已被广泛应用于模拟和估算田间尺度的温室气体排放,DNDC模型与地理信息系统(Arc GIS)结合,可进行区域尺度的温室气体排放模拟与估算。本研究以湖北省典型稻作区江汉平原为研究区域,运用DNDC模型模拟和估算江汉平原稻田区域尺度的温室气体排放。设置大田定点观测试验,监测中稻-小麦(RW)、中稻-油菜(RR)、中稻-冬闲(RF)3种种植模式下稻田温室气体CH_4和N_2O的周年排放特征。通过田间观测值与DNDC模拟值的比较进行模型验证,并利用获取DNDC模型所需的气象、土壤、作物及田间管理等区域数据,模拟江汉平原稻田不同种植模式下温室气体CH_4和N_2O的排放量。田间试验表明,江汉平原稻田RW、RR和RF模型的CH_4排放通量为-2.80~39.78 mg·m-2·h-1、-1.74~42.51 mg·m-2·h-1和-1.57~55.64 mg·m-2·h-1,N_2O周年排放通量范围分别为0~1.90 mg·m-2·h-1、0~1.76mg·m-2·h-1和0~1.49 mg·m-2·h-1;CH_4排放量RW和RR模式显著高于RF模式,N_2O排放量为RF显著低于RW和RR模式。模型验证结果表明,不同种植模式温室气体排放实测值与模拟值比较的决定系数(R2)为0.85~0.98,相对误差绝对值(RAE)为8.29%~16.42%。根据DNDC模型模拟和估算的结果,江汉平原区域稻田CH_4周年的排放量为0.292 9 Tg C,N_2O周年的排放量为0.009 2 Tg N,不同种植模式稻田CH_4排放量表现为RWRRRF,N_2O排放量表现为RWRFRR,增温潜势(GWP)表现为RWRRRF。不同地区稻田CH_4排放量表现为监利县荆门市公安县天门市仙桃市洪湖市松滋市汉川市潜江市石首市荆州市江陵县赤壁市嘉鱼县,N_2O排放量表现为监利县荆门市公安县洪湖市仙桃市天门市汉川市潜江市松滋市荆州市江陵县赤壁市石首市嘉鱼县。本研究结果表明DNDC模型能较好地应用于模拟江汉平原稻田温室气体排放,RR和RF模式相比RW模式可有效减少温室气体CH_4和N_2O的排放。

Greenhouse gases emission under different cropping systems in the Jianghan Plain based on DNDC model

Increased greenhouse gases emission contributes to global warming. Paddy field is considered to be one of the main sources of greenhouse gas CH₄ and N₂O emissions. The rice planting area in the Jianghan Plain is about 8×10⁵ hm², accounting for about 40% of the total rice planting area in Hubei Province. Studies on characteristics of greenhouse gases emission in the Jianghan Plain are important for evaluation and reduction of regional greenhouse gases emission. So far, several models, such as DNDC model, have been used for simulating the greenhouse gases emission, which in conjunction with ArcGIS may be used for simulating the regional greenhouse gas emission. In this study, we used DNDC model to simulate the greenhouse gases emission in the Jianghan Plain. The field experiment was carried out for investigating the characteristics of CH₄ and N₂O emissions under rice-wheat (RW), rice-rape (RR) and rice-fallow (RF) cropping systems. Meteorologic, soil, crop and field management data were obtained for DNDC-stimulating CH₄ and N₂O emissions under different cropping systems in the Jianghan Plain. The results of field experiment showed that the CH₄ fluxes were from -2.80 mg·m^-2·h^-1 to 55.64 mg·m^-2·h^-1,and the N₂O fluxes were from 0 to 1.90 mg·m^-2·h^-1 in the Jianghan Plain. CH₄ emission was mainly concentrated in rice season, and the peaks occurred at rice heading and tillering stages. N₂O emission in rice season was higher than in non-rice season. And the peaks occurred after wheat or rape sowing in non-rice season and during field drying period in rice season. CH₄ emission under RW and RR systems were significantly higher than that under RF system, while N₂O emission was significantly higher under RF system than under RW and RR systems. The DNDC model stimulating results were verified by comparing the observed values with the stimulated values. The R² and RAE between the observed and the stimulated values under different cropping systems were form 0.85 to 0.98 and from 8.29% to 16.42%, respectively. The high R² and the low RAE suggested that the stimulated values of CH₄ and N₂O emissions with DNDC model were in good agreement with the observed values. According to the simulation results, the annual emissions of CH₄ and N₂O were 0.292 9 Tg C and 0.009 2 Tg N in the Jianghan Plain from 2010 to 2016, respectively. For different crop systems, CH₄ and N₂O emissions were presented as RW > RR > RF and RW > RF > RR, respectively, and the global warming potential (GWP) was RW > RR > RF. The CH₄ and N₂O emissions were also different for different regions. The annual average CH₄ emission from 2010 to 2016 was in the order of Jianli > Jingmen > Gong''an > Tianmen > Xiantao > Honghu > Songzi > Hanchuan > Qianjiang > Shishou > Jingzhou > Jiangling > Chibi > Jiayu. And the annual average N₂O emission from 2010 to 2016 was in the order of Jianli > Jingmen > Gong''an > Honghu > Xiantao > Tianmen > Hanchuan > Qianjiang > Songzi > Jingzhou > Jiangling > Chibi > Shishou > Jiayu. The results of our study indicated that the DNDC model could preferably stimulate the greenhouse gases emissions in the Jianghan Plain. And RR and RF could reduce CH₄ and N₂O emissions compared with RW.