广州地区稻田甲烷和氧化亚氮排放及模拟研究

【作者】 任万辉；

【导师】 王振会； 许黎；

【作者基本信息】 南京气象学院 ， 大气物理学与大气环境， 2004， 硕士

【摘要】 甲烷（CH₄）和氧化亚氮（N₂O）是两种重要的温室气体，自工业革命以来，由于人类活动的加强大气中甲烷和氧化亚氮浓度有了明显的增加，研究表明，稻田是甲烷和氧化亚氮的主要生物排放源之一。因此，近年来在全球气候变化中稻田甲烷和氧化亚氮排放得到了广泛的关注。 本文利用静态箱法对广东清远地区双季稻生态系统CH₄和N₂O的排放进行了连续的观测研究，对观测数据进行了分析；利用生物地球化学模型DNDC（Denitrification and Decomposition）对早晚稻稻田CH₄和N₂O的排放进行了模拟，并与实际观测结果进行了比较；利用DNDC模型对影响稻田CH₄和N₂O排放的共同因子进行了一系列的敏感性实验，分析了各种因子对两种气体综合排放的贡献，提出了合理的减排措施；最后利用DNDC模型对广东省稻田CH₄和N₂O排放量进行了初步估算。 早稻田CH₄排放通量季节变化基本为三峰型，三个阶段的峰值分别出现在返青、分蘖拔节期和成熟期，而且后两个时期的排放峰值非常明显，季节平均排放通量为4.38 mg／m²·h。晚稻田CH₄排放通量存在明显的三个排放峰值，呈现“前高后低”的趋势，最高峰值出现在分蘖盛期，季节平均排放通量为6.09 mg／m²·h。稻田水位和土壤Eh（氧化还原电位）值对CH₄排放有明显的影响。当稻田水位在2cm左右时，容易出现CH₄排放的峰值，为了减少稻田CH₄排放应该避免2cm左右的浅水位，或者采取间歇灌溉的方式。早稻田土壤Eh值低于-100mv才有大量的CH₄产生，晚稻田土壤Eh值（-60mv—-150mv）比早稻田的高。不同水稻品种对稻田CH₄排放和水稻的产量有很大的影响。品种1（金优99）和品种2（七丝尖）相比，不仅CH₄排放少而且产量高，所以在选择水稻品种时应选排放少且产量高的。 DNDC模型能较好的模拟出早晚稻田CH₄排放的季节变化规律和主要排放峰值。模式的敏感性表明：①温度和稻田CH₄和N₂O排放之间是一种正相关关系，温度升高会引起稻田CH₄和N₂O排放量的增加，从而又引起温度的升高。②增加土壤有机质含量（SOC）对于稻田CH₄和N₂O的排放都有促进作用；土壤pH对稻田CH₄和N₂O排放的影响是不同的，最大值出现在不同的范围内，CH₄的最大值出现在偏碱性环境中，N₂O则出现在偏酸性环境中。但是这两个因素都是由土壤本身的特性决定的，不同类型的土壤有不同的SOC和pH值，因此通过控制SOC和pH值来减少稻田CH₄和N₂O的排放是不可能。③要想减少稻田CH₄和N₂O的排放只有通过农田管理措施（水管理、施肥等）来实现。根据CH₄和N₂O排放的特点以及敏感性实验，建议在水稻生长初期土壤有机质比较丰富的情况下，尽量使土壤保持在干湿交替的状态；生长中期进行中耕晒田，能南京气象学院顶士学位论文广东地区稻田甲烷和氧化亚氮排放及模拟研究减少CH;的排放;在水稻生长的中后期，由于此时土壤中的有机质大部分已经被吸收或分解，采用浅水灌溉，为了增加水稻的产量，应追施化肥，此时水稻田处于淹水状态可以抑制NZO的排放。 利用DNDC模型初步估算出广东省稻田C执和N20的排放量分别为0 .205一0.557TgC和0.04一0.042TgN。更多还原

【Abstract】 Methane (CH4) and nitrous oxide (N2O) are two important greenhouse gases. For the reason of human activities the concentrations of CH4 & N2O have been increasing clearly since the industrial revolution. A study indicates that rice paddy fields are one of the most important biology sources of CH4 & N2O. Therefore, in recent years CH4 & N2O emissions from rice fields are given more attentions in the field of global climate change.In this paper an experiment study of CH4 & N2O emissions were carried out by using static chambers in rice-rice rotation system in Qingyuan region of Guangdong province. The experiment data were analyzed. Beside the measurements of CH4 & N2O fluxes, the biogeochemical model-DNDC (Denitrification and Decomposition) was used to simulate CH4 & N2O emissions from the early and later rice. The simulations were compared with observations. On the basis of control-experiment a series of sensitive experiment about the factors affecting CH4 & N2O emissions were conducted. Many reasonable mitigation methods were brought out according to the sensitive experiments. In the end, total amount of CH4 & N2O emissions from rice fields of Guangdong province was preliminary estimated by using DNDC model.The seasonal variation of CH4 emission flux from the early rice fields is three-peak model. Three peak values appear respectively in the phase of regreening, tillering and fruiting. The two peak values in tillering and fruiting term are very obvious. The average CH4 emission flux of the whole early rice growing season is 4.38mg/m2 h In the growing season of the later rice there are three clear CH4 emission peaks. In the beginning (tillering term) of the later rice there is a high emission flux, and in the middle term (tasseling) there is a low methane emission flux. The highest peak value appears in the phase of tillering. The seasonal average CH4 emission flux of the whole later rice is 6.09mg/m2 h Water level and the Eh value have obvious effects on CH4 emission. When the water level is about 2cm, there is often a corresponding peak of CH4 flux. We should avoid shallow water level of about 2cm or choose intermittent irrigation in order to decrease CH4 emission from rice fields. When Eh<-100mv, there are a lot of CHU production from the early rice. The Eh value of later rice(-60mv--150mv) is higher than that of early rice. CH4 emission and the yield have a large difference for different rice cultivar. Jinyou 99 has not only little CH4 emission but also a large yield comparing Qisijian.So, we should choice the rice variety which has little CH4 emission and large yield.The processes of CH4 emission are discussed in detail by comparing the DNDC model outputs with the results from field measurements. Results show that DNDC model can elucidate well the seasonal change of CHU emission and most of CH4 emission pulses in the region. On the basis of these sensitive experiments are carried out. Sensitive experiments indicate that: CD There is a positive correlation between temperature and CH4 & N2O emissions from rice paddy fields. Temperature increasing can arouse CH4 & N2O emissions fluxes increasing. CHU & N2O emissions fluxes increasing can result in the greenhouse effect enhancing. Therefore, the temperature increases. (2) when soil organic carbon increases, CH4 & N2O emissions fluxes will increases. Soil pH has different effect on CHU & N2O emissions. The highest value of CH4 emission appears in the environment of alkalescence, but N2O appears in acidity. Soil pH and soil organic carbon lie on the characteristic of soil. Therefore, reducing CH4 & N2O emissions through controlling SOC and pH is not impossible. (3) In order to reducing CH4 & N2O emissions water management and fertilization are necessary methods. According to the trait of CHU & N2O emissions and sensitive experiments, the following advices are brought out. If soil organic matter is abundance at the beginning, the rice field should be in the station of dry-wet alternating. The mid-season draining which can reduce CH4 emission is use更多还原